FIRE HISTORY OF A PONDEROSA PINE DOUGLAS-FIR FOREST IN THE COLORADO FRONT RANGE

Changes in fire regime over time were quantified for a 600 ha area of ponderosa pine (Pinus ponderosa var. scopulorum)/Douglas fir (Pseudotsuga menziesii) forests in Fourmile Canyon, Boulder County, Colorado. Fire dates were determined using four methods: fire scar wedges, increment core samples of fire scars, post-fire cohort age, and growth rates of remnant trees. Fire scar wedges were more reliable than increment cores, although increment cores did yield fire dates within 1-3 years of the true fire date. Age structure, in some stands initiated by fire, yielded approximate (within 5-10 years) fire dates. Of twelve remnant trees measured to quantify changes in growth patterns following fires, eight were released 2-12 years after the fire, while the remaining four showed no release. A mean fire interval of 15.2 years characterized the entire study area. Mean fire intervals were 31.8 years for the pre-settlement era (pre-1859), 8.1 years for the settlement era (1859-1920), and 28.0 years for the suppression era (post-1920). Pre-settlement era fire frequency was probably underestimated due to removal of fire-scarred trees by extensive burning during the late-nineteenth century mining era.