Fire history in the gallery pine-oak forests and adjacent grasslands of the Chiricahua mountains of Arizona

Many authors have speculated about presettlement fire frequencies in semidesert grasslands and the relative importance of fire in the ecology of these systems. Yet, lack of direct evidence (e.g. fire scars) has hampered attempts to reconstruct the role of fire in these areas. Tangible evidence, however, is available from fire-scarred pines in canyon-gallery forests of the Madrean Province that recorded surface fires spreading from adjacent grasslands and savannas. Given the highly dissected topography that typically separates canyons, it is likely that many fires spread primarily into and between canyons from the lower savanna/grasslands, as opposed to originating at higher elevations. Inter-canyon synchrony of fire dates would provide supporting evidence for this hypothesis. Conversely, asynchrony would suggest lack of fi re spread between canyons. If true, fire frequencies recorded in these gallery forests should approximate the minimum fire frequencies sustained in the adjacent grasslands. Fire intervals at the canyon sites range between 3.0 and 4.0 years, while the synchronous intercanyon intervals range between 7.4 and 8.1 years. The range of fire frequency in the semidesert grasslands, given our interpretations, falls approximately between the individual canyon site fire frequency of four years, and the intercanyon fire frequency of eight years.