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

Abstract

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. [Key words: forest fire, montane forest, mean fire interval, Colorado Front Range.]