ECOLOGICAL STUDIES IN CONTRASTING FOREST TYPES IN CENTRAL AMAZONIA A thesis presented for the degree of Doctor of Philosophy at the University of Stirling by Flavio J. Luizio Department of Biological and Molecular Sciences Stirling, Scotland, UK October 1995 I hereby declare that this thesis has been composed by myself and that it contains the results of my own research. Where appropiate I have acknowledged the nature and the extent of the work which has been carried out in collaboration with others. Luiza-o "Stand still and show yourself attentive to the wonderful works of God." (Job 37,14). "We still do not know why species should be so variable in this (wide interspecific variations in nutrient concentrations) respect." (Dr J. Proctor, 1995). 111 Acknowledgements I thank the following: •The British Council who sponsored my PhD grant in the UK. •INPA (Institut° Nacional de Pesquisas da AmazOnia) for support in many ways. Projects INPA/CEC (Community of European Countries), and BIONTE (Forest Biomass and Nutrients) INPA/ODA (Overseas Development Administration) who funded this study. BION'TE's Laboratory, supervised by Ms. Fatima Marques, for the soil analyses. CENA (Centro de Energia Nuclear na Agricultura, Piracicaba) for the inorganic chemical analyses of the litter. Laboratory of Aquaculture (INPA) for analyses of organic compounds in litter. Dr. John Proctor for his supervision. Drs. Armand Chauvel and Thierry Desjardins (ORSTOM - Institute Francais de Recherche Scientifique pour le Developpment en Cooperacion) for helping with the soil survey and analyses. Dr. Sheila Ross (Societe Generale de Surveillance' Environment, Liverpool), Dr. Armand Chauvel, Dr. Catherine Grimaldi (Rennes, France) and Professors Peter M. Vitousek (University of Stanford) and Patrick Lavelle (ORSTOM/Universite de Paris) for suggesting improvements to the text. Mrs. Walane Mello and Dr. Yvan Biot (Project BIONTE) for help in the field work. Dr. Bruce Nelson (INPA-Botany) for the colour pictures of the study site, and Mr. Dionisio Coelho and Mr. Jose Ramos for the plant collection and identification. Mrs. Cilene Palheta and the team of students at INPA (Valquiria Alves, Dayse Campista, Heron Costa, Vania FrOes, Maria Jose Macedo, Kikue Muroya, Neizia Nunes, Enir Salazar and Claudio Yano, for much help with the field and laboratory. The technicians of Pedobiologia (INPA), Mrs. Lucia Paz and Mr. Claudio Sena, for their separating and identifying the litter animals. My colleagues in the DBMS for their friendship and support, with especial thanks to Dr. Chris Wernham and Ms. Wendy Smith for the help editing the text. Our big family, the Jehovah's Witnesses in Alloa and Stirling for their loving concern and care. Finally, my wife and colleague, Regina, for unfailing support, help, encouragement and love. iv Photo credits (Fig. 3.1): Air photo taken August 1991 by Dr. D. Roberts (University of Washington). Large trees in open sand are specimens ofAldina heterophylla. Landsat satellite image, Thematic Mapper bands 3, 4, and 5 colour composited as blue, green and red, respectively. Date was 21 August 1990 (dry season). The open sand area of the campina is shown in red due to the strong reflectance of band 5 from the dry sand. The surrounding campinarana is shown as a dark crescent, probably because of having fewer and older leaves on the trees at that time of the year. The red and yellow lines show a road and a power-line cut. respectively. Pixels measure 30 m x 30 m. Source: Brazilian National Space Institute (INPE). Image enhanced and interpreted by Dr. B. Nelson (INPA - National Institute for Amazonian Research). Contents Acknowledgements ii Abstract ix Chapter 1. GENERAL INTRODUCTION 1 Forest types in Amazonia 1 The causes of heath forests 2 Aims of this study 7 Chapter 2. SITES AND SOILS 8 INTRODUCTION 8 GENERAL FEATURES OF THE STUDY SITES 8 Climate 8 Rainfall and water balance in the study area 12 Geology and geomorphology 16 Geology and geomorphology of the study areas 16 Soils 18 Study plot selection 20 SOILS OF THE STUDY PLOTS 21 Soil sampling 21 Soil analysis 21 Organic and upper mineral soil moisture 22 Groundwater level 23 Soil water tension 24 Data analysis 25 RESULTS 26 Profile pits 26 Top organic layer 26 Soil chemistry 26 Moisture of organic and upper mineral soil layers 30 Soil water potential 33 Groundwater levels 34 DISCUSSION 38 Soil chemistry 38 Moisture dynamics in SHF, THF, and LERF soils 42 Organic and upper mineral soil moisture 42 Soil water potential . 