No abstract

Abstract:Precise estimation of root biomass is important for understanding carbon stocks and dynamics in tropical rain forests. However, limited information is available on individual root masses, especially large trees. We excavated 121 root systems of various species (78) and sizes (up to 116 cm in dbh), and estimated both above- and below-ground biomass in a lowland primary dipterocarp forest in the Pasoh Forest Reserve, Peninsular Malaysia. A tree census was conducted in four research plots (each 0.2 ha) and stand-level biomass was estimated. We examined relationships between tree size parameters and masses of coarse roots (roots ≥5 mm in diameter) and derived a dbh-based allometric equation. The amounts of coarse roots that were lost during excavation were corrected. Coarse-root biomass before and after correction for lost roots was estimated to be 63.8 and 82.7 Mg ha−1, indicating that significant amounts of roots (23%) were lost during the sampling. We also estimated the biomass of small root (<5 mm) by applying pipe-model theory. The estimate, 13.3 Mg ha−1, was similar to another estimate of small roots, 16.4 Mg ha−1, which was obtained directly by the soil-pit sampling method. Total below-ground (BGB) and above-ground biomass (AGB) was estimated to be 95.9 and 536 Mg ha−1, respectively. The biomass-partitioning ratio (BGB/AGB) was about 0.18. In conclusion, the dbh-based allometric equation for coarse roots developed in this study, which kept good linearity even including the data of larger trees, might be useful for evaluating below-ground carbon stocks in other stands of similar forest (old-growth dipterocarp) in South-East Asia.

No abstract

No abstract

To clarify consistency in the size of carbon pool of a lowland tropical rainforest, we calculated changes in above-ground biomass in the Pasoh Forest Reserve, Peninsular Malaysia. We estimated the total aboveground biomass of a mature stand using tree census data obtained in a 6-ha plot every 2 years from 1994 to 1998. The total above-ground biomass decreased consistently from 1994 (431 Mg ha -1 ) to 1998 (403 Mg ha -1 ) (1 Mg = 10 3 kg). These are much lower than that in 1973 for a 0.2 ha portion of the same area, suggesting that the the total above-ground biomass reduction might have been consistent in recent decades. This trend contrasted with a major trend for neotropical forests. During 1994-1998, the forest gained 23.0 and 0.88 Mg ha -1 of the total above-ground biomass by tree growth and recruitment, respectively, and lost 51.9 Mg ha -1 by mortality. Overall, the biomass decreased by 28.4 Mg ha -1 (i.e. 7.10 Mg ha -1 ·year -1 ), which is almost equivalent to losing a 76-cm-diameter living tree per hectare per year. Analysis of positive and negative components of biomass change revealed that deaths of large trees dominated the total above-ground biomass decrease. The forest biomass also varied spatially, with the total above-ground biomass density ranging 212-655 Mg ha -1 on a 0.2-ha basis ( n = 30 subplots, 1998) and 365-440 Mg ha -1 on a 1 ha basis. A large decrease of the total above-ground biomass density ( > 50 Mg per ha per 2 years) in several 0.2-ha subplots contributed to the overall decrease in the 6-ha total above-ground biomass. In the present study, we discuss the association between forest dynamics and biomass fluctuation, and the implication for carbon cycling in mature forests with emphasis on forest monitoring and assessments of soil and decomposition systems.