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 卤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.
There is limited information regarding plant functional traits for plant communities in tropical coastal sand dunes. This study investigated differences in species trait compositions and the relationship between community-weighted mean (CWM) traits and soil properties on the windward and leeward sides of the Bang Boet coastal sand dunes in southern Thailand. Ten sampling plots were randomly selected from each side of the dune. All woody plant species were collected and their functional traits were assessed. Soil samples were also collected. A redundancy analysis (RDA) was used to examine the relationship between CWM traits and soil properties. The results showed that species trait compositions and the CWMs of specific leaf area, leaf thickness, and leaf toughness were significantly different between windward and leeward sides. The RDA showed significant correlation between CWM traits and soil properties, particularly for specific leaf area, a functional trait that plays an important role in nutrient turnover on the leeward side. These results indicate that soil properties are predictable based on CWM traits and that leeward sand dune sides can support greater soil formation than windward sides. Hence, functional traits, as well as species, should be considered in coastal sand dune restoration and conservation programs.
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