Species distributions within local landscapes often mirror broader scale biogeographic patterns. For example, species restricted to cool and/or moist locations in a local landscape (potential refugia) will usually occur in cooler/moister geographies at a regional scale. In addition, restriction to refugial sites within landscapes may indicate that the species are at the hot/dry edge of their range, and thus represent trailing edge populations that would be susceptible to a warming climate. We test the hypothesis that refugial sites may be particularly sensitive to climate change because 1) they are preferentially occupied by trailing edge populations, and 2) because warmer-adapted immigrants will be located nearby on the landscape, reducing dispersal limitation to these sites.
Results/Conclusions
At a local scale (Pepperwood Preserve, California, USA), we found that tree communities on cooler topographic positions have greater potential for shifts in community composition due to predominance of cool-adapted species near their warm/dry climatic limits, and presence of hotter adapted species at low abundance, coupled with abundant seed sources from nearby hotter sites. Similarly, at a regional scale, minimum dispersal distances for arrival of new, hotter adapted species are lower for communities in cool and moist regions. These analyses suggest that communities occupying cool and/or moist landscape locations may exhibit more rapid biotic change in response to a warming climate.