Simulation of Quaking Aspen Potential Fire Behavior in Northern Utah, USA

R Derose,A Leffler

doi:10.3390/f5123241

Abstract

Current understanding of aspen fire ecology in western North America includes the paradoxical characterization that aspen-dominated stands, although often regenerated following fire, are “fire-proof”. We tested this idea by predicting potential fire behavior across a gradient of aspen dominance in northern Utah using the Forest Vegetation Simulator and the Fire and Fuels Extension. The wind speeds necessary for crowning (crown-to-crown fire spread) and torching (surface to crown fire spread) were evaluated to test the hypothesis that predicted fire behavior is influenced by the proportion of aspen in the stand. Results showed a strong effect of species composition on crowning, but only under moderate fire weather, where aspen-dominated stands were unlikely to crown or torch. Although rarely observed in actual fires, conifer-dominated stands were likely to crown but not to torch, an example of “hysteresis” in crown fire behavior. Results support the hypothesis that potential crown fire behavior varies across a gradient of aspen dominance and fire weather, where it was likely under extreme and severe fire weather, and unlikely under moderate and high fire weather. Furthermore, the “fire-proof” nature of aspen stands broke down across the gradient of aspen dominance and fire weather.

Highlights

Quaking aspen (Populus tremuloides Michx.) stands are an important forest type in the intermountain region of the United States [1]
Mean canopy bulk density (CBD) decreased from low to medium aspen dominance, the difference was not significant (p < 0.076) and there was no difference in CBD between medium and high aspen dominance (Figure 2)
Results for the severe weather scenario mirrored the extreme with one important exception, mean crowning index (CI) for medium aspen dominance class fell above the wind speed threshold (Figure 3b)

Summary

Introduction

Quaking aspen (Populus tremuloides Michx.) (hereafter aspen) stands are an important forest type in the intermountain region of the United States [1]. It is assumed that fire was an integral driving process in historic aspen stand dynamics [6]; the role of fire likely varies between seral and stable aspen stands. While seral stands eventually succeed to conifer-dominated stands in the absence of disturbance, stable aspen stands can remain in aspen cover for multiple centuries [7,8]. Failing to understand the seral-stable dichotomy in aspen fire ecology has resulted in this paradoxical characterization of aspen-dominated stands. We use simulation modeling to quantify potential fire behavior across a gradient of seral aspen stand dominance in order to increase understanding of aspen ecology and management

Objectives

Methods

Results

Conclusion