Edi Mirmanto

Habitat differentiation among tree species with small-scale variation of humus depth and topography in a tropical heath forest of Central Kalimantan, Indonesia

Small-scale spatial association of the distribution for 55 abundant tree species with two environmental factors (humus depth and surface microtopography) was examined in two 1-ha plots of a heath (kerangas) forest in Central Kalimantan, Indonesia. More than 80% of the 55 species showed a significant habitat preference in humus depth and/ or relative elevation in at least one plot. In particular, ten species occurring in both plots showed a consistent significant preference for humus depth or relative elevation in the two plots. Using randomization tests, however, only five species significantly associated with humus depth and no species with relative elevation. These results suggest that edaphic and topographic factors, especially humus depth, contribute to determining local spatial distribution and floristic composition of abundant tree species in the forest.

Long-term carbon sink in Borneo's forests halted by drought and vulnerable to edge effects

Less than half of anthropogenic carbon dioxide emissions remain in the atmosphere. While carbon balance models imply large carbon uptake in tropical forests, direct on-the-ground observations are still lacking in Southeast Asia. Here, using long-term plot monitoring records of up to half a century, we find that intact forests in Borneo gained 0.43 Mg C ha−1 per year (95% CI 0.14–0.72, mean period 1988–2010) in above-ground live biomass carbon. These results closely match those from African and Amazonian plot networks, suggesting that the world’s remaining intact tropical forests are now en masse out-of-equilibrium. Although both pan-tropical and long-term, the sink in remaining intact forests appears vulnerable to climate and land use changes. Across Borneo the 1997–1998 El Niño drought temporarily halted the carbon sink by increasing tree mortality, while fragmentation persistently offset the sink and turned many edge-affected forests into a carbon source to the atmosphere.The existence of a pan-tropical forest carbon sink remains uncertain due to the lack of data from Asia. Here, using direct on-the-ground observations, the authors confirm remaining intact forests in Borneo have provided a long-term carbon sink, but carbon net gains are vulnerable to drought and edge effects.

Forest Structure and Productivity of Tropical Heath and Peatland Forests

Allometric relationships between tree dimensions, aboveground forest structure and productivity were examined in tropical heath (kerangas) forest and peatland forest in Central Kalimantan, to determine the stand level properties of these forest types growing under stressful conditions, by comparing with those in mixed dipterocarp forests. In the peatland forest, tree density, trunk diameter-height relationships and aboveground biomass differed between sites, partly due to differences in disturbance history such as the intensity of selective logging in the past. The heath and peatland forests shared common characteristics such as high leaf mass per area and long leaf residence time at the stand level. Both forest types had high wood mass increment rates (maximum of 8.2 Mg ha−1 year−1 in the heath forest and 10.9 Mg ha−1 year−1 in the peatland forest), which fluctuated greatly during and after the severe 1997–1998 drought. The results here suggest that the heath and peatland forests maintain moderately high productivity under stressful conditions, probably owing to the adaptive leaf properties. The results also suggest that the aboveground forest structure of these forest types as well as peat deposit has the potential to play a significant role in the carbon balance in an area. To be able to properly conserve these forest ecosystems, more attention must be paid to elucidating the mechanisms maintaining primary productivity of heath and peatland forests.

Author Correction: Long-term carbon sink in Borneo’s forests halted by drought and vulnerable to edge effects

The original version of this Article contained an error in the third sentence of the abstract and incorrectly read “Here, using long-term plot monitoring records of up to half a century, we find that intact forests in Borneo gained 0.43 Mg C ha−1 year−1 (95% CI 0.14–0.72, mean period 1988–2010) above-ground live biomass”, rather than the correct “Here, using long-term plot monitoring records of up to half a century, we find that intact forests in Borneo gained 0.43 Mg C ha−1 year−1 (95% CI 0.14–0.72, mean period 1988–2010) in above-ground live biomass carbon”. This has now been corrected in both the PDF and HTML versions of the Article.