Promotion of Natural Regeneration to Establish Productive Managed Forests on Fallow Land Near Pucallpa, in the Peruvian Amazon

Promotion of Natural Regeneration to establish productive managed Forests on Fallow land near Pucallpa, In the Peruvian Amazon

Thesis submitted in partial fulfilment of the requirements of the Degree Doctor rer. nat. of the Faculty of Forest and Environmental Sciences, Albert-Ludwigs-Universität Freiburg im Breisgau, Germany

Juan Clemente Díaz Gonzáles

Freiburg im Breisgau, Germany 2007

Dean: Prof. Dr. Heinz Rennenberg Supervisor: Prof. Dr. Jürgen Huss 2nd Reviewer: Prof. Dr. Siegfried Fink Defence: January 31, 2008

ACKNOWLEDGEMENTS

My first thanks are given to my supervisor, Prof. Dr. Jürgen Huss not only for the acceptation of a foreigner from the tropics, but for all and first for this great guidance and support by a long time in Silviculture Institute.

This thesis has been made possible due to numerous forms of assistance I have received from individuals and institutions both in Perú and Germany. Although not all can be acknowledged by name here, I would particularly like to thank the German Academic Exchange Service (DAAD) for awarding me a scholarship at the first years. In Perú, the study was supported by the Project MADEBOSQUES and „Proyecto de Investigación Manejo de Bosques Secundarios en América Tropical“ of CIFOR, CATIE and UNALM.

At Silviculture Institute of Freiburg University, I appreciated the support of Prof. Dr. Jürgen Bauhus and Prof. Dr. Albert Reif, as well as the colleagues Dr. Stefanie Gärtner, Dr. Winfried Meier, Dr Grzegorz Kochaniewiecz and special to Dr. David Buttler-Manning for the helpful contribution with the laborious english corrections.

Por el respado a las actividades realizadas en Perú deseo expresar mi agradecimiento al Dr. Cesar Sabogal, Dr. Ulrike Wagner, Dr. Carlos Reynel, Ing. Marco Romero, Sr. Fernando Razzeto, a mis colegas M.Sc.Violeta Colán, M.Sc. Octavio Galván y M.Sc. Hector Vidaurre, a los agricultores de la carretera Neshuya-Curimana que me brindaron importante información de la historia de sus barbechos y al mismo tiempo permitieron su evaluación, de igual forma a los colegas y trabajadores del proyecto MADEBOSQUES.

Finalmente quiero agradecer profundamente a mi gran y querida familia que desde España y Perú han sabido brindarme apoyo, comprensión, paciencia y coraje.

ABSTRACT

Inventories of secondary forest in the study area revealed the farmers’ desire to maintain as fallow areas where there is an abundance of commercially valuable timber species. These areas a left fallow for a few years until the trees develop the dimensions appropriate for commercial exploitation. Only small surfaces are dominated for commercial species. The ecological conditions influencing the natural regeneration of 4 fast growing commercial species and the factors leading to the development of homogenous stands dominated by these species were evaluated. The influence of seed trees about the establishment of natural regeneration was evaluated in the field in conjunction with the vegetation recordings made on the fallow areas. The phenology of the 4 species studied was evaluated in the field. The changes to the morphology of the species were described and illustrated. Vegetation inventories were carried out on fallows with different histories and subject to different growing conditions. The changes occurring to the vegetation and the possibilities for the establishment of the commercial species of interest were analysed by means of comparison of inventories made at 2 different periods in the year. Germination and direct seeding experiments were carried out under semi-natural conditions. The mere presence of seed tress of the desired commercial species provides no guarantee for the establishment of stands dominated by any of these species. It was observed that the successful establishment on fallow land of the species studied was closely linked to the timing of agricultural activities.

KEYWORDS:

Secondary forest, fallow, natural regeneration, fast growth, establishment, phenology, morphology, germination, direct seeding, seed tree.

Contents i

CONTENTS

1 GENERAL INTRODUCTION AND PROBLEM STATEMENT 1

1.1 OPPORTUNITIES TO AVAIL OF SUCCESSIONAL VEGETATION IN THE PUCALLPA REGION 1 1.2 SECONDARY SUCCESSION IN TROPICAL COUNTRIES 2 1.2.1 Terminology of secondary succession in tropical rainforests 2 1.2.2 Secondary forests and succession in the tropics 5 1.2.3 Secondary forest regeneration in the American tropics 5 1.3 LANDSCAPE TRANSFORMATION IN THE PERUVIAN AMAZON 7 1.3.1 Peru’s geographical diversity and land uses 7 1.3.2 The Peruvian Amazon 9 1.3.3 Deforestation in the Peruvian Amazon 9 1.3.4 Land use dynamics in the Pucallpa region 9 1.4 CULTURAL AND FOREST CONDITIONS IN THE STUDY AREA 10 1.4.1 Political and social aspects 10 1.4.2 The settlement of farmers in the Pucallpa region 11 1.4.3 Agricultural production systems employed in the Pucallpa region 12 1.4.4 Timber industry in Peru and in the Pucallpa region 13

1.5 PERSPECTIVES FOR THE SUSTAINABLE MANAGEMENT OF SECONDARY FORESTS IN THE REGION 14 1.5.1 Knowledge of natural resource management in the study area 15 1.5.2 Timber from young secondary forests 15 1.6 HYPOTHESES AND OBJECTIVES 16 1.6.1 Hypotheses 16 1.6.2 Objectives 16 1.6.2.1 General objectives 16 1.6.2.2 Specific objectives 17 2 DESCRIPTION OF THE STUDY AREA 18

2.1 LOCATION AND COLONISATION OF THE STUDY AREA 18 2.1.1 Location of the study area. 18 2.1.2 Colonisation of the study area 18 2.2 ENVIRONMENTAL FACTORS 19 2.2.1 General climate conditions 19 2.2.2 Physiography, geology and soils of the region and the study area 20 ii Contents

2.2.2.1 Physiography 20 2.2.2.2 Geology 21 2.2.2.3 Soils 22 2.3 FORESTS IN THE PUCALLPA REGION 22 2.3.1 Primary forests in the study area 22 2.3.2 Secondary forests in the Pucallpa region 23 2.3.2.1 Heterogeneous secondary forest stands 23 2.3.2.2 Homoneous secondary forest stands 27 2.3.3 Use of secondary forests in the Pucallpa region 28 2.4 MANAGEMENT OF SECONDARY FOREST IN TROPICAL REGIONS 29 2.4.1 Secondary forest management strategies 29 2.4.2 Possibilities for managing secondary forests in the Pucallpa region 30 2.4.3 Selection criteria for the species investigated 30

3 BIOLOGICAL REQUIREMENTS OF PIONEER TREE SPECIES FOR THEIR ESTABLISHMENT ON FALLOWS 32

3.1 INTRODUCTION: CLASSIFICATION OF ECOLOGICAL GROUPS OF TREE SPECIES AS A SILVICULTURAL TOOL 32 3.1.1 Advantages and disadvantages of tree classification according to ecological groups 32 3.12 Objectives 33

3.2 FIELD IDENTIFICATION OF THE PHASES OF THE INITIAL STAGE OF GROWTH OF THE SELECTED TREE SPECIES 33 3.2.1 Objectives of the description of the morphological characteristics 34 3.2.2 Methods of the morphological identification of the various phases of the initial stage of growth 34 3.2.2.1 Definition of seedling and the initial growth stage 34 3.2.2.2 Obtaining seedlings 35 3.2.2.3 Differentiation within the initial stage 35 3.2.2.4 Description of morphological characteristics 36 3.2.2.5 Illustration of seedlings 36 3.2.3 Results: description of the morphology of the various phases of the initial stage of development of the studied species 37 3.2.3.1 Description of the morphology of the initial stage of development in Calycophyllum spruceanum 37 3.2.3.2 Description of the morphology of the initial stage of development in Croton matourensis 38 3.2.3.3 Description of the morphology of the initial stage of development in Guazuma crinita 41 3.2.3.4 Description of the morphology of the initial stage of development in Jacaranda copaia 43 3.2.4 Discussion of seedling morphology 45 Contents iii

3.3 PHENOLOGY OF THE SEED TREES OF THE SPECIES STUDIED 45 3.3.1 Objectives of the phenological evaluation 46 3.3.2 Phenological evaluation methods 46 3.3.3 Results: graphic description of the phenology of the selected tree species 47 3.3.3.1 Phenology of Calycophyllum spruceanum 47 3.3.3.2 Phenology of Croton matourensis 48 3.3.3.3 Phenology of Guazuma crinita 49 3.3.3.4 Phenology of Jacaranda copaia 49 3.3.4 Discussion: seed dispersal and natural regeneration on fallow land 50 3.3.4.1 Dispersal during the rainy season 50 3.3.4.2 Pioneer tree establishment on fallow land 51 3.4 GERMINATION OF COMMERCIAL PIONEER SPECIES ON FOUR SUBSTRATE TYPES 51 3.4.1 Introduction and objectives of the study of substrate type 51 3.4.2 Materials used in the of substrate experiment 52 3.4.2.1 Substrate types in areas colonised by pioneer trees 52 3.4.2.2 Seed characteristics of the studied species 54 3.4.3 Methods: research design, field preparation and sowing 55 3.4.3.1 Design of the experiment 55 3.4.3.4 Preparation of the sites of the experimental plots 56 3.4.3.5 Seed sowing 57 3.4.4 Results of the germination experiment and discussion 57 3.4.4.1 Germination rates of Calycophyllum spruceanum in the substrate experiment 57 3.4.4.2 Germination rates of Guazuma crinita in the substrate experiment 58 3.4.4.3 Germination rates of Jacaranda copaia in the substrate experiment 59 3.4.5 Conclusions on the effect of substrate type on germination 60

3.5 GERMINATION OF BURIED Croton matourensis SEED 61 3.5.1 Objectives of the test of the germination of buried seed 61 3.5.2 Method of testing the germination of buried seed 61 3.5.2.1 Site description of the forest with Croton matourensis seed trees 61 3.5.2.2 Design of the buried seed germination experiment 62 3.5.3 Results of the Croton matourensis germination experiment and discussion 63 3.5.3.1 The seedling abundance associated with the substrates 63 3.5.3.2 Seedling abundance as a function of distance from the seed tree 64 3.5.3.3 Analysis of the interaction between distance and treatment 64 iv Contents

3.5.4 Germination of Croton matourensis and practical implications for regeneration 65

3.6 PRACTICAL IMPLICATIONS OF THE ECOLOGICAL REQUIREMENTS

OF THE SPECIES FOR EARLY ESTABLISHMENT 66

4 PIONEER VEGETATION AND NATURAL REGENERATION IN THE STUDY AREA 67

4.1 PIONEER VEGETATION ON FALLOW LAND ABSENT SEED TREES OF THE COMMERCIAL SPECIES 67 4.1.1 Objectives of the vegetation analysis 68 4.1.2 Methods for the evaluation of the vegetation 68 4.1.3 Results of the vegetation evaluation 69 4.1.3.1 Plant type coverages on fallow land without seed trees of commercial species 69 4.1.3.2 Species coverages on fallow land without seed trees of commercial species 70 4.1.3.3 Simplified profile of the area of fallow land without seed trees of the commercial species 71 4.1.4 Discussion of the vegetation of fallow land without seed trees of commercial species 71 4.2 NATURAL REGENERATION OF COMMERCIAL PIONEER TREE SPECIES ON FALLOWS 72 4.2.1 Objectives of the vegetation analysis on fallow land with seed trees of commercial species 72 4.2.2.1 Variations in the vegetation of the fallow areas studied 73 4.2.3 Results: establishment of commercial tree species on fallow land 74 4.2.3.1 Natural regeneration of Guazuma crinita on fallow land 74 4.2.3.2 Natural regeneration of Calycophyllum spruceanum on fallow land 87 4.2.3.3 Natural regeneration of Jacaranda copaia on fallow land 90 4.2.3.4 Natural regeneration of Croton matourensis on fallow land 94 4.2.3.5 Observations on the natural regeneration of commercial species establishing on fallow land 99 4.3 DISPERSAL DISTANCE AND DENSITY OF NATURAL REGENERATION OF COMMERCIAL SPECIES ON FALLOW LAND 101 4.3.1 Objectives of the study of dispersal distance and natural regeneration density 101 4.3.2 Methods for the evaluation of the dispersal distance and natural regeneration density 101 4.3.2.1 Evaluation of the dispersal distance and natural regeneration density of Guazuma crinita. 102 4.3.2.2 Evaluation of dispersal distance and natural regeneration density of Croton matourensis 102 4.3.3 Results of the study of seed dispersal distance and natural regeneration density 102 Contents v

4.3.3.1 Dispersal distance and natural regeneration density of Guazuma crinita 102 4.3.3.2 Dispersal distance and natural regeneration density of Croton matourensis 104 4.3.4 General conclusions on seed dispersal distance and the density of natural regeneration 105

4.4 GENERAL CONCLUSIONS FROM THE ANALISYS OF THE VEGETATION ON FALLOW AREAS 106

5 DIRECT SEEDING ON FALLOW LAND 107 5.1 DIRECT SEEDING IN TROPICAL AREAS 107 5.2 OBJECTIVES OF DIRECT SEEDING ON FALLOW AREAS 108 5.3 METHODS FOR THE EVALUATION OF GERMINATION AFTER DIRECT SEEDING 108 5.4 RESULTS OF DIRECT SEEDING ON FALLOW AREAS 109 5.4.1 Direct seeding of Guazuma crinita 110 5.4.2 Direct seeding of Jacaranda copaia 111 5.5 DISCUSSION OF DIRECT SEEDING ON FALLOW LAND 113 6 GENERAL CONCLUSIONS 115

6.1 ECOLOGICAL REQUIREMENTS OF TREES DURING EARLY ESTABLISHMENT AND ANTHROPOGENIC ACTIVITIES ON FALLOW LAND 115 6.2 REDUCTION OF THE PRIMARY FOREST SURFACE AREA AND ESTABLISHMENT OF NEW COMMERCIAL TREE SPECIES 116 6.3 REQUIREMENTS OF THE FARMERS 117 6.4 NECESSARY FUTURE RESEARCH 117

7 SUMMARY, ZUSAMMENFASSUNG & RESUMEN 118

7.1 SUMMARY 118 7.2 ZUSAMMENFASSUNG 122 7.3 RESUMEN 125 8 BIBLIOGRAPHY 130

9 APPENDIX 144 vi Tables

TABLES

Table 1.1 Distribution of the Peruvian population in the natural regions 8 Table 1.2 Land use suitability of the Peruvian high and low jungle 8 Table 1.3 Economic activities in the Ucayali Department in 1999 11 Table 2.1 Proportion of volume according to the abundance of species in neotropical forests 23 Table 2.2 Stand parameters of secondary forests in the 3 sectors studied within the Pucallpa region. Age classes: 5-7 years, 8-10 years, >10 years 24 Table 2.3 Stand parameters in secondary forests according to age class 25 Table 2.4 Relative importance value index (IVI %) of secondary forest species in 26 Pucallpa Table 2.5 Number of Jacaranda copaia individuals/ha according to diameter class in naturally established stands of different ages in the Pucallpa region 27 Table 2.6 Evaluation of potential species for investigation prior to initiation of the 31 research Table 3.1 Seed characteristics of the species studied in the substrate experiment 55 Table 3.2 Germination rates (%) of Calycophyllum spruceanum seeds on the 4 substrate types and the control 58 Table 3.3 Germination rates (%) of Guazuma crinita seeds on the 4 substrate types and the control 58 Table 3.4 Germination rates (%) of Jacaranda copaia seeds on the 4 substrate types and the control 59 Table 3.5 Average germinated seedlings/m2 for each soil treatment 64 Table 5.1 Distribution of the % germination in the Guazuma crinita seeding experiment 111

Figures vii

FIGURES Fig. 1.1 Illustration of a successional process depicting the formation of secondary forests 4 Fig. 1.2 Schematic model of succession in secondary tropical rainforests 6 Fig. 1.3 Map of Perú’s natural ecoregions 7 Fig. 1.4 Land use change in the Pucallpa region 10 Fig. 1.5 Settlements in the Pucallpa region 11 Fig. 1.6 National industrial timber products: 1995-1999 13 Fig. 2.1 Deforestation in the Pucallpa region 18 Fig. 2.2a Mean monthly temperature and rainfall for Pucallpa 20 Fig. 2.2b Mean monthly temperature and rainfall for San Jorge 20 Fig. 2.3 Characteristic vegetation types in the plain/undulating landscape 21 Fig. 2.4 Distribution of trees according to age and diameter class in the secondary forests around Pucallpa 25 Fig. 2.5 Distribution of the numbers of trees/ha according to use and age class 28 Fig. 3.1 Phases of seedling development of three different germination types 36 Fig. 3.2 Morphology of the phases of the initial stage of seedling development of Calocophyllum spruceanum 38 Fig. 3.3 Morphology of the phases of the initial stage of seedling development of Croton matourensis 39 Fig. 3.4 Morphology of the phases of the initial stage of seedling development of Guazuma crinita 42 Fig. 3.5 Morphology of the phases of the initial stage of seedling development of Jacaranda copaia cotyledon phase protophyllous phase 43 Fig. 3.6 Morphology of the phases of the initial stage of seedling development of Jacaranda copaia metaphyllous stage terminal sprout bipinnate leaf of the metaphyllous stage 44 Fig. 3.7 Phenological behaviour of Calycophyllum spruceanum in the Neshuya- Curimana sector, 1999-2000 48 Fig. 3.8 Phenological behaviour of Croton matourensis in the Neshuya-Curimana sector, 1999-2000 48 Fig. 3.9 Phenological behaviour of Guazuma crinita in the Neshuya-Curimana sector, 1999-2000 49 Fig. 3.10 Phenological behaviour of Jacaranda copaia in the Neshuya-Curimana sector, 1999-2000 50 Fig. 3.11 Design of the field experiment to study germination on 4 substrate types 56 Fig. 3.12 Layout of experimental plots around a seed tree located in the residual primary forest. 63 Fig. 4.1 Distribution of the transects and plots established to record the vegetation in a fallow area 68 Fig. 4.2 Coverages of different plant types across the fallow area evaluated 69 Fig. 4.3 Species coverages in the field left fallow after rice cultivation 70 Fig. 4.4 Simplified profile of the fallow land vegetation 71 Fig. 4.5 Coverages of the most important plant species that developed on a fallow after rice cultivation (Flores family land). 75 Fig. 4.6 Coverage of the plant types on a fallow area previously cultivated for rice. 76 Fig. 4.7 Vegetation coverages on the fallow land after rice cultivation, according to height class and plant type. 77 Fig. 4.8 Coverages of the most important plant species that developed on a fallow after rice cultivation (Castro family land). 79 viii Figures

Fig. 4.9 Coverages of the plant types on fallow land with Guazuma crinita seed trees. 80 Fig. 4.10 Coverages of the species that developed on a fallow after maize cultivation (Gomez family land) 81 Fig. 4.11 Coverages of the plant types on fallow land after maize cultivation 82 Fig. 4.12 Vegetation coverages on the fallow land after maize cultivation, according to height class and plant type 83 Fig. 4.13 Coverages of the species on a pasture with a Guazuma crinita seed tree 85 Fig. 4.14 Vegetation coverages on fallow land with a Guazuma crinita seed tree previously used as pasture 85 Fig. 4.15 Vegetation coverages on fallow land previously used as pasture, according to height class and plant type 86 Fig. 4.16 Coverages of the most important plant species that developed on a fallow with a Calycophyllum spruceanum seed tree after rice cultivation 88 Fig. 4.17 Coverages of the plant types on a fallow area with a C. spruceanum seed tree previously cultivated for rice 89 Fig. 4.18 Coverages of the most important plant species that developed on a fallow in the vicinity of a Jacaranda copaia seed tree after rice cultivation (Mozombite family land) 91 Fig. 4.19 Coverages of the plant types on a fallow area in the vicinity of a Jacaranda copaia seed tree previously cultivated for rice 91 Fig. 4.20 Coverages of the most important plant species that developed on a fallow in the vicinity of a Jacaranda copaia seed tree after the cultivation of manioc and pineapple 92 Fig. 4.21 Coverage of the plant types on a fallow area in the vicinity of a Jacaranda copaia seed tree previously cultivated for manioc and pineapple 93 Fig. 4.22 Coverages of the most important plant species that developed on a fallow in the vicinity of Croton matourensis seed trees after rice cultivation (Suelperez family land) 95 Fig. 4.23 Coverages of the plant types on a fallow area in the vicinity of Croton matourensis seed trees after rice cultivation 96 Fig. 4.24 Coverages of the most important species that developed on a fallow with a Croton matourensis seed tree after maize cultivation (Gomez family land) 97 Fig. 4.25 Coverage of the plant types on a fallow area with a Croton matourensis seed tree previously cultivated for maize 98 Fig. 4.26 Abundance of saplings and pole stage Guazuma crinita as a function of distance from the stem of the seed tree 103 Fig. 4.27 Maximum dispersal distance of Croton matourensis seed 104 Fig. 4.28 Density of naturally regenerated Croton matourensis as a function of distance from the stem of the seed tree 104 Fig. 5.1 Plot distribution of the direct seeding experiment with Guazuma crinita and Jacaranda copaia 109 Fig. 5.2 Germination rate (%) of Guazuma crinita seeds between 04.01–05.04.2000 subject to 2 clearing intensity treatments 110 Fig. 5.3 Germination rate (%) of Jacaranda copaia seeds between 14.05– 23.07.2000 subject to 2 clearing intensity treatments 111

General introduction and problem statement 1

1 GENERAL INTRODUCTION AND PROBLEM STATEMENT

1.1 OPPORTUNITIES TO AVAIL OF SUCCESSIONAL VEGETATION IN THE PUCALLPA REGION

Successional vegetation in the Pucallpa region, as in other areas of humid tropical forest in Perú, is mainly the outcome of timber exploitation and migratory agriculture. This has given rise to a patchy mosaic of crops and pasture, as well as areas of early succession, secondary and residual forests, each of a distinct age and expanse, with a wide range in terms of both structure and floristic composition. Secondary forests, an intermediate phase of successional vegetation, consist of tree species characterised by their rapid growth and low timber density, most of which lack any commercial value. The few species capable of attaining utilisable timber dimensions have recently been commercially exploited, especially in relatively homogeneous stands. Homogenous secondary forests, with fast growing commercial species, form patches covering only small expanses and are irregularly distributed throughout the region. The local demand for sawn timber originating from secondary forests has existed for several years. This timber is associated with very low transport and transformation costs, in contrast to larger dimension trees derived from primary forests. Generally, secondary forests are located near either roads or rivers. Here timber exploitation represents a limited form of local industry and provides an additional source of income for small landholders. The growing demand for this useful resource has resulted in a decline in the quantity of trees, and in the exploitation of smaller trees. Despite the rapid growth rates of species found in secondary forests, the low value of the timber renders plantations consisting of these species unprofitable. Therefore, knowledge of the ecological conditions necessary for the establishment of the few secondary forest species capable of attaining commercial dimensions is required. The presence of stands dominated by few commercial pioneer tree species suggests strongly the necessity to obtain knowledge of the ecological conditions essential for their establishment. Techniques such as soil scarification and direct seeding are employed in temperate forests in Europe and North America to promote the successful natural regeneration of pioneer species. Such approaches may also prove beneficial in tropical regions. In this study, early secondary succession involving natural regeneration initiated by seed trees is evaluated. The application of direct seeding techniques to establish productive stands comprising four pre-selected native tree species is also considered. Each of the following is handled in the study: • The description of seedling morphology for the identification of naturally regenerated seedlings. • The evaluation of seed tree phenology. • Germination on different substrate types. 2 General introduction and general statement

• The density, growth and establishment of naturally regenerated seedlings. • Seedling establishment distances from seed trees. • Regression curves for height and diameter growth. • Germination and survival rates of direct sown plants. The soils of many of the colonised areas of the Pucallpa region have been only slightly degraded, and the seed sources required to establish productive forest on fallow land are present. The potential incomes derived from timber harvested from secondary forests can act as an enticement to the local population to maintain these forests for longer, encouraging greater volume growth, or to combine other possible uses, such as agroforestry systems prolonging the soils’ vegetation cover. Without the occurrence of opportune interventions in areas boasting excellent conditions for growth, there exists a risk that this potential will be wasted and these areas will degrade further.

1.2 SECONDARY SUCCESSION IN TROPICAL COUNTRIES

With the ongoing reduction of the surface area of primary forest in the tropical regions, a growing interest in successional vegetation has development, principally in relation to its role, structure and function. Various disciplines have engaged in the definition and classification of the vegetation that has developed after the discontinuation of agricultural activities.

1.2.1 Terminology of secondary succession in tropical rainforests

There is considerable ambiguity and confusion in the current use of terms ‘fallow’, ‘secondary succession’ and ‘secondary forest’, both in the literature and in people’s perceptions.

Fallow In general, the term fallow refers to the recuperation of agricultural land. On occasion it is used to designate the period of time required for the restoration of soil fertility before the next planting. At other times it refers to the vegetation that has developed on the land left to recuperate. The most specific definitions are those that refer to the physical location or to a production system. TURNER & SHAJAAT (1996) considered as fallow that parcel of land on a farm that lies uncultivated for a period of time. The FAO (2001) referred to a whole farm or a production system with one or more parcels lying temporarily uncultivated. In tropical regions fallow land can be classified as either long or short. • Long fallow is a mosaic of mature forests, secondary forests, various stages of natural regrowth and cultivated areas, the latter covering between 5 and 30 % of the total area. • Short fallow is a mosaic of young secondary forests, various stages of natural regrowth and cultivated areas, the latter covering 30-50 % of the total area.

General introduction and problem statement 3

In recent times, the concept of ‘improved fallow’ has been widely incorporated in the tropical regions. Improved fallows consist of deliberately planted species, usually legumes,

with the principal purpose of fixing N2 as part of a crop-fallow rotation (SANCHEZ 1999). The advantage of improved fallows is the in-situ accumulation of biomass, the optimisation of nutrient cycling, the enhancement of soil biological activity and the maximisation of the efficiency of minimal external inputs (SANCHEZ 1994).

Secondary succession

Secondary succession occurs on land previously colonised but disturbed back to some earlier state in its development. Examples include cleared forests or ploughed fields. Succession begins with the arrival of the pioneer species and leads eventually to the establishment of a climax community. Although the process of succession represents a continuum, it may be divided into several phases. SALDARRIAGA & UHL (1991) estimated that 140-200 years are required for an abandoned parcel of land to reach biomass levels comparable to that of a mature forest. The successional stages have been allocated several names. These may differ from zone to zone, from country to country, and even within a country, depending on the ethnic groups, the type of landowner and the local customs.

Terms such as ‘purma’ in Perú; ‘capoeira’ in certain parts of Brazil, ‘charral’, ‘tacotal’ or ‘guamil’ in Central America are largely used to refer to fallow land in general, without providing any major indication in relation to its degree of development. Often a reference to the age of the fallow is included, namely young, intermediate or old (adult or mature). Nevertheless, it is known that the indigenous people of the region developed an elaborate terminology to refer to the different types of forest fallow, demonstrating their skill in the management of these ecosystems. For example, GÓMEZ-POMPA (1991) demonstrated the manner in which the Mayas classified vegetation according to the age of the succession. HOMMA et al. (1993) referred to the different terms used by the caboclos (mestizos) in the Brazilian Amazon: quiçassa, juquira and massega. These terms are three names widely used to designate roughly the same type of secondary growth where herbaceous weeds and shrubs dominate (vegetation <2 years old). Capoerinha indicates a slightly more advanced stage than referred to by quiçassa, juquira and massega. In capoerinha the saplings of pioneer successional trees are also present, with a slight dominance of tree species over herbaceous weeds and shrubs (vegetation 2-4 years old). Capoeira refers to a stage in which pioneer trees are present. This category can include a broad range of ages, height and structural features (vegetation 4-10 years old). Capoeirão and mata fina are used to indicate a stage where successional species dominate the composition of the secondary growth. In this stage it is almost impossible to differentiate secondary growth from primary forest using current remote sensing approaches (vegetation >10 years old).

Secondary forest

BLASER & SABOGAL (2002) defined secondary forests as the woody successional vegetation that regenerates after the forest cover has been removed through human intervention. If spared the disruptive effects of grazing, tree felling and frequent fires, this secondary vegetation is slowly invaded by primary forest trees and can eventually develop into a community similar to that which originally occupied the site. The speed of change depends on the availability of seed trees and the health of the forest. In the first few years change is usually rapid, but later becomes much slower. The whole process of recovery probably extends over centuries rather than decades. If the secondary vegetation is subject to recurrent fires, grazing or other disturbances, deflected (‘retrogressive’) succession sets 4 General introduction and general statement in leading to permanent biotic climaxes no longer corresponding to those found prior to degradation. Secondary forests differ from degraded primary forests. In the case of degraded forests, the initial cover of primary, old-growth or managed forests has been affected by the unsustainable and excessive harvesting of wood and/or extraction of non-timber forest products. The consequence of these uses is to alter the structure, processes, functions and dynamics beyond the recovery potential of the forest ecosystem. Secondary forest is also different from degraded forest land where the initial forest cover has been removed completely and the physical conditions have been severely impacted upon by over- exploitation, repeated occurrences of fire, excessive grazing or other intensive disturbances arising from alternate land uses. Such conditions delay, or even inhibit entirely forest regrowth after abandonment. The land cover is generally dominated by grasses, shrubs and creepers, or in some cases may remain barren. A high degree of soil degradation and a lack of seed sources are the main factors hampering natural succession towards secondary forests. Secondary forests vary in age. However, for practical purposes the application of the term is confined to forests that are <60-80 years old, because forests beyond this age are often indistinguishable from primary forests (BUDOWSKI 1961) and are included in the ‘undisturbed’ or primary forest category of the Food and Agricultural Organization’s assessment of tropical forests (LANLY 1982).

Secondary forest vs. secondary vegetation

Fig. 1.1 is an illustration of the successional process from open land to primary forest. Secondary forest is positioned in the middle area between the dotted lines. This phase includes trees and the presence of forest, as distinct from scrub, grassland and other secondary vegetation, situated to the left of the dotted line. Trees have been variously defined as woody vegetation greater than 3-5 m in height. The existing definitions of forest also vary.

Biomass Primary forest Mature secondary forest Young secondary Shrubland/ forest grassland

Time

Fig. 1.1: Illustration of a successional process depicting the formation of secondary forests (adapted from BLASER & SABOGAL 2002).

The successional process from grassland and non-forest vegetation to secondary forest and ultimately primary forest illustrated in Fig. 1.1 takes place over a protracted period of time. Very gradually structures and functions similar to those occurring within the original forests can develop, although they are not identical.

General introduction and problem statement 5

1.2.2 Secondary forests and succession in the tropics

The changes occurring to the composition and structure of fallow land during the successional stages subsequent to the farmers’ cessation of agriculture represent the earliest subjects investigated in secondary forests (GREIGH-SMITH 1952, RICHARDS 1955, BUDOWSKI 1961, GOMEZ-POMPA & VASQUEZ-YANES 1974). A wide array of regeneration processes has been described. These range from the regeneration of pioneer tree species in natural gaps in primary forests (WHITMORE 1978, HARTSHORN 1978, BROKAW 1982, BROKAW 1985) to possibilities for the recuperation through regeneration of great expanses of land deforested for livestock (UHL 1988, NEPSTAD et al. 1991). These studies also cover an enormous gradient in terms of the landscapes, conditions and land use histories. The relationship between ‘shifting cultivation’ and the productive capacity of the soils is another well investigated topic in many tropical regions of the world (AWETO 1981, TOKY & RAMAKRISHNAN 1983, JORDAN 1982, GOMEZ-POMPA & DEL AMO 1985, UHL 1987, SALDARRIAGA 1994). Biomass, carbon and the nutrient dynamics of secondary forests in humid tropical regions have been the object of great interest in the last decade (HUGHES et al. 1994, SANTOS et al. 2003, DAVIDSON et al. 2004). Most research projects concerning alternatives to traditional ‘shifting cultivation’, also referred to as ‘slash and burn agriculture’, focus on increasing the rates of recuperation of soil fertility during the fallow period (UHL & JORDAN 1984). Researchers have devoted less attention to the farmers’ economic reasoning for managing their fallow-based ‘shifting cultivation’ using particular methods (DVORAK 1992, YANGGEN & ALEGRE 2002). Certain anthropological and social studies (BEDOYA 1984, DENEVAN & PADOCH 1987) described the influence of indigenous people on the establishment and composition of the successional vegetation in the Peruvian Amazon.

1.2.3 Secondary forest regeneration in the American tropics

Where the soil is not degraded, and where seed sources are located close by, the first 100 years of lowland rainforest secondary succession may be described in terms of three phases, during which forest canopy height, tree stocking density and basal area sometimes attain levels found in mature forests on comparable sites in less than 30 years (Fig. 1.2, next page). Despite the diverse range of studies of secondary forests in the tropics, there are no studies of the manipulation of species that regenerate in the first phase of development of these forests. Current silvicultural options involve conversion and transformation employing the planting of commercial species (CONIF 1986; YARED & CARPANEZZI 1981), or favour the natural regeneration of species from the subsequent phase of succession, such as the Tropical Trinity Shelterwood System in Costa Rica (FINEGAN & SABOGAL 1988; FINEGAN 1992). Over the last decade the silvicultural options have involved improving the increment of pioneer trees already established (HUTCHINSON 1993, CHIARI 1999, MESQUITA 2000). In Central Europe different methods of substrate preparation have been employed to facilitate the natural regeneration of different temperate species (HUSS & BURSCHEL 1972; BURSCHEL & HUSS 1997; JUNGBLUTH & DIMITRI 1980). 6 General introduction and general statement

100

1 2 2 1 3 3

biomass 4 % maximum

10 100 Time (years)

Fig. 1.2: Schematic model of succession in secondary tropical rainforests (FINEGAN 1996). In the first phase, recently abandoned land is colonised by a dense growth of herbs and climbers (1 on the graph). Seedlings of fast growing, short-lived pioneer tree species quickly emerge, initiating the second phase. These trees may form a continuous woody canopy in less than three years (2 on the graph), under the shade of which the species of the first phase largely disappear. The second phase may last 10-30 years – this corresponds to the lifespan of the short-lived pioneer trees, which form an approximately even-aged population. These are replaced as dominant trees by individuals of long-lived pioneer species in the third phase of succession. In order to reach the forest canopy in 10-30 years, long-lived pioneer species generally colonise the site in the first few years of succession, so that their populations are also approximately even-aged (3 on the graph). The duration of the third phase, like the second, is as long as the lives of the dominant species – in this case perhaps 75-150 years. During this interchange of dominance between pioneer tree species, an almost continuous colonisation of the site by increasingly shade-tolerant species of all life forms takes place (4 on the graph). Two principal factors are assumed to underlie successional change: (1) the set of intercorrelated differences in the growth rate, shade tolerance, longevity and size at maturity of the different species, most of which colonise the site soon after its abandonment, and (2) competition between the individuals of these species.

