Spatial patterns of functional diversity in old-field plant communities

Background/Question/Methods

A central goal of community ecology is to understand how biological diversity is distributed in space. While spatial patterns of species diversity (e.g., species-area curves) have been intensively studied, the spatial distribution of functional diversity, an ecologically-relevant component of biodiversity, is largely unknown. I explored spatial patterns of functional diversity using a dataset of key plant functional traits- vegetative height, specific leaf area (SLA), and leaf dry matter content (LDMC)- measured at the individual level in old-field plant communities in central New York across a range of spatial scales (1-1500 m). I used semivariograms and novel “trait-area curves” to describe spatial patterns of functional diversity and address the following questions: 1) Is the distribution of functional diversity spatially structured or random? 2) Do the scale and strength of spatial structure differ between species diversity and functional diversity? 3) How do spatial patterns differ among functional traits? 4) How do interspecific and intraspecific trait variation contribute to spatial patterns of functional diversity?

Results/Conclusions

Functional and species diversity were both spatially structured (i.e., had non-random spatial distributions), but differed in the strength and scale of spatial structure. While species diversity gradually increased across the range of spatial scales included in the study, most functional diversity was concentrated at very fine scales. Spatial patterns also differed among traits, suggesting different functional responses to environmental heterogeneity. Height had relatively strong spatial structure and fine-scale patchiness, congruent with the spatial heterogeneity of soil depth. In contrast, SLA and LDMC had much weaker spatial structure, with > 90% of site-level variation occurring within 1-m² plots. Spatial patterns of interspecific and intraspecific trait variation were largely decoupled, and the relative importance of intraspecific variation depended on the trait and scale in question. This study provides one of the first descriptions of spatial patterns of functional diversity in plant communities, using methods that should be broadly applicable across ecosystems, and illustrates how the spatial structure of functional traits can provide new insights into community assembly and spatial patterns of biodiversity.