Inter-annual variations of net ecosystem productivity of a primeval tropical forest basing on a biometric method with a long-term data in Pasoh, Peninsular Malaysia

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 125-150 m from the tower for ECM. Annual NEP at a 2-ha stand ranged from -5.0 t Carbon ha -1 y -1 to 2.1 t 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 ±1.52 t 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 800 ha in area.

Spatial variations in the net ecosystem productivity of a primeval tropical forest in a 50-ha plot in Pasoh, Peninsular Malaysia

“…The western and southern regions of Pasoh FR had been selectively logged previously under a regime of the Malayan Uniform System in the 1950s, and the biomass of the regenerating forest is still less than that of the primary forest, even 40 years after logging (Okuda et al 2003). A carbon cycling (Kira 1987, Yoneda et al 2016 and stand dynamics (Hoshizaki et al 2004) of a mature forest stand have been intensively studied at a 2-ha plot (Plot 1), located 2 km southwest of the 50-ha plot, since 1969 (Fig. 1).…”

“…A coefficient of decay is a parameter, which is affected by external environmental conditions such as temperature and moisture, to determine decay rates of CWD on the logistic process (Yoneda 1986). We adopted β＝0.43 y -1 and ID＝ 0.7×(dbh/2) 0.2 ÷1.75 for CWD, and the initial necromass of CWD＝23.6 t C ha -1 , which provided optimum results for CWBBM at Plot 1 in Pasoh FR (Yoneda et al 2016). The initial weight of coarse woody organs including roots of a dead tree was estimated by the allome tric regressions obtained in this forest reserve (Kato et al 1978, Niiyama et al 2010.…”

“…We simulated spatial-temporal variations in NEP in a 50-ha plot using the CWBBM (Yoneda et al 2016) and a tree database from 1987 to 2005, with census data collected at 5-year intervals. The CWBBM is a method to estimate carbon metabolisms of a forest ecosystem caused by coarse woody organs with the assumption of the equilibrium state of fine organs and soil organic matters, and NEP is defined as a difference between a carbon fixation rate of live coarse woody organs by net primary productivity (NPP c ) and a carbon release rate of CWD by decomposition (HTR c ).We considered the year of the first census to be 1987 (Condit et al 1999), while the plot was established between 1985 and 1988.…”

“…We first aimed to clarify the spatial variations in NEP with respect to the spatial distribution of these communities and to examine the mechanisms causing the variations in relation to the biotic and abiotic features of the communities. The second aim of this study was to evaluate the spatial variation of the carbon cycling in the 50-ha plot basing on the temporal variation of a 2-ha plot in the same forest reserve, which is in a dynamic equilibrium state (Yoneda et al 2016), and to predict spatial variations in the 50-ha plot in the future.…”

“…Our previous paper (Yoneda et al 2016) dealt with interannual variations in the net ecosystem productivity (NEP) of a primeval tropical rain forest using a coarse-wood-based biometric method (CWBBM). The study revealed that the large variations were caused by temporal variations in the death rates of large trees.…”