In Latin America the skills required to manage substrates for the promotion of the natural regeneration of pines also exist in Mexico (CHACÓN 1983). VIDAURRE (1992) improved the germination of seeds of Cedrelinga catenaeformis by means of the mechanical removal of the litter and the elimination of other understorey species of a primary forest in the Peruvian Amazon. GRANADOS (1995) observed differences in the establishment of seedlings of tree species resulting from different litter elimination methods in the understorey of secondary forest in Costa Rica. Controlled superficial fire brought about a higher quantity of seedlings than the mechanical removal of the litter. However, the mechanical removal of the litter resulted in higher survival rates amongst the established saplings (30 cm height, 5 cm DBH). Neither treatment demonstrated a statistically significant difference in the survival of pole stage trees (5-10 cm DBH). As a consequence of the unprofitable objectives of rehabilitation, it is vital that the establishment of trees be low cost. Direct seeding was probed for the rehabilitation of degraded areas in Pucallpa region (SOUDRE et al. 1999), the Brazilian state Sao Paulo (ENGEL & PARROTTA 2001) and the Brazilian Central Amazon (CAMARGO et al. 2002). Species with large seeds demonstrated greater rates of establishment after direct sowing. Seeds of pioneer species, which are generally small, are produced in huge quantities and under favourable conditions may exhibit a high germination rate. However, at the beginning of their development, tiny seedlings appear to be more susceptible to environmental fluctuations and are unable to withstand prolonged periods of adverse conditions. No studies of the direct seeding of pioneer species (very small/small seeds) in non-degraded areas in the American tropics are known.

General introduction and problem statement 7

1.3 LANDSCAPE TRANSFORMATION IN THE PERUVIAN AMAZON

1.3.1 Peru’s geographical diversity and land uses

The Andes mountain range crosses the country from not north to south. The presence of the mountain range results in 3 major geographic units from west to east. These contrast geomorphologically and climatically, namely coast, highland and jungle. The territory of Peru comprises 84 of the 104 life zones or ecosystems that exist on earth (ONERN 1976). The classification of natural ecoregions (BRACK 1986) clearly illustrates this geographic diversity (Fig. 1.3).

Fig. 1.3: Map of Perú’s natural ecoregions (BRACK 1986). 8 General introduction and general statement

As a consequence of its geographical location, all of Peru could have a tropical climate with abundant precipitation and high temperatures, and lush vegetation. However, the climate is also influenced by the Andes mountain range that crosses the country longitudinally, the cold Humboldt ocean current and the South Pacific anticyclone, bringing about extreme variations in climate conditions over short distances. The distribution of the Peruvian population (Tab. 1.1) is also strongly influenced by geography. The extreme contrast in the prevailing geographic conditions has led to great differences in cultural, social and economic aspects. The Andes are a great physical obstacle limiting access to the jungle region. They also hinder trade, investment and the development of infrastructure. However, this inaccessibility has protected the natural resources, allowing them to remain relatively intact.

Tab. 1.1: Distribution of the Peruvian population in the natural regions (INEI 1997).

Natural region Total area Population Density (km2) % (Millions) % (Inhabitants/km2) Coast 128 000 10 12.6 51 98 Highland 410 000 32 8.7 36 21 Tropical high jungle 300 000 23 2.0 8 7 Tropical low jungle 447 000 35 1.2 5 3 Total / Average 1 285 000 100 24.5 100 19

The area of farming land in Peru is limited. The coastal belt is extremely arid, the highlands are dry and boast little plain surface. The soils in the Peruvian Amazon region are also generally too unproductive for agriculture (Tab. 1.2).

Tab. 1.2: Land use suitability of the Peruvian high and low jungle (ONERN, 1982).

Classification Land surface area 1 000 km2 % Shifting agriculture 24 4 Permanent cultivation 22 3 Grass / livestock farming 51 8 Forest 460 60 Protection (no use) 190 25 Total 747 100

The best Amazon soils are found on terraces near rivers, and most of these areas have already been planted with annual crops (corn, rice, manioc, beans and vegetables). Some cleared forest land yields harvests once or twice a year through the traditional system of cultivation, which takes place until crop yields diminish as a result of the depletion of soil nutrients and competition from weeds and pests. Once the land becomes infertile it is abandoned and forest is cleared to provide new farmland. The slash and burn agricultural system is practised by native communities and by the majority of settlers living in the Peruvian Amazon.

General introduction and problem statement 9

1.3.2 The Peruvian Amazon

Amazon is a deceptive term. The region, spread over parts of seven nations, is far from uniform. Not only does plant and animal life differ within the Amazon Basin, but so too the amount of human activity, thereby causing the condition of the natural resources to vary across the region. Some areas have remained ‘pristine’ forest, whereas others are severely degraded agricultural land. The areas of the Amazon with higher levels of agricultural activity are ecologically important. By virtue of the nearby Andes, the primary forests exhibit greater levels of biodiversity than are found in other parts of the Amazon, and contain an exceptionally high number of endemic plants (ca. 20 000). Peruvian rainforests host 23 % and 44 % of the known tropical plant and bird species found in the tropics, respectively (RODRIGUEZ & YOUNG 2000). The varied topography (100-2 500 m a.s.l.) and the associated annual rainfall, ranging from 1 100-5 000 mm, provide the conditions necessary for numerous species to thrive. Nearly 60 % of the national territory of Perú is considered part of the Amazon. Despite the relatively large area it encompasses, the Amazon region of Perú is remarkably different to, and isolated from, the rest of the country. To the west, the cooler sierra and drier coastal regions contrast starkly with the hot and humid tropical forests.

1.3.3 Deforestation in the Peruvian Amazon

Covering 646 000 km2, Perú is host to the second largest part of the tropical forests found in Latin America behind Brazil, which has 5 389 000 km2. In contrast to regions outside of the tropics, where forest areas have increased in recent years, deforestation has continued. Between 1999 and 2000, 142 000 km2 of forest were cleared (FAO 2001). These forests are exploited for their timber initially and subsequently used for cultivation and as pasture. Up until the year 2000, the total area of Perú that had been deforested was 56 760 km2. The annual rate of deforestation between 1990 and 2000 was estimated at 1 500 km2, the 2 equivalent of 4.1 km /day (CONAM-INRENA 2005). It has been estimated that the cover of 80 % of the deforested areas consists of secondary forests and pioneer vegetation in the first phase of succession (INRENA 1996). Large areas of secondary forest have been exploited for farm use under a system of shifting cultivation. This includes a fallow period, important as it facilitates the restoration of soil fertility. At the same time, the forests that develop during this fallow period contribute to the restoration of resources with different potentials such as timber and non-timber forest products, as well as protection and environmental services.

1.3.4 Land use dynamics in the Pucallpa region

The dynamics of land use in the study area were described by YANGGEN (2003). Land use in Pucallpa changed dramatically with the arrival of settlers. During the course of the first 10 years the principal change in land use was from primary forest to agricultural production (Fig. 1.4, next page). 10 General introduction and general statement

60 Primary (1) 50 forest Secondary 40 forest Annual 30 crops Pasture (2 20 Land use (%) (3) Perennial 10 (4) crops (5) 0 0 - 5 5 - 15 15 - 2 5 >2 5 Years farming Fig. 1.4: Land use change in the Pucallpa region (adapted from YANGGEN 2003). After 1-3 years of cultivation, land parcels were left fallow and here secondary forests began to regenerate naturally. The intensity of pasturing was relatively low initially but after 10 years the conversion of primary forest continued with a marked increase in area of pasture land. This land use change was not direct, but rather a result of the prevention of the regeneration of secondary forest after the cultivation of annual crops. The farmers employed shifting cultivation techniques because of the low capital input requirements involved. The majority of the settler-farmers lacked the financial resources necessary for the purchase of cattle (YANGGEN 2003). They increased the area of land held in pasture due in part to the declining fertility of the soils after repeated cycles of shifting cultivation. Rather than move to new holdings, the farmers often changed their land use system to pasture and perennial crops.

1.4 CULTURAL AND FOREST CONDITIONS IN THE STUDY AREA

1.4.1 Political and social aspects

The Peruvian Amazon has been occupied for thousands of years, by many ethnic groups (DENEVAN 1976). Currently there are only 300 000 indigenous people living in the Peruvian tropical forests. The low population density and the production systems employed by the indigenous people are well suited to the ecological conditions and result in no degradation of the land. The difficult living conditions and the resistance of the indigenous people to the exploitation of resources by outsiders made the colonisation of the Amazonian region difficult for centuries. Spaniards and mestizos were the first to colonise the high jungle. The actions of missionaries trying to convert the indigenous people and later the exploitation of rubber trees encouraged Peruvians to begin the colonisation of the northern low jungle territory (Iquitos was founded in 1864). This was subsequently followed by the colonisation of the middle low jungle territory (Pucallpa was founded in 1883) and finally the southern low jungle territory (Puerto Maldonado was founded in 1902).

General introduction and problem statement 11

Pucallpa, the capital city of the Ucayali Department, is located 85 km west of the Brazilian border, in the middle of the Peruvian lowland rainforest. An 800 km paved road that crosses the Andes mountains connects it with the national capital Lima. With 200 000 inhabitants, Pucallpa is the second largest and fastest growing city in the Peruvian Amazon. Low incomes, a scarcity of land and poverty in other parts of the country have forced many people to migrate to the region. New infrastructural development, cheap and abundant land, job opportunities and, more recently, coca leaves production, have all been major enticements (RIESCO 1993, LABARTA 1998). Ucayali’s economy still revolves primarily around timber, tourism, agriculture, gas and oil (Tab. 1.3).

Tab. 1.3: Economic activities in the Ucayali Department in 1999 (INEI 2000a).

Source of income Net income Millions of US $ % Timber industry 342 51 Tourism 124 19 Agriculture 112 17 Gas and oil 27 4 Others 62 9 Total 667 100

1.4.2 The settlement of farmers in the Pucallpa region

The Pucallpa region (Fig. 1.5) was colonised by agriculture and, in particular, livestock enterprises. These colonists, however, later directed >70 % of their economic activities towards forest production, but have exhibited no interest in managing the forests, protecting them from damage or in reforesting.

Fig. 1.5: Settlements in the Pucallpa region (adapted from : http://www.asb.cgiar/gallery/PERU/Aguaytia-Caserios.jpg) 12 General introduction and general statement

In 1965 the state established the Alexander von Humboldt National Forest near Pucallpa (Fig. 1-5). This forest originally covered 645 000 ha, and an ambitious plan was developed for forest research, management and production. With assistance from the FAO, important efforts were made in the 1970s, of both scientific and practical significance (DOUROJEANNI 1976).The proposed forest management plan, incorporating state administration and exploitation, proved unrealistic however, and was not implemented successfully. This national forest was the largest and most important production forest in the Peruvian Amazon. Since its establishment, it has been depleted by illegal timber extraction and migratory agriculture. Today, those areas of the national forest located near rivers and roads are fully occupied and almost entirely divided up between timber exploitation concessions (LINARES 1995). In the 1970s many cattle ranches were established along with the roads constructed adjoining the main route connecting Nueva Requena, Campo Verde and Tournavista (Fig 1.5). The road between Neshuya and Curimana was completed in 1990. Many farmers have since established oil palm plantations along this route.

1.4.3 Agricultural production systems employed in the Pucallpa region

There are diverse and often multiple land use strategies evident in the Pucallpa region. Agricultural activities include slash and burn agriculture with a variety of annual and perennial crops, cattle ranching and pasturing, and oil palm plantations. The staple crops include plantain, rice, cassava and maize (primarily for animal consumption). The perennial crops include pineapple, citrus fruits and papaya. Fishing provides the main source of protein and is often supplemented with meat from wild animals hunted in the surrounding forests. The extraction of timber, fruits and other materials is carried out for both commercial and subsistence purposes. Sites across the region differ in terms of the diversity of the land use activities taking place, as well as with respect to the dominant land use strategies. The most obvious ecological differences exist between the fertile floodplains (or varzea) and the highly weathered soils of the upland forests. The type of agriculture practised, and the production cycles, varies between these areas. The fertile river banks and forests in the lowlands are available for cultivation only during the dry months, and provide farmers on the floodplain with a brief opportunistic period of production before the rains begin and the rivers flood their banks. There exist, however, more subtle differences within these two landscape types. In the floodplain there are areas that are flooded annually and others that are flooded only during years of high rainfall (usually every 5-7 years). Here there are subsequently differences in the soil types and thus the suitability for different agricultural crops. Similarly, there are pockets of fertile areas to be found within the upland forests. The exploitation of resources in the surrounding landscape types results in diverse seasonal combinations of farming, fishing, logging, hunting and gathering activities. In the study area, the dominant land use strategies, access to markets and involvement in the

General introduction and problem statement 13 market economy range from primarily subsistence livelihoods combining fishing, farming, hunting and logging to monocultures, commercial cattle ranching and oil palm cultivation subsidised by the United Nations and the national government. These differences are closely linked to location with respect to rivers, roads, markets and the availability of natural resources (MURRAY & PACKHAM 2002). In the uplands farmers begin the preparation of the land for cultivation with the slash of primary or secondary forests at the beginning of the dry season (June/July). After a 3 month desiccation period, they burn the vegetation before the end of the dry season (September/October).

1.4.4 Timber industry in Peru and in the Pucallpa region

Almost 90 % of the timber industry in Peru practices the mechanical transformation of round wood into timber. In order of importance, the following products are produced for exportation: sawn timber, plywood, parquet, veneer, others. Firewood is not included (Fig. 1.6). This industry supplies itself essentially with timber from tropical forests. The wood transformation industry has three large centres of development: Loreto, Ucayali, and the central forest, which covers the regions Oxapampa, Villa Rica and Satipo, among others. In these areas, 95 % of the economic activities are centred on the timber industry.

10 0 0

TOTAL

10 0 Sawn timber 3

Plywood

Parq uet 1000 m 1000 m 10 V eneer Ot hers

1 19 9 5 19 9 6 19 9 7 19 9 8 19 9 9 Year

Fig. 1.6: National industrial timber products: 1995-1999 (INEI 2000b).

The international demand for tropical forest products is high. The main consumers are Asia (especially Hong Kong, Japan, Korea and Taiwan), North America and Europe. In 1996, these regions consumed 34, 33 and 24 % of the world’s tropical timber products respectively (INEI 2000b). The supply situation has changed drastically as a consequence of the exhaustion of the forests of the Southeast Asian countries. Added to this is the constant growth of the 14 General introduction and general statement international demand for tropical timber generally, rendering the Amazon basin, including Peru, an important strategic reserve for the sustainable production of timber products for the rest of the world. Peruvian timber exports in the year 2000 represented only 1.1 % of the total income derived from national exports. Pucallpa occupies a strategic position, situated at the centre of the low Amazon region and located at the edge of the River Ucayali, which serves as a main port for a gigantic network of rivers and facilitates the transport of timber. During the rainy season, the high quantities and long duration of the precipitation feed the rivers and make possible the extraction of logs through the narrow ravines. Pucallpa is an important centre of communication and connects the main cities of the central Andes, the capital city on the Pacific Ocean Lima and the rest of the lowland Peruvian Amazon. For the last 30 years this city has been the centre of the Peruvian timber industry. The national timber industry has improved significantly in recent decades, but its progress is limited by several factors, including insufficient production to meet the current high demand, poorly diversified industrial production, insufficient product quality control, an inefficient system of harvesting and transport, poorly developed wood technology and the availability of only a limited number of tree species. Altogether, 80 % of the national timber industry relies on 12 species, including spanish cedar (Cedrela odorata), mahogany (Swietenia macrophylla) and tornillo (Cedrelinga catenaeformis). These three species make up more than 35 % of the national lumber production. Even though these species usually occur in low densities per ha, together they provide an average volume of 3.5 m3 round wood/ha nationally, and 2 m3 per ha lumber.

1.5 PERSPECTIVES FOR THE SUSTAINABLE MANAGEMENT OF SECONDARY FORESTS IN THE REGION

Timber extraction always targets high value timber to ensure that a profit is recouped after the high costs of transformation and transport have been met. The consumers come mainly from other regions of Peru or abroad. To date the traditional timber industry has paid scant consideration to the needs of the local inhabitants. Peruvian forest legislation obliges concession holders to replace the exploited timber resources. Early forestry activities in Perú in the 1960s and 1970s saw the establishment of plantations with both local and exotic tree species, followed in the 1980s by natural regeneration strips (HARTSHORN 1989). Species/Silvicultural trials carried out at the time were not successful as consequence of technical, economic and social difficulties. Round timber has always been one of the most important products of secondary forests in rural areas, but was of no commercial significance. In the last decade, small dimension timber produced from some tree species of the secondary forests has provided rural inhabitants with an extra source of income and encouraged them to increase the forest

General introduction and problem statement 15 coverage, or to persist with it for longer within the production cycle of the slash and burn agricultural system. The current crop of small dimension timber is produced from homogeneous stands regenerated in secondary succession areas. Plantations and management activities are too expensive given the current timber prices.

1.5.1 Knowledge of natural resource management in the study area

Many difficulties arising in relation to the use of the land by rural inhabitants have originated from cultural differences evidenced between the various landowners and their lack of knowledge of the management of the local natural resources. Migrants to the Amazon region from the Andes possess knowledge obtained over the span of only a single generation. The traditional non-intensive methods of land exploitation are readily adopted by the new arrivals settling in the Amazon. However, these methods are no longer appropriate given the much higher current population density. It is, therefore, necessary to develop and promote knowledge of more suitable forms of management of natural resources, to be employed by both old and new rural Amazon inhabitants. New production activities may be developed to help farmers reduce deforestation without impacting upon incomes.

1.5.2 Timber from young secondary forests

As the principal commercial species of neotropical secondary forests are fast growing light demanding species forming even-aged populations, FINEGAN (1992) proposed a uniform system (for example, the Trinidad Shelterwood System) as an appropriate general framework for the silviculture of secondary forests. This system focuses timber production on species of the 3rd phase of succession, defined by the dominance of long-lived intolerant species (Fig. 1.2). The period of time required for the restoration of the productivity of the soils in most areas of the Peruvian Amazon (Fig. 1.4) where the shifting cultivation system is practised does not permit timber production until the 3rd phase of the succession process. The farmers of the Peruvian Amazon have been urged to find methods of land management requiring low investment and to generate the required resources without degrading the productive capacity of the soils. In the last 10 years, both in the Pucallpa region and at a national level, changes in the supply of and demand for timber have opened markets for the timber of trees of small dimensions derived from secondary forests. Some species typical of intermediate stages grow very quickly and often establish homogeneous stands. Ten years ago these homogeneous stands were burned. Today many small landholders use this resource as a source of income. Higher prices for trees with greater dimensions can entice farmers to prolong the duration of the fallow period. The production of timber originating from secondary forests has become an important factor in stabilising the migratory population of the Peruvian Amazon, and in reducing the pressure on the remaining primary forests and the further degradation of already occupied land. Recently colonised areas offer better ecological conditions for the establishment and 16 General introduction and general statement management of secondary forests. However, these are generally located far from consumption centres. The promotion of productive secondary forests on non-degraded areas still possessing abundant seed sources, non-degraded soils and access to markets must take place urgently, before these characteristics are lost.

1.6 HYPOTHESES AND OBJECTIVES

1.6.1 Hypotheses

The hypotheses underlying the present study are:

• Seed trees can help to establish productive homogeneous stands of fast growing species on fallow land in the study area, and in similar areas elsewhere.

• The identification of seedlings and saplings of fast growing tree species in the first successional phase may be an important factor in deciding the management of fallow land.

• Adequate cleaning and tending of stands can aid the successful natural regeneration of commercial species threatened by aggressive successional vegetation.

• Substrate conditions can affect the germination and establishment of pioneer tree species.

• The preparation of soil for agricultural production before the rainy season clashes with the dispersion time of pioneer tree species. This coincidence favours those species adapted to seed dispersal in the dry season prior to the onset of the rainy season.

• The presence of an adequate quantity of established regrowth of commercial tree species in a young secondary forest will encourage farmers to wait until the appropriate time before harvesting timber from secondary forests and initiating a new phase in the agricultural production cycle.

• Homogenous stands of commercial tree species established through direct seeding may be cheaper than plantations.

1.6.2 Objectives

1.6.2.1 General objectives

The general objectives of the present study are:

General introduction and problem statement 17

• To obtain knowledge and to develop appropriate silvicultural techniques to regenerate productive secondary forests naturally, employing fast growing tree species.

• To obtain knowledge of the ecological conditions favouring the establishment of fast growing species on fallow land.

1.6.2.2 Specific objectives

The specific objectives of the present study are:

• To assess the financial benefits of timber production to farm families.

• To provide a means to facilitate the reduction of the areas currently under the slash and burn system of cultivation and to lessen the need for migration by rural families.

• To promote secondary forests as a renewable resource with the capacity to produce sustainable incomes for farm families in agricultural frontier zones.

• To evaluate the interaction between the establishment of homogeneous stands and the dispersion of the four pioneer tree species studied.

• To describe the morphology of the seedlings of the tree species studied.

• To evaluate the phenology of the tree species studied.

• To evaluate the influence of substrate type on the germination of commercial pioneer species.

• To describe the first successional phases of the pioneer vegetation on fallow land.

• To evaluate options for the regeneration of stands on non-degraded abandoned cropland without seed trees by means of direct seeding.

18 Description of the study area

2 DESCRIPTION OF THE STUDY AREA

2.1 LOCATION AND COLONISATION OF THE STUDY AREA 2.1.1 Location of the study area

The study area is located in the low jungle ecoregions of Peru (BRACK 1986). Politically it is part of the Ucayali Department, the capital city of which is Pucallpa. An area characterised by a relatively low degree of degradation of the vegetation resources was identified along a secondary road branching off the main road bisecting the district. This area was located at a distance of roughly 60 km from Pucallpa. The secondary road was built in 1990 to connect Neshuya and Curimaná (Fig. 2.1) At the time of the field work phase of this study the oldest secondary vegetation was 10 years of age.

Fig. 2.1: Deforestation in the Pucallpa region (IIAP/CRP, 1996).

The study area is located between the geographical coordinates 8° 24’ S-8° 36’ S and 74° 57’ W-75° 09’ W, at an average altitude of 300 m a.s.l.

2.1.2 Colonisation of the study area

As a consequence of the continuous process of colonisation of the Pucallpa region even the least accessible places were occupied. This led to a great decline in the primary forests situated near towns, roads and the borders of the great rivers. In these areas, pastures and permanently cultivated land have been established. In the remote areas a mosaic of residual

Description of the study area 19 primary forest, secondary forests in different successional phases, pastures and areas of temporary cultivation can be observed. Fig. 2.1.1 provides an indication of the status of the vegetation and soils on the basis of the age of the respective settlements and their proximity to the nearest transport routes. SMITH et al. (1997) referred to a classification developed by RICHARDS (1996) for the definition of the different stages of frontier development in relation to slash and burn farming. The presence of 3 stages of development in the Pucallpa region represented an important aid in the localisation of land suitable for the field experiments carried out as part of this study. The 3 stages are: • Early pioneer stage This stage is characterised by minimal infrastructure, governance and participation in market activities. It refers to the time immediately after the settlers’ arrival in a forested area. • Emerging market economy Infrastructure and market access has improved and land tenure has become more formal. These areas are relatively accessible and comprise residual areas of primary forest, secondary forest and fallow land close to rich seed sources. • Closed frontier There is little forested land still available for colonisation, and infrastructure and market integration show further improvement. By the third phase the land in question is situated close to primary routes and large towns. As consequence of the high levels of degradation of the soils and the poor availability of seed sources, these areas do not provide favourable ecological conditions for the successful management of secondary forests.

2.2 ENVIRONMENTAL FACTORS

2.2.1 General climate conditions

The climate of the study area corresponds to that of the tropical moist forests, according to the Holdridge life zones system (HOLDRIDGE 1967). The climate diagrams in Fig. 2.2.1 are based on data from weather stations situated in Pucallpa (Fig. 2.2.1a) and San Jorge (Fig. 2.2.1b, next page). These are located 60 and 20 km from the study area, respectively. That they reveal similarities despite the distance between them makes it reasonable to assume that no important climatic differences occur across the study area. Two marked seasons are evident in the region. A dry season occurs between June and August, and an intense rainy season between November and March. The temperatures are generally high, with averages of 24-26 °C. The minimum average temperatures fall to 18- 20 ºC, and the maximum values reach 33-36 ºC. The daily temperature oscillations (5-8 ºC) are greater than the yearly variation (1-2 ºC). The mean relative humidity is >75 % (CLAVO 1993). 20 Description of the study area

The evapotranspiration from the forests has a substantial function in the regional precipitation regime and the hydrological balance. A particular phenomenon is the occurrence of occasional frosts from May to August originating in cold fronts, called friajes or surazos. These frosts blow north from the southern tip of the subcontinent, hit the southern jungle and cause temperatures to fall to 12-15 ºC (MARENGO 1984, 1998).

San Jorge 1 773 mm 26 ° C P ucallpa 1 568 mm 26,1 ° C mm ° C mm ° C 300 300 12 0 60 12 0 60 200110 201100 10 0 50 10 0 50 90 90 80 40 80 40 70 70 60 30 60 30 50 50 40 20 40 20 30 30 20 10 20 10 10 10 0 0 0 0 JASONDJFMAMJ JASONDJFMAMJ

Fig. 2.2a: Mean monthly temperature and Fig. 2.2b: Mean monthly temperature and rainfall for Pucallpa. rainfall for San Jorge.

2.2.2 Physiography, geology and soils of the region and the study area

2.2.2.1 Physiography

The elevation gradients in the Amazon plain (90-500 m a.s.l.) are often small. However, in areas close to the Andes and in any of the low mountains (Contamana, Cerro del Divisor), with elevations reaching approximately 100 m above the surrounding areas, there may occur elevation gradients that are very significant for the flora and fauna inhabiting the region. The geomorphology shows various relief types in the different zones within the region, for example, alluvial plains, high terraces, hillocks and hills with different slopes. This occurs in a very complex form in the region, and hence the Selva baja appears as a great mosaic of areas differing greatly in their geomorphology. The soil types and their drainage systems follow the relief variations, thereby contributing to a wider range of substrate types, which in turn influences the distribution of the floral species (KALLIOLA et al. 1993). In the study area (Neshuya) 2 greatly differing landscape types exist, namely plains and hills (EGOAVIL 1989).

Description of the study area 21

The plain landscapes make up 80 % the study area, characterised by flat to lightly undulating and undulating surfaces with slopes of between 0-8 % (Fig 2.3). This landscape is located from a point near the town Neshuya to the 29 km marker along the Neshuya– Curimaná road. The hill landscape is characterised by hills and hillocks, and possesses a complex relief. The slopes vary between 8-25 %. The landscape extends from the 29 km marker along the Neshuya–Curimana road to the River Aguaytia.

Fig 2.3: Characteristic vegetation types in the plain/undulating landscape. Grasses and herbs are evident in the foreground, shrub vegetation in the middle ground, and residual areas of primary forest in the background.

2.2.2.2 Geology

The Occidental Amazon, a strip of some 100 km in width, is a sedimentary basin running parallel to the Andes. The sedimentary formations of the upper zone reveal variable patterns, with a wide range of deposits of different ages and origins (PEÑAHERRERA 1989). In the mid Miocene Period, approximately 15-20 million years ago, a large part of the Peruvian Amazon was characterised by a very particular ecological condition, namely a coastal ecosystem. One of the oldest clay sediments deposited in the Amazon is known as the Pebas Formation (HOORN 1983; RÄSÄNEN et al. 1998). In recent geological periods, lakes of great dimensions and long durations have been absent from the Occidental Amazon. The Subandean Basin is divided into different minor basins. These were subject to the continuous sedimentation of material transported by the rivers. More recently, sediments of Holocene origin have been identified in the flood plains (younger than 10 000 years). Diverse terraces dating back to the Pleistocene also exist. The remainder of the Peruvian Amazon plain is characterised by superficial processes of leaching and weathering, resulting in the creation of a hilly landscape with poor soils (ONERN 1982; HOOM 1993; RÄSÄNEN et al. 1995).

22 Description of the study area

2.2.2.3 Soils

Generally, the soils of the non-inundated areas and terraces of the Amazon plain are acid and of low fertility. They are also well drained, deep and have a high clay content. Additionally, there are very infertile, heavily leached sandy soils with a high quartz content. These are referred to as white sands (KAUFFMAN et al. 1998). On the more recent terraces the soils are young and poorly differentiated. Occasionally these soils are very poorly drained. The inundated areas by contrast possess fertile and well drained soils (RODRIGUEZ 1990). CLAVO (1993) described the soils of the non-inundated areas of the Pucallpa region as red-brown soils, with high levels of exchangeable Al, and low N, P, K and organic matter. In the taxonomy these are classified as Ultisols. Their main characteristic is their low fertility. The Neshuya sector is situated in a continental sedimentation basin, formed by the deposition of detritic (sedimentary) materials during the Tertiary and Quaternary periods. The soils derived from residual materials are widely distributed, filling plains and plain- undulating physiographic positions with light slopes. The soils have a low to medium genetic development, medium to fine texture, and are extremely acid. The soil classification indicates that 86 % belong to the Inceptisol order (great groups Eutropept and Dystropept), or to the Cambisol group according to FAO classification (BUOL et al. 1991). Only 14 % belong to the Entisol order. These are alluvial soils located in the valleys and in the plains flooded by the main streams in the region (EGOAVIL 1989).

2.3 FORESTS IN THE PUCALLPA REGION

2.3.1 Primary forests in the study area

From the ecological map of Perú (ONERN 1976, according to HOLDRIDGE 1947, 1967), the study area is located in the tropical humid premontane forest life zone, at the transition to tropical humid forest. The UNESCO international classification system and mapping of vegetation (1973) defined the forests in the study area as ombrophilous lowland forests and evergreen seasonal lowland forests. The forests are adapted to the local soils and physiographic conditions. Although the nutrient status of the soils in the study area is too low for agriculture, the humid tropical forests in this zone are highly productive, with an average biomass in excess of 400 m3/ha. As much as 40 % of this is exploitable timber. Of the >2 500 tree species encountered in Peru’s tropical forests, many do not produce valuable timber or are not common enough for commercial exploitation. Forest inventories carried out in Peru have recorded 250-400 species per region, with the most abundant species represented by 10-15 individual trees/ha and the least abundant by 0.01 trees/ha. Despite the seemingly very high numbers of tree species found in tropical forests, some are much rarer than others, and only a few species account for most of the total volume (MALLEUX 1982). Neotropical humid forests in their natural state are relatively complex.

Description of the study area 23

Whereas they are heterogeneous floristically, they are homogeneous with respect to volume (Tab. 2.1).

Tab. 2.1: Proportion of volume according to the abundance of species in neotropical forests (DOUROJEANNI 1982).

The 10 most The 20 most The 50 most abundant species abundant species abundant species % % % 44 62 78

2.3.2 Secondary forests in the Pucallpa region

Different types of vegetation have developed on the colonised land in the Pucallpa region, depending principally on the intensity and on the time of exploitation. ALVA & LOMBARDI (2001) classified 3 categories of successional vegetation within Terra Firma forests in Pucallpa: • Natural succession fallow. • Secondary vegetation on degradated areas. • Fallow with kudzu (Pueraria phaseoloides). Only the first of these 3 categories has the potential to be managed for the production of commercial timber (FINEGAN 1992), due to the low level degradation of the soils and the presence of sufficient seed sources. Secondary forests may have different origins, depending on the history of human intervention. According to their composition, they may be classed as either heterogeneous or homogeneous. The most common secondary forests are dominated by different pioneer tree species, also known as heterogeneous secondary forest. This type of secondary forest is that most commonly encountered in the study area, and in other tropical countries. It is, therefore, also the type that has been studied most intensively and described in the greatest detail. When a single pioneer tree species dominates the composition of a forest, the vegetation is referred to as homogeneous secondary forest. This forest type covers only a small portion of the surface area in comparison with the first type. The purpose of the description and analysis of the composition, structure and growth of the secondary forests of different ages in the study area is to provide the knowledge necessary for the prediction and interpretation of the changes that can occur with the initiation of secondary succession. In the following paragraphs the heterogeneous and homogeneous forest types encountered in Pucallpa will be described in greater detail.

2.3.2.1 Heterogeneous secondary forest stands

GALVAN et al. (2000) and CORONADO et al. (2002) defined 3 subcategories of secondary forest in the Pucallpa region on the basis of age.

24 Description of the study area

,years 5-7 ־ years and 8-10 ־ .years 10< ־ The reason for the age division is that some secondary fallows <5 years of age do not clearly constitute forest. In forests between 8-10 years of age important changes to the composition of the dominant species occur. In forests >10 years certain species characteristic of the intermediate stages of succession appear. Terra Firma secondary forests were evaluated in 3 sectors of the Pucallpa region. Forest exploitation took place at different times in each sector, corresponding with the different time of construction each secondary roads branching off from the primary Pucallpa-Lima road. GALVAN et al. (2000) and CORONADO et al. (2002) evaluated the floristic composition and stand parameters of secondary forests with a view to the potential for utilisation. ALVA & LOMBARDI (2001) evaluated the historical and socio-economic aspects of the secondary forests in the region. According to the classification of the stages of colonisation proposed by RICHARDS (1996), the sector Neshuya corresponds to the aforementioned ombriphilous areas. The sectors Nueva Requena and Semuya are closed frontier areas. No great differences in the stand parameters of the secondary forests (CORONADO et al. 2002) were evident between the 3 sectors evaluated (Tab. 2.2). Tab. 2.2: Stand parameters of secondary forests in the 3 sectors studied within the Pucallpa region. Age classes: 5-7 years, 8-10 years, >10 years (CORONADO et al. 2002).

Sector Age Abundance Average Maximum Average Basal Volume class height height DBH area years trees/ha m m cm m2/ha m3/ha Neshuya 381 12.1 16.9 13.7 6.2 38.1 Nueva Requena 5-7 463 11.6 15.7 13.4 6.9 42.4 Semuya 373 12.2 17.0 13.7 5.9 37.7 Neshuya 483 12.5 18.8 15.1 9.8 69.2 Nueva Requena 8-10 490 11.9 21.3 14.6 8.9 57.8 Semuya 438 12.7 21.0 15.6 9.4 70.5 Nueva Requena 364 12.4 20.0 17.8 10.9 76.4 Semuya >10 498 13.7 20.7 16.5 11.8 87.7 In almost all cases, the Neshuya and Semuya sectors exhibited higher stand parameter values than Nueva Requena. This may be explained by the better soil conditions in these sectors than offered by the sandy soils of Nueva Requena. As was expected, the average and maximum height values at 5-7 and 8-10 years demonstrated fast growth in comparison with other secondary forests (BROWN & LUGO 1990). The lower maximum height values evidenced for stands >10 years of age than those of 8-10 years may be explained by the extraction by farmers of the tallest trees in the older successional forests. GALVAN et al. (2000) summarised the tree diameters in the stands present in these 3 sectors, and revealed the dynamic of secondary forests on the basis of diameter and age class. All diameter classes follow a characteristic inverted J or left skewed curve (Fig. 2.4 next page).

Description of the study area 25

600

510 500 I (5-7 years) 452 406 400 II (8-10 years) III (>10 years) 297 300 284

200 194 157 147 Number of trees / ha

10 0 94 70 46 26 14 10 9 5 3 3 2 1 0 10-15 15-20 20-25 25-30 30-35 35-40 40 + TOTAL Diameter class (cm) Fig. 2.4: Distribution of trees according to age and diameter class in the secondary forests around Pucallpa (GALVÁN et al. 2000).

