Droughts and insect outbreaks are primary disturbance processes that link climate change to ecological impacts. Refugia from these extreme events—locations where disturbance is less severe relative to the surrounding landscape—may be priorities for conservation, restoration, and monitoring. We used remotely-sensed vegetation indicators to identify potential refugia, i.e. locations where vegetation demonstrated minimal spectral response to disturbance. We then asked what landscape characteristics (e.g. topography, soil, vegetation, or hydrology) were associated with refugia locations. At the local scale, we delineated potential refugia at 30-m resolution in a southern Oregon conifer forest during a combined drought and mountain pine beetle outbreak in 2009. At a regional scale, we identified potential refugia at 1-km resolution in forest and sage-steppe ecosystems across the Pacific Northwest during episodic droughts from 2000 to 2016.
Results/Conclusions
At the local scale, refugia from drought and mountain pine beetle mortality were associated with steep, topographically shaded slopes along ridgelines in lodgepole pine stands and with topographically shaded valleys and headwater streams in whitebark pine stands. Spatial variation in snowmelt timing and rate, soil water storage, and vegetation characteristics (e.g. drought tolerance and insect resistance) may have created localized disturbance refugia. At the regional scale, preliminary results indicate that drought sensitivity for both forest and sage-steppe ecosystems is lower in areas below 2000 m with low soil bulk density and that shallower water-table depths may moderate sage-steppe sensitivity. Our results suggest that drought refugia discernible by remote sensing may arise through interactions of physical processes (e.g. determinants of soil water availability) and biological traits (e.g. drought-tolerance mechanisms). Questions remain, however, as to whether refugia from future disturbances will be supported by landscape processes similar to those that supported refugia from past disturbances, especially as climate change alters disturbance regimes (e.g. spatial extent, severity, duration, and frequency of droughts and insect outbreaks).