The impact of climate change on serpentine endemic plants in California

Background/Question/Methods Climate change poses a threat to many plant communities.  Our ability to predict the effect of climate change depends on our understanding of how abiotic and biotic factors interact to influence the distribution of species, which is currently limited, especially for rare or endemic species.  Serpentine endemics, plants that specialize on serpentine soil, are major contributors to California’s biodiversity; however many are threatened or endangered.  Because these species tend to be narrowly distributed with small, patchy populations, they may be particularly vulnerable to climate change.  In addition, serpentine grasslands are often imbedded within a matrix of more fertile, chemically benign grasslands dominated by non-native grasses.  These non-native grasses are generally unable to tolerate serpentine soil but are strong competitors off serpentine.  In an attempt to understand how edaphic endemics will respond to climate change, I am conducting field experiments to determine how changes in precipitation interact with competition to influence the growth and reproduction of three serpentine grassland endemics.  The study is designed to experimentally test the hypotheses that 1) competition from other species on fertile soil is the primary mechanism of soil specialization and 2) soil specialization is stronger when the climate, specifically precipitation, is favorable. 

Results/Conclusions

Results from research at McLaughlin, a University of California Reserve, suggest that the response to increases (via water additions) and decreases (via rainout shelters) in spring precipitation may depend on species identity and soil type.  For instance, on serpentine soil the effect of competition was lower in experimental drought treatments for one serpentine endemic, Navarretia jepsonii (Polemoniaceae), but was greater in the same treatment for another endemic, Clarkia gracilis ssp. tracyii (Onagraceae); the reverse was observed on non-serpentine soil.  Specifically, in drought treatments, competition reduced the biomass of N. jepsonii by 87% on non-serpentine soil, but only by 50% on serpentine soil.  In contrast, in the same drought treatment, competition reduced C. gracilis biomass by 36% on non-serpentine soil and 92% on serpentine.  The results of this study indicate that climate change may favor some serpentine endemics over others and suggest that endemic responses to climate change may depend on particular species traits.