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Contributed Talk

Session: : Climate Change: Plants 1

COS 8-3 - Region-wide climate-driven grassland community shifts in a biodiversity hotspot

Monday, August 7, 2023
2:00 PM – 2:15 PM PDT
Location: B118
Abstract: Ecological communities are shifting rapidly under recent climate change, with alarming consequences for biodiversity and ecosystem services. However, the generality and causality of such shifts are difficult to establish for entire floras in complex spatiotemporal contexts. We focus on grasslands in the California Floristic Province (CFP), a global biodiversity hotspot spanning 300,000 km2, where considerable climate warming (annual mean temperature increase by 0.0260 ℃ yr−1) and drying (annual precipitation decrease by 5.45 mm yr−1) occurred from 1980 to 2019. To examine climate change impacts, we leveraged long-term grassland community composition datasets from both 12 observational sites (8–33 yr) and a warming experiment (16 yr). We used historical climate data to calculate ~350 species’ climate niches from ~700,000 occurrence records, and we estimated changes in community-weighted means of temperature (Community Temperature Index, CTI) and precipitation (Community Precipitation Index, CPI) for the long-term observations and experiment.

We found that grassland species occurred along geographic and climatic gradients in distinct patterns, where the species’ temperature and precipitation niches were significantly negatively correlated (r = −0.667, p ≤ 0.001). From the long-term observations, we found a general region-wide shift in grassland community composition, where eight out of the 12 sites had significant increases in CTI (average +0.0327 ℃ yr−1) and significant decreases in CPI (average –4.32 mm yr–1), consistent with the observed climate warming and drying. From the long-term experiment, we found that the warming treatments led to higher CTI (12 out of 16 yr) and lower CPI (11 out of 16 yr) of plant communities compared to ambient treatments. Moreover, the community differences became more significant when stronger warming treatments were imposed. Taken together, the observational and experimental communities consistently shifted dominance toward species associated with warmer and drier climates. These communities shifted along a common trajectory of thermophilization (increasing CTI) and xerophilization (decreasing CPI). In conclusion, our observational evidence reveals region-wide grassland community shifts to a warmer and drier species composition, and our experimental evidence demonstrates that these ecological community shifts in the biodiversity hotspot are a predictable fingerprint of climate change.