Abstract
Inter-annual variability of net ecosystem productivity (NEP) was assessed by a biometric method observing dynamics of coarse woody organs in a primeval lowland tropical rain forest in Pasoh, Peninsular Malaysia. Yearly changes of NEP estimated by biometric method well agreed with those measured by Eddy Covariance Method (ECM), when we observed a stand within a distance of 125‐150m from the tower for ECM. Annual NEP at a 2-ha stand ranged from -5.0t Carbon ha-1 y-1 to 2.1t Carbon ha-1 y-1 during the last 43 years (1969-2012) with two times depressions. They were caused by man-made and natural disturbances that affected as much as 10% of the 2-ha stand area, and negative NEP was maintained during around 10 years after disturbances. Inter-annual variances of NEP, biomass and necromass of coarse woody debris were evaluated by a mathematical simulation with observed properties of net primary productivity and a death rate of coarse woody organs. Simulated NEP was 0.00±1.52t C ha-1 y-1 under equilibrium regimes, and the variance increased under the conditions of a higher mean death rate leading to decrease of biomass. Basing on variances of NEP, we estimated a turnover time of an equilibrium system at 400 years for a 2-ha stand, which is equivalent to 800ha in area.
