Little is known on how species assembly respond to variation in coarse-scale climatic factors and its interaction with fine-scale environmental gradients created by human-caused disturbances in Seasonally Dry Tropical Forests (SDTFs). We assess changes in the distribution of woody plant functional traits in response to interactive gradients of resource availability (precipitation, soil moisture and fertility) and disturbance intensity (wood extraction and grazing) in Caatinga, a SDTF in Brazil.
Material and Methods
We measured species functional traits related to resource-use and size-related trade-offs in different plant organs and used RLQ analysis to identify the most relevant trait-environment relationships, and Ward’s hierarchical clustering to define species response groups.
Species abundances changed predictably in response to the environmental gradients considered, according to their traits. Water availability appears to act as the main driver of species assembly. Conservative resource-use strategies (high stem density and leaf dry matter content) were positively correlated with precipitation and negatively with the ability of soils to retain moisture (SM), while species with very low stem density, acquisitive leaves and large seeds were favored specifically under extremely low precipitation but high SM. These strategies evidenced the emergence of a drought-resistant and a drought-avoidance trait syndrome, respectively. Second, high wood extraction intensity and decreased soil fertility selected for smaller and more acquisitive leaves, suggesting early succession-adapted strategies.
Overall, our results reinforce the notion that niche partitioning along gradients of resource availability may drive species distributions and community patterns. Moreover, they suggest that the impacts of future global and regional climate changes in SDTFs will depend on how rainfall patterns covary with fine-scale environmental factors that can be modified by human activities.