Identifying regional influences on beta diversity of vascular plants within and among British Columbia ecosystems

Background/Question/Methods

Local environmental conditions are typically important drivers of landscape-scale diversity patterns of plants, but historical and regional-scale factors, such as dispersal and the size of the regional species pool, are also influential. The challenge remains to disentangle the relative importance of regional and local scale factors. One approach, and the goal of this research, is to compare diversity patterns among sites that share very similar environmental conditions, thereby controlling for local environmental variation, and to repeat comparisons across a range of environments that have contrasting species richness. Plot data from standardized (400-500m²) vegetation surveys contributing to the hierarchical Biogeoclimatic Ecosystem Classification system in British Columbia Canada enable such comparisons.  For the present study, 1208 classification plots (out of >30000 total) from 8 biogeoclimatic units (areas of similar regional climate) and 31 site units (sites sharing similar local environments) were provided by government agencies. Alpha, beta and gamma diversity were analyzed within and among classification units of different hierarchical levels. Beta diversity within classification units was measured using the Jaccard dissimilarity index, while null models were used for comparison among classification units to control for differences in alpha and gamma diversities.

Results/Conclusions

Preliminary results show that mean alpha diversity is similar across 8 biogeoclimatic units (mean=21.2, SD=4.53 species) despite substantial variation in gamma diversity (range: 145-272 species). Across all 1208 plots, species occupancy  is low (49% of species occur in ≤ 5 plots) and consequently, comparisons of composition among plots reveals high beta diversity. In the most species rich biogeoglimatic unit (ICHdw1), mean Jaccard dissimilarity is 0.760 (sd=0.116). For the focal site unit (ICHdw1/101) within the ICHdw1, mean Jaccard dissimilarity is 0.486 (sd=0.097).We hypothesize that beta diversity is lower at finer levels of classification because of increased site and environmental similarity; however the relatively high beta diversity observed at the site unit level requires explanation, especially because site units are foundational units for forest and biodiversity management. Building on the results thus far, comparative analysis within and among the remaining biogeoclimatic and site units will reveal whether patterns are consistent and whether the size of the regional species pool is influential. This research is important for ecosystem management in British Columbia because it improves the understanding of "baseline" levels of variation in vascular plant composition. Further, findings are easily integrated into ecosystem management through Biogeoclimatic Ecosystem Classification.