Patterns of slash-and-burn land use and their effects on forest succession: Swidden-land forests in Borneo [Indonesia]

To evaluate the impact of increased numbers of pyrophytic tree species on succession and the role of pyrophytic tree stands as carbon sinks and reservoirs, the floristic composition and bioeconomics of swiddenland forests were studied in lowland and lower montane Borneo. For our survey of stand floristic composition, 218 secondary forests were chosen in 4 regions including 2 remote areas; most forests were fallowed stands. In 2 of these forests, stand biomass was estimated. The floristic composition of swidden-land forests was characterized by a lack or low density of dipterocarps and the successional ascendance of pyrophytic tree species less vulnerable to felling and fire and with high sprouting capacity such as Schima wallichii, Vitex pinnata, Peronema canescens, and Vernonia arborea. In remote areas, pioneer trees with fruiting and functioning seed dispersal mechanisms were also dominant. Dipterocarps other than Shorea balangeran were not found or were sparse in the fallowed land, which resulted from swidden agriculture, although dipterocarps were the most dominant species in the original vegetation of lowland and lower montane Borneo. MAI (mean annual increment) values of 3.26 and 3.61 Mg ha(-1) year(-1) of biomass were estimated in a Schima wallichii fallowed stand, versus 6.46 Mg ha(-1) year(-1) in a Peronema canescens stand. Equivalent MAI values were estimated in fallowed pyrophytic tree stands in South Sumatra (3.85-10.62 Mg ha(-1) year(-1)); the mean of these MAI estimates is not significantly different from the mean MAI of planted forests of non-fast-growing tree, 10.71 +- 7.18 Mg ha(-1) year(-1) (range, 1.90-18.80) under similar climate conditions. Because a relatively few hardy tree species selected by the people of the region have replaced the original tree species in the fallowed forests, young sprouts from tree stumps of pyrophytic species may rapidly close the canopy when slash-and-burn fields are fallowed.