STAND-REPLACING FIRE HISTORY AND CLIMATE ANALYSIS IN THE UPPER ELEVATION FORESTS OF THE SOUTHWESTERN UNITED STATES

MARGOLIS, E.Q.¹, SWETNAM, T.W.¹ AND ALLEN, C.D.²

¹University of Arizona, Tucson, AZ, ²U.S. Geological Survey , Los Alamos, NM

We sampled sixteen sites in the upper montane vegetation zone of eight mountain ranges in Arizona, southern Colorado and New Mexico to date historical stand-replacing fires. Stand-replacing fire dates were determined from seral, post-fire quaking aspen stands using multiple lines of tree-ring evidence.  The four lines of evidence included: 1) aspen inner-ring dates, 2) fire-killed conifer bark dates, 3) tree-ring width changes or other morphological indications of injury and 4) fire scars.  Ten unique stand-replacing fire dates were reconstructed between 1842 and 1904.  Multiple sites, separated by hundreds of kilometers, recorded fires during three years (1851, 1861, and 1879).  All stand-replacing fires occurred during drought years, as indicated by negative reconstructed summer PDSI.  The average PDSI value for all fire years (-2.53) indicates moderate to severe drought conditions associated with stand-replacing fire occurrence.  It is possible that an anomalous, multi-year pluvial followed by a multi-year drought in the mid 19^th century was the cause of the documented stand-replacing fires.  Similar oscillations from multi-year wet to multi-year dry conditions in the early 21^st centuries may be partially responsible for recent stand-replacing fires in the upper elevation forests of the region.