Fire, Cattle and Soil Characteristics Affect Regeneration of Attalea Phalerata in a Forest-Savannah Mosaic
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Fire, cattle and soil characteristics affect regeneration of Attalea phalerata in a forest-savannah mosaic Iris Hordijk February 2017 Fire, cattle and soil characteristics affect regeneration of Attalea phalerata in a forest-savannah mosaic MSc thesis by Iris E. Hordijk, MSc student Forest and Nature Conservation, Wageningen University February 2017 FEM 80436 Supervisor: Prof.dr.ir. L. Poorter, Forest Ecology and Forest Management Group, Wageningen University External supervisor: T. Boorsma Msc, Barba Azul Nature Reserve Coordinator, Asociación Armonía, Santa Cruz, Bolivia The MSc report may not be copied in whole or in parts without the written permission of the author and the chair group. ii Table of contents Summary ................................................................................................................................................. iv Introduction ............................................................................................................................................. 1 Factors influencing the life cycle of A. phalerata ................................................................................ 2 Methods .................................................................................................................................................. 5 Study area ............................................................................................................................................ 5 Biology of Attalea phalerata ................................................................................................................ 5 Research design ................................................................................................................................... 5 Plot measurements ............................................................................................................................. 6 Palm measurements ............................................................................................................................ 6 Data analysis ........................................................................................................................................ 6 Results ..................................................................................................................................................... 9 The (a)biotic conditions and population abundance in the forest islands and gallery forest............. 9 The (a)biotic factors influencing the A. phalerata population .......................................................... 10 Population structure and dynamics of the forest islands and gallery forest .................................... 10 Discussion .............................................................................................................................................. 12 Life cycle of A. phalerata is mainly influenced by cattle pressure, fire and condition of adults ...... 12 Implications of population dynamics for the landscape mosaic ....................................................... 14 Management implications ................................................................................................................. 15 Strengths and limitations of this study ............................................................................................. 15 Suggestions for further research ....................................................................................................... 16 Conclusions ............................................................................................................................................ 17 Acknowledgements ............................................................................................................................... 18 References ............................................................................................................................................. 19 Appendix I Form leaves juveniles .......................................................................................................... 24 Appendix II Principal Component Analysis ............................................................................................ 25 Appendix III Transition matrix and population structure ...................................................................... 26 Appendix IV Structural equation model on plot level ........................................................................... 30 iii Summary Justification The palm species Attalea phalerata shapes the forest-savannah mosaic in the Beni savannah in Northern Bolivia. A. phalerata is an ecosystem engineer, because it dominates the two principal landscape elements; the forest islands and gallery forest. A. phalerata is also a vital food and nesting source for numerous plant and animal species, such as the critically endangered blue- throated macaw. The population of this palm species is declining in the forest islands, due to low regeneration. Aim In this case study on shifting landscape mosaic I examine the (a)biotic factors influencing the population structure and dynamics of A. phalerata in the forest islands and gallery forest. The conceptual model hypothesizes that landscape mosaic, density-dependent mortality, environmental conditions and disturbance affect the lifecycle of this palm species. Study design To study the different habitat types of A. phalerata 91 plots of 10x20 meter were established. Data on habitat characteristics, as sand content of the soil, vegetation cover, cattle pressure and position in the landscape mosaic and data of 500 palms and 3700 juveniles on among others condition, fire damage and light availability were collected. Matrix projections were executed to predict population development in 50 years and a structural equation model was developed to reveal causal relations affecting the juvenile density. Results Matrix projections show that in 50 years the landscape mosaic of the gallery forest is likely to remain stable, but that the forest islands tend to decline in size due to a decrease of juveniles in the forest island edge. Juvenile density is positively related to the condition of the juveniles, the amount of fruits, the bare soil surface, probably because of a reduced competition for resources, and sand content of the soil, which could be a measure for inundation or facilitate root penetration. Juvenile density is indirectly negatively affected by fire because it reduces the condition of the adult and so the fruit production. Juvenile density is also indirectly negatively affected by grazing, which reduces the condition of the juvenile. Conclusions This study shows that even for A. phalerata, a species adapted to a human influenced and dynamic ecosystem, the lifecycle is mostly influenced by disturbance, such as fire and cattle grazing, followed by environmental factors, such as soil characteristics. The population is not resistant to a high cattle and fire disturbance, and soil characteristics, such as sand content and bare soil surface, are important for the juvenile density. To restore the regeneration and population structure on the forest islands it is recommended to reduce cattle pressure and fire frequency. Keywords: landscape mosaic, Attalea phalerata, regeneration, population dynamics, fire, cattle iv Introduction Natural landscapes and how they change over time is directed by dynamic processes on different scales. The landscape is a composition of ecological communities expressed in patches, which together form the landscape mosaic (Watt, 1947). The biodiversity of a landscape is therefore formed by populations or individuals of different species within these patches. At the community level the species within and between patches interact with each other and are influenced by abiotic factors such as nutrients and water (Loreau, 2010; Naeem et al, 2012). Landscapes and species are influenced by human activity and with the high human population pressure in the Anthropocene this alterations become, especially in the tropical regions, more visible than ever (Hansen et al, 2005; Brook et al, 2006). The palm family (Arecaceae) shows distinct spatial patterns of species distribution in landscapes and are often abundant across the (sub)tropical regions on this globe (Dransfield et al, 2008). Palms deliver important products for man, as food, medicine, fuel and construction materials (Balick, 1988; Sosnowska & Balslev, 2009) and are a keystone resource for pollinators and frugivores (Terborgh 1986; Zona & Henderson, 1989). It is identified that there is a knowledge gap on biotic interactions, especially competition and trophic interactions, and that often an important factor is not taken into account in studies on palm distribution in an ecosystem (Eiserhardt et al, 2011). In this case study on shifting landscape mosaic the (a)biotic factors influencing the population structure and dynamics of the palm species Attalea phalerata are investigated. A. phalerata is an ecosystem engineer, as it dominates the principal landscape elements (Yamashita & de Barros, 1997) and provides an important microhabitat and food source in the dynamic and human influenced Beni savannah of Bolivia (Pimentel & Tabarelli, 2004; Rios & Pacheco, 2006; Corrêa et al, 2012; Galetti & Guimarães Jr, 2013). The Beni savannah is a landscape which is characterised by a high beta biodiversity promoted by a mosaic of different ecosystems. The ecoregion is therefore identified as a centre of plant diversity and endemism