Landscape structure, soil fertility, and tree diversity during 200 years of shifting cultivation in West Kalimantan, Indonesia

The goal of this research is to understand how and why tree diversity changes during 200 years of shifting cultivation in a tropical rainforest. To determine the relative importance of dispersal and nutrient limitation to tree diversity, I collected data on changes in the structure of the landscape, soil nutrient stocks, and the species richness and composition of seedlings, saplings and trees in secondary forest surrounding a Dayak village in West Kalimantan, Indonesia. I used a series of 1.5 km transects to describe the distribution and abundance of secondary forest types and household interviews to determine transition rates between forest types over time. Seed traps were established to test for differences in the richness of seed rain as a function of distance from primary forest. Soils (to 30 cm) and vegetation were sampled intensively along a gradient of cultivation history--ten sites having experienced from zero to ten cycles of long-fallow shifting cultivation. A nested sampling regime of quadrats (5;The landscape was dominated by secondary forest regenerating after shifting cultivation, but rubber is increasing in importance. Species richness was related to soil fertility at several scales, and fertility changed with cultivation history. Total soil phosphorus remained constant, but P shifted from the labile inorganic to the non-occluded organic pool and some became occluded. Regional species pools, through local dispersal limitation and indirect effects largely determined species richness at the scale of a fallow; soil texture and fertility affected richness at smaller scales. Species composition changed predictably with continued cultivation--primary forest species were lost, richness and increase in rubber may more profoundly influence tree diversity in the future than changes in soil nutrients or local dispersal feedbacks on fallow species composition.