The 5-7 year old trees were mainly concentrated in the first diameter class. Their numbers decreased notably in the higher diameter classes. A similar trend was observed in the older forests. Secondary forests of age 5-7 years revealed a lower total number of trees than observed in older forests because a considerable number of trees in them were <10 cm DBH, and as such were not recorded. By comparison, the number of individuals in forests >10 years of age decreased. This is a consequence of the mortality of the short-lived tree species and great competition. Tab. 2.3.2 shows the biomass increment within the 3 age classes.

Tab 2.3: Stand parameters in secondary forests according to age class (GALVÁN et al. 2000).

Parameter Age class (years) 5-7 8-10 >10 Basal area (m2/ha) 6.4 10.6 11.5 Volume (m3/ha) 39.9 75.9 82.4

To evaluate the ecological relevance of the species making up the secondary forests inventoried, the abundance, frequency and dominance of each species were determined using the importance value index (IVI) (CURTIS & MCINTOSH 1951). Tab. 2.4 (next page), based on data presented by GALVÁN et al. (2000), provides a good overview of the more important species of the secondary forests in the region. The species are presented for each of the 3 forest age classes, and ordered using the IVI. The species are listed in decreasing order of the total IVI values for all of the forests evaluated. A total of 6 species constituted > 50 % of the IVI in all of the secondary forests of the 5-7 year age class evaluated, and 7 species in the other forests. This indicated that half of the IVI was made up of only 10 % of the species (GALVÁN et al. 2000).

26 Description of the study area

Tab. 2.4: Relative importance value index (IVI %) of secondary forest species in Pucallpa (GALVÁN et al. 2000).

Species Age class (years) 5 – 7 8 –10 > 10 Cecropia spp. 10.8* 31.9* 12.2* Guazuma crinita 5.6 5.9* 13.8* Heliocarpus popayanensis 11.0 6.3* 5.7* Inga spp. 9.5* 8.9* 2.2 Inga spp. 4.0 5.1 7.3* Cecropia engleriana 6.3* 7.7* 2.2 Ochroma pyramidale 9.0* 4.3 Croton matourensis 4.5 4.5 2.9* Cordia alliodora 3.8 5.4* 2.7* Rollinia spp. 4.2 2.8 1.8 Miconia spp. 7.1* Trema micrantha 6.1* Cecropia membranaceae 5.6* Jacaranda copaia 2.6 Myriocarpa stipitata 2.5 Zanthoxylum spp. 2.5 Isertia alba 2.4 Vismia spp. 2.2 Apeiba membranaceae 2.2 Guatteria spp. 2.0 Parkia spp. 1.9 Vismia ferruginea 1.8 Subtotal (2 species) 21.8 22.8 26 Subtotal (50 % IVI)* 52.7 53.7 51.7 No. of species 6 7 7 Subtotal (75% IVI) 74.8 75.2 74.8 No. of species 11 13 18 IVI other species 25.2 24.8 25.2 No. of species 42 52 53 IVI total species 100 100 100 No. of species 53 65 71

Cecropia (Cecropiaceae), a genus containing 71 species and limited to the neotropics (BERG et al. 2005), is well known as a pioneer plant abundant in gaps and amongst the secondary vegetation in tropical rainforests. It has positive restorative effects in degraded areas, although often it establishes on very poor soils. Most of the species of this genus exhibited the fastest growth rates in the forests studied. They dominated the canopy in the first and second phases of succession. The higher IVI value of Cecropia spp. in the forests of 8-10 years indicated the moderate lifespan of these species. In the secondary forests >10 years of age the species’ IVI values decreased.

Description of the study area 27

The substantial increase in Guazuma crinita in forests >10 years of age may be explained by the fact that smallholders recognised its local commercial importance. They preserved the stands with a significant proportion of trees of this species. The reduction in the IVI values of Ochroma pyramidale and Heliocarpus popayanensis in the forests of 5-7 and 8-10 years of age could be explained by their natural mortality. These species have only a short lifespan (VÁZQUEZ-YANES et al. 1999). Inga is a genus with a high diversity of species (GENTRY 1993). Most of these tree species grow in the intermediate stages of succession. Its use as firewood is widespread in the American tropics (PEETERS et al. 2003), which explained the reduction in the IVI values of the first Inga spp. group in the age classes II and III. The opposite occurred in the case of the second Inga spp. group. A possible explanation for this difference was that some cultivated species produce large, nutritious fruits (SOTELO & WEBER 1997), and as a consequence some trees regenerate spontaneously over the course of succession. Cordia alliodora is a species producing medium value timber in other neotropical countries (SALAS 1981) and even in other regions of Peruvian Amazon, but in Pucallpa it attains only small dimensions and low growth rates. Trema micrantha is an abundant tree species of the first phase of succession with a short lifespan. It appeared only in forests of the 5-7 year age class. Species of the second and third phases of succession such as Myriocarpa stipitata, Zanthoxylum spp., Apeiba membranaceae, Parkia spp., Guatteria spp. and Parkia spp. arose in forests of age class III. The number of species increased according to the age of the forests evaluated.

2.3.2.2 Homogeneous secondary forest stands

The presence of homogeneous stands of commercial species in the study area may be illustrated on the basis of CORDOVA´s (1992) evaluation of Jacaranda copaia (Tab. 2.5). Revealed in the table is a high concentration of natural regrowth in the younger stands. The density of the natural regrowth decreased in the 8 and the 20 year old stands. A logical explanation for the decline was the mortality of suppressed individuals and the recruitment to the larger DBH classes of the more vital trees. On the other hand, the presence in the 15 year old stands of a high number of individuals belonging to the smallest DBH class may be explained by the subsequent establishment of new individuals.

Tab. 2.5: Number of Jacaranda copaia individuals/ha according to diameter class in naturally established stands of different ages in the Pucallpa region (CORDOVA 1992).

Age DBH class (cm) (years) <1 1-5 5-10 10-15 15-20 20-25 25-30 30-35 35-40 40-45 Σ 5 1500 344 244 33 2121 8 2500 1200 133 155 133 44 4165 15 1666 400 78 111 156 100 22 2533 20 1000 289 200 89 67 55 11 1711 25 33 44 89 78 67 11 11 333

28 Description of the study area

In the 5, 8 and 15 year old stands, the abundance of individuals belonging to the low DBH classes could be explained by the continuous recruitment of new trees as a consequence of the presence of seed trees. In the 20 year old stands, and the younger stands, the number of individuals per DBH class followed an inverted J curve. The abundance per DBH class in the 25 year old stands revealed a normal distribution. The absence of individuals belonging to the lower classes was probably the result of mortality arising from competition. Despite of lack of management, the stands were characterised by a high number of individuals with fast growth rates. These stands possess great potential for timber production. With appropriate silvicultural intervention, such as the regulation of spacing and density, the growth and the quality of these trees may be improved.

2.3.3 Use of secondary forests in the Pucallpa region

Secondary forests possess several features of value for human use. Studies have indicated the importance of successional processes as a basis for different forms of sustainable land use by rural people, and the management potential of secondary forests for the production of food and forest products (SIPS 1997). The restoration of agricultural productivity may be the most important use of this type of vegetation at present. However, it is well known that the sustainability of slash and burn agriculture appears to be questionable in light of current socio-economic conditions (FINEGAN 1997). The direct utilisation of plants from secondary forests in the region is highlighted in Fig. 2.5.

250

234 Uses

5-7 years 1. High value timber 200 8-10 years 2. Low value timber 3. Small dimension timber

> 10 years 157 4. Local construction 150 149 (round timber) 5. Firewood

107 6. Fruit and nuts 10 0 7. Medicinal use

88 87 84

82 8. Handcraft Tree number / ha 75 72 68 9. Unknow / no use

50 48 22 12

11 9 9 8 8 7 7 5 6 4 1 0 1 0 1234 56789 Us es

Fig. 2.5: Distribution of the numbers of trees/ha according to use and age class (GALVÁN et al. 2000). The very low number of trees extracted from secondary forests for use as firewood may be explained by the fact that farmers prefer the dry trunks of hardwood species standing on abandoned agricultural land, the last remnants of primary forests. Most of the species of secondary forests produce softwood, and are not suitable for energy production purposes.

Description of the study area 29

According to the data presented in Fig. 2.3.3, the trees harvested from secondary forests are used mainly for local construction, as small dimension timber, low value timber and for food production. Similar results were evident for the 3 age classes.

2.4.1 MANAGEMENT OF SECONDARY FOREST IN TROPICAL REGIONS

The arousal of interest in secondary forests in the neotropics began in places with high population densities, especially in the Caribbean, Central America and southern Mexico, where the areas of primary tropical forests had been strongly depleted (GREIG-SMITH 1952, BUDOWSKI 1963; GOMEZ-POMPA et al. 1976, RAMOS et al. 1982). In these areas, the initial interest in secondary forests focused on management for timber production. This arose as a consequence of the decline in the availability of timber from primary forests (MARTINEZ 1979, FINEGAN 1992, RAMOS & DEL AMO 1992, GUILLÉN 1993, HUTCHINSON 1993, FEDLMEIER 1996, SIPS 1997; CHIARI 1999).

2.4.1 Secondary forest management strategies

DE JONG et al. (2001) adjudged that the principal reasons for farmers to leave secondary vegetation to develop were to restore soil fertility and to reduce the number of weeds in agricultural fields. In this case, the indirect use of secondary forest also constitutes a form of secondary forest management. In the low restingas (inundated forests) soil recuperation was an important reason for allowing secondary vegetation to develop. Most low restinga sites are understood to be flooded yearly, and subsequently possess constant levels of relatively high soil fertility. This, however, appears not to be the case for all low restinga sites, as 20 % of a total evaluated area of 270 ha was left fallow because of low fertility. Overall, the presence of weeds was a more important reason for leaving fields fallow. Another important aspect of the development of secondary vegetation is the fact that frequently landowners do not possess the resources necessary to cultivate the land (DE JONG et al. 2001). There have been few experiments involving the management of secondary forest to date. SIPS (1997) divided these experiments into two groups based on the treatments applied:

- Manipulations to improve the growing conditions of existing trees (HUTCHINSON 1993; CHIARI 1999; MESQUITA 2000); - experiments with tree planting/enrichment (RAMOS & DEL AMO 1992; VIDAURRE 1992, PEÑA-CLAROS et al. 2001). There have not been many attempts made to promote the germination and establishment of the natural regrowth of fast growing trees by manipulation of either the canopy (GUARIGUATA 2000) or the upper soil layer (GRANADOS 1995). There is no information about the manipulation or steering of the establishment of trees in the first phase of succession.

30 Description of the study area

2.4.2 Possibilities for managing secondary forests in the Pucallpa region

TERBORGH (1990) claimed that seed dispersal and seedling establishment are the most critical stadia in the process of forest regeneration in the tropics. He suggested these issues represent the most sensible areas of investigation, though it may prove very difficult to find any practical solution that can be applied in the field. The process of secondary forest regeneration is not as complex as the regeneration process in climax forests. It is possible to combine the high regeneration potential of certain commercial species of the secondary succession process in areas where favourable ecological and socio-economic conditions exist. The classification of colonisation stages (RICHARDS 1996) helps in the localisation of areas where the potential for the management of secondary forests is high. The appropriate conditions exist in many areas of the Pucallpa region, corresponding to the emerging market economy stage. According to GALVÁN et al. (2000), the most important reason to conserve high secondary forest (h >10 m) in the uplands of the Pucallpa region is the presence of timber resources. The use of secondary forests is widespread in the region. The necessary period of restoration for agricultural land allows for the planting of fast growing tree species. However, the high planting and maintenance costs and the low product values mean that this option is not currently profitable. Many farmers preserve parcels of secondary succession hosting abundant fast growing timber species. As a consequence of a lack of silvicultural knowledge, they do not recognise either the need for or the value of silvicultural treatments such as thinnings. Farmers generally wait a few extra years until the commercial trees have attained marketable dimensions, and can be processed by a semi-rural sawmill industry. After these trees have been harvested a new cycle of slash and burn agriculture begins. Many farmers demonstrate an interest in obtaining silvicultural training so as to enable them to promote the establishment of commercial successional vegetation, at little cost. Some of the management techniques employed in temperate regions to facilitate establishment, such as direct seeding and soil preparation, can be applied in tropical regions like Pucallpa.

2.4.3 Selection criteria for the species investigated

One of the most critical aspects of silviculture in developing countries is the selection of species for both plantation and natural forest management. However, there is a lack of both experience and knowledge in relation to the adaptation of species to different sites (WEBB et al. 1980). The simultaneous investigation of species with similar dispersion and establishment strategies has the advantage that it offers more than one option for forest establishment, according to the site conditions and circumstances of the abandoned land in question.

Description of the study area 31

A number of the pioneer species of the secondary forests of the Pucallpa region have only been either partially studied or not at all. However, the planting and tending costs are usually higher than the current product prices. Nevertheless, use of the secondary forest resource continues as the farmers successfully obtain raw materials derived from natural regeneration, without making any financial investment. In any case, the available information and silvicultural knowledge in relation to the pioneer tree species found in Pucallpa is either solely empirical, or has never been appropriately published. A total of 8 species were pre-selected for investigation prior to initiation of the study. However, for logistical and budgetary reasons it was necessary to reduce the number of species studied to 4. The criteria for the selection of the species were both subjective and empirical. Each species was rated with respect to each of the criteria (Tab. 2.6).

Tab. 2.6: Evaluation of potential species for investigation prior to initiation of the research. Criteria ratings: 5: Very good, 4: Good, 3: Medium, 2: Low, 1: Very low.

Tree Criterion species

acceptance acceptance acceptance Growth rate Growth management Timber quality Future commercial commercial Future Current commercial commercial Current Current timber price price timber Current stand establishment establishment stand Natural regeneration regeneration Natural Abundance in region region in Abundance Maximum dimensions Seed dispersion capacity capacity Seed dispersion Capacity for homogenous homogenous for Capacity Total

Guazuma crinita 3 4 3 3 3 4 5 5 5 5 40 Calycophyllum spruceanum 3 4 4 5 3 4 4 5 3 3 38 Croton matourensis 2 4 3 5 2 4 5 3 5 3 36 Jacaranda copaia 2 3 2 5 1 4 5 5 5 4 36 Ochroma pyramidale 2 3 2 3 2 4 4 5 5 3 31 Schizolobium amazonicum 3 3 2 5 1 3 3 2 5 2 29 Apeiba membranaceae 3 3 2 3 2 3 2 2 5 2 27 Cordia alliodora 2 3 4 4 2 2 3 3 4 2 27

The four species ultimately selected for the study were those with the highest points totals in Tab. 2.4.1. These were Guazuma crinita, Calycophyllum spruceanum, Croton matourensis and Jacaranda copaia. The species with lower points totals not selected for study were Schyzolobium amazonicum, Ochroma pyramidale, Apeiba membranaceae and Cordia alliodora.

32 Biological requirements of pioneer tree species for their establishment on fallows

3 BIOLOGICAL REQUIREMENTS OF PIONEER TREE SPECIES FOR THEIR ESTABLISHMENT ON FALLOWS

In the chapter 2.4, four pioneer tree species of special interest for studies of natural regeneration were selected. These species offer favourable ecological and socio-economic conditions for the establishment of homogeneous stands on land previously used for agriculture, and for subsequent management targeting timber production. Under natural conditions these species establish at the beginning of the secondary stage of succession, which continues until the formation of large gaps in the stand, and at the beginning of primary succession along the edges of rivers. In natural forests, favourable microsites for the establishment of pioneer trees are quite limited. With increasing human activity, the surface area of suitable microsites increases considerably and, consequently, so too the abundance of pioneer trees. The range of pioneer tree species is lower than that of the tree species characteristic of the more advanced stages of succession. In the majority of cases, pioneer tree species undergo processes of establishment that are relatively simple in comparison to those of species of the more advanced successional stages. For both of these reasons, the pioneer species selected for management purposes should be largely similar in terms of their biological requirements for establishment.

3.1 INTRODUCTION: CLASSIFICATION OF ECOLOGICAL GROUPS OF TREE SPECIES AS A SILVICULTURAL TOOL

3.1.1 Advantages and disadvantages of tree classification according to ecological groups

The species richness of tropical rain forests creates difficulties with regard to ecological analysis. This richness may usefully be simplified by defining ecological species groups whose members share characteristics of importance with respect to determining forest structure and composition. The classification of species according to groups or guilds imposes a degree of simplification which reduces the information content, but serves to highlight general patterns and facilitates predictions in relation to forest processes (SWAINE & WHITMORE 1988). The urgent requirements of ecological and silvicultural applications in the tropics have often resulted in the classification of many useful tree species into specific ecological groups, in spite of a lack of sufficient knowledge of the species characteristics. Other authors have attempted classifications based on direct evaluations of local species and their interactions with the environment (HUBBEL & FOSTER 1987, CLARK & CLARK 1992, DIAZ 1995, GUZMAN 1997). The judicious use of relevant information and a basic ecological knowledge of certain representative tree species can help in the forecasting of the behaviour of other ‘similar’ species.

Biological requirements of pioneer tree species for their establisment on fallows 33

The mode of dispersal of a plant species is frequently associated with other attributes of the plant, and its habitat (HUGHES et al. 1994). The same authors reviewed these associations and presented a set of hypotheses which, when considered together, made a probabilistic prediction of the mode of dispersal of a plant species. In this way, the ecological requirements and/or the silvicultural behaviour of pioneer species at establishment may be not so difficult to forecast for other species within the same strategic group. Despite the fact that the pioneer species’ establishment strategies are less complex than those of late successional species, this generalisation only helps as a description of a general trend, used to design experiments to assess the actual establishment strategy. It is necessary to carry out investigations providing more precise explanations of specific establishment strategies because in some cases establishment proves successful, whereas in others this is not the case and the process of succession becomes dominated by other undesirable species, in spite of the presence of abundant seed sources. The purpose of this chapter is to develop upon basic biological knowledge helping to better understand the early successional establishment phases. The main items are seedling identification, phenological behaviour and germination on different substrates.

3.1.2 Objectives

The specific objectives of this part of the study were:

(1) To develop a more precise knowledge of the silvicultural applications of the species studied. (2) To expand upon the little existing knowledge of the four selected pioneer tree species, thereby providing a basis for the explanation of the propagation methods of many other species with similar ecological strategies. (3) To facilitate the field identification of the various phases of the initial stage of growth of naturally regenerated seedlings of the species studied. (4) To analyse the relationships between phenology and the seed dispersal strategies of the trees studied, and their establishment on fallow land within the research area.

3.2 FIELD IDENTIFICATION OF THE PHASES OF THE INITIAL STAGE OF GROWTH OF THE SELECTED TREE SPECIES

The young growth of pioneer trees may establish either in groups or mixed with weeds on fallow land. To inventory the young growth accurately, it is necessary to be able to identify precisely the species of the seedlings in the initial stage of growth. The mis-identification of seedling species can lead to great difficulties in the management of tropical forests. Close cooperation with botanists is often indispensable. Most of the existing studies of seedling morphology are taxonomic in nature (DUKE 1969, DUKE & POLHILL 1981, PONCY 1986). In

34 Biological requirements of pioneer tree species for their establishment on fallows many cases, these studies possess a direct practical application, as they facilitate the identification of plants in the field (BURGER 1972, DE VOGEL 1980, RICARDI et al. 1987, DIAZ & RIOS 1993). There are great differences between the seed produced by pioneer tree species and those species characteristic of the late successional phases. Pioneer species frequently produce large numbers of seeds to colonise ephemeral and unpredictable treefall gaps that may arise in the stand. Although the seeds are small, the resulting seedlings can grow rapidly in the energy-rich gaps (GÓMEZ-POMPA & VÁSQUEZ-YANEZ 1974). Non-pioneer species produce larger seeds, containing a rich nutrient reserve to facilitate seedling survival in the darker, energy-poor understorey. The number of seeds produced is, therefore, considerably lower (FOSTER & JANSON 1985, FOSTER 1986).

3.2.1 Objectives of the description of the morphological characteristics

The objectives of the description of the morphological characteristics included:

The development of a system for the identification of the seedlings and saplings ־ of timber species characteristic of the early successional vegetation present on fallows. The examination of the natural regeneration of pioneer plants appearing after ־ agricultural crops have been harvested.The description of the morphological characteristics of the studied species in the different stages of their early development.

3.2.2 Methods of the morphological identification of the various phases of the initial stage of growth

3.2.2.1 Definition of seedling and the initial growth stage

The definition of seedling varies, depending on whether it is viewed from a physiological or a silvicultural perspective. In the case of the former, a seedling is defined as the young plant immediately after germination, still dependent upon the energy and food provided by the cotyledons, or reserve tissues (SCHÜTT et al. 1992). Silviculturalists, alternatively, define seedlings on the basis of arbitrarily fixed sizes, for purposes of practical convenience in inventory (SOCIETY OF AMERICAN FORESTERS 1983). Given the varying definitions of ‘seedling’ between the disciplines, it is not surprising that the terms used to describe the stages of seedling development vary greatly in the literature. Unfortunately the criteria used to separate the stages are rarely stated clearly (GARWOOD 1996). BURGER (1972), DE VOGEL (1980) and RICARDI et al. (1987) described the morphology of the initial stages of development of tropical tree individuals from the point at which the seedlings are independent of the reserves stored in the seed (GARWOOD 1996). Ecologists and silviculturalists are generally more interested in the established seedlings of species of

Biological requirements of pioneer tree species for their establisment on fallows 35 later successional phases. Although many species have foliaceous cotyledons that later develop as photosynthetic leaves. DIAZ & RIOS (1993) proposed the term ‘initial stage’ to illustrate that within a short period of time, and within the span of only small changes to the plant dimensions, the individual plants undergo great physiological and morphological change. It is important to distinguish between and to describe these changes. As a consequence of the initial slow growth of the small seedlings, and the fast growth subsequently, it is necessary to describe the seedlings at different phases. This contrasts with the approach adopted in a number of earlier studies (DUKE 1969, BURGER 1972, DE VOGEL 1980, RICARDI et al. 1987, SAHA et al. 1998).

3.2.2.2 Obtaining seedlings

The seedlings used in the phenological evaluations were derived from the seed of identified trees. The plants were cultivated in containers with sandy soil. The illustrations and descriptions were made at different phases of growth.

3.2.2.3 Differentiation within the initial stage

During the initial stage, dicotyledons exhibit extreme changes in their morphology. Many of these changes are of great value for taxonomical studies. Some organs and forms appear only once, and but for a short period of time (EAMES 1961). Certain authors (RICARDI et al. 1987, SAHA et al. 1998) neglected to take into consideration the changes occurring within plant organs, describing and illustrating each species only once. DIAZ & RIOS (1993) claimed that it is necessary to define all of the phases occurring within the initial stage. He divided the development of tree seedlings into three clearly distinguishable stages on the basis of seedling leaf development: • Cotyledons are embryonal leaves. • Protophyllous leaves are the first leaves developed by the new plant, and differ from those of the adult individual. • Metaphyllous leaves are morphologically similar to those carried by the adult individual.

These stages are shown in fig. 3.2.1:

Most of the existing morphological studies of tropical tree seedlings refer to species of late successional forests (DUKE 1965, 1969, DE LA MENSBRUGE 1966, RICARDI et al. 1987). In many cases, this has meant the study of species with relatively large seeds, and producing large seedlings. These studies merely described the morphology of seedlings in the metaphyllous stage, after the most important morphological changes taking place within the initial stage had been completed.

36 Biological requirements of pioneer tree species for their establishment on fallows

Fig. 3.1: Phases of seedling development of three different germination types. EC= cotyledons phase, EP = protophyllous phase, EM = metaphyllous phase, CC= fleshy cotyledon, CF= foliaceus cotyledon, P= protophyllous leaf, M= metaphyllous leaf, R= root, H= hypocotyl, E= epicotyl (Adapted from DIAZ & RIOS 1993).

3.2.2.4 Description of morphological characteristics

The morphological characteristics of the plants studied were described using terminology adapted from descriptions of the initial stage of plant development, employing plant classifications developed by DE LA MENSBRUGE (1966), DUKE (1965, 1969), FONT QUER (1985) and RICARDI et al. (1987). The terminology used to describe the leaves of the adult individuals was that of HICKEY (1979).

3.2.2.5 Illustrations of seedlings

The illustrations depict selected plants growing in containers. The purpose was to present graphically the distinctions between the germination types, and the morphological changes that occur.

Biological requirements of pioneer tree species for their establisment on fallows 37

3.2.3 Results: description of the morphology of the various phases of the initial stage of development of the studied species

3.2.3.1 Description of the morphology of the initial stage of development in Calycophyllum spruceanum

The three phases making up the initial stage of development in this species are as follows: • Cotyledon phase

Characterised by the following details:

Epigeal germination. The seed envelope opens completely. The cotyledons are ־ arranged face to face in the interior of the seed. :Foliaceous cotyledons, equals, opposites, horizontally arranged. Leaf shape ־ whole symmetric lamina. Form: oblong-ovate, 2 mm wide, 3 mm long. .Primary venation with no recognisable pattern ־ Seedling axis: cylindrical hypocotyl, 8-10 mm long. Epicotyl not yet ־ developed, showing only the beginning of the terminal sprout. .Radicle: white, tapered cylindrical form, 3-5 mm long ־ A 4 day old seedling in the cotyledon phase is depicted in fig. 3.2 A ־

• Protophyllous phase

Characterised by the following details:

.Leaf arrangement: opposite decussate ־ .Leaf shape: simple, elliptical with symmetrical lamina, apex acute, base acute ־ Margins entire with light undulations. Winged petiole. Brochidodromous venation. Very fine straight primary vein. Secondary veins ־ at moderate diverging angle, dispersed with no definite pattern. Arrow shaped terminal bud covered by triangular elongated stipules. Stipules ־ remain for the first weeks, but are later shed, leaving transverse scars. A 32 day old seedling in the protophyllous phase is depicted in fig. 3.2 B ־

• Metaphyllous phase

Characterised by the following details:

38 Biological requirements of pioneer tree species for their establishment on fallows

Fig 3.2: Morphology of the phases of the initial stage of seedling development of Calocophyllum spruceanum. A=cotyledon phase, B=protophyllous phase, C=metaphyllous phase. .Leaf arrangement: opposite decussate ־ .Leaf shape : simple, elliptical with symmetrical lamina, apex acute, base acute ־ Margins entire with undulations. Winged petiole. .Brochidodromous venation. Straight primary vein without branches ־ Secondary veins at moderate diverging angle. Foliaceous triangular stipule protects the arrow shaped terminal sprout. It stays ־ at the last 2 or 3 leaf pairs, later shed leaving elongated scars. .Seedling axis with quadrangular cross section ־ .No secretions ־ A 70 day old seedling in the metaphyllous phase is depicted in fig. 3.2 C ־

3.2.3.2 Description of the morphology of the initial stage of development in Croton matourensis

The three phases making up the initial stage of development in this species are as follows:

• Cotyledon phase

Characterised by the following details:

Biological requirements of pioneer tree species for their establisment on fallows 39

.Epigeal germination type ־ .Foliaceous cotyledons, elliptic blade, entire border, very fine primary venation ־ .Rounded short petiole, 2 mm long ־ .Terminal bud developed immediately with the protophyllous phase ־ .Hypocotyl with a rounded section, 15 mm long ־ Two six day old seedlings in the cotyledon phase are depicted in fig. 3.3 A ־

Fig. 3.3: Morphology of the phases of the initial stage of seedling development of Croton matourensis. A=cotyledon phase, B=protophyllous phase, C=metaphyllous phase, terminal sprout with latex secretion.

• Protophyllous phase

Characterised by the following details:

.Leaf arrangement: helicoidal alternate ־

40 Biological requirements of pioneer tree species for their establishment on fallows

Leaf shape: simple lanceolate-ovate lamina, apex acuminate, base obtuse ־ asymmetrical. Serrated border. Petiole round and short. Eucamptodromous venation. Primary vein straight. Secondary veins diverging ־ at acute angles. .Terminal sprout shaped like a spear point ־ .The seedling produces light yellow latex, presence of peltate pubescence ־ .and 25 day old seedlings are depicted in fig. 3.3 B 15 ־

• Metaphyllous phase

Characterised by the following details:

.Leaf arrangement: helicoidal alternate ־ Leaf shape: simple lanceolate-elliptic lamina, apex acuminate, obtuse ־ asymmetrical base. Border entire with undulations. Petiole round and short. Brochidodromous venation. Primary vein straight. Secondary veins diverging ־ at acute angles. ,Two cylindrical elongated stipules, 2 cm long, on each side at the petiole ־ produce a round scar when shed. Two rounded glands 2 mm in diameter on both sides at the base of the lower leaf surface. Terminal sprout shaped like a spear point. Abundant intense yellow latex, presence of peltate pubescence all over the ־ plant. .A 90 day old seedling in the metaphyllous phase is depicted in fig. 3.3 C ־

• Protophyllous phase

Characterised by the following details:

.Leaf arrangement: helicoidal alternate ־ Leaf shape: simple lanceolate-ovate lamina, apex acuminate, base obtuse ־ asymmetrical. Serrated border. Petiole round and short. Eucamptodromous venation. Primary vein straight. Secondary veins diverging ־ at acute angles. .Terminal sprout shaped like a spear point ־ .The seedling produces light yellow latex, presence of peltate pubescence ־ .and 25 day old seedlings are depicted in fig. 3.3 B 15 ־

• Metaphyllous phase

Characterised by the following details:

.Leaf arrangement: helicoidal alternate ־ Leaf shape: simple lanceolate-elliptic lamina, apex acuminate, obtuse ־ asymmetrical base. Border entire with undulations. Petiole round and short.

Biological requirements of pioneer tree species for their establisment on fallows 41

Brochidodromous venation. Primary vein straight. Secondary veins diverging ־ at acute angles. ,Two cylindrical elongated stipules, 2 cm long, on each side at the petiole ־ produce a round scar when shed. Two rounded glands 2 mm in diameter on both sides at the base of the lower leaf surface. Terminal sprout shaped like a spear point. Abundant intense yellow latex, presence of peltate pubescence all over the ־ plant. .A 90 day old seedling in the metaphyllous phase is depicted in fig. 3.3 C ־

3.2.3.3 Description of the morphology of the initial stage of development in Guazuma crinita

The seedling morphology of Guazuma crinita was described by DIAZ & RIOS (1993). Because of the high importance of this species in the secondary forest of the studied region it was considered necessary to include it again in the present study. The three phases making up the initial stage of development in this species are as follows:

• Cotyledon phase

Characterised by the following details:

.Epigeal germination ־ Foliaceous cotyledons, rounded lamina, wider than long at the initially, as it ־ grows it becomes sub-rounded with rounded base, truncate apex oblique to subemarginate. Trinervate venation, straight midvein, laterals in the form of an arch. Border ־ entire. Petiole flat. .A 6 day old seedling is depicted in fig. 3.4 A ־

• Protophyllous phase

Characterised by the following details:

.Leaf arrangement: alternate ־ ,Leaf shape: simple ovate lamina, cordate base, acute apex. Border serrated ־ teeth of the leaves mucronate, angular sinus, compound series of teeth of different sizes. Simple craspedodromous venation. Secondary veins with moderately acute ־ insertion angle, ending at the tips of the teeth. Cylindrical petiole, 3-5 mm long, 1 mm wide with simple hairs. Axillary bud pubescent at the petiole base. Presence of simple and stellate ־ hairs all over the plant. .A 48 day old seedling is depicted in fig 3.4 B ־

42 Biological requirements of pioneer tree species for their establishment on fallows

Fig. 3.4: Morphology of the phases of the initial stage of seedling development of Guazuma crinita. A=cotyledon phase, B=protophyllous phase with photosynthetically active cotyledons, C=metaphyllous phase. (From DIAZ & RIOS 1993)

• Metaphyllous phase

Characterised by the following details:

.Leaf arrangement: alternate ־ .Leaf shape: simple ovate lamina, cordate base, attenuate apex, lightly curved ־ Serrated border, teeth irregularly mucronate and angled sinus. Petiole semi- quadrangular, 2-3 cm long. Pinnate craspedodromous venation. Secondary veins with moderately acute ־ insertion angle, curved to the upper side ending in the tip of the tooth. Hairs stellate on the stems, petiole, primary and secondary veins of upper and ־ lower surface of lamina, simple hairs all over the plant. ,Simple stipules on both sides of the petiole base, like thin needle like scales ־ they are deciduous and produce scars. .A 75 day old seedling is depicted in fig 3.4 C ־

Biological requirements of pioneer tree species for their establisment on fallows 43

3.2.3.4 Description of the morphology of the initial stage of development in Jacaranda copaia

The three phases making up the initial stage of development in this species are as follows:

• Cotyledon phase

Characterised by the following details:

.Epigeal germination ־ ,Foliaceous cotyledons horizontally arranged. Lamina round, base rounded ־ apex deeply emarginate. Very short flat petiole. Hypocotyl relatively wide. Epicotyl growth 2-3 mm before entering the next ־ stage. .A 10 day old seedling is depicted in fig 3.5 A ־

Fig. 3.5: Morphology of the phases of the initial stage of seedling development of Jacaranda copaia. A=cotyledon phase, B + C= protophyllous phase.

• Protophyllous stage

Characterised by the following details:

.Leaf arrangement: opposite decussate ־

44 Biological requirements of pioneer tree species for their establishment on fallows

Leaf shape: Once pinnately compound (imparipinnate), first pair of ־ protophyllous leaves have 3 folioles, next 3 pairs have 5 folioles. Lateral folioles have an elliptical asymmetrical form, terminal folioles lanceolate. Serrated border. Apex acuminate. .Eucamptodromous venation. Petiole and petiolule with a caniculate section ־ .Quadrangular plant axis. Spear shaped terminal sprout ־ .Without secretion ־ (Seedlings in the protophyllous phase are depicted in fig. 3.5 B (36 days old ־ and fig 3.5 C (50 days old).

• Metaphyllous stage

Characterised by the following details:

.Leaf arrangement: opposite decussate ־ Leaf shape: bipinnately compound (imparipinnates) at the base and in the ־ terminal folioles exists folioles with transition to pinnula, characteristically bipinnately compound towards the middle of the leaf. Serrated border, acuminate apex. .Eucamptodromous venation ־ .Axillary buds at the petiole base ־ .Cross section of the main seedling axis is quadrangular ־ .No secretion ־ .A 95 day old seedling is depicted in fig. 3.6 ־

Fig. 3.6: Morphology of the phases of the initial stage of seedling development of Jacaranda copaia. A=metaphyllous stage, B=terminal sprout, C=bipinnate leaf of the metaphyllous stage.

