Indigenous forests across North America have been and continue to be transformed. The implications of these changes are far reaching and include the loss of habitat, biological diversity, and ecological services, as well as diminished air and water quality. The northern ﬂying squirrel is a forest obligate that achieves its highest density in old growth, facilitates critical symbiotic relationships, and is an essential prey of disturbance-sensitive predators. Its reliance on old-forest attributes varies with community diversity, and its sensitivity to isolation renders it an ideal indicator of landscape connectivity. The results of numerous studies reveal the squirrel’s acute sensitivity to disturbance at multiple spatial scales, which renders it an effective sentinel of forest ecosystem processes and condition over both geological and ecological time scales. Therefore, a thorough understanding of its ecology can inform projections and the effectivemitigation of continued disturbance of ecological communities of boreal and montane coniferous forests.