Establishment of exotic plantations is one of the most effective ways to induce natural regeneration for the restoration of degraded lands, as it has the potential to improve soil properties and creates favorable microclimates. This study aims to determine the effects of stand structure and composition as well as environmental factors under the canopies of three exotic plantations in northeastern Thailand on the regeneration of native species. For each plantation, we conducted three 10 m × 150 m transect lines with fifteen 10 m × 10 m subplots along a forest remnant gradient. The canonical correspondence analysis (CCA) was used to identify the environmental factors responsible for the differences in natural regeneration among these stands. Three exotic plantations had different stand structure in terms of number of tree species, basal area, and tree density but similar dominant native tree species. Across all stands, 74 native tree species, 60 genera, and 30 families were observed. Some physical and chemical properties in the topsoil were significantly different between species but similar among stands within a species. On the other hand, differences in environmental factors such as RLI were significant among species and stands within a species. The CCA ordination identified that the soil particles, soil pH, and light intensity were key factors influencing the native species composition, which could be categorized into three groups: drought-tolerant pioneer species; light-demanding pioneer species; and shade-tolerant climax species. However, most of the climax species were incapable of regenerating and maturing along the forest edge gradient to plantation stands. To accelerate the restoration process by converting these old exotic plantations to a dry evergreen forest, further research is required to determine the appropriate canopy management and/or dominant climax species for planting beneath their canopies.

Fast-growing tree species, including Eucalyptus sp. and Acacia sp., are widely used to rehabilitate degraded tropical forestland quickly, while mitigating climate change. However, the extent of carbon losses through soil respiration (R_S) often remains unknown. Moreover, the promotion of these non-native species has raised concerns over their impact on other ecosystem services, including N₂-fixation-induced soil acidification and nutrient cycling. This study compared two non-native and native species, with one of each being N₂-fixing, growing in 11-year-old monospecific plantations in NE Thailand. Hourly R_S was measured monthly over one year and combined with stand characteristics, as well as soil microclimatic and chemical properties. Mixed-effects models were used to capture this hierarchical, diurnal, and seasonal dataset. R_S rates were influenced by soil temperature and moisture following a parabolic relation, and negatively affected by acidity. Overall, R_S varied significantly according to species-specific microclimates and productivity. Despite the high input of organic matter, non-native species failed to ameliorate extreme soil moisture or temperature; limiting microbial decomposition and reducing R_S. Hopea odorata produced moderate levels of carbon sequestration, but maintained soil fertility. The choice of tree species can significantly affect carbon sequestration and storage, as well as nutrient cycling, and careful species selection could optimize these ecosystem services.