Climatic refugia, landscape physiography, and species distributions

Background/Question/Methods

Microrefugia are sites that support locally favorable climates amidst unfavorable regional climates, which allow populations of species to persist outside of their main distributions. Knowledge of the distribution of microrefugia has important implications for climate change research as it will influence our understanding of the spatial distribution of species through time, their patterns of genetic diversity, and potential dispersal rates in response to climate shifts. Despite widespread acceptance of their existence, we know very little about microrefugia, and in particular their climatic basis; what climatic processes can support their subsistence, where they may occur, their climatic traits, and the relevance of these locations for climate change research. Here, using data on the occurrence of woody plant species within the Lake Tahoe Basin, CA and physiographically informed climate data, I demonstrate that environmental niche models can be used to identify potential microrefugia. For comparative purposes, I contrast these model outputs to niche model outputs built with climate data that does not take into account local terrain effects on climate.

Results/Conclusions

Under current conditions both niche model types predict similar distributions for five woody species. Under a 1^o C warming scenario, the niche models built with physiographically informed climate data identifies suitable habitat at both higher elevations and in convergent environments. In contrast, the niche models based on more naïve climate data predictably forecast upslope movement of species and thus less suitable habitat. Under a 3 ^o C warming scenario, the difference between the model outputs are stark. For some species, the naïve niche models predict the effective disappearance of suitable habitat within the study region. In contrast, niche models that utilize more realistic climate patterns identify potential microrefugia in valley bottoms and local depressions. This research highlights the importance of landscape physiography in shaping the adaptive response of biota to climate change.