Category: Theses and Dissertations
Title: Pre-fire treatment effects and post-fire forest dynamics on the Rodeo-Chediski burn area, Arizona
Author: * Strom, B.A.
Subject: Rodeo-Chediski, Fire effects, Tree thinning, Treatment prescription, Prescribed burns
Abstract: The 2002 Rodeo-Chediski fire was the largest wildfire in Arizona history at 189,000 ha (468,000 acres), and exhibited some of the most extreme fire behavior ever seen in the Southwest. Pre-fire fuel reduction treatments of thinning, timber harvesting, and prescribed burning on the White Mountain Apache Tribal lands (WMAT) and thinning on the Apache-Sitgreaves National Forest (A-S) set the stage for a test of the upper boundary of effectiveness of fuel reduction treatments at decreasing burn severity. On the WMAT, we sampled 90 six-hectare study sites two years after the fire, representing 30(percent) of the entire burn area on White Mountain Apache Tribe lands, or 34,000 hectares, and comprising a matrix of three burn severities (low, moderate, or high) and three treatments (cutting and prescribed burning, prescribed burning only, or no treatment). Prescribed burning without cutting was associated with reduced burn severity, but the combination of cutting and prescribed burning had the greatest ameliorative effect. Increasing degree of treatment was associated with an increase in the number of live trees and a decrease in the extremity of fire behavior as indicated by crown base height and bole char height. Ponderosa pine regeneration was very low in untreated areas, with no ponderosa regeneration in high severity untreated areas; over half the study area had no ponderosa regeneration, and 16(percent) of the study area had no ponderosa regeneration and no surviving ponderosa trees. On the A-S, we sampled seven pairs of thinned/unthinned study sites two years after the fire. Thinned areas had more live trees, higher survival, and less extreme fire behavior as indicated by crown base height and bole char height. Ponderosa pine regeneration was patchily distributed over the study sites, and lower in untreated areas. Differences between thinned and untreated areas persisted for several decades after the fire in stand structure characteristics and for at least 100 years in species dominance when modeled using the Forest Vegetation Simulator. Our findings strongly indicated that thinning, timber harvesting, and prescribed burning were associated with reduced burn severity even in an extraordinarily intense fire, provided that the treatments occurred within the decade before the fire. Future forest development on the burn area will most likely take one of two trajectories: recovery to a ponderosa pine/Gambel oak forest or a shift to an alternative stable state such as an oak/manzanita shrubfield, with untreated and high-severity areas more apt to undergo a shift to a shrubfield state.
Source: Masters Thesis
Publisher: NAU School of Forestry, http://www.for.nau.edu