Leaf traits of African woody savanna species across climate and soil fertility gradients: evidence for conservative versus acquisitive resource‐use strategies

Abstract

Summary Establishing trade‐offs among traits and the degree to which they covary along environmental gradients has become a key focal point in the effort to develop community ecology into a predictive science. While there is evidence for these relationships across global data sets, they are often too broad in scale and do not consider the particularities of local to regional species pools. This decreases their usefulness for developing predictive models at scales relevant for conservation and management. We tested for trade‐offs between traits and relationships with environmental gradients in trees and shrubs sampled across southern African savannas and explored evidence for acquisitive versus conservative resource‐use strategies using a phylogenetically explicit approach. We found a distinct trade‐off between two major poles of specialization indicative of acquisitive (high leaf nitrogen concentration, leaf phosphorus concentration, leaf N:P, specific leaf area and average leaf area) and conservative resource‐use strategies (high leaf carbon to nitrogen ratios (C:N), tensile strength and leaf dry matter content). Although we found that trait variance and species occurrence were constrained by phylogeny, phylogenetically informed analyses did not contradict non‐phylogenetic analyses, strengthening relationships in most cases. The high intrasite trait variability and weak relationships with soils and climate may in part be explained by the high levels of deciduousness and disturbance (i.e. fire and herbivory) inherent in African savannas. Synthesis. The relationships between traits and between traits and environmental gradients were far weaker than, and often contradictory to, broad‐scale studies that compare these relationships across biomes and growth forms, cautioning against making generalizations about relationships at specific sites based on broad‐scale analyses.