Biological requirements of pioneer tree species for their establisment on fallows 45

3.2.4 Discussion of seedling morphology

A clear relationship between the size of seed and the size of the developed seedling was observed. Calycophyllum spruceanum, the species with the smallest seed (0.06 mg), develops very fragile seedlings, whereas the seed of Croton matourensis (50 mg) produces a relatively robust seedling. The cotyledons of the four species studied assume a photosynthetic function immediately. This is a characteristic typical of pioneer species, and contrasts with many climax species which rely on reserves stored in fleshy cotyledons without any chlorophyll (IBARRA- MANRÍQUEZ et al. 2001). As consequence of their very small size and the elongation of the cotyledons in the first days after germination, Calycophyllum spruceanum seedlings may be confused with the seedlings of certain grass and weed species. Later the cotyledons expand in width, adopting the form of a woody plant. Calycophyllum spruceanum exhibited small morphological changes between the leaves of the protophyllous and the metaphyllous phase. Guazuma crinita and Croton matourensis exhibited certain visible changes between the protophyllous and the metaphyllous phase. In contrast to the species with simple leaves, Jacaranda copaia demonstrated transitional changes in the leaf morphology during the protophyllous phase. A substantial change subsequently occurs during the transition from the protophyllous to metaphyllous phase as previously pinnately compound leaves give way to bipinnately compound leaves (comparation fig. 3.2.5 C with 3.2.6 C). The great morphological differences between the leaves produced in both phases were evident in all of the Jacaranda copaia seedlings evaluated. A number of distinguishing morphological characteristics are presented, facilitating the identification of the seedlings from amongst seedlings of other pioneer species. The morphological changes undergone by all of the seedlings studied from each of the four species included in the evaluation were the same; that is, the seedling development was homogeneous and constant for each species. The descriptions produced may, therefore, be used in the field to assist in the identification of the seedlings of the described species in the initial stage of growth. The growth rates of the plants cultivated for the study were also observed to be homogeneous. Although the growth rates observed in the field differed, the morphological development of the seedlings corresponded to that of the cultivated plants. Once the criteria and methods for the morphological description of the phases of the initial stage of seedling growth are developed, they should not prove difficult to apply to other species not studied here.

3.3 PHENOLOGY OF THE SEED TREES OF THE SPECIES STUDIED

The season in which seed is produced is a determinant of population success, as it can ensure the survival and establishment of juvenile plants. The phenology of a species is

46 Biological requirements of pioneer tree species for their establishment on fallows regulated by endogenous characteristics, as influenced by climatic variations, as well as other abiotic and also biotic factors. These are all factors of selective pressure determining the development of phenological patterns (JANZEN 1967, RATHCKE & LACEY 1985). Plant phenology depends on the timing of certain events, such as certain weather conditions or fire. The factors affecting the phenology of the species of lowland tropical rain forests are poorly understood, even though this ecosystem has the greatest diversity of phenological patterns. This lack of knowledge is a severe shortcoming given the importance of phenology for understanding the ecology and evolution of species and communities in the tropics. The rhythm of seed production can profoundly influence population dynamics. The evaluation of phenology is particularly important as a consequence of possible variations arising between individuals of the same species. Some tropical species fructificate more than once a year, whereas other species need a rest interval of two or three years before again producing high quantities of fruit. Observation periods lasting many years are required in order to gain greater knowledge of the phenology of tropical tree species. A primary function of silviculture is the propagation of desirable individuals. The need to have sufficient quantities of seed at opportune times has encouraged the development of tree monitoring activities, focussing on flowering, fructification and seed dispersal. Terrain that consists of a mosaic of primary forest residues, areas of secondary succession and land newly prepared for agriculture represents an opportunity for colonisation by plants with different establishment strategies. Knowledge of the phenology of the species studied should improve understanding of the conditions either favouring or impeding their establishment.

3.3.1 Objectives of the phenological evaluation

The principle objectives of the phenological evaluation were to gain knowledge of the timing of seed dispersion of the tree species under study and of the subsequent establishment of young plants on land previously cultivated.

3.3.2 Phenological evaluation methods

The phenology of plant species of the tropics has seldom been studied. Both an appropriate terminology and standardised methods of phenological evaluation are required for tropical regions. There is little information derived from long term research available. Generally, the existing studies are superficial, and the levels of analysis mixed (individual, population and the community level), seeking unsuccessfully to describe complex, diverse and irregular patterns (NEWSTRON et al. 1994). Several classifications have been proposed to describe tropical flowering patterns. Some of these are based on changes to the foliage brought about by water stress (REICH & BORCHERT 1982) or according to life form (SARMIENTO & MONASTERIO 1983). There are three main classifications based on flowering patterns alone:

Biological requirements of pioneer tree species for their establisment on fallows 47

A classification system referring to the timing or season of flowering derived ־ from the phenology of tree species of the temperate zones. .A classification based on the duration of flowering ־ .The most widely used classification is based on timing or year season ־

Graphs can aid in the detection of relationships between the phenological patterns because they show large amounts of information while retaining the relative arrangement of information in a way that numerical summaries cannot (TUFTE 1983, CLEVELAND 1985, PICKOVER 1990, all cited by NEWSTROM et al. 1994). By using graphs rather than numerical summaries to demonstrate patterns of phenology, previously unclear flowering patterns can be detected (NEWSTROM et al. 1994). An effective means of phenological interpretation was developed by FLORES (1997), who compiled his own observations with those of other researchers to evaluate the phenological development of 89 tropical tree species over a 10 year period. The timing of each phenological event is represented by means of a curve, indicating the proportion (%) of trees and the corresponding time of the year. Three phenological events were evaluated in this study, namely flowering, fructification and seed dispersal. Normally, studies of phenology to characterise the pattern of phenological events as they pertain to a specific species are carried out over a long period of time (FLORES 1997). For the purposes of this study, the phenological observations were intended mainly to corroborate the causes and effects on the other aspects of seedling establishment, namely dispersion, germination, competition with pioneer vegetation and fire resulting from human activities. Five mature individuals of each of the four studied species were selected in the study area. Five is the minimum allowable tree number required to take into consideration variations in the beginning and the duration of the phenology events within a species (FOURNIER & CHARPANTIER 1975). The selected trees were healthy and had a good form.

3.3.3 Results: graphic description of the phenology of the selected tree species

3.3.3.1 Phenology of Calycophyllum spruceanum

The flowering period of Calycophyllum spruceannum was 3 months long, lasting from June to August, as depicted in fig. 3.7 (next page). Flowering peaked in July (80 % of individuals). Fruit production lasted 4½ months and occurred almost parallel to seed dispersal. The period of seed dispersal was 3 months long, beginning in mid September and ending in mid December. The peak in seed dispersal coincided with the beginning of the rainy season. The flowers of Calycophyllum spruceannum are small but numerous, and influence the crown appearance. The white flowers can be readily distinguished at a distance, as can the fine white carpet of fallen flowers lying on the ground. Frequently the crown is either partially or entirely defoliated during the period of seed dispersal. The dry fruits usually remain on the branches for a few weeks after dehiscence.

48 Biological requirements of pioneer tree species for their establishment on fallows

10 0 10 0

80 80 Flowering ees 60 Fruit ing 60 tr

of Dispersal

% 40 40

20 20

0 0 Apr May June July Aug Sept Oct Nov Dec Jan Feb Mar Time Fig. 3.7:Phenological behaviour of Calycophyllum spruceanum in the Neshuya-Curimana sector, 1999-2000. The seed is very small, flat and has long wings. A quantity of seed weighing 1 g contains approximately 5 000 seeds. There is little specific information available in relation to the seeds of Calycophyllum spruceannum, in contrast to Jacaranda copaia. However, the seedexhibits characteristics similar to that of poplar, willow and birch, and may be dispersed some kilometres (BURSCHEL & HUSS 1997).

3.3.3.2 Phenology of Croton matourensis

The entire reproductive cycle of Croton matourensis occurs over the space of a five month period in the year (fig. 3.8). Flowering begins in January and finishes at the start of April. Fruiting occurs between mid January and the beginning of May. Seed dispersal occurs between mid February and early June.

10 0 10 0

80 80 Flowering 60 60 Fruit ing

% of trees 40 Dispersal 40

20 20

0 0 Dec Jan Feb Mar Apr May June July Aug Sept Oct Nov Time Fig. 3.8: Phenological behaviour of Croton matourensis in the Neshuya-Curimana sector, 1999-2000. The flowers and fruits of Croton matourensis are small. They exert very little influence on the general appearance of the tree crown as the species is an evergreen. The phenological changes can only be observed at short distances from the tree. Croton matourensis is the only one of the four species studied without anemochory seed dispersal. Rather, seed dispersal is autochory (ballistic dispersal), like other species of the Euphorbiaceae (GOVAERTS et al. 2000). The round seeds are thrown distances of only 10- 20 m from the parent tree. Although large quantities of seed may be observed on the forest

Biological requirements of pioneer tree species for their establisment on fallows 49 floor at the time of dispersal, only few seedlings are observed under the seed tree in the months thereafter.

3.3.3.3 Phenology of Guazuma crinita

From fig. 3.9 it can be seen that the flowering period of Guazuma crinita begins in mid June and finishes in mid September. During the two months of flowering the tree crowns assume a light pink tone.

10 0 10 0

80 80 Flowering 60 60 Fruit ing

% of trees 40 Dispersal 40

20 20

0 0 May une July Aug Sep Oct Nov Dec Jan Feb Mar Apr J Time

Fig. 3.9: Phenological behaviour of Guazuma crinita in the Neshuya-Curimana sector, 1999- 2000.

The fruiting period is three months long, lasting from mid July to mid October. The fruit possesses long fine hairs to facilitate wind dispersal. The dispersal period is 3 months long, and coincides with the dry period. COLAN (1992) studied seed dormancy in Guazuma crinita, determining that, where storage conditions are good, high rates of seed germination occur six months after production of the seed crop. The timing of the reproductive events were very similar for the 5 Guazuma crinita trees evaluated. Often abundant naturally regenerated young growth may be observed close to the parent trees. and coincides with the dry period. COLAN (1992) studied seed dormancy in Guazuma crinita, determining that, where storage conditions are good, high rates of seed germination occur six months after production of the seed crop. The timing of the reproductive events were very similar for the 5 Guazuma crinita trees evaluated. Often abundant naturally regenerated young growth may be observed close to the parent trees.

3.3.3.4 Phenology of Jacaranda copaia

The phenological activity of Jacaranda copaia spanned almost the whole year (fig. 3.10, next page). The duration of flowering was 3½ months long, from July to mid October, coinciding with the dry season. The flowers produced by Jacaranda copaia are very conspicuous. The crowns of all trees turn an intense violet colour for 2 months, and can be distinguished from very great distances. Fruiting begins in mid September and finishes in mid February. In contrast to with the other 3 species studied, the fruit produced by Jacaranda copaia is relatively large. This may explain the long duration of the maturation process. Seed

50 Biological requirements of pioneer tree species for their establishment on fallows

10 0 10 0

80 80 Flowering Fruit ing

trees 60 60 Dispersal of

% 40 40

20 20

0 0 June July Aug Sept Oct Nov Dec Jan Feb Mar Apr May Time

Fig. 3.10: Phenological behaviour of Jacaranda copaia in the Neshuya-Curimana sector, 1999-2000. dispersal begins in January and finishes in mid April, during the rainy season. The dehiscence of the empty fruits does not occur until long after dispersal. The seed requires humid conditions for germination. However, it cannot tolerate prolonged wet periods as the species is susceptible to fungal infection (COLÁN, pers. comm.). Adult Jacaranda copaia trees were not observed in flooded areas. This contrasted with the other 3 species studied. A 1 g sample of seed comprises approximately 160 individual seeds (AUGSPURGER 1986). The seed has very flat, fine papery wings, for wind dispersal. AUGSPURGER (1986) determined that Jacaranda copaia seeds liberated from the crown at a height of 30 m may be transported up to ~540 m at a wind speed of 7 m/s.

3.3.4 Discussion: seed dispersal and natural regeneration on fallow land

3.3.4.1 Dispersal during the rainy season

Guazuma crinita and Calycophyllum spruceanum trees release all of their seed at the beginning of the rainy season. There exists a strong relationship between the season of fruit production, the fruit type (dry or fleshy) and the means of seed dispersal (FRANKIE et al. 1974, MORELLATO 1992). Anemochory seems to be favoured by specific environmental conditions, such as greater wind circulation in the canopy and less rainfall (GRIZ & MACHADO 2001). Certain tree species of tropical forests have no leaves during the dry season, allowing for greater wind circulation in the stand. The dispersal of seed at the end of the dry season and the beginning of the humid season can be advantageous for regeneration (JANZEN 1967). The possibilities for germination and subsequent development of the radicle before the onset of the next dry season are better (MORELLATO & LEITÃO-FILHO 1992). FOSTER (1992) suggested that the timing of fructification is controlled by the timing of the season most favourable for seed germination. In the case of Jacaranda copaia, the peak in the dispersal of seed occurs at the end of the rainy season. The seeds require humidity for germination, but the roots of the next phases of plant growth probably cannot tolerate excessive moisture in the soil.

Biological requirements of pioneer tree species for their establisment on fallows 51

The establishment strategy of Croton matourensis is peculiar, as the germination rates after dispersal of large numbers of seeds are quite low. Only isolated individuals germinate under the crown of the mother tree.

3.3.4.2 Pioneer tree establishment on fallow land

The process of colonisation of the farm land incorporated in this study followed the system of roads used for the exploitation of timber. As evidenced for other tropical forests, the abundance of anthropogenically created surfaces favoured the establishment of pioneer species and other heliophytic trees (TERBORGH 1990). In the study area, as in most parts of the Peruvian Amazon region, numerous gaps and extraction routes have been created as a result of selective forest exploitation. The subsequent deforestation, or ‘land preparation’, activities engaged in by farmers facilitate the colonisation by pioneer tree species of old gaps and extraction roads. For example, Guazuma crinita is at present an abundant pioneer species in areas where just 20 years ago it was rare (NALVARTE pers. comm.). Five mature Croton matourensis trees with similar dimensions (50 cm DBH and 40 m height) were located growing within old extraction gaps, distributed in ~1 ha of residual primary forest. The phenological observations made as a part of this study help to identify the reasons why certain pioneer species are able to successfully establish homogeneous stands on slash- and-burn areas. These species readily establish where mature trees are situated along the border with or close to newly prepared agricultural land. Calycophyllum spruceanum, Guazma crinita and Jacaranda copaia are tree species capable of profiting from slash-and-burn agricultural methods. The fact that the timing of the peak in the dispersal of seed coincides with the beginning of the rainy season, prior to which the land intended for crop cultivation must be prepared, represents a fortuitous coincidence. Homogeneous natural and semi-natural stands of Calycophyllum spruceanum and Guazuma crinita can often be observed along riverbanks (LINARES et al. 1992, DE JONG 2001). Both species are adapted to growth in temporarily flooded areas. Water obviously also helps in the dispersal of seed and/or fruit (COLAN 1992). Only Croton matourensis does not disperse its seed during the dry season, shortly before or at the beginning of the rainy season. Rather peak seed dispersal occurs at the end of the rainy season, when weeds dominate the ground after the crop of cultivated plants has been harvested. Apparently, the seed of this species has a dormant period. It lies in storage on the forest floor for a number of months after dispersal and germinates when the farmers burn their fields for cultivation, before the beginning of the wet season.

3.4 GERMINATION OF COMMERCIAL PIONEER SPECIES ON FOUR SUBSTRATE TYPES 3.4.1 Introduction and objectives of the study of substrate type

52 Biological requirements of pioneer tree species for their establishment on fallows

The substrate type in which the tree seeds are dispersed represents an environmental factor that can have either a positive or a negative influence on initial establishment. In this project, the effects of the more common types of substrate associated with the slash-and- burn system of agriculture were evaluated. In contrast to primary forests, agricultural land and land in the first stages of succession exhibit high proportions of exposed mineral soil. Litter is usually scarce, and where it occurs it generally only forms a shallow layer. In the project area, plots of land newly prepared for agriculture are generally >1 ha in size. The solar radiation over these large areas is much higher than the radiation that penetrates through to the ground in large gaps in primary forests. Pioneer trees with small seeds experience difficulties establishing on such open areas because of a high risk of desiccation, possibly sufficient to kill the seedlings in the first weeks after germination. The seedlings of cultivated species like maize and rice grow very rapidly. They are able to overcome the competition of the grass and weed species requiring high levels of solar radiation. The combination of cultivated plants and bare mineral soil may create special microclimate conditions that influence the first phases of establishment. The objective of this project component, therefore, was to study the effects of the 4 most common substrate types found in slash-and-burn areas on the germination of the seeds of the pioneer species studied.

3.4.2 Materials used in the of substrate experiment

3.4.2.1 Substrate types in areas colonised by pioneer trees

Human activities have the potential to cause extreme changes to the soils of tropical forests. Settled areas are characterised by a mosaic of primary forest residues, areas of secondary succession and land prepared for agriculture. The most abundant substrate types found in the study area can be grouped according to bare mineral soil, litter, ash and ‘vegetation.’ These four groups are discussed in greater detail in the following.

• Bare mineral soil

Exposed mineral soil is a substrate type relatively rarely found in tropical rain forests. It can be observed along the edges of rivers during the dry season, when the sand and lime deposits are uncovered. Short-lived pioneer species avail of this dry period to colonise these exposed areas, and succession begins (PUHAKKA et al.1993). In primary forests, the gaps in the canopy and the upturned mounds of soil created on the forest floor as a result of the toppling of large trees provide conditions under which pioneer tree species can establish. The soil exposed by the upheaval of the root plate provides places where seeds can germinate, free of litter and open to high levels of solar radiation. Exposed mineral soil is advantageous for species that produce small seeds. As the seed begins to germinate the roots come directly into contact with the soil. This is very important for species with small seeds as a litter layer normally hinders the penetration of the small

Biological requirements of pioneer tree species for their establisment on fallows 53 roots into the soil, depriving seedlings of the nutrients required and increasing the risk of desiccation during periods of drought. PUTZ (1983) found that the disturbance caused to the soil by uprooted trees is partially responsible for the abundance of pioneer trees in large treefall gaps.

• Litter

The litter layer covering the soil can also affect plant establishment by influencing the microclimate (FOWLER 1988), nutrient cycling (STAAF & BERG 1982, PROCTOR et al. 1983, MCCLAUGHERTY et al. 1985), by inducing allelopathic interactions (DATTA & CHATTERJEE 1980), or by creating a physical barrier (AHLGREN & AHLGREN 1981, HAMRICK & LEE 1987). In the tropical forest of Barro Colorado Island, Panamá, it was observed that the distribution of litter was very heterogeneous, varying considerably across distance intervals >20 m. Experiments with seeds of 6 different sizes and of plants belonging to different ecological guilds revealed that seeds germinate very differently at litter depths of between 0.6-12 cm. This allows for the conclusion that variability of the litter depth may increase biodiversity as a consequence the heterogeneous site conditions present in the establishment phase, and the effect that this has on the germination and establishment of different species (MOLOFSKY & AUGSPURGER 1992, WHITMORE 1996). Litter is frequently referred to as a factor favouring the establishment of tropical species with large seed (NG 1978, DE VOGEL 1980, FOSTER 1986 cited by GARWOOD 1996). Litter may exert a nursing effect, holding sufficient moisture for the germination of large seeds. In primary forest, where litter may accumulate to depths of a number of centimetres, this may also pose difficulties for the establishment even of seedlings of certain species with large seeds. Cedrelinga catenaeformis, for example, establishes poorly where there is a deep litter layer as the roots have difficulty penetrating though to the soil (VIDAURRE 1992). These difficulties are even more pronounced for species with small seed. In temperate forests the soils are manipulated to create varying regeneration conditions, facilitating the establishment of mixed forests (GRAHAM et al. 1990, SATO 1998). After mature trees have been harvested, strips are prepared on the forest floor, alternating between strips covered by a litter layer and strips cleared of litter. In a study of regenerating broadleaves in southern Sweden, KARLSSON (2001) found that soil scarification generally promotes the natural establishment of seedlings. A greater degree of scarification improves the rates of establishment of tree species with small seed. GRANADOS (1995) tested different methods for the elimination of the litter in a tropical secondary forest in Costa Rica. The objective of the study was to determine the substrate treatments most favourable for germination and subsequent seedling establishment. Litter was eliminated by means of both controlled fire and mechanical removal with a rake. The raking treatment was found to encourage higher seedling and sapling survival rates. Both of the applied treatments had a significant effect on the former natural regeneration on the pole size category.

54 Biological requirements of pioneer tree species for their establishment on fallows

• Ash

The ash produced as a consequence of slash-and-burn agriculture increases the alkalinity of the soil. Ash can be used to neutralise acidic soils in humid tropical regions. It also contributes to the success of cropping, through the addition of macro- and micronutrients (SANCHEZ 1976, RUTHENBERG 1980). There is a strong correlation between ash concentration and the establishment of plants from newly dispersed seeds. The concentration depends on the origins of the ash; whether from primary forests, old secondary forests or from annual crops. Where large timber is burned, excess nutrients and lime may kill some germinants. The burning of all of the stems in a primary forest can produce >300 kg/ha of Ca (ALEGRE pers. comm.). On slash-and- burn areas ash distribution is generally irregular, and over-liming is often common in spots close to completely burned tree trunks.

• ‘Vegetation’ cover in agricultural fields

Studies of the dynamics of tropical forests have shown extreme differences in the light conditions within forests. These differences have a direct effect on seed germination, seedling establishment and sapling growth. Several pioneer species have mechanisms that delay or restrict germination. Of the factors inhibiting germination, light is the most common and may be the principal factor influencing dormancy in seeds (PONS 1992). In places where solar radiation is very high, there is a high risk of desiccation of the seedlings. A light vegetation cover, however, may facilitate seed germination in the majority of tropical forests. This vegetation layer regulates the light and water conditions on the ground below. Although ‘vegetation’ is not a ‘substrate’ as such, it offers an important ecological alternative to bare soils devoid of any shelter. Agricultural fields are typically characterised by a homogeneous cover of cultivated plants. This ‘substrate’ type, therefore, offers advantages for seed germination and seedling establishment, acting as a ‘micro- shelterwood’ of sorts.

3.4.3.2 Seed characteristics of the studied species

In table 3.1 (next page) the biological characteristics of the seeds of 3 selected species of secondary forests that are of economic importance in the Pucallpa zone are described. These species are now considered commercial species, on the basis of their common usage in rural zones. Initially Croton matorurensis, the fourth species considered elsewhere in this study, was also to be included in the experiment to assess germination in different substrate types. However, as the fresh seeds failed to germinate in the preliminary tests, sowing in the field was abandoned. It was suspected that the seed of Croton matourensis has some type of dormancy. Pre-germinative treatments were not carried out, because the aim was to adhere to natural conditions in the experiments.

Biological requirements of pioneer tree species for their establisment on fallows 55

Table 3.1: Seed characteristics of the species studied in the substrate experiment.

SPECIES TYPE OF FRUIT/SEED AND MEANS OF ECOLOGICAL DEMANDS DISPERSAL

Dry dehiscent fruit, an elongated Under natural conditions the seeds have capsule (8-12 mm long) contains very only a very short viable period. fine seeds (0.00033 g), 3 mm long Germination begins a few days after and winged (RUSSELL et al. 1999). release if substrate conditions are Calycophyllum Highest rates of dispersal between favourable. spruceanum July - November. This species prefers moist places

(LINARES et al. 1992). It grows satisfactorily on soils with low fertility (SOTELO & WEBER 1997).

Dry dehiscent windborne fruit, 1 cm The seeds have a relatively flat surface. globe-shaped hirsute capsule. Each Viable seeds sink in water. The coat is fruit contains about 20 seeds, hard and impermeable. Higher released when the fruit falls to the germination rates are achieved after ground. Seeds have an ovoid form seeds have been stored for 2 months Guazuma and are very small (0.005 g). (COLAN 1992). 24 hours soaking softens crinita Highest rates of dispersal between the impermeable coat and accelerates August - November. the beginning of germination. This species requires adequately managed soil with a cation exchange complex for good establishment and growth (ARA 1999).

Dry dehiscent fruit (flat round silique), Seeds remain viable for 6 months when contains flat winged wind dispersed stored in shade at moderate Jacaranda seeds (0.008 g) (PEÑA-CLAROS 2001). temperatures (LORENZI 1992). copaia Highest rates of dispersal between This species prefers high and well December - April. drained sites (COLAN pers. comm.).

3.4.3 Methods: research design, field preparation and sowing

3.4.3.1 Design of the experiment

It is difficult to simulate in a laboratory the environmental conditions prevailing at the soil surface under the coverage of local crops such as maize and rice. It was necessary, therefore, to carry out the experiment in the field. As was mentioned previously, the field experiment involved 4 substrate types and 3 tree species. Due to expected variations in the soil conditions, it was deemed necessary to include 6 replications. This resulted in a total of 4 x 3 x 6 = 72 plots. For reasons of practicality, the plots were arranged in a block form with the substrate type representing the main unit and the species the sub-units. A plot area as small as 1m2 was sufficiently large for the distribution of 100 seeds/plot, sown 10 x 10 cm apart. The design of the whole experiment is illustrated in fig. 3.11 (next page).

56 Biological requirements of pioneer tree species for their establishment on fallows

Block 5 Block 6 GG JCGCCG CJ J JG GG CJC C G JCJ J

Block 3 Block 4 GGGJGC CJ CGJ JCC G JC JCGJ C JG

Block 1 Block 2 JC J G JGG J GJC GC GG C CJC CJJGC

Substrate types Studied species 1 m

Ash C Calycophyllum spruceanum 10 x 10 Bare mineral soil G Guazuma crinita 1 m = 100 seeds Litter J Jacaranda copaia each species "Vegetation"

Fig. 3.11: Design of the field experiment to study germination on 4 substrate types.

The variable incorporated into the statistical analysis was the germination rate for every 100 seeds sown. The germination percentages were transformed (arcsin √%) to normalise the distribution before being subjected to an analysis of variance (ANOVA). The results were compared using DUNCAN’s new multiple range test (p≤0.05). Differences between the substrate types were interpreted and discussed. The germination rate of each species was evaluated simultaneously, employing a control test for the germination of seeds in PETRI dishes with wet filter paper.

3.4.3.2 Preparation of the sites of the experimental plots

As was mentioned, the aim of the experiment was to reproduce the main agricultural site conditions. A flat area with clay soils and covered by grass was selected. Using a farm tractor the land was ploughed to level the surface and to eliminate the covering vegetation, including grass roots. The surface was subsequently cleaned of roots and other plant residues. The 4 substrate variants finally looked as follows:

.The bare mineral soil variant consisted of a very clean area of exposed soil ־ The litter variant consisted of bare mineral soil covered by a homogeneous layer ־ of Dyctioloma peruviana leaves. The litter layer was 1 cm in depth. Dyctioloma peruviana is a very common shrub in the first phase of succession. Its leaves normally produce an homogeneous layer of this thickness.

Biological requirements of pioneer tree species for their establisment on fallows 57

2 .The ash substrate was prepared by burning 20 kg/m of dry vegetative matter ־ This was equivalent to the quantity of crop residues left behind on agricultural fields prior to burning (SALDARRIAGA 1994). Rain mixed the ash into the soil before the seeds were sown. The preparation of the ‘vegetation’ cover variant was initiated 2 months prior to ־ the sowing of the tree seeds. Almost mature rice plants (40-50 cm high) cast an homogeneous shadow over the bare mineral soil. This shade reduced the establishment of weeds.

3.4.3.3 Seed sowing

The seeds were inserted lightly into the different substrate types. The main reason for doing this was to avoid the removal of seed to rain, or wind in the case of Calycophyllum spruceanum and Jacaranda copaia. The seeds of each species were sown at different times, depending on the timing of the dissemination of fresh seeds, and also logistical considerations. The Guazuma crinita seeds were sown in January 2000; Jacaranda copaia in April 2000 and Calycophyllum spruceanum in September 2000. The time of sowing corresponded with the rainy season in the study area (cf. figs. 2.2a and 2.2b ).

3.4.4 Results of the germination experiment and discussion

The results of the experiment are presented separately for each of the 3 species. Great differences were observed between the germination rates of the seeds in the PETRI dishes (control) and on the substrate types. Clearly under field conditions certain factors existed that hindered germination; factors not evident under the moist conditions in the PETRI dishes used for the control test. In the field there is also a greater risk of fungal infection, and seed predation by insects, mice and birds.

3.4.4.1 Germination rates of Calycophyllum spruceanum in the substrate experiment

There were significant differences in the mean germination rates of Calycophyllum spruceanum seeds on the different the substrate types. From table 3.2 (next p.) it becomes apparent that the DUNCAN comparison test clearly differentiated 2 groups. The first group comprised the substrate types ‘vegetation’ and bare mineral soil, the second ash and litter. On the substrate types ‘vegetation’ and bare mineral soil, the fine roots can penetrate the soil directly. That the seed germination rate was somewhat higher on the ‘vegetation’ substrate type may have been due to the shelter provided by the rice crop. The rice plants served to diminish the direct solar radiation during the day, and increase the moisture level in form of dew at night. The rice plants also served to intercept the direct impact of heavy rains, which might otherwise have washed away some of the soil, proving detrimental where the fine roots of the seedlings had not yet become firmly anchored in the soil.

58 Biological requirements of pioneer tree species for their establishment on fallows

Table 3.2: Germination rates (%) of Calycophyllum spruceanum seeds on the 4 substrate types and the control.

SUBSTRATE TYPE

PETRI dish (control) ‘Vegetation’ Bare mineral soil Ash Litter

51.9 43.1 a 37.3 a 24.4 b 21.3 b

Means with the same letter are not statistically different according to the DUNCAN test (p≤0.05)

The low rates of germination on the ash substrate may be explained by the abrasive effects of Ca2+ on the very small Calycophyllum spruceanum seeds. A possible explanation for the low germination rate of Calycophyllum spruceanum on the litter substrate is that the litter presented a barrier between the small seeds and the mineral soil that the roots could not penetrate. Although germination may readily occur on top of the litter, the very fine roots are exposed to drought and the seedlings subsequently die.

3.4.4.2 Germination rates of Guazuma crinita in the substrate experiment

There were significant differences in the mean germination rates of the Guazuma Crinita seeds according to the substrate type. The statistical comparison of the germination rates using the DUNCAN test again revealed two groups, as can be seen from table 3.3.

Table 3.3: Germination rates (%) of Guazuma crinita seeds on the 4 substrate types and the control.

SUBSTRATE TYPE

PETRI dish (control) Litter ‘Vegetation’ Bare mineral soil Ash

53.7 23.3 a 22.0 a 18.0 a b 13.8 b

Means with the same letter are not statistically different according to the Duncan test (p ≤ 0.05)

The substrates litter, ‘vegetation’ and bare mineral soil made up the first DUNCAN group. There were no statistically discernable differences between the germination rates on these substrate types. The results of the germination on bare mineral soil and ash represented a second DUNCAN group. The germination rates were lowest on these two substrates. An important factor that can influence the germination rates of seeds on litter is the higher water holding capacity than some of the other substrates. Apparently the relatively thin 1 cm litter layer did not act as an impediment preventing the roots produced by the Guazuma crinita seeds from reaching the mineral soil. This contrasts with the deep litter layer found on the floor of a primary forest, however. The high relative weight and round form of Guazuma crinita seeds facilitates their transfer to the mineral soil as a consequence of the mechanical effects of heavy rains in the wet season.

Biological requirements of pioneer tree species for their establisment on fallows 59

Although the Guazuma crinita seeds were sown during the rainy season, periods of 4-5 days with prolonged solar radiation and no rain dried the upper layer of the soil. The result was a hard, cracked soil surface. The differences between the surfaces of the exposed soils and those in the ‘vegetation’ and the litter substrate plots were visible. No moisture and temperature measurements were made in this study. Under the shade of rice plants and under the litter layer the soil was moist, whereas the exposed soils were dry on the surface. Obviously, the low moisture content of the bare mineral soil and of the ash substrate was a determining factor impeding germination. The ash substrate type demonstrated the lowest rates of germination. An explanation for this is that the fire probably burned the vegetative material and hardened the soil surface. After the first rains the ash was either swept away or mixed into the soil. Ash has a strong influence on soil pH. In the present case, a laboratory analysis indicated a pH value of 4.4 for the soil of the experimental site. This increased to 8.2 under the ash. Clearly these environmental conditions were very adverse for the germination of small seeds because they produce small seedlings that are not resistant like bigger seedlings. The ash was distributed very irregularly over the agricultural land ‘prepared’ a short time before. The ash produced by the burning of large trunks felled in primary forest formed a layer some centimetres in depth. This ash prevented the germination of all plant types for many months. The colonisation of these microsites eventually occurred when creeping plants invaded from outside and covered the plots. It should be pointed out that only few spots within the agricultural landscape exhibited high concentrations of ash. Nevertheless, it was necessary to test the germination under representative conditions occurring in the field. In most cases the ash is mixed in with the soil after heavy rain. The high pH values subsequently decline again.

3.4.4.3 Germination rates of Jacaranda copaia in the substrate experiment

The experiment revealed significant differences in the means of the germination rates of Jacaranda copaia seeds between the different substrate types. The results of the DUNCAN test in table 3.4 indicated the existence of 2 groups. The first group comprised the litter and bare mineral soil substrate types. The germination rates were higher for this substrate type group than for the second group composed of ‘vegetation’ and ash.

Table 3.4: Germination rates (%) of Jacaranda copaia seeds on the 4 substrate types and the control.

SUBSTRATE TYPE

PETRI dish (control) Bare mineral soil Litter ‘Vegetation’ Ash

68.1 36.7 a 34.2 a 23.3 b 20.2 b

Means with the same letter are not statistically different according to the DUNCAN test (p ≤ 0.05)

60 Biological requirements of pioneer tree species for their establishment on fallows

The higher rate of germination of Jacaranda copaia seeds on the bare mineral soil was probably favoured by the fact that the seed coat of this species is a thin permeable membrane, which facilitates the absorption of water when buried in the substrate during the rainy season. As the seeds of Jacaranda copaia are very flat and winged it is unlikely that they are transported to the more moist lower litter layers by rain. The mass of a Jacaranda copaia seed is 10-13 times that of a Calycophyllum spruceanum seed. The corresponding greater nutrient supply within the seed possibly supports the growth of the radicle long enough for it to penetrate the 1 cm thick litter layer and to reach the mineral soil. A possible explanation for the low germination rate on the ‘vegetation’ substrate type, is the susceptibility of Jacaranda copaia to the higher moisture levels, contrasting with the beneficial effect of this observed for Guazuma crinita and Calycophyllum spruceanum (COLAN pers. comm.). The germination of Jacaranda copaia was lowest on the ash substrate. This corresponded with the findings observed for the other two species. Again this seems to have been a consequence of the abrasive effects of Ca2+ and other cations liberated by the burning of the vegetative material.

3.4.5 Conclusions on the effect of substrate type on germination

The rate of germination of all 3 evaluated species was generally highest on the bare mineral soil. This was the only substrate that belonged to the DUNCAN group with the highest mean germination rates in each case. The substrate ‘vegetation’ demonstrated higher germination rates for Calycophyllum spruceanum and Guazuma crinita, and litter for Guazuma crinita and Jacaranda copaia. Ash revealed the lowest germination rates for all 3 evaluated species. Although a litter substrate proved favourable for the germination of Guazuma crinita and Jacaranda copaia, it is apparently unsuitable for Calycophyllum spruceanum because it prevents the very thin roots from making contact with the mineral soil. The experiment showed that the ‘vegetation’ substrate type may be favourable for the germination of both Guazuma crinita and Calycophyllum spruceanum, two species associated with wet sites. The germination rate observed for Jacaranda copaia on this substrate type was relatively low; the higher content of moisture level associated with this substrate type promoting fungal infection. The bare mineral soil substrate type demonstrated satisfactory germination rates for seeds of both Jacaranda copaia and Calycophyllum spruceanum. The substrate type presenting the greatest difficulties for the germination of all 3 evaluated species was ash, created after the burning of agricultural land. Ash returns mineral nutrients to the soil but small seeds are susceptible to changes to the soil pH.

