Abstract
Mangrove forests play crucial roles in the coastal ecosystems of the tropics. Few studies have addressed long-term changes in the net primary productivity (NPP) of mangroves in relation to the tropical monsoon climate. We conducted a tree census from 2008 to 2018 in a permanent plot at a secondary mangrove forest under the tropical monsoon climate of Eastern Thailand. During this period, the mortality of fast-growing species and the increasing number of newly recruited trees revealed a temporal change in the plant composition and distribution. Total tree biomass linearly increased from 283.64 to 381.72 t·ha−1 during the study period. The NPP was calculated by using the summation method, which included fine root production. The NPP ranged from 21.19 to 29.04 t·ha−1·yr−1. The fluctuation in NPP and its components were analyzed in relation to climatic factors by the linear regression model. The NPP did not relate with the annual climatic factors, such as the mean temperature and annual rainfall. However, both increments in the basal area and living tree biomass, which is a major component of NPP, were negatively related with the maximum and mean monthly temperatures in the dry season. The annual mortality rate related positively with annual rainfall and the maximum monthly temperature in the dry season. Linear regression analyses showed that some major components of NPP were chiefly affected by the temperature environment in the dry season. These results indicated that the weather in the dry season was largely restricting the mangrove NPP due to effects on the saline water dynamics of the soils under the tropical monsoon climate, which were revealed by our recent study. It implies that the hot-dry season may lead to high mortality, long-term reduction in the increment of living-trees biomass, and thus lowered the ability to maintain high NPP of mangrove forests over the long-term.
Highlights
Mangrove ecosystems are ecologically significant contributions to coastal areas, i.e., acting as marine animal nurseries [1], enhancing the stability of coastal areas [2,3], and storing high carbon stocks in vegetation [4,5]
When we considered the potential of carbon stocks accumulated in the forest biomass of the secondary mangrove forest in Trat together with temporal changes in species distribution and composition in the study plot, it showed a trend of rapid biomass development over the study decade
We demonstrated that a secondary mangrove forest under a tropical monsoon climate might have a rapid development of forest biomass within a decade
Summary
Mangrove ecosystems are ecologically significant contributions to coastal areas, i.e., acting as marine animal nurseries [1], enhancing the stability of coastal areas [2,3], and storing high carbon stocks in vegetation [4,5]. Vegetated carbon stocks in coastal ecosystems were proposed as a strategy for climate change mitigation on a national scale [6]. Mangrove mortality and loss of area due to climate change and enhanced extreme events have been reported [9]. The carbon budgets have been mainly reported in the form of NPP; this metric has been estimated with the summation method using various components, such as the growth increment in the aboveground and belowground parts, coarse woody debris flux, and coastal phytoplankton NPP. The variation in the NPP estimation of mangrove forests depends on the components included in the NPP estimation and geographical regions with different climatic conditions [10,12]
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