Fundamental changes in tropical forest structure and biomass have been observed at many sites in the world, based on tree inventories spanning years or sometimes decades. The consistency of these changes and hypothesized causes remain contentious. We have studied the Pasoh Forest in Malaysia using a large scale and precise tree inventory for over 20 years. To ascertain the carbon pool estimates, we have conducted an analysis on the above-ground biomass in the Pasoh Research Forest, Malaysia. We estimates the biomass of all trees above 1 cm dbh of more than 300,000 individuals in the  50 ha demography plot based on four consecutive census conducted in 1986, 1990, 1995 and 2000 using a standardized measurement procedures. Above-ground biomass was estimated based on the allometric regression models for moist tropical forest developed by Chave et al. (2008). The species were categorized into two major groups: dipterocarps and non-dipterocarps. The species group had been used to prescribe appropriate selective cutting in managed mixed dipterocarp forest of Malaysia.

Results/Conclusions

Here we reported the long-term changes of standing biomass in the 50 ha plot. Our results showed that total stand biomass ranges from 335 to 360 Mg  ha^-1. Mortality rate has been increasing throughout the census period for both species group from 1.13 to 2.79  Mg ha^-1yr^-1 for dipterocarps and 2.62 to 4.56 Mg ha^-1yr^-1. The growth rate however showed opposing trend with dipterocarps declining from 2.33 to 1.84 Mg ha^-1yr^-1 and non-dipterocarps from 6.6 to 3.89 Mg ha^-1yr^-1. Both species group showed decreasing net change in biomass estimate and registered negative value in the third census period (1995-2000). The decreasing trend of net biomass change is associated with the increasing mean annual temperature recorded in the area. The results on forest dynamics in relation to biomass stocking and changes among species groups were discussed with emphasize on its impact to sustainable management practices of mixed dipterocarp forest. Using economic data on the value of different species, we will examine how long-term forest changes may alter the potential timber value of the forest.