Snowmelt variation contributes to topoclimatic refugia under montane Mediterranean climate change

Improved knowledge of the influence of climate parameters on the distribution of plant species is needed to identify potential refugia under climate change. Species abundance of trees, mainly conifers, as measured by species relative cover, was evaluated on 132 sites in the southern Sierra Nevada mountains of California, USA. These mountains experience a montane Mediterranean climate characterized by a deep winter snowpack and an extended summer drought. The cover data was analyzed in terms of the average snowpack water content at its maximum and the average date when snow on each site is finally melted. These snow-related parameters were calculated from a semi-empirical snow model, taking into account site slope and aspect. For the pine, juniper and oak species studied these parameters were found to have a much stronger effect on species abundance at a site than does elevation. For the conifer species, this allows the identification of topographic refugia from climate change. This result appears to be related to growth phenology. Elevation was found to be more important for the fir species studied. The results on the importance of growth phenology should be useful in identifying topographic refugia in mountains experiencing a Mediterranean climate worldwide.