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Tropical forests are well-known as highly productive terrestrial ecosystems, which contribute significantly to the global carbon (C) cycle. Studies indicate a correlation between the structural diversity of forests and carbon stocks in the overall forest carbon stocks, and this relationship varies across tropical ecosystems. Understanding this connection is crucial to preventing the transfer of threats to unprotected areas when safeguarding specific forests. The present study was conducted in the undisturbed natural forests of Rema Kalenga Wildlife Sanctuary, Habigonj, Bangladesh. The study aimed to estimate C stocks within the soil-vegetation system of this forest ecosystem and elucidate relationships with stand structural diversity, focusing on vertical stratification and spatial association of tree species. Stand-level C stock models, constructed through tree-level carbon stocks using allometric equations, were based on stand variables such as basal area and mean or dominant tree height. Results identified five canopy strata, with strata two and three accounting for 60% of C stocks. The importance value index of tree species demonstrated a significant association with the C stocks contribution of tree species. The total ecosystem carbon stock ranged from 185 to 220 Mg ha−1, with aboveground 103 to 132 Mg ha−1, belowground 21 to 26 Mg ha−1, litter 2.4 to 4.4 Mg ha−1, dead wood 0.5 to 4.9 Mg ha−1 and soil 11 to 44 Mg ha−1. Species diversity indices exhibited weaker relationships with C stocks, while Pielou's evenness index demonstrated a strong negative relationship (P < 0.05) to C stocks. This comprehensive assessment provides insights into the C dynamics of the forest ecosystem. It offers valuable information for policymakers devising climate change mitigation strategies through the conservation management of tropical forests as crucial C sinks.

The rural landscape is undergoing rapid changes. In China, the expansion of rural settlements is widespread, causing problems to the environment. Previous studies have focused on the effects of built-up land expansion on ecosystem carbon, and this paper further explores the effects of rural settlement changes on ecosystem carbon and investigates the spatial heterogeneity of the relationship. The result shows: rural settlement expansion has led to a significant loss in carbon sinks and vegetation carbon stock, respectively. The main pathway of ecosystem carbon loss is the occupation of cropland. A total of 31% of the regions have a negative coupling relationship between the area of per capita rural settlement and the growth of carbon sinks. The regions where both rural settlements and carbon sink function have declined are mainly concentrated in the northwest, and ecological and rural development in these regions requires additional attention. 63% of the regions show great resilience in terms of carbon sink function in the face of rural settlement expansion. • Terrestrial carbon variations are analyzed from the aspect of the seldom-mentioned rural settlement. • The corrected population data were included in the coupling analysis. • Rural settlement is still expanding in China together with fast urbanization. • Most regions show a negative correlation between carbon sink and rural settlement expansion. [ABSTRACT FROM AUTHOR]

[Display omitted] • Coseismic landslides cause a significant decrease of ecosystem C stock. • Postseismic debris flows perform a major process to transport ecosystem C out of catchment. • Earthquake-induced geohazard chains introduce over 90% reduction of ecosystem C stock. Earthquake-induced geohazards, in particular landslides and debris flows, have the ability to disturb large stocks of organic carbon. Even a slight change in these stocks of organic carbon could affect atmospheric CO 2 concentrations. Yet, the fate of ecosystem carbon delivery caused by a mega-earthquake over a short timescale is not well understood. In this study, a methodology is proposed to study the impact of earthquake-triggered landslides and post-seismic debris flows on ecosystem carbon (C). Pairs-plots were established on undisturbed areas, coseismic landslides or debris flow in one of the most representative catchments, in the 2008 Wenchuan earthquake hit regions. Results showed that coseismic landslides greatly reduced vegetation C stock from 34.48 Mg ha - 1 to 6.85 Mg ha - 1 and soil C stock from 96.38 to 6.77 Mg ha - 1 , thereby leading to 89.6% reduction for total ecosystem C stock. Similarly, debris flow deposit led to a reduction of 97.8% of ecosystem C stock. Overall, it is estimated that there was a loss of 0. 118 × 10 6 M g C across the study area, indicating a large amount of carbon change after the mega-earthquake. This study has an important implication for the role of mega-earthquake on regional ecosystem C storage and fills our knowledge gaps of the impact of ecosystem C cycle along with earthquake-induced geohazard chains. [ABSTRACT FROM AUTHOR]