Abundance and diversity of plant functional groups in response to environmental gradients in southwestern Virginia

Michelle Uchitel, Conservation Managment Institute, Virginia Tech, Blacksburg, VA and Verl R. Emrick, Conservation Management Institute, Virginia Tech, Blacksburg, VA

Background/Question/Methods
Ecosystem resilience is often correlated with the diversity of traits, or functions, of individual plant species. As biodiversity declines, the diversity of traits decreases likely resulting in diminished ecological resilience. Thus, ecological resilience can be estimated by examining plant functional diversity. Vegetation diversity is a function of the interaction of environmental factors, and disturbance/land use. The high levels of plant diversity present in the Southern Appalachians, coupled with a multitude of environmental gradients, provided an ideal location to examine how environmental factors and disturbance affect plant functional diversity and presumably ecosystem resilience. Our objective was to examine the relationships within and among the plant functional types and environmental gradients at Radford Arsenal in southwest Virginia to identify areas with highly resilient plant communities for conservation and/or restoration. We allocated 54 plots in stratified random manner with land cover class as the primary strata. To determine plant functional group composition and diversity, we used fixed area vegetation plots at each plot location. At each plot, we determined the abundance for each species using the Braun-Blanquet cover abundance scale within four height strata. Using raw plot data, all plant species were placed into one of 7 functional groups (C4 grasses, C3 grasses, forbs, legumes, woody deciduous, woody needle-leaved and woody vine).
Results/Conclusions
We calculated overall abundance, richness, and diversity (using the Shannon-Weiner diversity index) within each plot, and for the functional groups present within each plot. Using linear regression, we examined the correlation between environmental variables (e.g. aspect, elevation, etc.), and abundance and diversity within functional groups. Both functional richness and functional diversity were correlated with aspect (p < 0.00, r2 = 0.22; p < 0.05, r2 = 0.08 respectively) but not elevation. While forb and C4 grass abundances were negatively correlated with elevation (p < 0.00, r2 = 0.28; p < 0.05, r2 = 0.13 respectively), and woody needle-leaved abundance was positively correlated with elevation (p < 0.00, r2 = 0.16). In addition, forb and legume functional richness was correlated with aspect, while C3 grass richness showed a negative correlation with elevation. The complex nature of the environmental gradients found in mountainous terrain resulted in localized differences in functional diversity and abundance. Understanding these patterns will allow for the conservation of diverse and highly resilient plant communities and provide critical guidance for management and conservation activities.