Functional trait variation and CSR ecological strategies of Bornean tree species: Implications for post-mining restoration

The harsh environmental conditions of post-mining landscapes strongly influence plant establishment and community development, underscoring the importance of understanding the ecological strategies of native tree species for restoration planning. This study investigated functional trait variation and Competitor–Stress tolerator–Ruderal (CSR) ecological strategies of 27 Bornean tree species sampled from a natural forest within a coal mining concession area in East Kalimantan, Indonesia. Six leaf functional traits, including leaf area (LA), leaf fresh weight (LFW), leaf dry weight (LDW), specific leaf area (SLA), leaf dry matter content (LDMC), and leaf thickness (Lth), were measured. CSR strategies were estimated using the StrateFy method. Principal component analysis (PCA), Relative importance analysis (RIA), Pearson correlation, and hierarchical cluster analysis (HCA) were used to assess trait variation, identify key traits associated with CSR strategies, examine relationships with environmental factors, and evaluate species functional grouping. Leaf functional traits varied substantially among species. The first two principal components explained 80.36% of the total variation, revealing trade-offs between acquisitive and conservative resource-use strategies. StrateFy analysis showed that most species were positioned within the CS spectrum, whereas R-related strategies were relatively uncommon. RIA identified LA as the primary predictor of C strategy, while SLA contributed most strongly to S and R strategies, with its contribution to S potentially reflecting the importance of light acquisition under dense growing conditions. Environmental variables showed generally weak relationships with CSR strategies (r < 0.5), suggesting that ecological strategies are influenced by multiple interacting factors rather than single environmental drivers. HCA revealed considerable functional heterogeneity among species despite the predominance of CS-related strategies, resulting in distinct functional groups with differing ecological characteristics and proposed restoration functions. These groups provide a trait-based framework for interpreting species differences and supporting restoration planning. However, because trait measurements were derived from individuals in natural forest conditions, their applicability to post-mining environments requires validation in the field due to substantial differences in soil properties, microclimate, and disturbance regimes. Overall, these findings demonstrate that native tropical tree species differ markedly in their resource-use strategies and functional characteristics. Integrating functional traits, CSR strategies, and species grouping provides an initial understanding of species adaptation and community assembly for selecting species in post-mining restoration.