The distribution of mangrove forests is limited to the coastal zones of tropical and subtropical regions, and their total area is far smaller than that of upland forests (Spalding et al. 2010). Mangrove forests often show unique patterns of biomass allocation and carbon dynamics because they are periodically submerged by tides (Komiyama et al. 2008). Therefore, the contribution of mangrove forests to the global carbon fixation process should be carefully evaluated even though their distribution area is limited.

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.

The structural complexity, especially canopy and gap structure, of old‐growth forests affects the spatial variation of soil respiration (Rs). Without considering this variation, the upscaling of Rs from field measurements to the forest site will be biased. The present study examined responses of Rs to soil temperature (Ts) and water content (W) in canopy and gap areas, developed the best fit modelof Rs and used the unique spatial patterns of Rs and crown closure to upscale chamber measurements to the site scale in an old‐growth beech‐oak forest. Rs increased with an increase in Ts in both gap and canopy areas, but the effect of W on Rs was different between the two areas. The generalized linear model (GLM) analysis identified that an empirical model of Rs with thecoupling of Ts and W was better than an exponential model of Rs with only Ts. Moreover, because of different responses of Rs to W between canopy and gap areas, it was necessary to estimate Rs in these areas separately. Consequently, combining the spatial patterns of Rs and the crown closure could allow upscaling of Rs from chamber‐based measurements to the whole site in the present study.

The increase in forest wood biomass is an important carbon sink in the biogeochemical carbon cycle. The effect of forest succession on carbon sequestration is essential for predicting the impact of future global warming. However, there are limited studies considering the temporal changes of net primary production (NPP) with secondary succession in cool-temperate forests based on long-term data. Therefore, we monitored changes in forest structures over 23 years in a cool-temperate secondary forest (Takayama Forest), which is dominated by Quercus crispula, Betula ermanii, and B. platyphylla var. japonica, to determine how individual stem growth and wood NPP changes with succession and thereby affect biomass accumulation. For Q. crispula and B. ermanii, the population size reduction (71% and 66% of the initial number, respectively) exhibited density-dependent mortality in the self-thinning process. Conversely, B. platyphylla var. japonica decreased from 125 to 51 stems ha⁻¹, or a reduced to 41%, due to interspecific competition and/or short longevity of the species. The individual stem growth of the smaller shaded trees was suppressed, and the mean individual biomass did not increase notably with decreasing density compared to that of Q. crispula and B. ermanii. The aboveground wood NPP for this forest averaged 2.44 Mg ha⁻¹ year⁻¹ over 23 years and exhibited no significant temporal trend. The increased mean individual stem growth of Q. crispula and B. ermanii with decreasing density compensated for the total wood NPP. As a result, the aboveground biomass of the forest increased by 21% over 23 years from 132.4 to 160.2 Mg ha⁻¹, and the rate of biomass accumulation increased with decreasing mortality. It is unlikely that the wood NPP of these pioneer secondary forests will decrease with forest development after canopy closure because the individual stem growth of the long-lived pioneers, such as Q. crispula and B. ermanii, is maintained for extended durations.