Biological requirements of pioneer tree species for their establisment on fallows 61

3.5 GERMINATION OF BURIED Croton matourensis SEED

Croton matourensis seeds were also tested for inclusion in the germination experiments on different substrate types (chapter 3.4). However, as the seeds did not germinate in the preliminary control test the species was excluded from the field trial. The other 3 species germinated in the preliminary control test, apparently not subject to a dormancy mechanism. Seed dormancy can be assumed if viable seeds fail to germinate when exposed to conditions normally favourable for germination. Dormancy has evolved as a strategy designed to prevent seeds from germinating under unfavourable environmental conditions. According to the phenological observations, Croton matourensis is adapted in such a way as to produce and to disperse its seeds at the end of the rainy season (April-May). The Croton matourensis trees tested in the phenological studies produced abundant quantities of seed. The seed is predominantly dispersed via autochory, the shell of the fruit bursting when conditions are sufficiently dry. The seeds are broadcast short distances, spread a few metres beyond the crown of the seed tree. Recently dispersed seeds located on the ground appeared to be mature and healthy. Farmers often prove a very important source of information, many of them permanent observers of the development of the fields and forests. In the vicinity of Croton matourensis trees on their land, or in places once occupied by these trees, farmers reported abundant young growth of this species. They observed an abundance of recently germinated seedlings on land burned in preparation for the sowing of rice (rainy season November- April). Seedlings of Croton matourensis grow together with the cultivated crops, and those that survive the agriculture activities may reach maturity. Sometimes homogenous stands then become established.

3.5.1 Objectives of the test of the germination of buried seed

The objective of the test of the germination of buried seed was to determine the effect of fire on the germination of Croton matourensis seeds contained in the soil seedbank.

3.5.2 Method of testing the germination of buried seed

A germination experiment was carried out in a degraded primary forest to determine the viability of seed of Croton matourensis stored for 5 months under natural conditions in the soil. It was not possible to ascertain the quantity of seeds present in each plot. It was considered likely that the quantity of seeds in the soil depended upon the distance from the seed tree. A higher quantity of seeds was, therefore, expected near the stem of the tree. It was assumed that the seed dispersal conditions were similar in all plots. Factors such as the litter conditions and the solar radiation on the ground couldn’t be controlled.

3.5.2.1 Site description of the forest with Croton matourensis seed trees

62 Biological requirements of pioneer tree species for their establishment on fallows

The experiment was established under the crown of a Croton matourensis tree located in a degraded primary forest in the Curimana sector. The terrain is even, with well drained sandy soil. This forest was affected by intensive timber exploitation 20 years prior to the establishment of the experiment. A gradual transformation to agricultural land and fallows is currently taking place. The large gaps created by the loss of the harvested trees have been filled in by heliophyte tree species. Big trees are now scarce and the current vegetation has a homogeneous structure. This has created relatively homogeneous environmental conditions in the understorey. However, as the canopy is not completely closed, the light conditions on the ground varied in some sectors. On the ground under the canopy of the residual primary forest there was more litter than on the fallow land. There were 2 further Croton matourensis trees between the forest and the neighbouring fallow land. As the light conditions under the crowns of both trees were heterogeneous and the accompanying vegetation varied in terms of age and structure, the study was only carried out under the first tree. This tree was 35 m high and had a diameter of 55 cm.

3.5.2.2 Design of the buried seed germination experiment

It was assumed that the abundance of seed was inversely correlated with the distance from the tree. More seed should have been located under the crown than on the ground beyond the radius of the crown projection. The analysis of the data collected in the plots provided an opportunity to gain information about the quantity of seed that germinated. The influence of the distance from the tree, the soil treatment, and their interaction, could be studied. The average rates of germination associated with the treatments and the distances were compared using the F-test. The comparison of the germination rates determined for each treatment, with equal distances, were compared using the DUNNETT t-test. Three parallel rows of plots, each plot 1m² in size, were placed 5, 10 and 15 m from the seed tree. The tree stem marked the centre of the experiment. The experiment featured 4 repetitions. The experiment design is presented in fig. 3.12 (next page) The litter lying on the ground required some time to dry. After a dry period of >2 weeks it could be burned completely. This was possible at the end of the dry season. The evaluations were carried out in October, 5 months after seed dispersal had ceased. It was not possible to count how many seeds were deposited in each of the plots evaluated, or how many of these seeds were still viable after 5 months buried in the tropical soil. The quantity of Croton matourensis seedlings that germinated in each of the following 3 treatments was evaluated:

(control (undisturbed litter on the forest floor ־ (bare mineral soil (the litter was removed ־ .burned litter ־ Litter helps to stabilise certain environmental influences such temperature and humidity. In exposed areas bare mineral soil provides no protection for seedlings against direct radiation and high temperatures.

Biological requirements of pioneer tree species for their establisment on fallows 63

15 m

10 m

5 m

Plots (1 x 1 m) with: undisturbed litter (control) Croton matourensis bare mineral soil seed tree burned litter Crown limit

Fig. 3.12: Layout of experimental plots around a seed tree located in the residual primary forest. Some species depend on phytochromes, or receptor pigments, to intercept light signals in order to initiate germination (VASQUEZ-YANEZ & OROZCO-SEGOVIA 1990), whereas the seeds of certain other species require high temperatures. The burning of litter produces high temperatures for a brief period. The evaluations were completed after 1 month of observation. After this time no further germinating seedlings were observed.

3.5.3 Results of the Croton matourensis germination experiment and discussion

The results and the discussion of the experiment are presented in the following order:

,the factor treatment ־ ,the factor distance ־ .and finally the interaction between both factors ־

3.5.3.1 The seedling abundance associated with the substrates

In table 3.5.1 (next page) the results of the analysis of variance of the plots using the F test (p ≤ 0.05) are shown. It was found that the germination rates in the controls, the undisturbed litter plots (DUNNETT group a), were lower than in the plots with burned litter and the bare soil treatments (DUNNETT group b). There was no significant difference between the latter two treatments. When the treatments were compared in relation to the distance of the plot from the seed tree using the DUNNETT t-test (p ≤0.05), it could be seen that in the plots 5 m from the tree (first column) the number of seedlings was higher on the bare mineral soil (c) than on the

64 Biological requirements of pioneer tree species for their establishment on fallows

Table 3.5: Average germinated seedlings/m2 for each soil treatment. * t groups identified using the DUNNETT t-test.

Treatment Distance from tree (m) Dunnett group 5 t* 10 15 x Undisturbed litter (control) 5.8 a 5.0 a 2.0 a 4.3 A Burned litter 13.5 b 10.0 a 7.0 a 10.2 B Bare mineral soil 20.3 c 10.0 a 4.5 a 11.6 B x 13.2 8.3 4.5 8.7 burned litter (b), which in turn hosted more seedlings than the plots with an undisturbed litter layer (a). There were no significant differences between the germination rates on the soil treatments for the plots 10 and 15 m from the seed tree (second and third columns). Some differences in the values obtained for certain plots were apparent, but the high variability of the seedling numbers ruled out any significant differences. The coefficient of variation (CV) calculated for the treatment values was 79 % (cf. ANOVA, Appendix 1). There was a strong but brief (2-3 min.) temperature increase on the plots where the litter was burned. Other than that, there was practically no difference between the burned litter and the bare mineral soil treatments. In both cases, the elimination of litter meant that direct solar radiation reaching the mineral soil was higher, and subsequently also the temperature. The fact that the quantity of Croton matourensis seedlings was lowest in the control plots (undisturbed litter) may be explained by the fact that the litter impeded the direct solar irradiation of the mineral soil, and by the correspondingly lower light and temperature levels, and by the fact that the litter represented a physical barrier to the development of the seedlings. The experiment was carried out in the dry season, when some tree species had shed their leaves. As a result, the light levels were higher locally, explaining sporadic germination observation in other areas not evaluated.

3.5.3.2 Seedling abundance as a function of distance from the seed tree

The analysis of the effect of distance (tab. 3.5.1), using the F-test (p≤0.05), revealed no significant differences in the seedling abundance as a function of distance. Although the average seedling number in the plots 10 m from the seed tree was almost double that of the plots 15 m distant, the high variability ruled out significant differences. The coefficient of variation (CV) calculated for the distance values was 76 % (cf. ANOVA, Appendix 1).

3.5.3.3 Analysis of the interaction between distance and treatment

The F-test of the ANOVA (Appendix) indicated that there was no interaction between the treatment and distance. However, with increasing distance, the seedling abundance on bare mineral soil declined more rapidly than on burned litter. The decrease was similar for

Biological requirements of pioneer tree species for their establisment on fallows 65 treatments. This tendency was presumably the result of the fact that the number of seeds dispersed to the more distant plots was lower. The variability of the seedling numbers was very high. A possible explanation may have been differences in the number of viable seed in the plots, and the different environmental conditions during the experiment. The differences between the seedling numbers in the various treatments were high in the plots located 5 m from the seed tree. The difference lessened in the plots situated at a further remove.

3.5.4 Germination of Croton matourensis and practical implications for regeneration

Many tropical plant species germinate after a heat shock. The buried seed of certain plant species found in savannahs can, however, resist the heat produced by the fires that regularly occur (GASHAW & MICHELSEN 2002). In the case of Ochroma pyramidale (balsa tree), pre- germinative heat treatments are required to foster high germination rates (VASQUEZ-YANEZ 1974). Seeds of this species germinated after having been stored in a herbarium for 50 years. Any exposure of the mineral soil has a positive effect on the germination of Croton matourensis. There are no naturally occurring fires in the study region, but the short effect of the high temperature can substitute the heat produced on exposed soil in gaps or on land prepared for agriculture by prolonged direct radiation. In some cases, the burning of litter clears the soil surface and promotes the germination of species with high light requirements (OROZCO-SEGOVIA et al. 1993). The experiment presented could not provide information about the germination physiology of Croton matourensis, but it presented strong evidence of the need for external stimulation such as heating or light to initiate germination. The influences of temperature and light on the litter and on the mineral soil surface could not be evaluated. Nevertheless, the results suggested that these treatments can improve conditions for the germination of Croton matourensis. Germination experiments in which it can be arranged that each treatment contains the same quantity of seeds should provide results permitting better explanation. Spontaneous germination was also found to occur under the crown and in gaps. In the first situation, the chances of survival for seedlings growing in the shade were low. In the second, high mortality were observed as a consequence of drought. Certain agricultural activities such as forest clearance before the rainy season favour the germination and the growth of Croton matourensis. The results of this experiment can help to arrive at a suitable method for producing seedlings for the establishment of plantations. The conventional method of seed cropping and subsequent sowing in nursery beds has failed. A possibility to obtain large numbers of seedlings within a short time period is to stimulate germination by means of fire or by

66 Biological requirements of pioneer tree species for their establishment on fallows removing litter from beneath the crowns of seed trees. The seedlings may subsequently be transplanted to plastic bags filled with soil. More experimentation is required to determine the best way to stimulate the germination of Croton matourensis. If the option selected is to burn the litter layer, it is necessary to prevent the expansion of the fire into other parts of the forest. The germination experiment provided information in relation to the possible distances from the seed tree within which the substrate might usefully be manipulated to encourage the growth of the highest possible number of seedlings.

3.5.5 PRACTICAL IMPLICATIONS OF THE ECOLOGICAL REQUIREMENTS OF THE SPECIES FOR EARLY ESTABLISHMENT

It was observed that some of the particular requirements of the species studied for successful establishment are met as a consequence of certain agricultural activities engaged in in the study area. According the phenological evaluations, the dispersal of the seeds of some pioneer trees occurs at the end of the dry season. The timing of the dispersal of the seed of these tree species increases the likelihood of seed landing on bare mineral soil shortly before the beginning of the rainy season. For example, land is prepared for rice crops shortly before the onset of the rainy season, as cultivation requires high moisture levels. This was the case for both Calycophyllum spruceanum and Guazuma crinita. These species further profit from the cultivation of rice as the seedlings of both are protected from desiccation below the ‘micro-shelterwood’ conditions provided by the rice plant canopy. The seedlings of Jacaranda copaia, by contrast, are not adapted to high moisture levels, and the seed dispersal occurs at the end of the rainy season. The breaking of the dormancy of Croton matourensis seeds by the fires used in the preparation of agricultural land provides another example of the process of natural regeneration of a commercial pioneer tree species profiting from the positive influence of human activities. Knowledge of the establishment strategies of the species studied can serve to benefit certain agricultural production activities that permit the simultaneous establishment and cultivation of commercial pioneer tree species. Altering the tendency towards deforestation in order to clear land for agriculture will prove extremely difficult. It is, therefore, important to find alternatives for farmers whereby they can avail of the successional vegetation to produce timber. If such viable alternatives are found, the surface area of secondary forests and fallows will increase.

Pioneer vegetation and natural regeneration in the study area 67

4 PIONEER VEGETATION AND NATURAL REGENERATION IN THE STUDY AREA

In this chapter the vegetation of the first phases of succession is described, after the crops have been harvested and the land abandoned to fallow. In most cases there were great differences between the vegetation types of the fallow areas evaluated. The past human activities continued to exert a strong influence initially. After the land had been abandoned for a while other random factors exerted a decisive influence on the structure and the composition of the plant species of the next stages of succession. Two adjoining plots of agricultural land on the site of cleared residual primary forest established within a few months of one another, may undergo greatly different developments in relation to the vegetation composition. The opposite frequently also occurs, namely that plots of land in contrasting landscapes, such as hill or floodplain forests, develop a very similar vegetation composition and structure (DE JONG et al. 2001). It is not seldom the case that stands that have established after the cessation of agricultural use are dominated by a single or only few pioneer tree species. The prevailing site conditions favour these species, and strong inter- and intraspecific competition sets in. It is not difficult to forecast the composition of the developing secondary forests within only a short period of time after the abandonment of agriculture. In the following, an analysis of the young vegetation colonising fallow land is presented, highlighting both areas with and areas without seed trees of the commercial species focused upon in this study. The distribution and the stocking density of the naturally regenerated seedlings of the selected commercial species are also evaluated.

4.1 PIONEER VEGETATION ON FALLOW LAND ABSENT SEED TREES OF THE COMMERCIAL SPECIES

In the first phases of succession fallow land is usually colonised by non-timber species. GALVAN et al. (2000) and CORONADO et al. (2002) described the middle and advanced stages (secondary forests) of succession on fallow land in the study area. They identified 3 age classes in the secondary forests to have established in the area, namely 5-7, 8-10 and >10 years. Both authors made an inventory of the total vegetation occurring in 3 separate investigation areas. One of these areas (Neshuya-Curimana) corresponded with the study area described here. Inventories of young and old secondary forests produced information on the possible direct use of certain species, or suggesting silvicultural interventions to promote species already established for the purposes of future timber exploitation. Evaluations of very young fallow vegetation by contrast can help to provide information about the factors both favourable and unfavourable to the development of stands of certain desirable tree species. This would allow for the steering of succession to meet management objectives, rather than reacting to succession once already underway. Fallow land in the early stages of succession, as yet without any woody species, can serve as a control for

68 Pioneer vegetation and natural regeneration in the study area comparison of the development of the vegetation on land where seed trees are present and on land from which they are absent.

4.1.1 Objectives of the vegetation analysis

The objectives of the vegetation analysis were:

,to gain knowledge of the vegetation of the first stages of succession ־ ,to ascertain the vegetation composition and to identify the more important species ־ to derive information about the changes to the vegetation structure shortly after the ־ harvesting of the prior agricultural crop.

4.1.2 Methods for the evaluation of the vegetation

A single fallow area devoid of a seed tree of any of the 4 investigated species was available. The vegetation on this fallow was evaluated 10 months after the rice crop had been harvested. The terrain was homogeneous. Originally the rice plantation covered an area of approximately 1 ha. Only a small part of this area remained uncultivated subsequently, with the greater part used by the farmer to grow manioc and plantain. On the smaller area not planted, the vegetation was evaluated along 3 parallel transects established 5 m apart. Each transect was 50 m long and 5 m wide, and contained 10 plots of 5x5 m. The vegetation >1.5 m high was recorded in each plot. In a 5x1 m sub-plot contained within each plot the vegetation between 0.3-1.5 m height was recorded (fig. 4.1).

50 m Plots

Transect 112345678910 Veg. 0.3–1.5 m

Plots 5m

Transect 212345678910 Veg. >1.5 m

Plots 5m Transect 312345678910

Fig. 4.1: Distribution of the transects and plots established to record the vegetation in a fallow area.

The parameters evaluated were:

plant type, defined as one from the most common growth forms of the terrestrial ־ vegetation of the Pucallpa region, namely tree, shrub, palm, grass, herb or climber. .plant species ־ .heights of individuals ־ .crown diameter ־ .DBH ־

Pioneer vegetation and natural regeneration in the study area 69

From the data relating to the above parameters, the plant coverage of each transect was calculated, and the total species coverage. The results are presented below. A simplified profile representing a 10x1 m strip of fallow land was developed using the vegetation data collected. The species coverage, abundance and height were averaged to obtain representative quantities and dimensions of the species with the highest coverage. Samples of plants not identified during the field evaluations were collected, and subsequently identified using various guides (GENTRY 1993, CLAVO 1993, VASQUEZ 1997) and by comparing the samples with identified material kept at the Herbario Forestal La Molina (Lima).

4.1.3 Results of the vegetation evaluation

The results of the vegetation study of the fallow land devoid of seed trees of the commercial species of interest are described in the following.

4.1.3.1 Plant type coverages on fallow land without seed trees of commercial species

The pioneer vegetation did not cover completely the surface area of the plot left fallow. The total plant coverage of the evaluated area determined from the 3 transects was 80 %. The dead residues of rice plants created a hindrance to the establishment of other plants, by taking up space. The stems of rice plants can persist out in the open for a long period of time. They are so durable in fact that in many tropical rural areas they are used for making walls and as roof material. The high proportion of shrub cover revealed in fig 4.2 corresponds with the first phase of succession. Most of the non-timber producing pioneer tree species produced seed more or less continuously and were, therefore, able to establish in open areas (BAZZAZ 1996).

70 61,8 60 50

30 24,5 20 Coverage %

10 4,1 5,4 3,9 0,3 0 tree shrub herb grass palm climber

Plant type

Fig. 4.2: Coverages of different plant types across the fallow area evaluated.

70 Pioneer vegetation and natural regeneration in the study area

The proportion of trees was not very high. It is likely that the pioneer tree species arrived later than the non-woody species, but once in place they are adapted to growing very rapidly and to dominating the fallow area in the next phase of succession.

4.1.3.2 Species coverages on fallow land without seed trees of commercial species

Fig. 4.3 reveals the coverages of the most abundant plants on the area investigated. The shrub coverage was concentrated on 5 species. Of these Vernonia baccharoides, Baccharis floribunda and Clibadium sp. are all Asteraceae. Aegiphylla integrifolia is a Verbenaceae. All 4 of these species produce abundant seeds dispersed by the wind.

20 tree shrub herb grass palm climber 15,7

15 14,7 14,2 12,7 11,9 10

6,2 6,0

Coverage% 5 3,8 3,6 2,4 2,5 1,5 0,6 0,6 0,5 0,5 0,4 0,4 0,4 0,4 0,3 0,1 0,2 0,2 0,1 0 0,1

others Inga spp.Inga Miconia sp. Oryza sativa Oryza Uncaria sp. Physalis sp. Physalis Panicum sp. Panicum

sp. Imperata Solanum spp. Geonoma sp. Geonoma Clibadium sp. Cecropia spp. Passiflora sp. Hyospathesp. Phytolacca sp. Phytolacca Tachigalia spp. Pourouma minorPourouma

micrantha Trema Desmodium axilare Pteridium aquilinium Baccharisfloribunda Andropogon bicornisAndropogon Aegiphilla integrifolia

Axonopuscompressus Vernonia baccharoides Acalypha alopecuroides

Species

Fig. 4.3: Species coverages in the field left fallow after rice cultivation.

The fifth shrub species was Phytolacca sp., a Phytolacaceae the seed of which is possibly disseminated by zoochory. This shrub was not as widespread as the other 4, but was also found in other fallows in the study area. Trema micrantha (Ulmaceae) was the most important tree species on this fallow area. The number of individuals was low in comparison to those of the shrubs Baccharis floribunda and Vernonia baccharoides. However, this tree species grows very fast and some of the saplings were 2 m in height by the time of the recording, and some of them even almost 3 m high. Cecropia spp. (Cecropiaceae) is another typical pioneer tree species. The seed of Cecropia spp. is disseminated by bats and requires open spots on the ground with prolonged periods of solar radiation in order to germinate. Open land used for agriculture for but a short period of time provides unfavourable conditions for the establishment of grasses and herbs. In this case, the most important grasses were Andropogon bicornis and Oryza sativa. The most abundant herb Acalypha alopecuroides requires high light levels and has no chance of survival under the shadow cast by the larger shrubs and trees.

Pioneer vegetation and natural regeneration in the study area 71

Individual palm species such as Geonoma sp. (Asteraceae) are shade tolerant. Some quantity of buried seed, or old stumps, probably survived the effects of the fire ignited as part of the slash-and-burn system of agriculture. The seed of the climber Uncaria sp. (Rubiaceae) has very fine wings and is dispersed readily. The chances of survival of palm and liana species over the course of the succession process are good once the ephemeral tree species like Trema micrantha and Cecropia spp. reach the end of their life spans.

4.1.3.3 Simplified profile of the area of fallow land without seed trees of the commercial species

Fig. 4.4 is a simplified, idealised profile of the most representative vegetation on an area of fallow land of 10 m2. It highlights the abundance of the shrubs Baccharis floribunda and Vernonia baccharoides. However, the presence of tree species such as Trema micrantha and Cecropia spp. indicates that these species will dominate the next phase of succession.

Fig. 4.4: Simplified profile of the fallow land vegetation. 1 Baccharis floribunda, 2 Andropogon bicornis, 3 Vernonia baccharoides, 4 Geonoma sp., 5 Trema micrantha, 6 Oryza sativa, 7 Cecropia sp., 8 Phytolacca sp., 9 Clibadium sp.

4.1.4 Discussion of the vegetation of fallow land without seed trees of commercial species

The main plants dominating the cover of the area of fallow land studied were species with short life spans (see fig. 4.4). The plants that will come to dominate the stand in the future were not strongly represented at the time of the vegetation recording. The reasons for this were as follows:

.the vegetation develops slowly in the dry season ־ the tree species Trema micrantha occurred in abundance as it produces seed all ־ year round. The seed is primarily dispersed by birds. As a pioneer species it tends to dominate the ground vegetation.

72 Pioneer vegetation and natural regeneration in the study area

the previous cultivation of rice and the residual plant debris hindered the ־ establishment of many pioneer species. due to their effective seed dispersal traits, certain other pioneer species such as ־ Cecropia spp. and Ochroma pyramidale are able to colonise and subsequently to dominate secondary forests even though there are no seed trees in the vicinity. Crecropia spp. fruit, for example, is eaten by bats, and the seeds may be dispersed over long distances as a result. Ochroma pyramidale alternatively produces fruit and cotton-wool (kapok) containing seeds effectively dispersed by strong winds. The second phase of succession (chapter 1.2.3) is in many cases dominated by a smaller number of tree species.

4.2 NATURAL REGENERATION OF COMMERCIAL PIONEER TREE SPECIES ON FALLOWS

Some forest stands originating from fallow land were dominated by commercially used pioneer tree species. These stands arose from seed transferred to the site at the beginning of the process of succession. The seed and the seedlings that subsequently developed found the conditions favourable, allowing them to dominate over other fast growing tree species. However, the presence of mature individuals of certain commercial pioneer trees species does not guarantee the establishment of the species, even if seed has been dispersed to the site during cultivation or at the beginning of the succession process. It is frequently the case that these areas may come to be dominated by other fast growing tree species, even though there may be no mature trees of these species in the vicinity. Often a small number of individuals of the commercially important timber-producing tree species establishes together with non-timber tree species. When these trees reach maturity, the farmers use them mainly for the construction of rural buildings. Stands of fast growing tree species are only exploited commercially when there is a large number of individuals, enough to justify the effort and the expense of harvesting. This explains why some areas of fallow land dominated by fast growing commercial species are not cut but simply burnt to clear the land for agriculture, without using the timber. This fact provided a motivation to determine the reasons for the establishment, or non- establishment, of stands dominated by commercial species, so that the future stand composition can be either identified or determined early on in order to ensure that the eventual stocking density is sufficiently high to ensure the profitability of the commercial use of the stands that develop over time.

4.2.1 Objectives of the vegetation analysis on fallow land with seed trees of commercial species

The objectives of the vegetation analysis on fallow land hosting seed trees of commercially useful tree species were:

Pioneer vegetation and natural regeneration in the study area 73

to determine the main characteristics of the composition and the structure of the ־ vegetation of fallow areas on which the studied tree species play a dominant role, to gain insights into the establishment process in order to ascertain why certain ־ secondary forest stands are dominated by commercial tree species and why other stands lack these timber species.

4.2.2 Methods for the analysis of the vegetation on fallows with seed trees of the commercial species

4.2.2.1 Variations in the vegetation of the fallow areas studied

The vegetation was evaluated using a variety of methods because each of the species studied had different seed dispersal and establishment strategies. Furthermore, the site conditions varied from one location to the next, even though the same species may have dominated. For example, the sizes of the fallow areas studied varied. There were 2 approaches to the sampling of the vegetation:

the first consisted of parallel transects comprising sampling plots, as described in ־ chapter 4.1. (fig. 4.1). The evaluation of the vegetation employing transects provided for detailed information. This method of appraisal was intended for application in areas where succession was not far advanced, and the vegetation small and widespread. an alternative method was applied for the second recording of the vegetation. By ־ the time of the this second recording, there had been a significant increase in the number of individuals present, and in the dimensions of the trees present at the time of the first recording. The vegetation had become quite dense, rendering the set up of a systematic sampling plot design difficult. The time required for the measurement of the vegetation was also much greater as a result. A decision was made, therefore, to apply the COX method (COX 1971) to record the vegetation, a considerably faster approach. To ascertain the changes to the vegetation over time, the percentage cover values of the dominant species are compared. Changes are also assessed on the basis of a comparison of groups of species classed according to plant type. The plant type groups help to determine whether the tree species in question has the potential to dominate, to be an important stand component, or whether it is likely to be replaced in the next stage of succession. Subsequently, it is evaluated whether the plant type destined to dominate the intermediate and advanced stages of succession is able to establish readily, or whether establishment is likely to be delayed or impeded by the groups of plants characteristic of the early phases of succession, such as the herbs, grasses and shrubs. The evaluation of the grasses proved particularly complicated, as they spread vegetatively from the roots and developed dense swards across small areas. It was, therefore, difficult to count the number of individuals. In this case it was more practical to estimate the coverage.

74 Pioneer vegetation and natural regeneration in the study area

4.2.3 Results: establishment of commercial tree species on fallow land

In this chapter the tree species evaluated are presented in order of their abundance. Guazuma crinita was the most abundant tree species, and also produced the greatest number of seedlings. Calycophyllum spruceanum was the second most abundant species, at times found growing together with Guazuma crinita. Jacaranda copaia and Croton matourensis were the third and fourth most abundant species, respectively. The species recorded during the vegetation assessment were grouped by plant type. The coverages of each species are presented in fig. 4.5 (next page), separated by plant type. The bars indicate the aggregate coverage per species for all sample plots at the time of the first and the second recording. The species are ranked in order of highest abundance at the time of the first recording to the lowest. This applies for each plant type group.

4.2.3.1 Natural regeneration of Guazuma crinita on fallow land

The regeneration of Guazuma crinita was evaluated on 4 fallow areas belonging to 4 different small farmer families:

,(Flores (fallow after rice cultivation (1) ־ (Castro (fallow after rice cultivation (2) ־ Gomez (fallow after maize cultivation) and (3) ־ .(Alegria (fallow after pasture burning (4) ־

4.2.3.1.1 Guazuma crinita growing on fallow land after a rice crop: example 1 (Flores family land)

Coverages of vegetation species on fallow land after rice cultivation

Fig. 4.5 shows that at the time of the first recording in April rice (Oryza sativa) enjoyed the greatest coverage. A number of rice plants resprouted after the crop was harvested. New plants also grew from the grains not harvested. The second highest coverage was that of Vernonia baccharoides. This shrub was one of the most abundant species present at the beginning of the succession process on fallow land. Guazuma crinita accounted for the third highest coverage. While under cultivation, the rice plants occupied almost all of the surface area of the site in question, complicating the establishment of other species. The farmer also eliminated some invading plants manually. At the time of harvesting many of the plants that had established were cut with the rice, including young Guazuma crinita seedlings. By April the plants with a high capacity for growth had already achieved heights of 2.5 m. These plants grew unimpeded during the 7 months to the second recording, without any interference by the farmer.

Pioneer vegetation and natural regeneration in the study area 75

The coverage data collected in October (fig 4.5) revealed important changes to the vegetation dynamics. The rice coverage decreased dramatically because a third generation failed to establish. Vernonia baccharoides possessed the greatest coverage, occupying almost twice the area of Guazuma crinita, the second most abundant species.

Guazuma crinit a

Trema micrant ha Cecropia spp. tree Heliocarpus popayanensis April 2000 Sapium spp. Chorisia sp. October 2000 Eryt hrina sp. Inga spp. Calycophyllum spruceanum Vernonia baccharoides Solanum spp. Urera caracasana Baccharis floribunda Piper sp. shrub Clibadium sp.

Psychotria sp.

Aegiphila integrifolia Heliconia spp. Costus sp. herb

A marant hus sp. A calypha alopecuroides Pteridium aquilinum Physalis sp. Oryza sativa grass Rottboellia sp. Scheelea sp. Astrocaryum sp. palm Calathea sp. Bactris sp. Passiflora spp. climber others

0 5 10 15 20 25 30 35 Coverage %

Fig 4.5: Coverages of the most important plant species that developed on a fallow after rice cultivation (Flores family land). First and second evaluation.

This was the fallow area with the highest number of species. In April 70 species were registered, increasing to 79 species by October. Many stumps on the site survived the fire and eventually sprouted. Some of the species that established probably colonised the site from the adjacent residual primary forest. The timing of seed dispersal by these

76 Pioneer vegetation and natural regeneration in the study area neighbouring trees was either opportune or the seeds were already buried in the soil and survived the fire to germinate.

Coverages of the plant types on a fallow area after rice cultivation

The combined coverage values for each plant type are presented in fig 4.6, for both the first and the second vegetation recording. 60

50 A April 2000 G. crinita O October 2000 O. sativa 40 o thers % 30 verage

Co 20

0 AOAOAOAOAOAO tree shrub herb grass palm climber Plant ty pe Fig. 4.6: Coverage of the plant types on a fallow area previously cultivated for rice. First and second evaluation.

The plant types shrubs, grasses and trees all had similar coverage values at the time of the first recording in April 2000. The grasses consisted almost entirely of the single species Oryza sativa. As much as half of the tree coverage was accounted for by Guazuma crinita. The herbs accounted for the greater part of the remaining coverage, with only little cover contributed by either climbers or palms. The vegetation of the fallow in April still demonstrated the important influence of the crop previously cultivated on the site. Rice generally has a brief life cycle, unlike the grasses of pasture land, for example, which are very aggressive and persistent. The latter represent a barrier to the establishment of trees and shrubs, delaying the process of succession. By October important changes had occurred. The majority of the rice plants still present in April had died, and the coverage diminished drastically as a result. The shrubs clearly made the greatest contribution to the vegetation cover of the site, followed by trees. In the tree plant group, Guazuma crinita made up approximately 50 % of the coverage. The coverages of herbs, palms and climbers remained low, however.

Distribution of the species coverages according to plant size on fallow land previously used for the cultivation of rice with naturally regrowth of Guazuma crinita

The combination of the total height data collected for the plot and the species coverage data facilitated the analysis of the coverages of the vegetation types in conjunction with the

Pioneer vegetation and natural regeneration in the study area 77 height of the dominant vegetation. The vegetation height was assessed according to the following height classes: 30-75, 75-150, 150-225, 225-300, 300-375 and 375-450 cm (fig. 4.7).

50 G. crinita A April 2000 tree G. crinita O October 2000 40 shrub herb 30 grass Coverage % 20 palm climber 10

0 A O A O A O A O A O A O 30 - 75 75 - 150 150 - 225 225 - 300 300 - 375 375 - 450 Height class (cm)

Fig. 4.7: Vegetation coverages on the fallow land after rice cultivation, according to height class and plant type. First and second evaluation.

In April the vegetation cover was dominated by plants in the second height class, followed by the first, third and fourth height classes. The first height class was dominated by shrub species, whereas the second was dominated by grasses, mainly Oryza sativa. Guazuma crinita accounted for 50 % of the area occupied by tree species, but as a species of commercial interest, it is presented separately in fig. 4.7. Individuals of this species were present in all of the height classes. Notable changes in the vegetation height distribution on the site and the contributions of the various plant types to the respective height classes were observed by October 2000. Some plants grow very rapidly, surpassing two or more height classes in the seven month interval between recordings. The greater part of the coverage was still made up of plants in the height class 75-150 cm, but this dominance was not as clear as at the time of the first recording because almost all of the rice plants had died. Some plants in the class 30-75 cm in April 2000 achieved heights of 75-150 cm by October, but the majority of plants grew to the next higher height class. Just 1 year after burning, the expected dominance of trees and shrubs in the larger height classes was confirmed. Other plant types were present on the fallow plot but their coverage values declined from the first to the second recording, and they were restricted to the two smallest height classes. Herbs, grasses and palms were essentially absent from the third, fourth and fifth height classes.

78 Pioneer vegetation and natural regeneration in the study area

The second recording of the vegetation demonstrated the dominance of the shrubs, but also indicated a tendency towards eventual domination by trees. In addition to Guazuma crinita, other fast growing tree species such as Trema micrantha and Heliocarpus popayanensis were present. Also observed was Calycophyllum spruceanum, a slightly slower growing forest species but, able to tolerate the shade cast by the faster growing species in the initial stages, it survives in the understorey to become dominant when the trees of the aforementioned species have reached the end of their life spans. The larger shrubs recorded in October 2000 probably disappeared from the site 2-3 years after this final recording. The trees of the species recorded achieve heights exceeding those of the shrubs, and they live longer. The shrub species are unable to persist or to establish anew under the shade cast by the taller trees. It is likely that strong competition between the tree species present on the fallow set in. However, the species Trema micrantha and Heliocarpus popayanensis reach the end of the life spans after 5-6 years. If the proportion of the overall coverage occupied by Guazuma crinita at the time of the first and second vegetation evaluations were to remain similar (13.7 % and 18 %), and that of Cecropia spp. (3.9 and 3.7 %), the subsequent stage of the succession process on the fallow will be dominated by Guazuma crinita. The life span of Guazuma crinita is 10-15 years.

4.2.3.1.2 Guazuma crinita growing on fallow land after a rice crop: example 2 (Castro family land)

Coverages of vegetation species on fallow land after rice cultivation

The coverage values of the principal species growing on the plot of fallow land belonging to the Castro family are illustrated in fig. 4.8. (next page) In June Guazuma crinita covered more than ¼ of the area of the fallow area. Solanum spp., a very common shrub in the fallows of the region, was the second most widespread species. The third place was assumed by Pueraria phaseoloides, a very invasive neophyte climber, imported as fodder for livestock. As a legume, it is also used for its capacity to restore the soil. This plant climbs over shrubs and young trees, and as such it represents an impediment to the normal course of succession. Vernonia baccharoides and Clibadium sp. were also very common shrubs on fallows in the study area. The fruit producing Carica papaya grew as a consequence of the landowner spreading its seed. The coverages of other species were very low. By October the coverage of Guazuma crinita had increased slightly. Some change was evident in the order of importance of the other species. The coverage of Pueraria phaseoloides decreased as other plants demonstrated more rapid height growth, and the shade cast subsequently exerted a negative influence on the growth of the climber. The coverage of Solanum sp. also declined drastically between June and October. The coverage of Vernonia baccharoides, on the other hand, increased markedly.

