Climate change vulnerability of threatened and endangered plants in Tennessee: Species range representation matters

Background/Question/Methods

Conservation organizations understandably prioritize their efforts towards ‘species of concern.’ Attention is often focused on species designated as ‘threatened’ and ‘endangered’ at national levels, along with knowledge of their spatial status. We assessed vulnerability to climate change for Tennessee’s 22 federally-listed threatened and endangered plants using NatureServe’s Climate Change Vulnerability Index (CCVI) to address whether this index consistently prioritized species in the same manner as traditional species rankings (e.g., global, subnational or regional rankings) and whether the type of spatial information on the species matters. We calculated CCVI scores using species sensitivity information and calculation of exposure of known occurrences of each species to future climate change. We compared the CCVI score of each species to its global and subnational conservation status ranks using non-parametric correlation. To compare the effects of species range representation on final CCVI score we duplicated the analysis using both convex hull and county polygons, two other common sources used to represent species range. We conducted a topographic complexity analysis calculating average of standard deviation within 100m of all known occurrences for each species, and we tested if there was a relationship between topographic complexity and climate vulnerability using a basic linear regression.

Results/Conclusions

We found that 14 of the 22 species produced a final CCVI score of Extremely Vulnerable. Five were scored as Highly Vulnerable, two as Moderately Vulnerable, and one as Presumed Stable/Increase Likely. CCVI scores were not significantly correlated with global (‘G’) ranks, but were significantly correlated with the subnational or regional (‘S’) ranks. We found no relationship between topographic complexity and final CCVI score. Using convex hull ranges, the CCVI changed for only one species, Isotria medeoloides (to less vulnerable); this was the only species originally scored vulnerable with a low confidence of species information entered, suggesting uncertainty in the original. Using county occurrences an additional four species were scored less vulnerable. We also found that modifying the species range to either convex hull or county polygons lowered the confidence of CCVI estimates for the aforementioned species and an additional three species. Our results illustrate the sensitivity of the CCVI algorithm to the scale of information used to estimate the index, with known population occurrence polygons providing estimates with higher confidence. Conservation organizations interested in integrating climate change into their species prioritization are likely better served by utilizing subnational or regional rankings, suggesting the importance of state-level inventorying and monitoring.