The rugged mountains of the Sierra Madre Occidental, in north-central Mexico, support a mosaic of diverse ecosystems. Of these, the high-elevation, temperate pine-oak forests are ecologically significant for their extensiveness and biodiversity. They cover nearly half the land area in the states of Durango and Chihuahua (42%), and comprise a similar percentage of the temperate coniferous forest in Mexico as a whole (45%; World Forest Institute 1994; SARH 1994). These forests are globally significant centers of vascular plant diversity, and of endemism in both plant and animal species (Bye 1993; Manuel-Toledo and Jesús-Ordóñez 1993). For example, they have the highest number of pine and oak species in the world (Rzedowski 1991) and contain many of Mexico's Pinus, Quercus, and Arbutus species (33%, 30%, and 66%, respectively; Bye 1995). Surface fires were historically frequent in these forests, and variations in their frequency may have contributed to the maintenance of this biodiversity (Dieterich 1983; Fulé and Covington 1997, 1999; Park 2001). However, we know little about the drivers of variation in historical fire regimes.