**4. Discussion**

Our results suggest that climate change may pose additional threats, or exacerbate current stressors, for threatened and endangered plants in the Mojave Desert. Many listed plants are rare species characterized by relatively narrow ecological niches, small population sizes and restricted geographic ranges [34]. Although these traits may contribute to a species decline in a world increasingly influenced by human activity, these factors alone do not determine likelihood of extinction. Numerous species that were once locally common or abundant (e.g., elephants, lemurs, orangutans) have become endangered due to hunting, habitat loss, agriculture, or other human endeavors. Rarity may have been a contributing factor, but Mojave Desert listed plants became threatened or endangered primarily because of anthropogenic stressors. Climate change has not been considered in measures of extinction risk in the past, and this phenomenon has the potential to accelerate extinction processes for species already struggling to persist. For example, the five plant species classified as extremely vulnerable by our CCVI (Dwarf Bear-poppy, Shivwits Milkvetch, Holmgren's Milkvetch, Siler Pincushion Cactus, Gierisch's Globemallow) occur only in a small geographic area located in southern Utah and northern Arizona. Climate change is projected to be particularly severe for this part of the Mojave Desert, with a 2.2°C–4.4°C increase in annual temperature predicted by the end of the century (2070–2099) and a 30% reduction in snowpack, which functions as the regions' main source of water [35].

Although Shivwits Milkvetch occurs predominantly in a protected area (Zion National Park), the remaining four plants categorized as extremely vulnerable do not. These species are habitat specialists restricted to gypsiferous soils located largely on federally managed public lands where populations are also threatened by recreation, grazing, and gypsum mining. One frequent suggestion for managing imperiled species under climate change is to reduce existing threats in order to increase resilience to climate change [36]. Threats could be minimized by placing core habitat areas under protection status, which has been successful in

#### *Climate Change Vulnerability Assessment of Imperiled Plants in the Mojave Desert DOI: http://dx.doi.org/10.5772/intechopen.95783*

recovery efforts for another listed plant in the Mojave Desert, the Eureka Dune Grass. The species was recently down listed from endangered to threatened, mainly as a result of habitat areas becoming part of Death Valley National Park which prohibits OHV use in Eureka Dunes [37]. This strategy may not be effective throughout the Mojave Desert, however, as listed plant species in Ash Meadows National Wildlife Refuge continue to decline despite similar protection status [38]. Endemic species in this refuge rely upon rare, wet microhabitats sustained by desert springs or shallow groundwater, which are vulnerable to groundwater pumping and drought. Groundwater pumping is very likely to increase throughout the Mojave Desert as droughts become more frequent and dry conditions are intensified by climate change, and the future of many Ash Meadows species remains uncertain.

Similar to other studies related to CCVAs of imperiled plants, our vulnerability scores were strongly associated with two analogous factors, natural or anthropogenic barriers and dispersal ability. In highly urbanized and densely populated regions of California, anthropogenic barriers limited the dispersal capability of 63% of plant species assessed [39]. A lack of topographical variation presented a bigger challenge in other regions, as plant species inhabiting areas of topographical homogeneity may experience climate change effects sooner since they are unable to move up or down in elevation [40]. For plants in relatively flat regions of the United States, such as Illinois, latitudinal migration may be the only effective survival mechanism, which will require assisted migration as individuals will not be able to disperse through highly urbanized areas [40]. In contrast, the Mojave Desert is relatively undeveloped and topographically diverse, thus offers opportunities for plants to shift to higher elevations and more mesic microhabitats. Hot, dry desert valleys and other areas of unsuitable habitat may present similar barriers to dispersal, however. *Some* of the plant species assessed here *could* be good candidates for assisted migration, assuming appropriate substrates and ecological conditions (e.g., pollinators, hydrological regimes) are available on the landscape and successful restoration techniques are established.
