Forest structure and squirrel populations in relation to fire history; habitat use of endemic tree squirrels in Parque Nacional Sierra San Pedro Matir and Saguaro National Park - Final Report 2005

Koprowski, John

In the western United States and Mexico, fire is often considered to be the major disturbance under anthropogenic influence. Policies of fire suppression for nearly a century in the United States and portions of Mexico have resulted in significant changes in cool fire frequency, catastrophic fire frequency, and forest structure. The implications of these changes have only recently been realized and very few forests with natural fire regimes remain where an appropriate comparison can be made. Saguaro National Park (SAGU) practiced fire suppression for more than 50 years before initiating controlled burns in 1985; the importance of park-wide fire strategy has been summarized with the release of a 'Draft Saguaro National Park Fire Management Plan Environmental Impact Statement' in Feb 2004. The Parque Nacional Sierra San Pedro Martir (SSPM) is an isolate of forest that has never received substantial timber harvest or fire suppression in part due to its rugged terrain and isolation. As a result , the forest structure is considerably more open than in fire suppressed systems found within many parts of the United States. Additionally, SSPM presents a landscape that consists of a mosaic of past natural fires and this history has been well-mapped, thus providing g an excellent natural 'experiment'' for the study of fire impacts on forest wildlife. Tree squirrels have been suggested as excellent indicators of forest health and forest structure due to their dependence on mature forests for tree seed foods, nest sites, cover from predators, and maintenance of appropriate microclimates for food storage. As a result, the presence, demographics, and habitat use of tree squirrels can provide an indication of the status of the forested ecosystem. Two native endemic tree squirrels of special concern are found in these two parks, Mearns's squirrel and Santa Catalina gray squirrels. Ecological information is necessary to maximize the efficacy of management and interpretive efforts within these two national parks for the species are uncommon and unknown members of the forest ecosystems of these sky islands and likely excellent indicators of mature forest conditions for managers.