43 Groundwater fluctuations 43 vi Chapter 3. VEGETATION 45 VEGETATION OF THE REGION 45 VEGETATION OF THE STUDY PLOTS 49 Sampling 49 RESULTS 50 Forest structure and !bristles 50 DISCUSSION 57 Chapter 4. FINE LITTER-FALL AND LITTER-LAYER IN THE SHY, THF, AND LERF 60 INTRODUCTION 60 MATERIAL AND METHODS 61 Chemical analysis of fine litter 62 Data analysis 62 RESULTS 63 Litterfall 63 Mineral elements in litterfall 64 Fine-litter layer 67 Mineral elements in the fine-litter layer 71 Decomposition quotients 72 DISCUSSION 74 Litterfall 74 Fine-litter layer 74 Mineral element concentrations in litterfall and litter layer 77 Decomposition quotients (14) and quotients of mineral elements in litterfall / mineral elements in the litter layer (kE) 79 Chapter 5. LITTER DECOMPOSITION AND NUTRIENT RELEASE IN THE THREE FOREST TYPES 81 INTRODUCTION 81 MATERIAL AND METHODS 82 Litter-bag technique 82 Experiments A, B and C 83 Chemical analysis 86 Climatic and moisture data 86 Data analysis 86 RESULTS 87 Initial quality of the leaf litter in experiments A, B, and C 87 Physical and biological features of decomposing leaves in . experiments A, B, and C 89 EXPERIMENT A 92 Rainfall, litter and soil moisture during the experiment 92 vii Weight loss, root penetration in the litter bags, and decomposition rates of leaves 92 Nutrient release from decomposing leaves 97 Mineral element concentrations in fine roots penetrating litter bags 105 Factors influencing decomposition, fine root penetration, and mineral element release rates 105 EXPERIMENT B 109 Rainfall, litter and soil moisture during the experiment 109 Weight loss of the leaves and fine roots penetration 109 Nutrient release from decomposing leaves 113 EXPERIMENT C 118 Rainfall, litter and soil moisture during the experiment 118 Weight loss of the leaves 118 Nutrient release from decomposing leaves 118 DISCUSSION 129 Decomposition rates and patterns 129 Other factors influencing mass loss of leaf litter 133 Comparison of decomposition rates between experiments A and B 134 Fine roots penetrating litter bags and mineral elements in roots 137 Nutrient release from decomposing leaves 138 Factors influencing nutrient release from decomposing litter 142 Possible limiting nutrients for plant growth 144 Chapter 6. LITTER ANIMALS COLONIZING DECOMPOSING LEAVES IN SHF, THF, AND LERF 146 INTRODUCTION 146 MATERIAL AND METHODS 147 Data analysis 148 RESULTS 149 Rainfall, litter and soil moisture during the experiment 149 Litter animals colonizing decomposing leaves 149 Frequency 149 Density 153 Factors affecting litter animal densities in the litter bags 155 Biomass of litter animals colonizing the litter bags 159 Succession of litter animals on decomposing leaves 160 Relationships between litter animals, mass loss, and nutrient release rates 162 DISCUSSION 165 Density of litter animals 166 Colonization and succession of functional groups of litter animals 169 viii Biomass of litter animals 173 Influence of leaf species on litter animals 173 Succession of litter animals on decomposing leaves 175 Relationship between litter animals and mass loss, and mineral element release rates 179 Chapter 7. NUTRIENT ADDITION EXPERIMENTS WITHIN THE THREE FOREST TYPES 182 INTRODUCTION 182 MATERIAL AND METHODS 184 Plant-test assay 185 Native seedlings fertilization assay 186 Data analyses 186 RESULTS 186 Planted seedlings 186 Natural seedlings 187 DISCUSSION 190 Chapter 8. PLANTED SEEDLINGS IN GLASSHOUSE EXPERIMENTS USING SHF, THF, AND LERF SOILS 196 INTRODUCTION 196 MATERIAL AND METHODS 196 RESULTS 198 DISCUSSION 204 Chapter 9: GENERAL DISCUSSION 207 Soils and vegetation 207 Nutrient cycling 210 Nutrient limitation for plant growth 215 220 REFERENCES 239 APPENDICES ix Abstract Most of the Amazonia is covered by the lowland evergreen rain forest (LERF) formation. A small proportion of the region (5-6 % in total) is covered by heath forest, which is particularly common in the Rio Negro basin on Spodosols - white sand soils with a layer of mor humus. The smaller facies of heath forest (SHF) is called 'Camping' in Brazil and often lacks the mor humus; the taller facies (TBF) is called 'Campinarana'. The present study was made in central Amazonia, on a gradient from SHF through THF to well developed LERF. Soil, vegetation, and nutrient dynamics were studied in three 50 m x 50 m plots in each type of forest. Litterfall was measured during one year and litter standing- crop was measured three times a year. Three decomposition experiments, using bagged leaf litter, were made using leaves of two common species from the heath forests and one from the LERF. Fertiliser addition experiments in the field and in the laboratory were carried out to determine the potential nutrient limitations for plants in the three forest types. Annual litterfall was highest in the dry season and was 3.8 t ha-1 yr-1 in the SHF, 6.3 t ha-I yr4 in the THF and 7.8 t ha-I yr-1 in the LERF. The rates of weight loss of the enclosed leaf litter were most rapid in the LERF and slowest in the SHF. The leaves of the LERF species Clitoria racemosa decomposed faster than those of the heath forest species. Fine roots penetrating litter-bags differed significantly among forest types and leaf species, and increased the decay rates. There were no significant differences in decomposition rates between the wet and dry season experiments. Significant differences in the release of chemical elements were observed: higher immobilization of iron and aluminium in the LERF; higher potassium and copper release in THF; and lower calcium, but higher boron release rates in SHF.