Protected areas are critical for conserving California’s many sensitive plant species but their future role is uncertain under climate change. Climate-driven species losses and redistributions could dramatically affect the relevance of protected areas for biodiversity conservation this century. Focusing on the University of California Natural Reserve System (NRS), we predicted the future impact of climate change on reserve effectiveness with respect to sensitive plant protection. First, we evaluated the historical representation of sensitive plant species in the NRS reserve network by compiling species accounts from checklists, floras, and spatial queries of occurrence databases. Next, we calculated projected climate change exposure across the NRS reserve network for the end of the 21st century (2070–2099) relative to baseline (1971–2000) conditions under five future climate scenarios. We then predicted statewide changes in suitable habitat for 180 sensitive plant taxa using the same future climate scenarios in a species distribution modeling approach. Finally, from these predictions we evaluated suitable habitat retention at three spatial scales: individual NRS reserves (focal reserves), the NRS reserve network, and the surrounding mosaic of protected open space. Six reserves—Sagehen Creek Field Station, McLaughlin Natural Reserve, Jepson Prairie Reserve, Landels-Hill Big Creek Reserve, Sedgwick Reserve, and Boyd Deep Canyon Desert Research Center—were selected as focal reserves for analyses.
A considerable proportion of California’s sensitive plants have historical representation in the NRS reserve network
At the time of this report, over 2,300 vascular plant taxa have a California Rare Plant Rank (CRPR) status, 406 of which are state or federally listed NRS reserves comprise less than 1% of the state’s total land area yet represent as much as 16% (373 minimum rank taxa) of all CRPR vascular plants Many sensitive plants have been recorded in large parks associated with the NRS (97 taxa in Yosemite National Park; 105 taxa in Anza-Borrego Desert State Park), increasing the total number of sensitive plants historically represented in the greater NRS network to 526 taxa Over 70% (1,637 taxa) of all CRPR vascular plants in California have been recorded within 50 km of an NRS reserve or associated park
Projected climate change exposure varied by climate model and reserve geographic location
Projections for precipitation were highly variable across climate models Overall, reserves in central and northern California had greater exposure to increased precipitation while those in southern California had greater exposure to decreased precipitation Exposure to warming was greatest for reserves in the Sierra Nevada and East of the Sierra Nevada and lowest for those along the coast Climatic water deficit (CWD), a measure of drought stress experienced by plants, increased across all reserves, even under scenarios of increased precipitation, with reserves in the Sierra Nevada and East of the Sierra Nevada having particularly high exposure
By the end of this century, we predict climate change will drive considerable loss in suitable habitat for many of California’s sensitive plant species
25 of 180 species modeled had no geographic overlap between modeled baseline and future suitable habitat under three or more climate scenarios Assuming species are unable to migrate to future suitable habitat (no dispersal), an additional 73 species (41%) were at severe risk with 80–99% predicted loss in suitable habitat Dispersal could alleviate risk for some species – 53 species (30%) were at decreased risk with net habitat gain under future climate scenarios, assuming they are able to reach, establish, and persist in newly suitable habitat Even under an optimistic dispersal scenario, 62 species (34%) were still at severe risk
Climate-driven habitat loss and redistribution affected sensitive plant representation in the NRS
Focal reserves retained suitable habitat for less than 40% of modeled sensitive plant species under future climate scenarios Species retention increased as the extent of the area protected expanded to include the entire NRS reserve network and surrounding protected open space Allowing dispersal had little effect on species retention within individual focal reserves but increased representation in the NRS reserve network and surrounding open space
Historically, the NRS has played an important conservation role protecting California’s sensitive plant species. Because many reserves are located in areas rich in sensitive species, the NRS is well positioned to continue playing a key role in rare plant research and conservation, both locally and regionally. While we predict climate-driven habitat loss and species redistributions will negatively affect sensitive species representation within individual NRS reserves, many species may retain suitable habitat in the NRS network as a whole and in surrounding protected open space. Managing for species persistence and redistribution under climate change will likely require increased cooperation and partnerships among neighboring protected areas and open space as well as better integration of social, conservation, and ecological research. With a long history of research, stewardship, and stakeholder engagement, the NRS is well positioned to take the lead in both supporting the research needed to improve our understanding of the ecological effects of climate change and developing more dynamic and collaborative trans-boundary management strategies.