Understanding the spatial distribution of tree species in subtropical evergreen-deciduous broadleaf karst forest is fundamental to studying species coexistence and karst species diversity. Here, complete spatial randomness and heterogeneous Poisson process models were used to analyze the spatial distribution patterns of 146 species with at least one individual per ha in a 25-ha plot in southwest China. We used canonical correspondence analysis (CCA) and the torus-translation test (TTT) to explain the distributions of observed species. Our results show that an aggregated distribution was the dominant pattern in Mulun karst forests; the percentage and intensity of aggregated decreased with increasing spatial scale, abundance, mean diameter at breast height (DBH), and maximum DBH. Rare species were more aggregated than intermediately abundant and abundant species. However, functional traits (e.g., growth form and phenological guild) had no significant effects on the distributions of species. The CCA revealed that the four analyzed topographic variables (elevation, slope, aspect, and convexity) had significant influences on species distributions. The TTT showed that not all species have habitat preferences and that 68.5% (100 out of 146 species) show a strongly positive or negative association with at least one habitat. Most species were inclined to grow on slopes and hilltops.

Patterns of carbon (C) allocation across different stages of stand development in Eucalyptus urophylla × E. grandis plantations are not well understood. In this study, we examined biomass and mineral soil C content in five development stages (1, 2, 3, 4–5, and 6–8 years old) of a Eucalyptus stand in southern China. The tree biomass C pool increased with stand age and showed a high annual rate of accumulation. Stems accounted for the highest proportion of biomass C sequestered. The C pool in mineral soil increased initially after afforestation and then declined gradually, with C density decreasing with soil depth. The upper 50 cm of soil contained the majority (57%–68%) of sequestered C. The other biomass components (shrubs, herbaceous plants, litter, and fine roots) accounted for <5% of the total ecosystem C pool. Total C pools in the Eucalyptus plantation ecosystem were 112.9, 172.5, 203.8, 161.1, and 162.7 Mg ha⁻¹ in the five developmental stages, respectively, with most of the C sequestered below ground. We conclude that Eucalyptus plantations have considerable biomass C sequestration potential during stand development.

In karst ecosystems, plants absorbing smaller amounts of nutrients, owing to shallow soil, show limited growth. In addition, fine roots (diameter < 2 mm) contribute to the regulation of nutrient cycles in terrestrial ecosystems. However, the spatial and temporal variations of fine root biomass in different vegetation types of the karst region remains poorly understood. In this study, we investigated the seasonal and vertical variation in biomass, necromass, and total mass of fine roots using sequential soil coring under different stages of vegetation restoration (grassland, shrubland, secondary forest, and primary forest) in Southwest China. The results showed that the fine root biomass and necromass ranged from 136.99 to 216.18 g m⁻² and 47.34 to 86.94 g m⁻², respectively. The total mass of fine roots and their production ranged from 187.00 to 303.11 g m⁻² and 55.74 to 100.84 g m⁻² year⁻¹, respectively. They showed a single peak across the vegetation restoration gradient. The fine root biomass and total fine root mass also showed a single peak with seasonal change. In autumn, the fine root biomass was high, whereas the necromass was low. Most of the fine roots were concentrated in the surface soil layer (0–10 cm), which accounted more than 57% root biomass, and decreased with increasing soil depth. In addition, fine root production showed a similar vertical pattern of variation with biomass. Overall, our results suggested that fine roots show clear seasonal and vertical changes with vegetation succession. Moreover, there was a higher seasonal fluctuation and a greater vertical decreasing trend in late-successional stages than in the early-successional stages. The conversion of degraded land to forest could improve the productivity of underground ecosystems and vegetation restoration projects in the fragile karst region should, therefore, continue.

Understanding the driving factors of forest biomass are critical for further understanding the forest carbon cycle and carbon storage management in karst forests. This study aimed to investigate the distribution of forest aboveground biomass (AGB) and the effects of stand structural and abiotic factors on AGB in karst forests in Southwest China. We established a 25 ha plot and sampled all trees (≥1 cm diameter) in a subtropical mixed evergreen–deciduous broadleaf forest. We mapped the forest biomass distribution and applied a variation of partitioning analysis to examine the topographic, stand structural, and spatial factors. Furthermore, we used structural equation models (SEM) to test how these variables directly and/or indirectly affect AGB. The average AGB of the 25 ha plot was 73.92 Mg/ha, but that varied from 3.22 to 198.11 Mg/ha in the 20 m × 20 m quadrats. Topographic, stand structural, and spatial factors together explained 67.7% of the variation in AGB distribution. The structural variables (including tree density and the diameter at breast height (DBH) diversity) and topographic factors (including elevation, VDCN (vertical distance to channel network), convexity, and slope) were the most crucial driving factors of AGB in the karst forests. Structural equation models indicated that elevation, tree density, and DBH diversity directly affected AGB, and elevation also indirectly affected AGB through tree density and DBH diversity. Meanwhile, AGB was indirectly influenced by VDCN, convexity, and slope. The evaluation of stand structural and abiotic drivers of AGB provides better insights into the mechanisms that play a role in carbon storage in karst forests, which may assist in improving forest carbon management.

We investigated the spatial patterns of woody species and their relationships with environmental factors in the karst forest of southwest China. Data for 30 woody plant species with an importance value ≥ 5 and 15 environmental factors in 50 quadrats in a forest plot of 200 m × 100 m were used in this study. Two-way indicator species analysis revealed that the forest communities could be divided into 11 vegetation groups and classified into four ecotypes at the third divisional level. Detrended canonical correspondence analysis demonstrated that the variables significantly related to plant patterns were slope position, slope aspect, percentage of outcropping rocks, organic matter, total phosphorus, available nitrogen, and available phosphorus. Variation partitioning revealed that soil properties accounted for 21.0%, topographical features for 13.2%, and unmeasured variables and spatial processes for 47.7% of the variation in the species pattern, which suggest that both the deterministic factors (i.e., related to niche differentiation) and stochastic processes (i.e., related to dispersal limitation) are substantial determinants of the distribution of woody species. Our analysis suggests that picking the right late-succession species for a particular subregion or increasing soil nutrient content in poor habitats would promote species replacement in karst regions.