Pioneer vegetation and natural regeneration in the study area 79

Guazuma crinit a Triplaris poeppigiana

Acacia sp. tree

Calycophyllum spruceanum

Heliocarpus popayanensis June 2000

Cecropia spp. October 2000 Ochroma pyramidale Inga sp. Bixa plat ycarpa Solanum sp. Vernonia baccharoides shrub Clibadium sp.

Carica papaya

Baccharis f loribunda

Cassia sp.

Urera caracasana

Siparuna sp. herb Cost us sp.

Calat hea sp.

Calopogonium musciodes

Heliconia sp. Scleria pt erot a grass Geonoma sp. palm Pueraria phaseoloides

Passiflora sp. climber ot hers

0 5 10 15 20 25 30

Coverage %

Fig. 4.8: Coverages of the most important plant species that developed on a fallow after rice cultivation (Castro family land). First and second evaluation.

Coverages of the plant types on a fallow after rice cultivation

Fig 4.9 (next page) shows the coverage values for the Castro family fallow according to plant type. In June 2000, the trees and shrubs dominated the vegetation coverage with similarly high values. In third place were the climbers, predominantly Pueraria phaseoloides. This very aggressive species mainly occupied the edges of the fallow. The results of the second evaluation of the vegetation cover in October 2000 revealed that the percentage of the area covered by trees had increased slightly. Although there was a small reduction in coverage of the shrubs evident, this plant type continued to occupy an important position. The plant type climber decreased as consequence of the decline of Pueraria phaseoloides. The grass increased more than the double of coverage. Palms showed no important changes.

80 Pioneer vegetation and natural regeneration in the study area

J June 2000 G. crinita 40 O October 2000 o thers % 30

age

er 20

Cov

0 JOJOJOJOJOJO shrub tree herb grass palm climber Plant type

Fig. 4.9: Coverages of the plant types on fallow land with Guazuma crinita seed trees. First and second evaluation.

As in the previous example, Guazuma crinita was the dominant species on the Castro family fallow. It is foreseeable that within a period of roughly 2 years almost all of the upper vegetation stratum will be occupied by trees of this species. The shrubs were Vernonia baccharoides, Solanum spp., Baccharis floribunda and Clibadium sp. These have a maximum life span of 2-3 years, after which Guazuma crinita will dominate the new stands. It was observed that naturally regenerated young Guazuma crinita plants were abundant, and homogeneously distributed across the whole fallow. Another commercial tree species observed was Calycophyllum spruceanum, occupying a stratum under Guazuma crinita. This species’ shade tolerance allows it to persist in the early phases of succession before advancing to become an emergent tree species later on. Strong intraspecific competition in stands of Guazuma crinita – as evident from other stands in the studied area developed after rice cultivation – results in the development mostly of individuals with small crowns and weak stems. Thinning is required to encourage crown expansion and, correspondingly, diameter growth.

4.2.3.1.3 Guazuma crinita growing on fallow land after a maize crop: example 3 (Gomez family land)

Coverages of vegetation species on fallow land after maize cultivation

Fig. 4.10 (next page) demonstrates the dominance of maize (Zea mayz) on the fallow land belonging to the Gomez family at the time of the first recording in September 1999. Very low percentages coverage were attained by a small number of some pioneer tree species and some shrubs, palms, herbs and climbers. Maize was cultivated in the dry season, and harvested prior to the beginning of the rainy season. In general, crop plants such as maize are cultivated to grow very quickly over a short space of time. The other plants present all grew slowly over the dry season. The maize

Pioneer vegetation and natural regeneration in the study area 81

Trema micrant ha Inga spp. Guazuma crinit a Heliocarpus p op ayanensis Calycop hyllum spruceanum Trip laris p oep pig iana

Sapium sp. September 1999

Pipt adenia sp . July 2000

Ficus sp. Cecropia spp. Chorisia sp. tree Acacia sp. Rollinia sp. Sp o nd ias mo mb in Pseudo lmedia sp . Ochroma p yramid ale A d enaria f loribund a So lanum spp . Clibadium sp. shrub B accharis f loribund a

Vismia spp.

Vernonia baccharoides

Heliconia sp. herb Costus spp. Zea mayz grass Scheelea sp . palm Astrocaryum sp. Uncaria sp. climber o t hers

0 20406080100 Coverage %

Fig. 4.10: Coverages of the species that developed on a fallow after maize cultivation (Gomez family land). First and second evaluation. was sown at regular spacings. The distances between plants and the heights achieved allowed relatively high levels of direct radiation to penetrate through to the soil in comparison to rice crops, which are low to the ground and very densely grown, allowing little light to reach the soil or space for other plants. Following the end of the life cycle of maize, the disintegration of the dead plants lasted approximately 1 month. By this time part of the space previously occupied by the maize was free for other plants. The conditions favoured the establishment of Guazuma crinita seedlings, but also that of other rival plants, for example, Trema micrantha. The latter is a tree species that produces seed all year round.

82 Pioneer vegetation and natural regeneration in the study area

The number of plant species recorded on the Gomez family land at the time of the first vegetation study in September 1999 was 32. By the second recording in July 2000 considerable differences to the situation at the time of the first recording were apparent. The maize plants, overwhelmingly dominant in September 1999, had disappeared completely. The most abundant species in July 2000 were the trees Acacia spp., Guazuma crinita, Trema micrantha and Calycophyllum spruceanum. Other important species present were the palm Scheelea spp. and the shrub Clibadium spp. The number of species on the fallow land increased to 43.

Coverages of the plant types on a fallow after maize cultivation

In September 1999 the vegetation coverage of the fallow land principally comprised the grasses (maize) (fig. 4.11). The area occupied by trees was approximately ¼ of the coverage of the grasses. Some palm stumps survived the fire and crop cultivation, and had re-appeared by September. The coverages of shrubs, herbs and climbers were very low.

10 0 S September 1999 G. crinita 80 J July 2000 Z. M ayz o thers

Coverage% 20

0 SJSJSJSJSJSJ herb tree shrub grass palm climber

Plant type

Fig. 4.11: Coverages of the plant types on fallow land after maize cultivation. First and second evaluation.

By July 2000 the grass coverage had diminished drastically. The increase in the coverages of trees, palms and shrubs, alternatively, was also remarkable. Guazuma crinita accounted 1 for approximately /3 of the total tree coverage. The extreme reduction of the maize cover after harvesting initiated great competition between the woody species. The maize was cultivated in the dry season, mainly so as to avoid infections to the crop arising from the high levels of humidity at other times of the year. The maize life cycle finished at the end of the dry season. Once the space became available at the beginning of the rainy season the other species expanded, with the higher humidity also proving favourable for their development.

Pioneer vegetation and natural regeneration in the study area 83

Distribution of the species coverages according to plant size on fallow land previously used for maize cultivation with naturally regrowth of Guazuma crinita

Fig 4.12 illustrates the distribution of the vegetation coverage on the Gomez family fallow in September 1999 and July 2000 according to height classes, and subdivided by plant type. In September 1999 most of the vegetation across the site was roughly 2 m in height. This consisted almost solely of maize plants, however. The other plant types grew relatively slowly, and were less than 1.5 m in height. A possible explanation for this is that although many pioneer plant species disperse their seeds many times in a year, they can only establish and grow well once the rainy season begins, which is normally in October- November.

10 0 G. crinita S September 1999 tree G. crinita 80 J July 2000 shrub

herb 60 grass

age % palm 40 climber over C 20

0 SJ SJ SJ SJ SJ SJ 30 - 75 75 - 150 150 - 225 225 - 300 300 - 375 375 - 450 Height class (cm)

Fig. 4.12: Vegetation coverages on the fallow land after maize cultivation, according to height class and plant type. First and second evaluation.

The plant type that began to colonise the space below the maize plants was predominantly the trees. The other plant types such as the herbs and shrubs probably experienced great difficulty growing under the shade cast by the maize crop. By July 2000 the maize plants had disappeared from the fallow. As a result, there was a considerable reduction in the coverage of plants in the height class 150-225 cm. The plants still in the height classes 30-75 cm and 75-150 cm in September 1999 had already grown to the larger height classes by July 2000. The tree and shrub coverages were high in the height classes 30-75, 75-150 and 150-225 cm. Although shrubs and palms dominated the height classes 225-300 cm and 300-375, only trees were found in the height class 375-400 cm. Guazuma crinita did not dominate on the fallow land previously used for the cultivation of maize, as was the case for the two previous examples of land formerly cultivated for rice. The differences in the previous use of the land may provide a possible explanation for this. As maize cultivation began in May 1999, the site had already been colonised by other species. These plants grew slowly under the maize canopy, not all of them surviving until the end of the dry season. The dispersal of Guazuma crinita seeds began later, in August and lasted until October of the same year. In comparison of fallow after rice cultivation, quantity of Guazuma crinita seedlings were in this maize fallow lower.

84 Pioneer vegetation and natural regeneration in the study area

Other fast growing tree species suppressed the Guazuma crinita seedlings, which in July 2000 were only present in the height classes <225 cm. Though the herbs and grasses did not remain to cause strong mortality of Guazuma crinita. The plants that developed on the fallow land previously used for maize started to grow 3-4 months earlier than the same plants colonising fallow land formerly hosting a rice crop. This can mean differences in height growth of ~ 1.5 m with regard to the species of commercial interest. The tree species that successfully managed to attain the greater height classes were Trema micrantha, Cecropia spp. and Heliocarpus popayanensis. The natural tendency in the event of succession on former maize sites is towards a disappearance of Guazuma crinita shortly after germination. Only poorly developed isolated individuals may survive the early stages of succession. If promising individuals are to be promoted so as to achieve commercially useful dimensions, the elimination of competing non-timber species is required. The irregular distribution of the natural regeneration of the commercial species requires a combination of thinning in those areas where there is a high stocking density and a release from the competition posed by other vegetation in areas where there are few individuals.

4.2.3.1.4 Guazuma crinita growing on pasture: example 4 (Alegria family land)

In April one adult Guazuma crinita tree was observed at the edge of a recently burned area. Before this area of fallow land was burned, it was dominated by Brachiaria sp., a grass used for pasture. The Guazuma crinita seed tree dispersed its seed after the fire, landing on the ground while it was free of vegetation. Repeated burning in the preceding years had served to eliminate other plants common on fallow land. This brought about a halt to the process of succession, and facilitated the maintenance of this area of pasture land. Fig 4.13 (next page) reveals the clear dominance of Brachiaria sp. in April 2000. The fire eliminated the above ground vegetation on the pasture, but the roots persisted and sprouted again. Other species with low coverages but representative of this fallow such as Pueraria phaseoloides, Vernonia baccharoides and Musa paradisiaca are not fire-resistant. These species established after the fire, when abundant free space was available. Other species such as Paspalum sp., Scleria pterota, Scheelea sp. and Bauhinia sp. suffered from the effects of fire but survived. Almost no changes in the species coverages were observed in the following October. Only Brachiaria sp., Vernonia baccharoides and Guazuma crinita exhibited a slight increase in the areas covered. This increase in the area occupied by Guazuma crinita was very small in spite of the fact that the seed tree had effectively dispersed its seed all across the abundant open space available. The small seedlings had great difficulty establishing because they were exposed to direct sunlight. Unlike on the rice sites, there was no shelter for the Guazuma crinita seedlings. Another contrast to the rice sites was that the rice plants were largely eliminated during the harvest, whereas Bachiaria sp. is a permanent and hostile grass. Its dense root network and sward impede the establishment of other plants.

Pioneer vegetation and natural regeneration in the study area 85

Bauhinia sp. tree Guazuma crinita Vernonia bacharoides M usa paradisiaca shrub

Psidium guajaba April 2000 Piper sp. October 2000 Lantana camara

Brachiaria sp. Paspalum sp. grass Scleria pterota Scheelea sp. palm

Pueraria phaseoloides climber others

0 20406080 Coverage %

Fig. 4.13: Coverages of the species on a pasture with a Guazuma crinita seed tree. First and second evaluation.

Coverages of the plant types on a pasture with a Guazuma crinita seed tree

The dominance of the grasses at the time of both recordings was marked, as can be seen from fig 4.14. In comparison to other fallows evaluated, the changes to the plant type coverages from one evaluation period to the next were very small. This lack of change was a consequence of the very robust and aggressive nature of the grass Brachiaria sp. This species is favoured by human activities such as the repeated occurrence of fire, which eliminates other plant types.

80 G. crinita 70 A April 2000 O October 2000 Brachiaria sp. 60 others 50

30 Coverage % 20

0 AOAOAOAOAOAO tree shrub herb grass palm climber

Plant type

Fig. 4.14: Vegetation coverages on fallow land with a Guazuma crinita seed tree previously used as pasture. First and second evaluation.

86 Pioneer vegetation and natural regeneration in the study area

Distribution of the species coverages on pasture with Guazuma crinita seed tree according to plant size

The Brachiaria sp. pasture grew to about 1 m in height, with the grass species dominating the vegetation of the evaluated area. The differences between the first and second evaluation (fig. 4.15) were slight. Apart from the individuals that survived the fire and those with heights exceeding that of the grass, there were few species capable of establishing on the pasture in the short-term.

70 G. crinita A April 2000 60 O October 2000 tree G. crinita shrub 50 grass age % 40 palm er

ov 30 climber C 20

0 AOAOAOAOAOAO 30 - 75 75 - 150 150 - 225 225 - 300 300 - 375 375 - 450 Height class (cm)

Fig. 4.15: Vegetation coverages on fallow land previously used as pasture, according to height class and plant type. First and second evaluation.

Species such as Bauhinia sp. possess certain characteristics that allowed them to become established on the land formerly used as pasture. Their seeds are sufficiently large to allow them to develop big seedlings within a short period of time. Unlike the typical pioneer species with small seeds, the seedlings of these species can survive on the reserves stored within the seed. Bauhinia sp. also enjoys a certain degree of shade tolerance not observed in Guazuma crinita. The second species of importance on this area was Pueraria phaseoloides, an exotic fodder plant and climber. Pueraria phaseoloides climbs over woody plants, retarding their growth and even strangling them. This species also serves to impede the succession process as it successfully competes with the woody plants. In spite of the presence of a Guazuma crinita seed tree, the conditions required for the establishment of a productive stand did not exist in this area.

4.2.3.1.5 General observations on the natural regeneration of Guazuma crinita on areas of fallow land

Differences in the success of establishment of Guazuma crinita on the different sites evaluated with a seed tree may be explained by the following factors: the opportune timing of seed dispersal to coincide with the preparation of areas for cultivation and the special

Pioneer vegetation and natural regeneration in the study area 87 conditions for early growth in combination with a cultivated plant like rice, namely the cultivation period, the coverage density, the plant height and the life cycle. The preparation of land for the cultivation of rice coincides with the timing of the dispersal of Guazuma crinita seeds. Rice requires high moisture levels, unlike maize which is sown in the dry season. Even though the density of rice plants is much higher than that of maize, enough space exists to allow the young Guazuma crinita seedlings to grow. The rice is harvested precisely at that stage of Guazuma crinita seedling growth when the plants need to be released from competition. As the cultivation of maize is beginning, the establishment of other species – not Guazuma crinita – has already started. Other pioneer grass and shrub species already begin to grow 3 months prior to the dispersal of the Guazuma crinita seeds. This puts the timber species at a distinct disadvantage. Early interventions – the thinning of densely stocked patches of Guazuma crinita seedlings and release from the competition of other species – may allow for the establishment of a sufficient number, allowing them to overcome the threat posed by non-timber species in the first phase of succession on fallow land. Although fire eliminated the vegetation on the pasture land temporarily, coinciding with the dispersal of Guazuma crinita seed, the ground was quickly recovered by the grass species, impeding colonisation by other plant types. There was no possibility for the establishment of commercially relevant timber species.

4.2.3.2 Natural regeneration of Calycophyllum spruceanum on fallow land

The study of the natural regeneration of Calycophyllum spruceanum occurred on a plot of land influenced by a single Calycophyllum spruceanum seed tree. This area of fallow land was located 2 months prior to the date of the first vegetation recording. The area was approximately 1 ha in expanse and was formerly used for the cultivation of rice. At the time of the first vegetation recording the oldest plants of the fallow on the land left fallow were probably 21 months of age. This first recording took place approximately 6 months after the rice crop was harvested.

Coverage of naturally regenerated Calycophyllum spruceanum seedlings

The species with the highest coverages in June 2000 (fig. 4.16 next page) were Calycophyllum spruceanum and Vernonia baccharoides. Both species exhibited very similar coverage values, and combined accounted for half of the whole vegetation cover of the site. Three vegetation strata were observed on this fallow. The upper stratum, reaching 4-5 m, was composed of fast growing species like Vernonia baccharoides, Cecropia spp., Guazuma crinita and Trema micrantha. The second stratum was approximately 2 m high, and consisted mainly of larger Calycophyllum spruceanum saplings. The plant density was higher in the lower stratum than in the upper. Many of these suppressed Calycophyllum spruceanum individuals survived under the shade cast by the dominant plants for more than 1 year. A 1 m high third stratum of extreme density was conformed by suppressed plants of Calycophyllum spruceanum and in the majority of herbs and grasses.

88 Pioneer vegetation and natural regeneration in the study area

Calycophyllum spruceanum

Cecropia sp. tree Guazuma crinita

Apeiba membranaceae

Trema micrantha

Vernonia baccharoides shrub So lanum sp.

P iper sp.

Clibadium sp. June 2000 Aegiphila integrifolia November 2000 Adenaria floribunda

Baccharis floribunda

Calathea sp. herb Heliconia sp. Urera caracasana

Scleria pterota grass

Geonoma sp. palm others

0 5 10 15 20 25 30 35 Coverage %

Fig. 4.16: Coverages of the most important plant species that developed on a fallow with a Calycophyllum spruceanum seed tree after rice cultivation. First and second evaluation.

The most notable changes by November of the same year concerned the species with highest coverages at the time of the first recording. Calycophyllum spruceanum increased considerably, whereas Vernonia baccharoides declined. The reason for this reduction was connected to the natural mortality of this shrub, which had already reached the end of its short life span. The coverages of fast growing tree species such as Cecropia spp., Guazuma crinita and Apeiba membranaceae increased, however. The coverages of most of the non- tree species like Solanum sp., Piper sp., Calathea and Heliconia sp. fell. By the time of the second evaluation, the upper stratum had increased in height by a further 1-1.5 m. The crown density was lower, however, due to the mortality of individuals of Vernonia baccharoides, which were coming to the end of their natural life span. The height of the lower stratum had also increased by approximately 1 m. There was a notable differentiation in the height growth of the individuals of Calycophyllum spruceanum, most of which had survived.

Pioneer vegetation and natural regeneration in the study area 89

Coverages of the plant types on a fallow area with natural regeneration of Calycophyllum spruceanum

It was observed in June (fig. 4.17) that the two plant types shrubs and trees possessed very similar coverage values. The coverage of the herb vegetation was only half that of the first 2 groups. The grasses, palms and climbers all had low coverage values.

C. spruceanum 40 J June 2000 G. crinita N November 2000 others 30

20 % Coverage 10

0 J NJ NJ NJ NJ NJ N tree shrub herb grass palm climber

Plant type

Fig 4.17: Coverages of the plant types on a fallow area with a C. spruceanum seed tree previously cultivated for rice. First and second evaluation.

By November there was an appreciable decrease in the shrub cover evident due, as mentioned previously, to the natural mortality of Vernonia baccharoides. The tree coverage on the other hand increased as a consequence of the growth of Calycophyllum spruceanum, the dominant species on the site. The increase in the coverage of Guazuma crinita between the two evaluation periods was modest. There were no notable changes to the coverages of the other plant types. Though the time between both evaluations was short, a tendency towards the dominance of trees was evident. Guazuama crinita clearly dominated the upper stratum and Calycophyllum spruceanum the middle and lower strata.

4.2.3.2.1 General observations on the fallow with the Calycophyllum spruceanum seed tree

Though other fast growing species occupied the upper stratum on this fallow area, this was the only such site where Calycophyllum spruceanum was observed to be dominant in terms of the area covered. Naturally regenerated young Calycophyllum spruceanum and Guazuma crinita trees were observed growing together on many fallows elsewhere, yet nowhere was Calycophyllum spruceanum dominant. Both species established on this fallow in the same

90 Pioneer vegetation and natural regeneration in the study area season, as a consequence of similarities in their establishment strategies and the timing of seed dispersal. A year after the rice crop had been harvested 2 strata were evident on the site, a consequence of the differing growth rates of the two species. Guazuma crinita occupied the upper stratum and Calycophyllum spruceanum the lower. It is recommended that the non-commercial species present in the upper stratum, such as Cecropia sp., be eliminated as they compete with the Guazuma crinita trees. In the lower stratum, the high density of Calycophyllum spruceanum individuals urgently required the carrying out of a thinning operation. It is important to prevent the weakening of the majority of the individual C. spruceanum trees as a consequence of extreme intraspecific competition. It has been observed that Calycophyllum spruceanum can grow for many years under the shade of fast growing species. Initially it withstands the shade cast by the taller shrubs, and later the ephemeral pioneer tree species like Trema micrantha and Heliocarpus popayanensis. This accounts for the first 5 years, after which it continues to survive under Guazuma crinita and Cecropia spp., which persist for between 10-15 years. Once having established itself as dominant in the most advanced stages of succession, the adult individuals can grow up to 40 m in height and achieve diameters of 1 m (LAO 1970). On this fallow plot, and on others with abundant Guazuma crinita and Calycophyllu spruceanum individuals, it would be possible to establish productive stands employing a polycyclical system, with Guazuma crinita the focus of the first cycle and Calycophyllum spruceanum in the second.

4.2.3.3 Natural regeneration of Jacaranda copaia on fallow land

The natural regeneration of Jacaranda copaia was evaluated on 2 sites:

an area formerly primary forest left fallow after cultivation under a system of ־ slash-and-burn agriculture and .an agricultural plot that was once secondary forest left fallow ־

4.2.3.3.1 Natural regeneration of Jacaranda copaia on fallow land once a primary forest residue: example 1 (Mozombite family land)

The natural regeneration of Jacaranda copaia was evaluated on an area of fallow land that originated from a primary forest residue. Prior to the vegetation recording the land was used for a first crop cycle with rice. After a fallow period lasting 10 months, the colonising vegetation was partially eliminated using a machete to prepare the site for the establishment of a crop of plantain (March 2000). The timing of the plantain crop establishment coincided with seed dispersal by a Jacaranda copaia tree located at the edge of the primary forest residue bordering the site. Though the Jacaranda copaia tree began disseminating seeds in March 2000, the naturally regenerated seedlings were not detected until July 2000. The only recording of the vegetation of this site took place in September 2000.

Pioneer vegetation and natural regeneration in the study area 91

Coverages of vegetation species on fallow land with naturally regenerated Jacaranda copaia

The species coverages on this fallow area are shown in fig. 4.18. The more important species at the time of the evaluation were Vernonia baccharoides and Paspalum sp. The coverages of the other plant species present were mostly considerably lower. The species observed were plants commonly found on the fallows in the studied area. Though tree species like Trema micrantha and Cecropia spp. exhibited relatively low coverage values, they could potentially come to dominate the fallow in future because the species with the highest coverages at the time of the vegetation study have only a short life span. Jacaranda copaia was the tree species with the third highest coverage, and could potentially play a role in the intermediate stages of succession.

30 tree shrub herb grass palm climber 25

Coverage % 5 0

others Inga sp. Vismia sp. Miconia sp. Cecropia sp. Solanum sp. Calathea sp. Geonoma sp. Passiflora sp. Passiflora Clibadium sp. Clibadium Paspalum sp. Homolepis sp. sp. Phytolacca Trema_micrantha Jacaranda_copaia Banara_floribunda Musa_paradisiaca Calopogonium sp. Urera_caracasana Rottboellia_exaltata Pteridium _aquilinum Baccharis_floribunda Vernonia_baccharoides Species Fig. 4.18: Coverages of the most important plant species that developed on a fallow in the vicinity of a Jacaranda copaia seed tree after rice cultivation (Mozombite family land).

Coverages of the plant types on a fallow area with natural regeneration of Jacaranda copaia

From fig. 4.19 it becomes apparent that at the time of the vegetation recording in September 2000 the fallow was dominated by shrubs. The coverages of the grasses and trees were similar. The other plant groups were only of minor importance, however.

40 J. copaia 30 others

20 Coverage % 10

0 tree shrub herb grass palm climber Plant ty pe Fig. 4.19: Coverages of the plant types on a fallow area in the vicinity of a Jacaranda copaia seed tree previously cultivated for rice.

92 Pioneer vegetation and natural regeneration in the study area

The coverage of Jacaranda copaia, the only commercially important tree species present, was low. By eliminating those plants with the potential to suppress it, the successful establishment and growth of this species could be promoted. Examples of non-commercial tree species with a negative influence on Jacaranda copaia and requiring removal from the site were Trema micrantha and Cecropia spp.

4.2.3.3.2 Natural regeneration of Jacaranda copaia on fallow land that once hosted a secondary forest: example 2 (Araujo family land)

The natural regeneration of Jacaranda copaia was also evaluated on a plot of land where a young secondary forest that was 4 years old and 10 m high had recently been cleared. This area was burned for the cultivation of manioc (Manihot sculenta) and pineapple (Ananas comosus) in September 1999. The Jacaranda copaia seeds were disseminated as the two cultivated plants were in full development. The vegetation recording took place after the manioc and pineapple had been harvested. Due to logistical problems, it was only possible to record the vegetation on this site once. This recording took place in August 2000.

Coverages of vegetation species on fallow land with naturally regenerated Jacaranda copaia

Fig 4.20 shows the dominance of invasive species such as Paspalum sp. (grass) and Pueraria phaseoloides (climber). Although some individuals of the cultivated plants remained on the site, Jacaranda copaia seedlings were rare.

tree shrub herb grass palm climber 40

20 Coverage % 10

others

Costus sp. Costus Uncaria sp. Uncaria Clidemia sp. Clidemia sp. Solanum sp. Bauhinia sp. Calathea sp. Socratea Cecropiasp. Geonoma sp. Geonoma Clibadiumsp. sp. Paspalum Brachiariasp. Cajanus cajan Cajanus

sp. Centrosema Trema micrantha Trema Manihot sculenta Musa paradisiaca Ananas comosus caracasana Urera Jacaranda copaia

Baccharisfloribunda Pueraria phaseoloides Pueraria Vernoniabaccharoides Species Fig. 4.20: Coverages of the most important plant species that developed on a fallow in the vicinity of a Jacaranda copaia seed tree after the cultivation of manioc and pineapple.

The spaces between the cultivated plants allowed for the development of the tree species without competition from shrubs, herbs and grasses. The manioc plants can be harvested

Pioneer vegetation and natural regeneration in the study area 93 twice, but as the yield produced by the second crop is minor, the farmer decided to sow pineapple. Nevertheless, many manioc plants resprouted.

Coverages of the plant types on a fallow area with naturally regenerated Jacaranda copaia

As the results in fig. 4.21 show, this fallow was dominated by invasive species. Like grass, these are difficult to eradicate, and the climbers strangle the woody plants. Some plant types, for example, shrubs, tend to disappear spontaneously over the course of succession, but the grasses remain and impede the development of the tree species.

40 Jacaranda others 30

0 tree shrub herb grass palm climber

Plant type

Fig. 4.21: Coverage of the plant types on a fallow area in the vicinity of a Jacaranda copaia seed tree previously cultivated for manioc and pineapple.

4.2.3.3.3 General observations on the fallow with Jacaranda copaia seed trees

The Jacaranda copaia cover on the fallow derived from primary forest was relatively low. However, this was the case for the other tree species also. On the fallow originating from secondary forest the establishment conditions proved even more difficult for tree species. In the vicinity of the 2 sites evaluated, fallow areas in different stages of succession with abundant naturally regenerated Jacaranda copaia seedlings were observed. Both sites revealed that the dispersal of the seeds of Jacaranda copaia took place when the conditions for its establishment were inappropriate. In spite of the great dispersal distances of Jacaranda copaia seed, there were few stands dominated by this species in the study area. The reason for this is likely to have been that seed dispersal occurs when land is already covered by cultivated plants and pioneer species. Maize and beans are commonly cultivated in the region during the dry season, with the land prepared in April-May. This provides for only a short period of time in which the Jacaranda copaia seeds can colonise land free of vegetation.

94 Pioneer vegetation and natural regeneration in the study area

4.2.3.4 Natural regeneration of Croton matourensis on fallow land

The natural regeneration of Croton matourensis was evaluated on 2 sites:

an area previously used for rice cultivation and ־ .an area previously used for maize cultivation ־

4.2.3.4.1 Natural regeneration of Croton matourensis after rice cultivation (Suelperez family land)

Coverages of vegetation species on fallow land after rice cultivation

Three adult Croton matourensis trees were discovered at the edge of an area used for agriculture, distributed relatively homogeneously at equal distances from one another. This area was once a primary forest residue cleared for the cultivation of rice. The phenological study of Croton matourensis (chapter 3.3) revealed that the species disseminates its seed between the middle of the rainy season and the beginning of the dry season (February-May). The primary forest was burned in October 1998, shortly before the beginning of the rainy season. The farmer who owned this land confirmed that after burning abundant Croton matourensis seedlings were produced. This observation was the motivation behind the initiation of the Croton matourensis germination experiment described in chapter 3.5. The first vegetation recording took place when the Croton matourensis seedlings were approximately 20 months old, in June 2000. In some parts of the fallow, the density of naturally regenerated young plants was very high, whereas in other parts the density was low or else there were no Croton matourensis plants at all. The parent trees were felled prior to the burning of the land. According to the results of the vegetation study from June (fig. 4.22, next page), Croton matourensis and Cecropia spp. were the most important species, exhibiting similar coverages. Vernonia baccharoides was the third most important species. Its coverage was comparatively low, but still greater than that of Acacia sp. and Paspalum sp., the fourth and fifth most widespread species, respectively. The rest of the species present exhibited only minor coverage values. By November the coverages of the two most important species had increased considerably. Croton matourensis and Cecropia spp. combined covered almost 50 % of the site area. An increase in Acacia sp. was also evident. The coverage of Vernonia baccharoides reduced slightly as a consequence of natural mortality, and the main herb species Amaranthus sp. had disappeared almost entirely. Other typical fast growing tree species of secondary forests demonstrated low coverage values at the time of the first vegetation recording but had increased noticeably by November 2000. These species were: Trema micrantha, Sapium spp., Heliocarpus popayanensis, Jacaranda copaia and Apeiba membranaceae. The coverage of Banara guianensis decreased, probably due to suppression by the other tree species.

Pioneer vegetation and natural regeneration in the study area 95

Croton matourensis

Cecropia spp.

Acacia sp.

Ochroma pyramidale

Banara guianensis tree Trema micrantha Sapium marmieri June 2000 Heliocarpus popayanensis November 2000 Jacaranda copaia Apeiba membranaceae Vernonia baccharoides Piper sp. shrub Vismia sp.

Clidemia hirta Baccharis floribunda Amaranthus sp.

Heliconia sp. herb

Pteridium aquilinum

Urena lobata

Costus sp.

Calathea sp. grass Paspalum sp. Rottboellia exaltata palm Geonoma sp. others

0 5 10 15 20 25 30

Coverage %

Fig. 4.22: Coverages of the most important plant species that developed on a fallow in the vicinity of Croton matourensis seed trees after rice cultivation (Suelperez family land). First and second evaluation.

Coverages of the plant types on a fallow area in the vicinity of Croton matourensis seed trees after rice cultivation

In June 2000 trees dominated the fallow (fig 4.23, next page). These occupied approximately 50 % of the site. The shrubs occupied second place with 30 % coverage. The coverages of the other plant types were insignificant. By November the tree coverage had increased noticeably, to 80 % of the site area. By contrast, the shrub coverage had decreased markedly. This can be explained by the short

96 Pioneer vegetation and natural regeneration in the study area

10 0 J June 2000 C. matourensis 80 N November 2000 others

40 Coverage %

0 JNJNJNJNJNJN shr ub herb tree palm grass climber Plant type

Fig 4.23: Coverages of the plant types on a fallow area in the vicinity of Croton matourensis seed trees after rice cultivation. First and second evaluation. life spans of the shrub species and the shade produced by the young trees, which had grown to heights of 4 m by the time of the second recording. In should be noted that in those parts of the fallow area located close to the 3 mature Croton matourensis trees there was a clear dominance of this species. Beyond the dispersal range of the seed trees, Cecropia spp. and other ephemeral heliophytes were the dominant species. Where there was more than one seed tree of the other species studied here in the vicinity of an area of fallow land, the entire area of cultivation was homogeneously covered by the naturally regenerated young plants of these species. The reason for this was the considerably longer seed dispersal distances of these species.

4.2.3.4.2 Natural regeneration of Croton matourensis after maize cultivation (Gomez family land)

In June 1999 maize was sown on an area that had previously hosted secondary forest. The forest was felled and the area then burned in preparation for cultivation. Allowed to go fallow after harvesting, a Croton matourensis seed tree was situated on the site margin. The vegetation was evaluated by means of the COX method.

Coverages of vegetation species on fallow land with a Croton matourensis seed tree after maize cultivation

At the time of the first vegetation recording in July 2000 the tallest vegetation was 2 m in height on some parts of the fallow (fig. 4.24, next page). This was relatively low in comparison to other areas harvested at the same time. The dominance of Pteridium aquilinium was clear. This is a widespread exotic fern capable of dominating degraded sites.

Pioneer vegetation and natural regeneration in the study area 97

Croton matourensis Inga sp. Cecropia spp. tree Bauhinia sp. Trema micrantha Piper sp. shrub Solanum sp.

Vernonia baccharoides July 2000

Banara floribunda December 2000

Baccharis floribunda

Pteridium aquilinum

Costus sp. herb Urera caracasana Scleria pterota Paspalum sp. Homolepis aturensis grass Rottboelia exaltata Panicum pilosum Socratea sp. palm Geonoma sp. Scheelea sp. Pueraria phaseoloides climber Passiflora sp. others 05101520 Coverage %

Fig. 4.24: Coverages of the most important species that developed on a fallow with a Croton matourensis seed tree after maize cultivation (Gomez family land). First and second evaluation.

98 Pioneer vegetation and natural regeneration in the study area manage to reach maturity, sharing the upper canopy with individuals of Cecropia spp., Inga spp. and Trema micrantha. In the second stage of succession this stand will be dominated by the 3 latter tree species. However, to promote the establishment and the growth of more than isolated individuals of Croton matourensis it is necessary to eliminate the plants competing with this commercial species.

Coverages of the plant types on a fallow area with a Croton matourensis seed tree after maize cultivation

The results of the first vegetation recording in July 2000 (fig 4.25) showed a clear dominance of grass and herb species. The coverage values of shrubs and palms were similar. At <15 % coverage, trees were amongst the least abundant plant types present. Only climbers accounted for less of the total area.

