Leaf trait variability explains how plant community composition changes under the intense pressure of deer herbivory

There is growing evidence indicating that intraspecific trait variation (ITV) plays a prominent role in determining plant community composition. In this study, we investigated the significance of ITV in identifying the processes that shape the development of forest understory plant communities in an area in which excessive herbivory by overabundant deer populations has been an issue. We measured functional traits (height, leaf area, leaf mass per area, leaf dry matter content, and leaf toughness) of 13 forest floor plant species growing in two contrasting sites in which deer were overabundant or had been completely excluded, respectively, and examined the relationships between species dominance and interspecific trait variation and ITV. We detected variations in the trait plasticity of size and morphological features among species, reflecting species‐specific strategies in response to herbivory and consequently observed marked differences in species composition and diversity at the two sites. Notably, small stature and less costly leaves were identified as important traits that enable plants to persist under conditions of intense deer herbivory probably because such plants are less exposed to herbivory and simultaneously optimize carbon assimilation. In contrast, large‐sized plants with costly leaves tended to dominate the plant community in the absence of deer herbivory, as these plants would tend to gain a competitive advantage with respect to the acquisition of space and light. The findings of this study indicate that a focus on ITV represents a promising approach for determining the general ecological patterns of plant communities responding to environmental disturbance.