COS 7-3 - 105+ years of vegetation change in the Sonoran Desert: the impact of climate on species turnover and demography

Background/Question/Methods

The impacts of anthropogenic climate change on desert plant communities are unclear. Desert plant communities could be vulnerable if changes in climate push desert species that are already at a climatic extreme past their physiological limits. On the other hand, they could be relatively resistant to changes in climate due to species tolerance mechanisms. Complicating understanding of how desert plant communities may respond to future climate change is that many of these systems are comprised of long-lived species (i.e., 80+ years), a duration longer than most studies examining these communities. Here, we address this issue by using a 105+ year dataset on mapped individuals to test the impacts of climate on desert plant community change. Specifically, we examine the influence of temperature, seasonal precipitation, and drought frequency on species turnover and directional community change and whether species with different life-history strategies differ in their demographic responses to climate.

Results/Conclusions

Over the past 105+ years, the presence of cacti has increased slightly in these communities, but the relative abundances of species did not shift directionally. Temperature, seasonal precipitation, and drought frequency explain little variance in decadal-scale directional community shifts. Instead, climate explains more variation in species turnover independent of which species are changing and in which direction. This suggests that climate influences the magnitude of community change more than the direction of change, potentially due to functional redundancies in species. This is further supported by our finding that demographic responses to climate did not vary consistently with species longevity or early survival rates. However, another possible explanation is that influential climate factors are non-directional and variable through time, therefore, not consistently favoring particular species and plant strategies. We found evidence for this as seasonal precipitation anomalies, a climate variable that has been and is projected to be variable over time, was a significant predictor of community change in our models despite low explained variance in overall models. Overall, these results suggest that decade-scale climate has either invariable or unpredictable individualistic effects on desert species and may contribute little to altering community dynamics at a local scale.