J July 2000 C. matourensis D December 2000 others 30

Coverage% 10

0 JDJDJDJDJDJD tree shrub herb climber grass palm Plant type

Fig. 4.25: Coverage of the plant types on a fallow area with a C. matourensis seed tree previously cultivated for maize. First and second evaluation.

Grasses are very aggressive and persistent plants, often hindering the successful participation of other plant types in the process of succession. However, in contrast to the pasture with Brachiaria sp. discussed earlier, here the grasses did not form a dense and homogeneous layer both above and below ground, rather they were present in the form of discontinuous groups, and in mixture with other plant types. The heterogeneous occurrence of the grass species on this particular fallow site meant that it did not represent a barrier to the development of other plant types. In the absence of recurrent fire, this heterogeneity may persist, allowing the establishment of species typical of the second and third stages of succession. Fig. 4.2.21 reveals a moderate increase of the tree coverage by the time of the second recording, offset by a slight decrease to both shrubs and palms. There was little change to the grass coverage over the six month interval. It is likely that this grass coverage will have declined noticeably within another year, however.

Pioneer vegetation and natural regeneration in the study area 99

4.2.3.4.3 General observations on Croton matourensis on fallow land

Unlike the other species studied, the seed of Croton matourensis cannot be dispersed over long distances. The results of the germination experiment described in chapter 3.5 suggested that the seed of this species germinates after a period of dormancy. External stimulation such as by temperature or light may be necessary to initiate germination. Croton matourensis produces large seedlings that grow very quickly in open areas. This allows the species to compete with other pioneer species. So, in spite of the fact that the seed is not widely distributed like the other tree species studied, where seed trees are present at the margins of fallow land Croton matourensis has the potential to dominate future stands.

4.2.3.5 Observations on the natural regeneration of commercial species establishing on fallow land

4.2.3.5.1 Species composition of fallow land in the vicinity of seed trees of the commercial species

Calycophyllum spruceanum, Guazuma crinita and Jacaranda copaia all produce abundant small seeds once a year, during a certain period, and disperse their seeds by means of anemochory (windborne). Croton matourensis the fourth species studied, differs from the other species in that seed dispersal is by means of autochory (bursting of the fruit). Its seeds are also relatively large for a pioneer species, facilitating faster seedling growth than that characterising other colonising species. Non-commercial tree species such as Cecropia spp., Ochroma pyramidale and Trema micrantha are very common on fallow land. Also typical of fallows but not quite as common are Banara guianensis, Heliocarpus popayanensis and Sapium sp. The first of these two groups of non-commercial species have no defined seasonal seed production or dispersal. At any point during the course of the year certain individuals of each species will be producing seed. The life spans of these species are shorter than those of the commercial tree species. They do not persist within the succession process, but in many cases they compete with and can impede the establishment of the commercially relevant tree species. Agricultural land obtained through the clearance of primary forest residues is generally used for the cultivation of crops with high nutrient requirements such as rice and maize. It was observed that on land left fallow after the cessation of slash-and-burn agriculture on former primary forest land, the probability to finding naturally regenerated seedlings of commercial tree species is high. On former secondary forest land left fallow after slash-and-burn, the establishment of commercial tree species was less pronounced. This might be explained by a decline in the site fertility after successive periods of agriculture and fallow cycles. Prolonged agricultural use of the land favours the establishment and dominance of grasses, herbs and shrubs. These pioneer species create a barrier to the establishment of tree species. YANGGEN (2003) indicated that the difficulty eliminating weeds is often a more important reason for the cessation of agriculture than the loss of fertility. The farmers consequently abandon these areas leaving them fallow and open to succession.

100 Pioneer vegetation and natural regeneration in the study area

The vegetation of fallow land located on the sites of former secondary forests generally features a greater influence of invasive plants. These plants reach maturity within a short space of time. Situated at the margins of cultivated land, they produce seed continuously and/or seed is stored in the soil seedbank. The vegetation that develops on fallow land where previously there was primary forest reveals a greater influence of plants that have survived burning and later resprout, and plants that colonise from neighbouring areas of primary forest. Fast growing commercial tree species are scarce in intact primary forest. They occupy the gaps left behind as a result of timber exploitation in primary residual forests. That increase the chance that seed trees of commercial species to be located close or at the border of the newly prepared agricultural terrains. Generally, the fallow areas are dominated by non-commercial tree species. The establishment of a stand dominated by commercial species requires that:

,seed transferred to land free of vegetation or land where rice/maize is cultivated ־ opportune timing of seed dissemination, generally to coincide with the beginning ־ of the rainy season.

4.2.3.5.2 Implications for the management of fallow land hosting commercial tree species

Other important species were Scleria pterota and Socratea sp. Scleria pterota is a grass with an aggressive root system. Socratea sp., and also palms in general, grow well in flooded or badly drained places. In spite of the site conditions, Croton matourensis dominated the tree species coverage. However, at <5 %, its coverage was low after 1 year of fallow. The other tree species present, namely Inga sp., Cecropia sp. and Trema micrantha, are common tree species of fallow land. The low tree coverage overall may be explained by the sandy soil, low nutrient content, poor drainage and the excessive agricultural use of the site as a consequence of its proximity to a road. In December 2000 a noticeable decrease of Pteridium aquilinum was observed. Other species like Scleria pterota, Paspalum sp. and Socratea sp. exhibited no changes. The presence of seed trees close to an agricultural area does not guarantee the establishment of abundant seedlings of commercial species. The density of the naturally regenerated young plants established may be classified as absent-poor, low-medium and high. In each case a silvicultural intervention must take place within the first year after establishment. When the seedling density is low, it is necessary to locate the existing individuals of the desirable species and to release them from competition before they are suppressed by unwanted species. In the case of a low-medium stocking density, it is also necessary to release the commercially relevant individuals in the first year. Given the rapid growth of the species investigated, by the second or third year it is necessary to select potential final crop trees (thinning). Where there is a high stocking density, it is necessary to release the best individuals from competition in the first year so as to avoid the

Pioneer vegetation and natural regeneration in the study area 101 production solely of small stems. By the second or third year it is again necessary to select potential final crop trees. The naturally regenerated seedlings of the commercial species were generally irregularly distributed across the fallow areas. The management of the natural regeneration of commercial species requires the combination of thinning where there is a high stocking density and release from interspecific competition where there are few individuals. It is also possible to transplant seedlings and saplings from areas with a high stocking density to areas where there is no or only little regeneration taking place.

4.3 DISPERSAL DISTANCE AND DENSITY OF NATURAL REGENERATION OF COMMERCIAL SPECIES ON FALLOW LAND

The widespread dispersal of seed and fruit represent an important advantage for certain tropical tree species. Disease and predation decline when the young individuals are located further away from the parent trees, and when stocking densities are low (AUGSPURGER 1983). In the case of pioneer species, it is essential that seed is transported to open areas, as generally these species cannot establish under the shade cast by the parent trees (FINEGAN 1992). The seed of Calycophyllum spruceanum is winged and very small, with approximately 3000 seeds weighing 1 g (RUSSELL et al. 1999). There have as yet been no studies of the seed dispersal distance for the species. The seeds of other pioneer species with similar morphological characteristics such as Acer, Betula and Populus may be dispersed distances of some kilometres (HUGHES et al. 1994, BURSCHEL & HUSS 1997). Jacaranda copaia produces a very flat, fine papery winged seed, with approximately 160 seeds weighing 1 g (AUGSPURGER 1986). These are windborne. AUGSPURGER (1986) determined that Jacaranda copaia seeds liberated at 30 m height may be transported ~540 m in winds of 7 m/s. The dispersal distances for seed of Calycophyllum spruceanum and Jacaranda copaia could not be determined in the present study. It was, however, possible to estimate the distances that the seeds of Guazuma crinita and Croton matourensis were spread.

4.3.1 Objectives of the study of dispersal distance and natural regeneration density

The objective of the study was to calculate the dispersal distance and the density of natural regeneration of Guazuma crinita and Croton matourensis.

4.3.2 Methods for the evaluation of the dispersal distance and natural regeneration density

102 Pioneer vegetation and natural regeneration in the study area

4.3.2.1 Evaluation of the dispersal distance and natural regeneration density of Guazuma crinita

The dispersal distance of Guazuma crinita seed was calculated using the information provided by the study of the natural regeneration of the species on a plot of land left fallow after rice cultivation (Flores family land, chapter 4.2.3.1.1). This study required the identification of a location with only 1 isolated Guazuma crinita seed tree in the vicinity. Only one suitable site was found in the study area. The dispersal distances were deduced indirectly. It was assumed that the naturally regenerated individuals recorded on the fallow as part of the vegetation study originated from seed dispersed by the isolated Guazuma crinita seed tree. The 3 parallel transects used for the evaluation corresponded to the sampling design outlined in fig. 4.1.1. The seed tree was located at the starting point of the central transect. These transects were evaluated 7 and 12 months after the land had been prepared for rice cultivation. The density values for the naturally regenerated plant numbers presented in the following corresponded to the average values for the plots at the same distance along the 3 transects.

4.3.2.2 Evaluation of dispersal distance and natural regeneration density of Croton matourensis

The maximum dispersal distance of Croton matourensis seeds was calculated by measuring the distance of naturally regenerated seedlings from the stems of the 5 mature trees evaluated in 4 directions. Two of these mature trees were located on fallow land, 1 in a transition area between fallow land and a primary forest residue, and the final 2 were situated in a primary forest residue. To evaluate the density of the natural regeneration, 1 tree surrounded by an homogeneous vegetation cover was located. Four lines were drawn from the stem of the mature tree to assess the regeneration employing the COX method (COX 1971). The sample points along the 4 lines were located every 5 m.

4.3.3 Results of the study of seed dispersal distance and natural regeneration density

4.3.3.1 Dispersal distance and natural regeneration density of Guazuma crinita

As can be seen from fig. 4.26. (next page), the greatest densities of saplings and pole stage Guazuma crinita trees were located between 30-50 m from the seed tree. The maximum distance rarely exceeded 70 m from the seed tree. The maximum sapling density was 1.6 individuals/m2, at a distance of 50 m from the seed tree. The highest density of pole stage individuals was 0.32 individulas/m2, at 20 m and 40 m from the seed tree.

Pioneer vegetation and natural regeneration in the study area 103

2 Sapling-7 months

Sapling-12 months 2 Pole-7 months 1 Pole-12 months

Individuals / m

0 10 20 30 40 50 60 70 80 90 100

Distance from seed tree (m)

Fig. 4.26: Abundance of saplings and pole stage Guazuma crinita as a function of distance from the stem of the seed tree.

The distribution of saplings and pole stage individuals of Guazuma crinita as a function of distance from the seed tree was relatively variable. The curve of the average values obtained for the plots along the 3 transects shows that the dispersal curve followed the pattern typical for windborne propagules (GREENE & JOHNSON 1989). Although there were considerable differences in the sizes of the individuals recorded, all of the plants regenerated naturally during the same season. The size differentiation may have been due to the fact that some seeds germinated 2-3 months earlier, at the beginning of the period of seed dispersal. Others were transported to spots where the site conditions were optimal, as the competition from other fast growing plants was low. It is also possible that there was a short period of drought at the beginning of the rainy season and that many of those individuals that germinated early subsequently died. The prolonged nature of the seed dispersal period and the distances that the seeds of Guazuma crinita are disseminated represents a good regeneration strategy, providing for adaptability in space and time, and allowing for greater establishment success, at least of some number of individuals. In some cases, fallow areas with many Guazuma crinita seed trees were observed. These produced abundant quantities of naturally regenerated plants. The outcome of this, however, is to potentially complicate the eventual development of a productive stand as the high stocking density leads to high intraspecific competition and poor crown and stem development. In this case it is necessary to thin the stands before the end of the first year. Guazuma crinita trees are deemed ready for commercial exploitation once they have attained a crown area of 25 m2 (5x5 m). The results of the regeneration study revealed that following natural regeneration the stocking densities within 70 m of a seed tree are sufficient to ensure a full crop.

104 Pioneer vegetation and natural regeneration in the study area

4.3.3.2 Dispersal distance and natural regeneration density of Croton matourensis

According to the results of the study of the dispersal distance and regeneration density of Croton matourensis, presented in fig. 4.28, there was a high degree of variability in the distances that Croton matourensis seeds were dispersed. The seeds of this species are relatively big, with dispersal by means of autochory (fruit explosion). This means that the dispersal of seeds was restricted primarily to the area below the crown of the seed tree. This was clearly the case in relation to trees 1, 2 and 3 (fig. 4.27). The radius of the crowns of all 5 trees were 7-10 m.

Tree Height DB H (m) (cm)

1 25 64 12

2 37 58 14 3 36 55 15

4 33 72 26

5 38 85 34

0 5 10 15 20 25 30 35 40 Distance from seed tree (m) Fig. 4.27: Maximum dispersal distance of Croton matourensis seed.

The greater dispersal distances seen in the cases of trees 4 and 5 may be explained by secondary dispersal, for example, by floodwater. This assumption is not unreasonable as both trees were located at the edge of a river. The transport of Croton matourensis seed by ants was also observed. The effect of the transport of seed by this insect is not clear. In some cases seed may be transported merely centimetres and in other cases many metres. In fig 4.28 it is revealed that the highest density of naturally regenerated plants (0.6 individuals/m2) occurred 5-15 m from the main stem. The density had decreased drastically by 15-25 m from the stem (0.15 individuals/m2).

0,7

0,6 Seedling 2 Sapling 0,5 Pole 0,4 Total duals / m 0,3

divi In 0,2

0,1

0 0-5 5-15 15-25 25-35 35-45 Distance (m)

Fig 4.28: Density of naturally regenerated Croton matourensis as a function of distance from the stem of the seed tree.

Pioneer vegetation and natural regeneration in the study area 105

The study of the density of the naturally regenerated Croton matourensis involved no substrate preparation, in contrast to the examination of the germination in chapter 3.5. The naturally regenerated plants occupied different size classes. The reason for this was that the seeds germinated at different times during the year, with some seeds overcoming dormancy and germinating spontaneously. Some areas on the ground below the crown of the evaluated tree enjoyed direct solar radiation, with either the light or the resultant increase in the soil temperature apparently stimulating seed germination. The curve of the seedling density in fig. 4.28 indicates that the highest seedling density occurred close to the tree, at between 5-15 m. The seedlings present were all very young. The reason for the absence of larger individuals close to the seed tree was that they were unable to survive for long under the shade cast by the parent tree.

4.3.4 General conclusions on seed dispersal distance and the density of natural regeneration

In the case of both Guazuma crinita and Croton matourensis, the maximum seed dispersal distances measured were less than the perimeter lengths of the fallow areas evaluated. This facilitated the measurement of these parameters in the field, subject to the seeds finding favourable conditions for germination. The dispersal distances of species such as Jacaranda copaia and Calycophyllum spruceanum are very difficult to evaluate in tropical forests as their seeds are morphologically adapted to attain much greater dispersal distances. Smallholder farmers in the region normally cultivate areas of ~1 ha. It was very difficult to determine on these new fallow areas which particular seed tree was the source of origin for each individual plant. It may be assumed that the dispersal distance and the local densities of naturally regenerated plants depend on the prevailing wind direction. In the case of the study of Guazuma crinita, the seed tree was located at the border between a secondary forest in the second stage of succession and a newly developed fallow. It was, therefore, only possible to evaluate the dispersal distances in 1 direction. Croton matourensis seeds are dispersed by autochory. Ants were also observed to carry seeds that had fallen to the ground below the crowns of the seed tree. A specific study of this type of secondary dispersal is required to assess its effectiveness. DAVIDSON & MORTON (1981) measured seed dispersal of 77 m by ants in an arid zone in Australia. Dense natural regeneration means high levels of intra- and interspecific competition. This has certain advantages in plantations. However, individuals that are better adapted to the site conditions have greater chances of survival and are likely to grow faster. Fallow areas with dense natural regeneration require early silvicultural interventions such as thinning/release in the first year and the selection of potential final crop trees in the second.

106 Pioneer vegetation and natural regeneration in the study area

4.4 GENERAL CONCLUSIONS FROM THE ANALISYS OF THE VEGETATION ON FALLOW AREAS

The study of the effective establishment of the commercial tree species investigated revealed a high dependence on the occurrence of seed trees in the vicinity of fallow areas. Certain other non-commercial pioneer tree species may profit from seed dispersal by means of zoochory and their ability to produce seed more than once in a year. This is an efficient dispersal strategy that allows these species to be present on almost all fallow areas. There existed only a relatively short window during the year when the seeds produced by the species studied found suitable site conditions allowing for the establishment of abundant seedling numbers. This occurred after the preparation of land for cultivation and under the shelter of certain crops facilitating establishment. In the studied area, successful establishment took place at the end of the dry season and the beginning of the rainy season. Crop plants with short rotation periods such as rice favour the establishment of the studied species. Although rice plants impede the growth of weeds, the small tree seedlings can survive under the ‘micro-shelterwood’ conditions provided. The commercial tree species that manage to establish in such conditions, and to survive the harvesting process, grow subject to little competition from other species. Though parent trees disseminate abundant quantities of seed across areas in the first stage of succession, land with abundant grass, shrub and weed cover is not suited to the establishment of commercial tree species. The occurrence of natural regeneration of Guazuma crinita and Calycophyllum spruceanum on the same area of fallow land suggested it may be possible to accommodate the different life spans, growth rates and varying light requirements of both species during the initial phase of growth so that both species can establish in a polycyclical system. This would involve harvesting the mature Guazuma crinita trees first and later the Calycophyllum spruceanum. The chances for the successful establishment of Jacaranda copaia and Croton matourensis are lower than Guazuma crinita and Calycophyllum spruceanum but where these species have managed to regenerate naturally on fallow land they may also be managed to grow successfully.

Direct seeding on fallow land 107

5 DIRECT SEEDING ON FALLOW LAND

Direct seeding is the process by which woodlands are established by sowing tree seeds directly into their final growing position. The problems associated with direct seeding, such as seed predation by mice and birds, variable germination and prolific weed growth, have long been recognised by practitioners. This led, at the beginning of the 17th century, to the practice of sowing seed on small plots of land separate from the final planting site, where predation and weed growth could be controlled. This eventually resulted in the establishment of forest nurseries. Today it is common practice to raise seedlings in a nursery before planting them out in the field. More recently there has been a renewed interest in direct seeding, however. The reason for this has been a ‘rediscovery’ of the possible advantages in theory of direct seeding over planting, such as more rapid establishment, better quality timber, more natural appearance and lower costs. STEVENS et al. (1990) (cited by WILLOUGHBY et al. 2004) reviewed over 70 Forestry Commission sowing experiments carried out since 1920. The results of the experiments were highly variable, with the authors citing 3 main reasons for poor seedling survival: (1) the emergence of tree seedlings is slow, giving mammals, bird and insects time to inflict heavy losses on the seeds sown; (2) the emergence of the tree seedlings is unpredictable, and even laboratory tested seeds known to be viable and capable of germinating under optimum conditions often fail to germinate in the field; (3) the relatively slow early growth of direct sown trees means that they are not able to compete for scarce resources such as light, nutrients and moisture against other faster growing, annual and perennial species. These difficulties prompted STEVENS et al. (1990) to conclude that the conventional silvicultural practice of planting out trees raised in forest nurseries is preferable to direct seeding. However, most of the experiments reviewed were concerned with direct seeding for the purposes of restocking, where predation is likely to be high and the site conditions are challenging. The authors suggested that the technique might have greater potential for the afforestation of agricultural land.

5.1 DIRECT SEEDING IN TROPICAL AREAS

Direct seeding can be an important alternative to the traditional planting of seedlings. There are both benefits and drawbacks associated with the technique, depending on the species, climate, soil and on livestock. In the tropics, direct seeding may have potential advantages where there are difficulties regenerating trees which have recalcitrant seeds, for example, or when plants have to be transported from nurseries to planting sites. Studies have also shown that direct seeded trees can establish better root systems and enjoy faster initial growth. This can be advantageous in areas affected by drought. Direct seeding will normally be cheaper than planting, but will often require more seed due to predation in the

108 Direct seeding on fallow land field, higher seedling mortality, etc. (BELLEFONTAINE et al. 1997, FOREST & LANDSCAPE DENMARK 2005). Most of the available literature pertaining to direct seeding concerns the establishment of conifers in the temperate regions of North America and Europe, and also Scandinavia. Papers dealing with direct seeding in tropical and subtropical areas stem mainly from Australia, with very few from Africa (ENGEL & PARROTA 2001, FOREST & LANDSCAPE DENMARK 2005). It has been shown in this study that the conditions on many fallow areas are favourable for the successful natural regeneration of tree species intended for subsequent timber production. However, often these fallow areas lack seed trees of the desired species. The opposite scenario also occurs; mature trees of the desired species are present and seed produced, but the site conditions are not conducive to successful natural regeneration. From results mentioned in some of the previous chapters, the timing of seed dispersal is known for the 4 species of interest (chapter 3.3), as are the most suitable conditions for successful seedling establishment (chapter 3.4). The species studied produce abundant quantities of seed and are widely present throughout the landscape. The regeneration strategy of these species is to produce sufficient seeds to colonise areas where the site conditions are suitable, and at the best time of year. The 3 fast growing species studied can overcome the competition of weeds and shrubs within a short time. The other species studied, Calycophyllum spruceanum, can tolerate shade and survive beneath the fast growing tree species.

5.2 OBJECTIVES OF DIRECT SEEDING ON FALLOW AREAS

The objectives of the direct seedling experiment on fallow land were:

to establish commercial species where there were no seed trees and without ־ nursery stock. to determine differences in seedling establishment between 2 areas with ־ contrasting vegetation coverage.

5.3 METHODS FOR THE EVALUATION OF GERMINATION AFTER DIRECT SEEDING

A field experiment involving Guazuma crinita and Jacaranda copaia was established on an area of fallow land previously used for rice cultivation. There were no seed trees of either of the studied species in the vicinity. Due to logistical difficulties it was not possible to carry out the same experiment with Calycophyllum spruceanum and Croton matourensis. A total of 80 plots were established for the experiment each evaluated species. These plots were arranged in 8 columns and 10 rows (fig. 5.1, next page). There were 4 columns of plot clearing intensity 0.25 m2 and 4 of clearing intensity 1 m2. There were 40 plots per clearing intensity treatment.

Direct seeding on fallow land 109

Columns 12345678

1 2.5 m 2 2.5 m Clearing intensity 1: 2 3 1 m cleared area

4 Clearing intensity 2: 0.25 m2 cleared area 5

Rows 6 0.5 m 1m 7

50 seeds in 0.25 m2 10

Fig. 5.1: Plot distribution of the direct seeding experiment with Guazuma crinita and Jacaranda copaia.

In the middle of each 1 m² plot, an area of 0.25m² was sown with 50 seeds. The rates of germination (%) were evaluated for both clearing intensities. Neighbouring vegetation can affect great differences in the establishment of plants. It influences the microhabitat conditions such as light, temperature and moisture. These variables were not measured. However, the experiment design was set up to take account of contrasting vegetation coverage in the immediate vicinity of the sown plots. At the beginning of the experiment, the vegetation of the research site was very homogeneous, composed mainly of old rice plants and some weeds. As the experiment progressed the dried rice plant residues were replaced by the pasture grass Paspalum sp. Its physiognomy is similar to that of a rice crop, but the species is more aggressive. The experiment involved 2 different coverage types. The first treatment consisted of a plot of 1 m² completely cleared of vegetation. In the middle of the plot 50 seeds were sown. In the second treatment only the sown area (0.25 m²) was cleared of vegetation. The Guazuzma crinita seeds were sown the first week of January 2000; the rainy season began at the end of November 1999. The evaluations were concluded 3 months after sowing. Fresh Jacaranda copaia seeds became available in May 2000. The seeding experiment began in the second week of May, at the end of the rainy season. The evaluations concluded 2 months after sowing. Differences between treatment means were tested using analysis of variance (ANOVA), and the t-test to compare means.

5.4 RESULTS OF DIRECT SEEDING ON FALLOW AREAS

110 Direct seeding on fallow land

5.4.1 Direct seeding of Guazuma crinita

Fig 5.2 shows the rates of germination of Guazuma crinita over time for both vegetation cover treatments. The final germination values (%) were similar for both treatments. The variability was very high, however. No statistical differences in the means of the rates of germination (%) were found between the treatments. It was deemed probable that the contrasting microhabitats arising as a result of the extent of vegetation clearance were not the determining factor for any differences observed in the germination rates. An experimental design incorporating a wider range of vegetation coverages might more effectively reveal differences in the rates of germination as a function of vegetation coverage.

8 1 m ² 6 cleared area 4 0.25 m²

Germination % cleared 2 area 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 4.5.6.7.8.9.101112131415161718192021222324252627282930311.2.3.4.5.6.7.8.9.10111213141516171819202122232425262728291.2.3.4.5.6.7.8.9.101112131415161718192021222324252627282930311.2.3.4.5.0 1.1.1.1.1.1..1..1..1..1..1..1..1..1..1..1..1..1..1..1..1..1..1..1..1..1..1..1.2.2.2.2.2.2.2.2.2..2..2..2..2..2..2..2..2..2..2..2..2..2..2..2..2..2..2..2..2.3.3.3.3.3.3.3.3.3..3..3..3..3..3..3..3..3..3..3..3..3..3..3..3..3..3..3..3..3..3..3.4.4.4.4.4. 4.1.0 6.1.0 8.1.0 2.2.0 5.2.0 5.4.0

10.1.0 12.1.0 15.1.0 17.1.0 21.1.0 25.1.0 28.1.0 18.2.0 28.2.0 21.3.0 000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000

Time span Fig. 5.2: Germination rate (%) of Guazuma crinita seeds between 04.01–05.04.2000 subject to 2 clearing intensity treatments.

Although some seeds had already germinated in the 1st week after the sowing, it was not until between the third to fifth weeks that the majority of the seeds germinated. No newly germinated seedlings were observed after the sixth week. In comparison to the controlled tests of germination in PETRI dishes (62 %), the overall germination in the field was very low (9 %). Shortly after the experiment was established the soil was inundated in some areas. Guazuma crinita is adapted to establishing in flooded areas (VIDAURRE 1992) but fungal infection cannot be ruled out as a negative factor. There were also dry and very hot periods during the summer, and the effects of predation cannot be ignored. The 5 week difference between the beginning of seed germination and the end can be explained by differences in the hardness and the permeability of the covers of individual Guazuma crinita seeds. This is a strategy to facilitate variability in the timing of germination, so as to ensure the survival of at least some portion of the total number of seeds produced. COLAN (1992) tested the germination of Guazuma crinita seeds after between 1-12 months of storage. The highest germination rates were observed in seeds stored for 6

Direct seeding on fallow land 111 months. The Guazuma crinita seeds used in this experiment were stored for 4 months under laboratory conditions. Given the similar results obtained for both treatments, the aggregate % germination distribution is presented in tab. 5.1.

Tab. 5.1: Distribution of the % germination in the Guazuma crinita seeding experiment.

Seedlings % Proportion of plots % 0 36.3 1-10 35 11-20 12.5 21-40 12.5 41-60 3.7 61-100 0 100

By the end of the experiment only 5 Guazuma crinita plants had grown to 30-40 cm. All 5 of these plants were located in the same plot. They were the only individuals able to survive to the shrub-tree phase of development on this fallow. At the beginning of the experiment the soil was wet but the weather turned dry between March-April, as most of the plants were still very small (3-4 cm high). Only 5 % of the seedlings survived at the end of the experiment, but even these were unlikely to persist for much longer.

5.4.2 Direct seeding of Jacaranda copaia

The curve of the % germination for Jacaranda copaia (fig 5.3) reveals that germination had already started in the first week after seeding. There was a steady increase in the rate of germination until the fourth week. Almost all plants had germinated by the fifth. After this time the number of additional seedlings that germinated increased slowly, with no further germination after week six.

50 40 1 m ² c l e a r e d 30 area 20 0.25 m² cleared area 10

%Germination 0 14 1516 1718 192021222324252627282930311. 2.3. 4.5.6. 7.8.9. 1011.1213 14 1516 17 18192021222324252627282930 1. 2. 3.4.5. 6.7.8.9. 1011.12 13 1415 1617 18

.5..5..5..5..5..5..5..5..5..5..5..5..5..5..5..5..5..5.6.6.6. 6.6.6. 6.6.6..6.6..6..6..6..6..6..6..6..6..6..6..6..6..6..6..6..6..6..6..6.7.7. 7.2.7.00 7.7. 7.7.7.7..7.7..7..7..7..7..7..7..7. 22.5.00 6.6.00 20.6.00 14.5.00 17.5.00 19.5.00 3.6.00 10.6.00 13.6.00 16.6.00 25.6.00 18.7.00 0000000000000000000000000025.5.00 00000029.5.00 0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 Time span

Fig. 5.3: Germination rate (%) of Jacaranda copaia seeds between 14.05–18.07.2000 subject to 2 clearing intensity treatments.

112 Direct seeding on fallow land

The final % germination values were very similar for both treatments, with no statistical differences observed in the mean % germination values between the treatments. As was the case in the Guazuma crinita experiment, the contrasting microhabitats produced as a result of differences in the vegetation covers were not the determining factor for any difference observed in the germination rates. The germination rate of Jacaranda copaia in the field experiment was approximately half that of the germination test carried out in PETRI dishes, which resulted in 86 % germination overall. In the field, the moisture necessary for germination can undergo severe changes depending on the weather, with variations occurring from one plot to the next. The occurrence of dry periods during the germination experiment might explain the longer time required for germination than was observed by PIEDRAHITA (1997). The latter reported that the germination of directly seeded Jacaranda copaia seeds started on the 6th day and had finished by the 11th day. Under controlled favourable conditions in a laboratory the same author registered overall germination of 92 %. The early germination of Jacaranda copaia allows the escape from negative factors under the high liable stage of seed. It is favoured as the seed has a thin cover, long softening in a wet substrate is not necessary for germination to occur. Contrary to the germination curve of Guazuma crinita, which inclined very slowly initially before increasingly steeply over a short period, the experiment revealed that the germination of Jacaranda copaia is a continual process. Under natural conditions, the viability rates of Jacaranda copaia seeds are low as a consequence of the high linoleic acid content (TRIVIÑO et al. 1990). The linoleic acid degrades with time and causes seeds to die. The aggregate % germination distribution for both treatment types is revealed in table 5.2. In this case the overall germination was higher than for Guazuma crinita. All plots contained germinated seeds, in already 50 % of plots germination was at least 40 %.

Tab. 5.2: Distribution of the % germination in the Jacaranda copaia direct seeding experiment.

Seedlings % Proportion of plots % 0 0 1-20 13.7 21-40 30 41-60 27.5 61-80 22.5 81-100 6.3 100

The growth of Jacaranda copaia seedlings in the last 2 weeks of the experiment was very slow. This was probably brought about by water stress and intense sun radiation in the middle of the dry season. The observation of the experiment was cut short when the plot of land on which the experiment was set up burned.

Direct seeding on fallow land 113

The natural regeneration of Jacaranda copaia was described in chapter 4.2.3. The study was based on seed dispersed onto land on which plantain was cultivated. The timing of seed dispersal by the seed tree coincided with the timing of the direct seeding of Jacaranda copaia. The naturally regenerated plants growing with the plantain crop survived until the beginning of the rainy season. It is quite possible, therefore, that many of the seedlings in the direct seeding experiment would also have survived the dry season had the site not burned.

5.5 DISCUSSION OF DIRECT SEEDING ON FALLOW LAND

It was assumed that either the presence/absence of vegetation cover in a 50 cm strip surrounding the direct seeding plot would result in differences in terms of the protection provided the seeds/seedlings against dehydration and excessive direct solar radiation. However, the experiment revealed no significant differences in the rates of germination between the treatments. It was possible that neither treatment offered the seedlings of either Guazuma crinita or Jacaranda copaia enough protection. Although the seeding of Guazuma crinita occurred in the middle of the rainy season, the few seedlings that grew were unable to develop sufficiently to permit their survival during the dry season. Another reason for the failure may have been that the site quality was not adequate for Guazuma crinita. This species requires relatively good soils (SOTELO et al. 2000). It is well known that in certain species the seed dormancy must be broken either naturally or by means of an artificial pre-treatment before germination occurs. Future direct seeding experiments with Guazuma crinita and other species with dormancy should involve a pre- treatment. Most plants are more endangered as seeds and as seedlings than at any other stage in their lives. This is the period in which an individual is most likely to be exposed to variable and/or adverse conditions (HAMMOND & BROWN 1995). The combination of a high risk of mortality and a largely unpredictable set of establishment conditions places considerable importance on a species particular set of adaptations that allow for (1) the increased likelihood of encountering favourable establishment conditions (sensu HOWE and SMALLWOOD 1982) and (2) decease the risk of mortality upon arrival at a particular site (FOSTER 1986). To account for these selective pressures, a compromise between seed size and number is thought to take place (SMITH & FRETWEEL 1974). The experiment carried out in this study allowed for the drawing of certain conclusions in relation to the use of direct seeding in establishment experiments. It is necessary that direct seeding experiments incorporate the sowing of different quantities of seeds; that direct seeding be evaluated at different times of the year, possibly by repeat sowing on the same area 2 or 3 times, depending on the budget, so as to ensure that the experiment may be carried out at the time best suited to the establishment of a particular species. Seeding at 2 or 3 different times of the year can contribute to reducing the risk of failure; in natural conditions the trees of both species studied here disperse seeds over a period of 3 months.

114 Direct seeding on fallow land

It is also possible to combine 2 or more species, so as to observe which tree species can better adapt to the prevailing site conditions. The advantage of direct seeding is that it allows practitioners to synchronise site/site condition and the best timing of establishment for a particular species. In the case of species that produce abundant quantities of seeds the costs of direct seeding can be kept low.

General conclusions 115

6 GENERAL CONCLUSIONS

6.1 ECOLOGICAL REQUIREMENTS OF TREES DURING EARLY ESTABLISHMENT AND ANTHROPOGENIC ACTIVITIES ON FALLOW LAND

The present study represents an attempt to explain the interaction of certain biological factors and anthropological activities facilitating the establishment of productive stands of the commercial tree species studied. These natural factors include the presence of seed trees in the areas studied, the timing of seed dispersal and the substrate upon which these seeds land. The most important anthropogenic factor is the actual use to which the land is put; and the corresponding specific agricultural activities taking place before, during and after seed dispersal. The particular use of the land is central because where slash-and-burn cultivation is practised, for example, the land is open to colonisation by pioneer species. The preparation of land for agricultural purposes regulates the light levels above the ground and the exposure of the soils, and the substrate diversity. In a primary forest, by contrast, the deep litter layer on the forest floor frequently acts as a barrier to the establishment of species with small seed. There exists an interaction between the timing of seed dispersal and of site preparation in Guazuma crinita and Calycophyllum spruceanum, whereby the seed trees can deposit seed on land free of vegetation, and timed to coincide with the beginning of the rainy season. Thus, the plants enjoy the necessary moisture required for the fast growth of the commercial species studied. There is a short window of time during which the dispersal of the seeds of the commercial species is complemented by favourable conditions for the establishment of abundant natural regrowth. This period of time is at the end of the dry season, when land has been newly prepared for cultivation. Commercial crops cultivated over a short rotation such as rice provide partial shade, favouring the establishment of abundant naturally regenerated Callycophyllum spruceanum and Guazuma crinita seedlings. At the same time, the rice crop impedes the growth of weeds. After harvesting of the rice, the already established seedlings of the commercial tree species can avail of the site, unthreatened by competition from weeds. On land where there is an abundance of naturally regenerated seedlings of the desired commercial species, silvicultural intervention becomes a necessity. Thinning is essential in the first year after establishment, so as to avoid the development of large numbers of thin stems, unable to grow in diameter due to the high intraspecific competition for resources. In the second year it is recommended that potential final crop trees be selected and that these better individuals be released from competition, given space to develop their crowns and to increase their diameters. Although the timing of seed dispersal of many commercial species coincides with the timing of the preparation of land for cultivation or the beginning of crop establishment, a

116 General conclussions low stocking density or complete absence of naturally regenerated seedlings was often observed. Many seedlings and saplings that developed on land left fallow after the prior agricultural crop had been harvested were suppressed by species of no commercial value. Where small numbers of seedlings and saplings of commercially useable species are present in low numbers and threatened with suppression by other species, these need to be released from competition. In the first year of vegetation development on a site the processes that will determine the vegetation composition for the next 5-10 years occur. The conditions on many fallow areas are favourable for the establishment of fast growing commercial tree species. Often, however, the corresponding seed trees are absent. Given the low cost of seed, particularly in the case of species producing large seed quantities, direct seeding is an option. The rates of germination and survival in the direct seeding experiments carried out as part of this study were not entirely satisfactory. The reasons for this were largely logistical and related to the timing of the experiment, however. It is necessary to test direct seeding at that time of the year when seeds are dispersed naturally.

