Topoclimates and plant distributions: Modeling the impacts of climate change on Mediterranean-climate vegetation

Background/Question/Methods

Species distribution models have played a central role in projections of climate change impacts on biodiversity. In many cases, models suggest that plant and animal species may have to move significant distances in response to 21st century climate change, and dispersal constraints make such responses unlikely. I present two studies examining the influences of topography on climatic heterogeneity and plant distributions at fine spatial scales, to evaluate the potential for species to persist in heterogeneous landscapes with limited dispersal. The first study involves an application of multinomial logistic regression to vegetation distributions in the San Francisco Bay Area. The second is a study of topoclimate and plant distributions in the fynbos community in Table Mountain National Park, South Africa, including in situ calibration of topographic variation in temperature regimes.

Results/Conclusions

In the Bay Area study, multinomial analysis demonstrated highly significant effects of climatic water deficit on vegetation distributions, in part reflecting contrasting environments of north vs. south-facing slopes. Under a mid-century, A2 future climate scenario, changes in vegetation are projected across the region, especially in vegetation patches that lie near the edge of the climatic distribution for their respective vegetation type. Importantly, in more than 50% of the patches where a change in vegetation type was forecast, the future vegetation currently occurs within 1 km of the focal point. In the Table Mt. study, topographic heterogeneity generates up to 3°C variation in minimum and maximum temperatures at a local scale, due to cold air pooling and solar insolation, respectively. Interpolated climate surfaces will be used to generate fine-scale species distribution models for selected taxa and determine the extent to which this topographic variation will allow for local dispersal and distribution shifts in response to projected 21st century climate change. The two studies together highlight the importance of enhanced spatial resolution in both climate and biodiversity modeling, and the importance of landscape heterogeneity for biodiversity conservation in the face of climate change.