Abstract
Biomass changes in secondary succession on a large-scale shifting cultivation area, northeast Borneo Island were studied. The area around the study sites has been rapidly developed and primary forests were cleared on a large scale. Life form composition rapidly changed in this study sites: i.e., from weedy forb community (four-month and one-year-old), to grassland with sparse canopy trees (three-year-old) and further to forest community (ten-year-old). Pioneer trees (eg. Trema orientalis) reached to 6.5 cm dbh and 4.4 m high in three-year-old, and further to 15.5 cm dbh and 13.0 m high in ten-year-old. Correspond to these rapid successional changes, above-ground biomass linearly increased with age: namely 237 g m-2 (four-month), 650 g m-2 (one-year), 1573 g m-2 (three-year) and to 3463 g m-2 (ten-year). In comparison with the other studies of the biomass accumulation in tropical fallow, biomass increment in the ten-year-old stand was small. The adverse effect on biomass accumulation can probably be ascribed to limit the growth and/or invasion of primary forest tree species due to the severe artificial disturbance around the area. Moreover, the number of pioneer tree species might be low in the study sites, where are transition area from lowland forest to lower montane forest.
