The objective of this study is the documentation and interpretation of an unusual fire history in a southwest ponderosa pine (Pinus ponderosa) community. The fire-scar record from the Chuska Mountains shows an abrupt and persistent reduction in fire frequency at least four decades earlier than in other parts of the southwest. Fires were recorded in 95 years over a period of 594 years. The mean fire interval (MFI) from the date when all sample trees were established, 1660 to 1986, is 3.7 years, comparable to the fire frequency in similar habitats of the southwest. Savage and Swetnam concluded that based on Navajo pastoral history and a subjective assessment of fire frequency, the record can be divided into three periods, an early period when sheep herds were building, a pastoral period when sheep numbers were erratic but usually high, and a modern period when fire suppression was active. The coincidence of fire decline and early sheep herding on the Navajo Reservation, 45-70 years before the same association in the rest of the region, lends strong support to the hypothesis that heavy livestock grazing played a significant role in reducing fire frequency in ponderosa pine forests. The Chuska fire history suggests that major structural alteration of the forest landscape in this century must have been produced by anthropogenic disturbance coupled with a period of highly favorable climate conditions.
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