Many traditional land management activities and supporting research have concentrated on one or two resources, with limited evaluations of interactions among other potential values. An ecosystem approach to land management requires an evaluation of the blend of physical and biological factors needed to assure productive, healthy ecosystems. Ideally, social and economic values also should be considered. The U.S. Department of Agriculture Forest Service's Coronado National Forest and its partners have just completed a draft for the Peloncillo Programmatic Fire Plan to address fire management strategies for this mountain range, which lies along the southern Arizona–New Mexico border. The plan was designed to reintroduce prescribed or managed fires into an area where wildfires have been excluded since the late 19th century. One persistent question concerned the impacts of cool-season (November–April) and warmseason (May–October) fires on the oak (Quercus spp.) ecosystems that are common throughout these mountains. Fires normally occur in June or early July before the summer monsoon rains. However, hotter warm-season fires could damage important wildlife habitats by killing larger numbers of standing trees and shrubs used as nesting sites or cover or as sources of food, and thus some managers prefer burning during the cooler season.The Rocky Mountain Research Station's Southwestern Borderlands Ecosystem Management Project and its cooperators have initiated a research program to evaluate the impacts of season of burning on a large number of ecosystem components, including hydrology, sedimentation, vegetation, soil nutrient dynamics, small and large mammals, birds, and snakes and other reptiles. Our research is concentrated on 12 small, gauged watersheds that support oak savannas or open woodlands. We plan to burn four watersheds in the warm season, burn four in the cool season, and leave four as controls. The watershed and companion studies are currently in the pre-burn calibration phase. However, little is actually known about the oak ecosystems of the southwestern United States and northern Mexico, where most of these oak stands are found. The preliminary results have provided important new information about these lands. This paper describes the studies and initial results obtained during the pre-treatment phase of this project.