FIRE HISTORY OF MIXED-CONIFER FORESTS ON THE NORTH RIM, GRAND-CANYON NATIONAL-PARK, ARIZONA

This study documented fire history using cross-dated tree wedges and m aster chronologies developed from the montane mixed-conifer forest in the Grand Canyon National Park to assess occurrences of natura I fires prior to Euro-American settlement. Fire frequency was determined alon g an elevation gradient from the lower to the upper ecotones of the mi xed-conifer forest and along a temporal gradient from pre-Euro-America n settlement to the present. Mean fire interval generally increased wi th elevation, especially during the pre-Euro-American era, representat ive of the natural fire regime. Pre-Euro-American settlement fire inte rvals (prior to 1870) were longer than the settlement era (1870-1919) intervals, hut shorter than the suppression era (1920-1995) intervals. Seasonality of burn was determined by detecting the position of each fire scar within the annual ring. The majority of fires occurred in la te summer, coinciding with the July-August peak of the Arizona monsoon circulation (and lightning activity) in this region.