Erosion of refugia in the Sierra Nevada meadows network with climate change

Background/Question/Methods

Montane environments represent areas where climate change should impact species' ranges over short distances due to elevational gradients. However, topographically complex landscapes may produce refugia from climate change if habitat patches are sufficiently connected to promote metapopulation persistence. Focusing on montane meadows of the California Sierra Nevada, we examined multiple factors affecting connectivity, using circuit theory and simpler density measures. We then determined how connectivity of these patches has been and will be affected by past and future climate change, respectively. Climate change refugia were identified from downscaled climate layers, based on locations with minimal change from historical climate conditions that should promote population persistence. We evaluated common measures of climate, including change in annual mean temperature and annual mean precipitation, as well as measures of hydrologically relevant values such as climatic water deficit and snow water equivalent.

Results/Conclusions

Connectivity indices, based on topography, water courses, and roads, but not geographic distance, explained occupancy data of a meadow-specialist mammal (Urocitellus beldingi). We classified meadows as well-connected, more-connected, and less-connected, and examined specific characteristics that mapped their position across the landscape. Well-connected meadows tended to be larger and occur more frequently at higher elevations than other meadows. Yosemite, Sequoia, and Kings Canyon National Parks contain a greater number of well-connected meadows compared to Lassen Volcanic National Park. There were a disproportionate number of well-connected meadows considered refugial than non-refugial during the 20th Century, compared to other meadow classifications. Projected future climate changes further reduced the number of refugial meadows and resulted in a sparser network of potential refugia. Those meadows which are refuigal at the end of 21st Century, regardless of connectivity value, occur at high elevation in the central Sierra Nevada. Our results highlight the use of accounting for landscape connectivity when evaluating potential responses of  species to climate change. They also demonstrate the sensitivity of the structure of a habitat network to assumptions about important environmental conditions.