Using tree functional diversity to evaluate management impacts in a subtropical forest

The trait-based approach has received much research attention as it provides a heuristic framework for evaluating the ecological impacts of anthropogenic activities on communities and ecosystems. In this study, functional diversity (or structure) measures, such as functional richness, functional evenness, functional divergence, and functional composition, were used to examine management impacts on subtropical forests on the Ryukyu Islands of Japan. Functional indices were compared in tandem with taxonomic diversity indices between three forest types with different management histories: intact old-growth forests, secondary forests after clear-cutting, and abandoned Pinus luchuensis plantations. Species diversity indices were not significantly different among the three forest types. In contrast, functional diversity indices were significantly different among intact forests and managed forests. Functional richness and functional evenness were significantly lower in secondary forests than in intact forests and P. luchuensis plantations. Functional divergence was significantly higher in secondary forests and P. luchuensis plantations than in intact forests. These differences suggest that management activities affected niche space and the patterns of niche differentiation among component species in the functional space of managed forests. Community weighted means for each functional trait were also different among the forest types. The managed forests had greater leaf thickness, leaf dry matter content and maximum height, and lower specific leaf area and leaf nitrogen concentration than intact forests. These differences in functional composition of traits suggested potential functional impacts. This study demonstrated the utilization of species functional traits and community functional structure as a tool of natural experiment for assessing impacts of forest management practices on woodland ecosystems. It was also suggested that logging activities that include large-scale clear-cutting or establishment of P. luchuensis plantations may be incompatible with the conservation of natural ecosystem properties in subtropical forests.