Trait integration and functional differentiation among co‐existing plant species

Determining which traits best characterize the strategies of coexisting is a central challenge in functional ecology. Global dimensions, such as the leaf economics spectrum (LES), may not exist locally. Furthermore, the degree to which traits that are measured less frequently, i.e., root traits and whole plant traits including intrinsic water use efficiency (iWUE) and Δ15N, or categorical traits, constitute independent dimensions is not well understood. We examined relationships among 12 continuous and 7 categorical traits across 57 forest understory plant species in western Oregon, USA. We observed a strong LES, integrated with stem but not root economic traits and iWUE. Network analyses indicated some integration among trait modules. However, leaf nitrogen content, specific root length, seed mass, leaf size and Δ15N were weakly linked, if at all, to other traits in this network. Three ordination axes explaining 93% of variation among species were related primarily to: 1) rooting depth and plant size; 2) LES traits; and 3) leaf size and seed mass. Our results show that while the global LES is evident within local forest understory communities, the strategies of coexisting understory plant species cannot be reduced to a single, integrated dimension. However, species can be distinguished using just three commonly measured traits. Below-ground and whole plant traits that are more difficult to characterize were either integrated with these frequently measured traits, or did not contribute to distinguishing species.

Impact/Purpose

Land managers need simple tools to project how plant communities and ecosystem services will respond to changing environmental conditions. One group of tools are models based on plant traits such as leaf size and thickens to predict these responses. While a plethora of traits that may be important to understand how plants will respond, trait data are expensive to collect, and budget constraints frequently limit investigators to the use of functional groupings and literature-based traits. We ask the question: which traits are most important to understanding plant responses to environmental gradients within a forest understory in the Pacific Northwest. We found that species can be distinguished using just three commonly measured traits: plant height, specific leaf area (or evergreen vs. deciduous leaf lifespans), and leaf size. Finally, our results show that models developed using continuous trait data are indeed superior to those developed using species or functional groupings. However, groupings can reflect continuous trait variation to some extent – permitting a functional interpretation.

Citation

Burton, J., S. Perakis, J. Renee Brooks, AND K. Puettmann. Trait integration and functional differentiation among co‐existing plant species. Botanical Society of America Inc., ST. Louis, MO, 107(4):628-638, (2020). [DOI: 10.1002/ajb2.1451]

DOI: Trait integration and functional differentiation among co‐existing plant species