Effects of mountain pine beetle on fuels and expected fire behavior in lodgepole pine forests, Colorado, USA - PubMed (original) (raw)
Effects of mountain pine beetle on fuels and expected fire behavior in lodgepole pine forests, Colorado, USA
Tania Schoennagel et al. PLoS One. 2012.
Abstract
In Colorado and southern Wyoming, mountain pine beetle (MPB) has affected over 1.6 million ha of predominantly lodgepole pine forests, raising concerns about effects of MPB-caused mortality on subsequent wildfire risk and behavior. Using empirical data we modeled potential fire behavior across a gradient of wind speeds and moisture scenarios in Green stands compared three stages since MPB attack (Red [1-3 yrs], Grey [4-10 yrs], and Old-MPB [∼30 yrs]). MPB killed 50% of the trees and 70% of the basal area in Red and Grey stages. Across moisture scenarios, canopy fuel moisture was one-third lower in Red and Grey stages compared to the Green stage, making active crown fire possible at lower wind speeds and less extreme moisture conditions. More-open canopies and high loads of large surface fuels due to treefall in Grey and Old-MPB stages significantly increased surface fireline intensities, facilitating active crown fire at lower wind speeds (>30-55 km/hr) across all moisture scenarios. Not accounting for low foliar moistures in Red and Grey stages, and large surface fuels in Grey and Old-MPB stages, underestimates the occurrence of active crown fire. Under extreme burning conditions, minimum wind speeds for active crown fire were 25-35 km/hr lower for Red, Grey and Old-MPB stands compared to Green. However, if transition to crown fire occurs (outside the stand, or within the stand via ladder fuels or wind gusts >65 km/hr), active crown fire would be sustained at similar wind speeds, suggesting observed fire behavior may not be qualitatively different among MPB stages under extreme burning conditions. Overall, the risk (probability) of active crown fire appears elevated in MPB-affected stands, but the predominant fire hazard (crown fire) is similar across MPB stages and is characteristic of lodgepole pine forests where extremely dry, gusty weather conditions are key factors in determining fire behavior.
Conflict of interest statement
Competing Interests: The authors have declared that no competing interests exist.
Figures
Figure 1. Study area map.
Map of the study area in west-central Colorado, showing 40 sites sampled in four stages of time-since MPB attack.
Figure 2. Idealized progression of four stages of MPB attack.
Graphic characterizing an idealized sequence of Green unattacked stands, compared to the three stages subsequent to MPB attack. In this chronosequence, 40% of the trees were killed by MPB in the Red stand. In the Grey stand needles fall from the MPB-attacked trees with some attacked trees fallen, opening up the canopy and allowing for higher wind speeds. In the Old-MPB stand most of the MPB-attacked trees have fallen to the ground contributing to high 1000-hr surface fuel load and slightly diminished wind speeds compared to the Grey stand.
Figure 3. Dead surface fuels in four stages of MPB attack.
Comparison of average dead surface fuel loads among four stages of MPB attack (Green, Red, Grey, Old-MPB; see text for description of MPB stages), with bars representing standard errors. P-values from ANOVAs in upper right of each graph, with letters indicating significant difference based on Tukey's pairwise comparison of means.
Figure 4. Canopy fuels in four stages of MPB attack.
Total and proportion of total basal area of green, red/fading, and grey trees among four stages of MPB attack (Green, Red, Grey, Old-MPB; see text for description of MPB stages), and comparison of average canopy fuel loads among the four MPB stages of MPB attack with bars representing standard errors. P-values from ANOVAs in upper right of each graph, with letters indicating significant difference based on Tukey's pairwise comparison of means.
Figure 5. Surface and crown fire outputs modeled for four stages of MPB attack.
Comparison of predicted fire behavior: A) Surface Fireline Intensity, B) Critical Surface Intensity, C) Transition Ratio, D) Active Ratio, E) Crown Fireline Intensity for Green (light green line), Red (red line), Grey (grey line), and Old-MPB (dark green line) stages under Extreme Drought (XD), Very Dry (VD) and Moderately Dry (D) moisture scenarios (see text for description of MPB stages and moisture scenarios).
References
- Westerling AL, Hidalgo HG, Cayan DR, Swetnam TW. Warming and earlier spring increase western U.S. forest wildfire activity. Science. 2006;313:940–943. -PubMed
- Raffa KF, Aukema BH, Bentz BB, Carroll AL, Hicke JA, et al. Cross-scale drivers of natural disturbance prone to anthropogenic amplification: the dynamics of bark beetle eruptions. Bioscience. 2008;58
- Safranyik L, Shrimpton DM, Whitney HS. Management of lodgepole pine to reduce losses from the mountain pine beetle. Canadian Forest Service, Technical Report. 1974;1:24.
- Campbell E, Alfaro RI, Hawkes BC. Spatial distribution of mountain pine beetle outbreaks in relation to climate and stand characteristics: a dendroecological analysis. Journal of Integrative Plant Biology. 2007;49:168–178.
- Safranyik L. Mountain pine beetle epidemiology in lodgepole pine. In: Shore TL, Brooks JE, Stone JE, editors. Mountain Pine Beetle Symposium: Challenges and Solutions Info Report BC X 399. Victoria, BC: Natural Resources Canada, Canadian Forest Service, Pacific Forestry Centre; 2004. pp. 33–40.
Publication types
MeSH terms
LinkOut - more resources
Full Text Sources