Climate Change Vulnerability Assessment of Rare Plants in California

We assessed the vulnerability to climate change of 156 rare plant species. The species were selected from the 1625 rare species in California to comprise eight rarity types, classified according to range size, population size, and habitat specificity. For each of the 156 species, we first assigned a climate change vulnerability score using life history attributes and species distribution models, as specified by the Climate Change Vulnerability Index (CCVI) of NatureServe. The resulting CCVI scores were extremely vulnerable (n = 2), highly vulnerable (n = 40), moderately vulnerable (n = 57), presumed stable (n = 32), increase likely (n = 16), and insufficient evidence (n = 9). Piperia yadonii Rand, Morgan & Ackerman and Mimulus purpureus A. L. Grant were the species scored as extremely vulnerable. There was no correlation of the CCVI scores with rarity type, suggesting that climate change vulnerability cannot be inferred by simple categorizations based on geographic range and habitat preference. Second, we conducted a follow-up species distribution model sensitivity analysis that showed that the modeling results were highly dependent upon both model algorithm and choice of predictor variables. However, 60 of the 156 species were predicted to have declines in climatic suitability, regardless of modeling technique. Third, as an independent assessment of vulnerability, we calculated the topographic complexity around known occurrences of each species. Species in topographically dissected landscapes may be less vulnerable to climate change because they can find suitable climates locally as climate changes. We found that topographic complexity varied substantially, even within a single CCVI score level, and therefore provides unique information on vulnerability. Our results can be used to guide monitoring, management, and conservation plans for rare plant species.