PARENT SESSION
Oral Session #77: Biodiversity and Ecosystem Function II.
Presiding: G. Chong
Thursday, August 8. 9:00 AM to 11:30 AM. Coconino Meeting Room, TCC.
Erosion of tree diversity during 200 years of shifting cultivation in the rainforest of Indonesia.
Lawrence, Deborah*,1, 1 Environmental Sciences, Charlottesville, VA
ABSTRACT- I examined a gradient of cultivation history in Indonesia, to describe changes in the tree community over 10 cycles of shifting cultivation. I identified seven sites of the same age that had experienced from one to 10 cycles of shifting cultivation. I compared these forest fallows with three mature forests nearby. Using a nested sampling design, I examined species richness and evenness of stems down to 50 cm ht. Trees >10 cm dbh were measured in four 750-m2 plots; trees 5-10 cm dbh were measured in 12 100-m2 plots; stems >50 cm ht and <5 cm dbh were measured in 12 5-m2 plots. To determine whether dispersal was limiting species richness, I monitored seedfall along three transects running from primary forest toward the center of the cultivated area. Seedfall was sampled 100m into primary forest, and 100m, 300m, and 500m from the border; a total of 15 traps (0.7-m2) were arrayed at each distance. I analyzed changes in the landscape matrix as a function of distance from the primary forest to determine whether dispersal from the local neighborhood was limiting. Species richness of trees >10 cm dbh declined by 70% following the first cycle of shifting cultivation, and did not change significantly with subsequent cycles. However, evenness declined with each cycle of cultivation. Species richness of smaller trees continued to decline (by 6%) with every cycle. Analysis by non-metric multi-dimensional scaling indicated that species composition changed systematically with each cycle of cultivation. Analysis of seedfall suggests that long-range dispersal may limit the richness of fallows further from the forest edge. The composition of patches surrounding a focal fallow changes systematically with cultivation history, and this change may contribute to a depauperate species pool available for local dispersal into the fallow.
KEY WORDS: tree diversity, shifting cultivation, rainforest, Indonesia