6.2 REDUCTION OF THE PRIMARY FOREST SURFACE AREA AND ESTABLISHMENT OF NEW COMMERCIAL TREE SPECIES

Of the 4 species studied, only Calycophyllum spruceanum and Guazuma crinita have been used commercially in the study area in the last 20 years. A number of local farmers stated that prior to this the timber resource provided by these species was not used commercially. At that time farmers felled and burned large areas of pure stands to clear the ground for agriculture. As there was no demand for the resource it was not exploited. Going hand in hand with the process of land degradation is a simultaneous acceptance of timber products of inferior quality, that is, the development of new timber products from species not previously used in the study region. The commercial interest in Jacaranda copaia is much higher in Costa Rica, where large scale deforestation has occurred (80 % deforestation nationally), than it is in Perú where deforestation has not been as severe (30 % deforestation). The process of forest degradation is occurring at a considerably faster rate in Central America than is the case in the lower Amazon of Perú. The settlement of the high jungle predates that of the lowland of the Peruvian Amazon. Consequently, there is a longer history of the commercial use of Croton matourensis in the high jungle as the greater part of the other useable species had already been exploited. The timber produced by this species is of good quality, however, and recently there has been a greater recognition of its commercial value in Perú. Generally, the high rates of productivity achieved on cultivated areas are only of short duration. As yields decline, the alternative for the farmer families is to clear more of the residual areas of primary forest to make way for new agricultural land. The management of the naturally regenerated plants of the studied species so as to establish productive stands

General conclusions 117 on areas left fallow, can contribute to reducing the pressure on the primary forest remnants by providing an alternative source of income, without expanding the area cultivated. However, farmers are only interested in prolonging the period of time an area of land is left fallow when these host individuals of fast growing commercial tree species. Experiments to restore degraded land using other forest species (SOUDRE et al. 1999) have shown that only species with low soil nutrient requirements have a chance at establishment. Some of these can grow rapidly, and may be used for the provision of firewood and fodder.

6.3 REQUIREMENTS OF THE FARMERS

The management of secondary forest in the Peruvian Amazon is in an embryonic phase, the factors that define this situation are as follows:

- There are as yet no adequate techniques to facilitate the establishment of productive stands. These are established casually and constitute only a very low proportion of the total surface area of the existing fallow land. - The farmers must learn basic silvicultural techniques such as liberation and thinning. These techniques are necessary in the very first stage of the succession process in order to favour the establishment of the desired commercial, fast growing tree species. - Once a stand dominated by a commercial species has become established there is no management to regulate the distance between the trees. The farmers must learn to effectively liberate trees, and to select potential final crop trees so as to improve both the productivity and the quality of the existing fallow areas. - There already exists a market for the timber products of Guazuma crinita and Calycophyllum spruceanum. Although Jacaranda copaia and Croton matourensis are new to the Pucallpa region, they have the potential to become accepted.

6.4 NECESSARY FUTURE RESEARCH

The field experiments presented a number of difficulties because they took place under semi-natural conditions. For this reason, some of the experiments revealed no statistically meaningful results. The experiments were explorative, and hampered by limited time and resources. A number of the experiments had to be carried out simultaneously. The influence of the substrate type on germination and the influence of fire on the germination of Croton matourensis are areas requiring further research and may be assessed under controlled laboratory conditions. The direct seeding experiment must be repeated another 2 times or more, specifically during that time of the season when the seeds of the species studied are dispersed. It may also be beneficial to sow more than one species at a time so as to determine which species is better adapted to a particular site.

118 Summary, Zusammenfassung & Resumen

7 SUMMARY, ZUSAMMENFASSUNG & RESUMEN

7.1 SUMMARY

The slash and burn agriculture system requires that after cultivation a site is allowed a period of recuperation for the restoration of the soil fertility. This period of recuperation is termed fallow, and the process of vegetation development on the site is often referred to as secondary succession. Depending on the timing of fallow and the soil condition, trees may develop on the site, forming secondary forest. The area of primary forest has declined sharply in the study region as a result of over- exploitation, both to provide timber and for the use of the land for slash and burn agriculture. Secondary forests, however, represent an abundant resource at present. Farmers abandon the cultivation of specific areas of land because it becomes impossible to eradicate the weeds, or because after only a few short years of cultivation the soil fertility has become so severely impaired. Many of the plants that develop on land left fallow have local uses, but only small areas are actively exploited for commercial timber. Inventories of secondary forest in the vicinity of Pucallpa city revealed the farmers’ desire to maintain as fallow areas where there is an abundance of commercially valuable timber species. These areas a left fallow for a few years more than is usually the case, until the trees develop the dimensions appropriate for commercial exploitation.

Objectives

The objectives of this investigation were to evaluate the ecological conditions influencing the establishment of 4 fast growing commercial species and the factors leading to the development of homogenous stands dominated by these species.

Methods

This study was carried out in an area with an abundance of areas of fallow land, in the rural areas in the vicinity of Pucallpa city, in the Peruvian Amazon. The phenology of the 4 species studied was evaluated under natural conditions. The changes to the morphology of the species were described and illustrated. Vegetation inventories were carried out on fallows with different histories and subject to different growing conditions. The changes occurring to the vegetation and the possibilities for the establishment of the commercial species of interest were analysed by means of comparison of inventories made at 2 different periods in the year. Germination and direct seeding experiments were carried out under semi-natural conditions.

Summary, Zusammenfassung & Resumen 119

Results

Morphological description of the seedlings of the studied species Pioneer species have very small seeds. As a consequence, they produce very small seedlings initially. These may easily be confused with other species. On the basis of the observations of the morphological changes to the seedlings, 3 phases were differentiated. The morphology of all of 3 phases was described for each species, and illustrated.

Phenology of the studied species

The main objective was to determine the time of seed dispersal, and the influence of the rainy season and the site preparation of cultivated areas on germination and establishment. Guazuma crinita disperses its seed in August-November and Calycophyllum spruceanum between September-December. The timing of dispersal is such that in both cases the seeds may arrive on land recently prepared for cultivation and largely free of vegetation. This is occurs either just before or at the beginning of the rainy season. These conditions are ideal for the establishment of seedlings. Jacaranda copaia disperses it seed during the rainy season (January-April). In this case the moisture levels are good, but there is little land still free of vegetation cover. Croton matourensis disperses it seed between the middle of the rainy season and the start of the dry season (February-May). Again, the chances of seed arriving on open ground are slight, but the seed exhibits some degree of dormancy. This strategy is an adaptation increasing the likelihood that seeds germinate when conditions are appropriate; under natural conditions this might mean when a gap forms in the forest canopy and in anthropogenically influenced areas perhaps after site preparation.

Effect of 4 substrate types on the germination of the studied species

The effect of 4 different substrate types on the germination of Guazuma crinita, Calycophyllum spruceanum and Jacaranda copaia under semi-natural conditions was evaluated. The results indicated no general pattern in relation to a preferred germination substrate. It was observed that some substrate types such as ‘vegetation,’ and litter were characterised by higher moisture levels, favouring Guazuma crinita, this species is well adapted to germinate in exposed conditions that the values of bare mineral soil are also acceptables. The substrates ‘vegetation’ and bare mineral soil suited Calycophyllum spruceanu, whereas litter and bare mineral soil suited Jacaranda copaia. The substrate ash demonstrated the lowest germination rates for all 4 evaluated species.

Effects of fire and litter removal on the germination of Croton matourensis seeds stored in the soil seedbank

Croton matourensis failed to germinate on PETRI dishes used in a lab experiment. However, a number of farmers had observed abundant young Croton matourensis plants on

120 Summary, Zusammenfassung & Resumen recently burned land. These areas were burned shortly before the rainy season, in preparation of rice cultivation. Although seed dispersal occurred 4-6 months prior to burning, the germination rates under the crowns of the seed trees were low. It is likely that Croton matoruensis seed requires some external stimulation in order to germinate, such as a temperature increase or direct light. In the germination experiment carried out under the crown of a seed tree, the quantity of seedlings was observed to be higher in the plots where the litter had been removed by both raking and fire than was the case in the control plots. However, there was no significant difference between the two treatments. This knowledge is very important for the development of propagation methods for this species.

Influence of seed trees on the establishment of productive stands

The influence of seed trees was evaluated in the field in conjunction with the vegetation recordings made on the fallow areas. These plots of land had been subject to different prior uses. One area of fallow land out of the reach of any seed trees of any of the 4 commercial tree species in question was evaluated. The most important trees colonising the land were Trema micrantha, Ochroma pyramidale and Cecropia spp. These species were very common in the fallows in the study area. However, they are not used in the timber industry. These species have dispersal strategies that allow for their widespread establishment in the majority of areas left fallow. In some cases, certain of these species can dominate a forest stand, but their life span is only 3-5 years. In fallow areas within the range of seed trees of the species of interest, the species more commonly occurring were Guazuma crinita and Calycophyllum spruceanum. The synchronisation of the time of seed dispersal and the preparation of agricultural land at the end of the dry season for rice cultivation favours their establishment. The cover created by the rice plants functions as a micro-shelterwood under which the small seedlings can survive. At the same time, this cover impedes the growth of more light demanding grass and weed species. The establishment of Guazuma crinita on fallow land after maize cultivation is more problematic. Maize is cultivated in the dry season. At the time of seed dispersal of Guazuma crinita, abundant herb and grass vegetation hinders the establishment of this commercial tree species. On some fallows an abundance of Calycophyllum spruceanum and Guazuma crinita seedlings growing together was observed. Guazuma crinita grows very fast, and under favourable conditions it will occupy the upper stratum in the first stage of succession. Calycophyllum spruceanum, alternatively, grows relatively slowly initially. It is shade tolerant, and grows beneath the fast growing species. Its chances of survival amongst the short-lived herbs and grasses are good. Unlike Guazuma crinita, Calycophyllum spruceanum may establish on fallow areas after the cultivation of maize. The timing of Jacaranda copaia seed dispersal does not coincide with the preparation of land for the cultivation of the main crops such as rice and maize. The chances for the

Summary, Zusammenfassung & Resumen 121 establishment of Jacaranda copaia are probably better where, after the harvesting of the rice crop, the site is prepared again for a second crop. Exposed mineral soil free of vegetation will favour its establishment. The presence of secondary forest stands dominated by Croton matourensis may be the result of agricultural activity on land where seed had previously been disseminated. As was mentioned previously in relation to the germination experiment, it is likely that Croton matourensis seeds possess a dormancy mechanism.

Direct seeding experiment

A direct seeding experiment was carried out on a plot of fallow land, using Guazuma crinita and Jacaranda copaia seed. The germination and survival rates of the former were very low. The rates of germination of Jacaranda copaia was good by contrast, but seedling survival after the onset of the dry season was low. For logistical reasons, this experiment could not be carried out to coincide with the natural dispersal of the seed of the two species studied. Had this been the case, it is quite possible that the germination and survival rates would have been considerably higher.

Implications for the management of natural regeneration on fallow land

The mere presence of seed trees of the desired commercial species provides no guarantee for the establishment of stands dominated by any of these species. It was observed that the successful establishment on fallow land of the species studied was closely linked to the timing of agricultural activities. Generally in the study area the establishment of the 4 studied species occurs spontaneously. Farmers do not engage in any specific management activities to promote the establishment of the species. When either seedlings or saplings of species of commercial interest are observed, they are usually left to develop independently. If the numbers of seedlings established is too low to be of any commercial value, the farmers usually use the land to cultivate either plantain or cassava. These crops have low nutrient requirements. It is important to point out that the farmers are able to identify the naturally regenerated seedlings of the commercially interesting species, and that in most cases they allow them to grow. However, they do not engage in management; for example, releasing suppressed individuals from competition, the thinning of overstocked stands or the selection of potential final crop trees. It is, therefore, necessary to provide training for farmers so that they may avail of this resource. They must to learn how to promote the commercial species from the very beginning of the establishment process. The competition exerted by non-commercial species from the very outset of the succession process is very hard and management is essential.

122 Summary, Zusammenfassung & Resumen

7.2 ZUSAMENFASSUNG

Das Brandrodungswanderfeldbausystem bedarf einer Erholungsphase nach der Nutzung, um die Fruchtbarkeit der Böden wiederherzustellen. Die Vegetation, die sich nach dem Auflassen der Felder einstellt, nennt man „barbecho“ (Brache), auch als Sekundärvegetation bekannt. Je nach der Zeit und der Bodenbedingungen kann sich Waldvegetation einstellen, in diesem Fall als Sekundärwald. Viele Pflanzen der Brachflächen werden von der Lokalbevölkerung genutzt, aber auf einer sehr kleinen Fläche wird auch das Holz kommerziell genutzt. Die Bauern verlassen nach wenigen Jahren ihre Felder, weil es nicht möglich ist, die Unkräuter zu beseitigen oder weil die Bodenfruchtbarkeit stark abgenommen hat. Bestandsaufnahmen von Sekundärwäldern in der Umgebung von Pucallpa zeigten das Interesse der Agrikultoren, auf den Brachflächen viele kommerziell nutzbare Arten wachsen zu lassen. Diese Brachflächen unterhält man länger als üblich, bis die Bäume Dimensionen zur kommerziellen Nutzung erreichen.

Zielsetzungen

Zielsetzungen dieser Arbeit waren, die ökologischen Bedingungen zu bestimmen, die die Etablierung von vier schnellwüchsigen kommerziellen Arten beeinflussen und warum sich produktive Bestände einstellen, die von diesen Arten dominiert werden.

Methoden

Diese Studie wurde in der Umgebung der Stadt Pucallpa im peruanischen Amazonasgebiet, einem Gebiet mit vielen Brachflächen durchgeführt. Momentan sind die Sekundärwälder eine häufige Ressource als Folge der Überausbeutung des Holzes in den Primärwäldern und der Nutzung des Geländes für den Brandrodungswanderfeldbau. Es wurden verschiedene Evaluationen und Experimente durchgeführt, die veranschaulichen sollen, welche Bedingungen günstig für die Etablierung von Beständen sind, die von kommerziellen Arten dominiert werden. Mit Hilfe der Evaluierungen und Experimente wurden die Beziehungen zwischen den Umweltfaktoren, dem Verhalten der einzelnen Arten sowie dem Einfluss der landwirtschaftlichen Aktivitäten auf Flächen mit dem Vorkommen von Samenbäumen untersucht. Ergebnisse

Morphologische Beschreibung der Keimlinge der untersuchten Arten

Pionierarten haben sehr kleine Samen und demzufolge bilden sie anfangs sehr kleine Keimlinge. Diese können mit nicht evaluierten Arten verwechselt werden können, besonders Gräsern und andere krautige Arten, die auf den untersuchten Flächen häufig sind.

Summary, Zusammenfassung & Resumen 123

Nach der Beobachtung der morphologischen Veränderungen der Blätter unterscheidet man drei Phasen. Die Morphologie in jeder dieser Phase wurde beschrieben und illustriert.

Phänologie der untersuchten Arten

Das Hauptziel war, den Zeitraum der Bildung und der Verbreitung der Samen festzustellen sowie die Beziehung zwischen dem Klima und den Aktivitäten der Landwirte auf den Feldern, von wo aus die Samenbäume ihre Samen verbreiten. Guazuma crinita verbreitet seine Samen im Übergang der Trockenzeit zur Regenzeit (August bis November). Calycophyllum spruceanum verbreitet seine Samen vom Anfang bis zur Mitte der Regenzeit (September bis Dezember). In beiden Fällen treffen die Samen auf Felder, die für die Kulturen vorbereitet und mit spärlicher Vegetation bedeckt sind. Jacaranda copaia verbreitet seine Samen von Beginn bis zum Ende der Regenzeit (Januar bis April) und hat deshalb wenige Möglichkeiten, vegetationsfreie Felder anzutreffen. Croton matourensis verbreitet seine Samen von Mitte der Regenzeit bis zum Beginn der Trockenzeit (Februar bis Mai) und hat ebenfalls wenige Möglichkeiten, vegetationsfreie Felder anzutreffen.

Der Einfluss von vier Substrattypen auf die Keimung

Es wurden die Auswirkungen von vier Substrattypen auf die Keimung der Samen von Guazuma crinita, Calycophyllum spruceanum und Jacaranda copaia in halbnatürlichen Bedingungen untersucht. Die Ergebnisse weisen darauf hin, das es kein allgemeines Muster bei den untersuchten Arten gibt. Es konnte beobachtet werden, dass einige Substrattypen, die besser die Feuchtigkeit halten können, wie bei der „Vegetation“ und der Laubstreu, Guazuma crinita begünstigen. „Vegetation“ und Mineralboden begünstigen Calycophyllum spruceanum. Laubstreu und Mineralboden begünstigen Jacaranda copaia. Beim Substrat mit Asche zeigen sich die geringsten Keimraten.

Keimnachweise von Croton matourensis aus der Bodensamenbank

In den vorigen Keimversuchen für das Experiment mit den vier Substrattypen zeigte sich keine Keimung von Croton matourensis in den Petrischalen. Einige Bauern haben ausgiebiges Keimen von Croton matourensis beobachtet, nachdem sie ihre Felder brannten, um Reis vor der Trockenzeit zu säen. Obwohl die Verbreitung der Samen vier bis sechs Monate vorher stattfand, beobachtet man wenige Keimlinge unter dem Kronendach der Samenbäume. Es ist wahrscheinlich, dass die Samen von Croton matourensis eine externen Stimulus brauchen wie Zunahme der Temperatur oder direkte Sonnenbeleuchtung, um die Keimung zu initiieren.

124 Summary, Zusammenfassung & Resumen

Im Feld hat man ein Experiment unter dem Kronendach der Bäume durchgeführt, wo die Samen verbreitet wurden. Man stellte deutliche Unterschiede in den Parzellen fest, in denen man das Laub von Hand entfernt oder durch Verbrennen beseitigt hatte. Dieses Ergebnis ist von größter Bedeutung für Propagationspraktiken der Art.

Einfluss der Samenbäume auf die Etablierung von kommerziellen Beständen

Der Einfluss der Samenbäume wurde im Feld untersucht durch die Aufnahme der Vegetation auf Brachflächen, die eine unterschiedliche Nutzungsgeschichte haben. Es wurde eine Brachfläche ohne das Vorhandensein von Samenbäumen der kommerziell nutzbaren Arten untersucht. Auf diesen Flächen beobachtete man Trema micrantha, Ochroma pyramidale und Cecropia spp. Es handelt sich dabei um ziemlich häufige Arten der Brachflächen des Untersuchungsgebietes. Diese Arten werden jedoch nicht in der Holzindustrie genutzt. Sie haben Ausbreitungsstrategien, die es ihnen ermöglichen, in der Mehrzahl der Brachflächen präsent zu sein. In manchen Fällen dominiert eine einzige Art. Die Lebenszeit dieser Arten beträgt zwischen drei und fünf Jahren. Im Falle von Guazuma crinita und Calycophyllum spruceanum besteht eine Übereinstimmung zwischen der Zeit der Verbreitung der Samen und dem Vorhandensein von Feldern, die zu Beginn der Regenzeit für die Reisaussaat vorbereitet wurden. Die Reispflanzen wirken wie ein schützendes Mikrokronendach, das die Etablierung der empfindlichen Keimlingen von der Austrocknung schützt, andererseits aber erschweren extrem lichtbedürftige Unkräuter und Gräser das Wachstum. Die Möglichkeiten der Etablierung von Guazuma crinita auf Brachflächen nach dem Maisanbau sind gering, da diese Kulturen in den Monaten niedrigerer Niederschläge angelegt werden. Zur Zeit der Etablierung der Samen von Guazuma crinita existieren Kräuter und Gräser, die das Ankommen dieser kommerziellen Art erschweren. Auf einer Brachfläche wuchsen viele Keimpflanzen von Calycophyllum spruceanum und Guazuma crinita zusammen. Guazuma crinita zeigt schnelleres Wachstum und bei günstigen Bedingungen nimmt diese Art das obere Kronendach in der ersten Sukzessionsphase ein. Calycophyllum spruceanum zeigt mittlere Wachstums- geschwindigkeit in den Initialstadien, ist jedoch resistent gegen Schatten. Sie wächst unter dem Dach der Arten mit schnellem Wachstum, und diese Art hat deshalb gute Möglichkeiten, sich bei der Anwesenheit von Unkräutern und Gräsern kurzer Lebensdauer zu etablieren. Im Unterschied zu Guazuma crinita ist es möglich, dass Calycophyllum spruceanum sich in Brachflächen einstellt, wo man Mais kultiviert hatte. Der Zeitraum der Ausbreitung der Samen von Jacaranda copaia stimmt nicht mit der Zeit überein, in der die Felder für die Kulturen vorbereitet werden. Am weitesten verbreitet sind Reis- und Maiskulturen. Am wahrscheinlichsten ist es, dass Jacaranda copaia sich etabliert, wenn die Bauern die Felder für eine zweite Kultur nach der Ernte des Reises vorbereiten. Es existieren dann freie Flächen für die Etablierung der Keimlinge. Das Vorhandensein von dominanten Beständen von Croton matourensis lässt sich wohl durch die landwirtschaftliche Aktivität auf den Feldern erklären, auf denen sich vorher die Samen dieser kommerziellen Art ausgebreitet haben. Im Keimungsversuchsteil erklärt man

Summary, Zusammenfassung & Resumen 125 sich dies durch die Möglichkeit der Dormanz der Samen dieser Art. Einige Bauern haben eine üppige natürliche Regeneration nach dem Brennen, das man zum Vorbereiten der Felder für die Reisansaat unternimmt, beobachtet. Dieses Brennen führt man am Ende der Trockenzeit durch.

Direkte Ansaatexperimente

Man führte eine Direktansaat auf Brachflächen durch. Man verwendete Samen von Guazuma crinita und Jacaranda copaia. Die erste Art zeigte eine sehr geringe Keimungs- und Überlebensrate. Die zweite Art zeigte gute Keimungsergebnisse, die Samen zeigten jedoch geringe Überlebensmöglichkeiten zu Beginn der Regenmangelzeit. Aus logistischen Gründen wurden die Experimente in einer Zeit durchgeführt, die nicht mit der Zeit übereinstimmte, in der die Samenbäume ihre Samen verbreiten. Es ist zu erwarten, dass das Experiment, in der richtigen Zeit durchgeführt, bessere Ergebnisse über Keimung und Überlebensrate liefern wurde.

Bedeutung für das Management der natürlichen Regeneration auf Brachflächen

Das Vorhandensein von Samenbäumen kommerzieller Arten garantiert keineswegs die Etablierung von homogenen Beständen. Es wurde eine starke Abhängigkeit von den landwirtschaftlichen Aktivitäten bei der Etablierung der untersuchten Arten auf den Brachflächen festgestellt. Die Etablierung der vier untersuchten Arten erfolgt zufällig. Die Bauern unternehmen keinerlei Maßnahmen, um die Etablierung dieser Arten zu fördern. Wenn dies jedoch geschieht, respektieren sie normalerweise die natürliche Regeneration der kommerziellen Arten. Im allgemeinen säubern sie das Gelände, um andere Kulturen anzupflanzen, die weniger anspruchsvoll an Nährstoffen sind, wie Banane und Maniok. Bei den beobachteten Beständen. Es ist wichtig zu erwähnen, dass die Bauern die natürliche Regeneration der kommerziellen Arten kennen und in der Mehrzahl der Fälle sie weiter wachsen lassen, aber sie unternehmen keinerlei Managementmaßnahmen, wie Befreiung von den kompetitiven Arten, Auflichten oder Auswählen. Es ist eine Ausbildung der Bauern notwendig, damit sie die jungen Individuen von den ersten Lebensmonaten an begünstigen. Die Konkurrenz der nicht-kommerziellen Arten ist sehr stark von Anfang an, und aus diesem Grunde sind Eingriffe nach dem Auflassen der Kulturen notwendig.

7.3 RESUMEN

El sistema agrícola de tumba y quema requiere un periodo de tiempo de recuperacion despues de los cultivos para restaurar la fertilidad de los suelos. La vegetación desarrollada despues del abandono es llamada barbecho, conocida tambien como sucesión secundaria.

126 Summary, Zusammenfassung & Resumen

Dependiendo del tiempo, y de las condiciones del suelo se puede desarrollar un bosque, en este caso bosque secundario. Muchas plantas originadas en los barbechos tienen usos locales, pero solamente una reducida superficie es explotada para madera comercial. Los agricultures abandonan los terrenos despues de pocos años de cultivo porque no es posible erradicar las malezas o porque la fertilidad del suelo se ha reducido fuertemente. Inventarios de bosques secundarios en la zona de influencia de la ciudad de Pucallpa muestran el interés de los agricultures de mantener en crecimiento los barbechos con abundancia de especies de maderas comerciales. Estos barbechos son mantenidos algunos años mas que los usuales, hasta que los árboles desarrollen dimensiones para explotación comercial.

Objetivos

Los objetivos de esta investigacion fueron evaluar las condiciones ecologicas que influyen en el establecimiento de 4 especies comerciales de rápido crecimiento y de porque se establecen rodales productivos con dominancia de estas especies.

Métodos

Este estudio fué llevado a cabo en un area con abundancia de barbechos en la zona de influencia de la ciudad de Pucallpa, en la amazonia peruana. En la actualidad los bosques secundarios son un recurso abundante, como resultado de la sobre explotación de madera en los bosques primarios y el uso de esos terrenos para agricultura de tumba y quema. Fueron realizadas diversas evaluaciones y experimentos que pretenden esclarecer cuales son las condiciones favorables para el establecimiento de rodales con dominancia de especies comerciales. Estas evaluaciones y experimentos relacionan los factores ambientales, el comportamiento de las especies y la influencia de las actividades de agricultura en terrenos con presencia de árboles semilleros.

Resultados

Descripcion morfológica de las plantulas de las especies estudiadas Especies pioneras tienen semillas muy pequeñas y por consiguiente al inicio desarrollan plantulas muy pequeñas que se pueden confundir con especies no evaluadas, especialmente gramineas y otras malas hierbas que abundan en los terrenos donde se realizó las evaluaciones. Despues de observar los cambios morfológicos en las hojas se diferenciaron 3 fases. La morfologia de cada una de estas ha sido descrita, al mismo tiempo se presentan ilustraciones.

Summary, Zusammenfassung & Resumen 127

Comportamiento fenológico de las especies estudiadas

El objetivo principal era conocer la epoca de produccion y dispersion de semillas y la relacion con el clima y las actividades de los agricultores en los campos donde los arboles semilleros dispersaban sus semillas. Guazuma crinita dispersa sus semillas en la transicion del final de la epoca seca y el inicio de las lluvias (Agosto-Noviembre). Calycophyllum spruceanum dispersa sus semillas desde el inicio hasta la mitad de la epoca de lluvias (Septiembre-Diciembre). En ambos casos las semillas tienen la oportunidad de encontrar campos preparados para el cultivo y con escaza vegetacion. Jacaranda copaia dispersa sus semillas desde el inicio-mitad hasta el final de la época de lluvias (Enero-Abril), tiene pocas posibilidades de encontrar campos libres de vegetación. Croton matourensis dispersa sus semillas desde la mitad de la época de lluvias hasta el inicio de la época de seca (Febrero-Mayo) tiene pocas posibilidades de encontrar campos libres de vegetación.

Efecto de 4 tipos de substrato en la germinación

Se evaluó el efecto de 4 tipos de substrato en la germinacion de semillas de Guazuma crinita, Calycophyllum spruceanum y Jacaranda copaia en condiciones semi-naturales. Los resultados indican que no existe un patron general para las especies evaluadas. Se observó que existen algunos tipos de substrato que retienen mayor humedad como “vegetación” y hojarasca, lo que favorece a Guazuma crinita. “Vegetación” y suelo mineral favorecen a Calycophyllum spruceanum, Hojarasca y suelo mineral favorecen a Jacaranda copaia. El substrato con ceniza tiene la mas baja germinacion en las especies.

Pruebas de germinación de Croton matourensis en el banco de semillas del suelo

En las pruebas previas de germinacion para el experimento de 4 tipos de substrato, no se observó ninguna germinación de semillas de Croton matourensis en las placas PETRI. Algunos agricultores han observado abundante germinación de Croton matourensis cuando realizan la quema para sembrar arroz antes de la epoca seca. Aunque la dispersion de semillas ocurre 4-6 meses antes, se observa poca germinacion debajo de la copa de los árboles semilleros. Es probable que las semillas de Croton matoruensis necesitan de un estimulo externo como incremento de temperatura o iluminacion solar directa para iniciar la germinacion. Se realizó un experimento en el campo bajo la copa de los árboles donde las semillas han sido dispersadas. Se encontró diferencias significativas en las parcelas donde se removió la hojarasca en forma manual o se eliminó mediante la quema. Este resultado es de suma importancia para practicas de propagacion de la especie.

Influencia de árboles semilleros en el establecimiento de rodales comerciales

La influencia de los árboles semilleros fue evaluada en el campo mediante inventarios de la vegetación en barbechos que han tenido diferentes historias de uso.

128 Summary, Zusammenfassung & Resumen

Se ha evaluado un barbecho sin presencia de arboles semilleros de especies comerciales. En estos se observa la presencia de Trema micrantha, Ochroma pyramidale y Cecropia spp. Especies bastante comunes en los barbechos del area de estudio. Estas especies no se usan en la industria de la madera. Estas especies tienen estrategias de dispersion que les permite estar presente en la mayoria de los barbechos. En algunos casos existe una especie dominante. El periodo de vida de estas especies es de 3-5 años. En el caso de Guazuma crinita y Calycophyllum spruceanum existe coincidencia con la época de dispersion de semillas y la disponibilidad de terrenos preparados para la siembra de arroz al inicio de la epoca de lluvias. Las plantas de arroz actuan como un micro dosel protector que favorece el establecimiento de delicadas plántulas de la desecacion, por otro lado dificultan el crecimiento de malas hierbas y gramineas altamente exigentes en luz. Las posibilidades de establecimiento de Guazuma crinita en barbechos despues de cultivo de maiz son bajas porque este cultivo se realiza en los meses de la estacion de menos lluvias. Cuando se produce la dispersion de semillas de Guazuma crinita existen hierbas y gramineas que dificultan el establecimiento de esta especie comercial. En un mismo barbecho se ha observado abundancia de plántulas de Calycophyllum spruceanum y Guazuma crinita creciendo juntas. Guazuma crinita es de crecimiento mas rápido por lo que cuando encuentra condiciones favorables ocupa el dosel superior en la primera fase de la sucesión. Calycophyllum spruceanum es de velocidad de crecimiento intermedio en las etapas iniciales, pero es resistente a la sombra crece debajo del dosel de las especies de rapido crecimiento, por esos tambien tiene buenas posibilidades de establecerse con la presencia de malezas y gramineas de vida corta. A diferencia de Guazuma crinita es posible que Calycophyllum spruceanum se pueda establecer en barbechos donde se cultivó maiz. La época de dispersion de semillas de Jacaranda copaia no coincide con la época en que las tierras estan preparadas para los cultivos mas difundidos como son arroz y maiz. Lo mas probable es que Jacaranda copaia se establece cuando los agricultores limpian los terrenos para un segundo cultivo despues de la cosecha de arroz. Entonces existe superficies libres para el establecimiento de plantulas. La presencia de rodales con dominancia de Croton matourensis parece ser explicado por efecto de la actividades agrícolas en campos donde previamente se habian dispersado semillas de esta especie comercial. En la sección correspondiente a ensayos de germinación, se explicó la posibilidad de dormancia en las semillas de esta especie. Algunos agricultores han observado abundancia de regeneración natural despues de la quema para preparar los terrenos para la siembra de arroz. Esta quema se realiza al final de la época seca.

Experimento de siembra directa

Se realizó un experimento de siembra directa de semillas en un barbecho. Se emplearon semillas de Guazuma crinita y Jacaranda copaia. La primera especie presento resultados muy bajos de germinación y supervivencia. La segunda especie presento buenos resultados

Summary, Zusammenfassung & Resumen 129 de germinación pero las semillas presentaron pocas posibilidades de sobrevivir al inicio de la estación de escacéz de lluvias. Por razones de logística la época en que fué realizado el experimento no coincidió con la época en que los árboles semilleros dispersan sus semillas. Se espera que el experimento en la época adecuada proporcione mejores resultados de germinación y supervivencia.

Implicancias para el manejo de la regeneración natural en barbechos

La presencia de árboles semilleros de especies comerciales no garantiza el estableciemiento de rodales homogeneos. Se ha observado que existe una fuerte dependencia de las actividades de agricultura para el establecimiento de las especies estudiadas en los barbechos. El establecimiento de las 4 especies estudiadas ocurre de forma fortuita, los agricultores no realizan ningun tipo de manejo para favorecer el establecimiento. Cuando este ocurre, normalmente ellos respetan la regeneración natural de especies comerciales. Lo usual seria que limpien el terreno para otro cultivo menos exigente en nutrimentos como banano o mandioca. De los rodales observados. Es importante notar que los agricultores reconocen la regeneracion natural de especies comerciales y en la mayoria de los casos permiten que los renuevos sigan creciendo, pero no realizan ningun tipo de manejo, como liberación de especies competitivas, raleos o seleccion. Es necesario realizar capacitación para que los agricultores favorezcan a los individuos jóvenes desde los primeros meses de edad. La competencia de especies no comerciales es muy fuerte desde el inicio, por eso las intervenciones son bastante necesarias desde que se abandona el cultivo.

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144 Appendix

9 APPENDIX

Tab. 1 Analysis of Variance (ANOVA) for the experiment of Dormancy of Croton matourensis seeds.

Source of Variation gl Square Sum Mean Square F Blocks 3 680.67 226.9 Distances, Factor A 2 452.67 226.3 1.67 N.S. Error (a) 6 818.67 136.4 Treatments, factor B 2 363.17 181.6 4.97 ** Interaction AB 6 174.66 29.11 0.79 N.S. Error (b) 16 584.17 36.51 Total 35 3074

CV(a) = 136.4 / 4 X 100 = 76.1 % 7.67

CV (b) = 36.51 X 100 = 78.8 % 7.67