Aboveground and belowground biomass in logged-over tropical rain forests under different soil conditions in Borneo

Although an estimation of forest biomass is essential for the development of a carbon storage baseline in the “Reducing Emissions from Deforestation and Degradation in Developing Countries” scheme, few have been conducted in logged-over rain forests of Southeast Asia. We measured the aboveground and belowground biomass in logged-over mixed dipterocarp forests growing on an infertile soil with bleached white sand (Sabal) and on a clay and nutrient-rich soil (Balai Ringin) in Sarawak, Malaysia. We established four 0.5-ha plots on each site and calculated the biomass. Basal area and stand density of large trees (diameter at breast height, DBH ≥ 10 cm) were relatively similar in Sabal (27.0 m2, 720 tree ha−1) and Balai Ringin (28.9 m2, 586 tree ha−1). However, the corresponding measurements for small trees (1 ≤ DBH < 10 cm) were twice as large in Sabal than in Balai Ringin. Aboveground biomass (AGB) in the forests was less than half of the value recorded for undisturbed forests in Borneo, even 20 years after logging. Although total AGB was 20 % smaller in Sabal (205 Mg ha−1) than in Balai Ringin (242 Mg ha−1), the total belowground biomass (TBGB) was 20 % greater in Sabal (59.6 Mg ha−1) than in Balai Ringin (44.6 Mg ha−1). The larger TBGB in Sabal was due to the larger amounts of small roots (diameter <5 mm) in Sabal (26.8 Mg ha−1) compared to Balai Ringin (5.8 Mg ha−1). This accumulation of small roots at Sabal may have contributed to rapid nutrient absorption from infertile soil.