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Author(s):
Garrett W. Meigs, Harold S. Zald, John L. Campbell, William S. Keeton, Robert E. Kennedy
Year Published:

Cataloging Information

Hot Topic(s):
Topic(s):
Fire Ecology
Insects & Disease
Fire & Bark Beetles
Fire Effects
Ecological - First Order
Fire Intensity / Burn Severity
Fire Regime
Ecosystem(s):
Subalpine wet spruce-fir forest, Subalpine dry spruce-fir forest, Montane wet mixed-conifer forest, Montane dry mixed-conifer forest

NRFSN number: 14260
Record updated:

Understanding the causes and consequences of rapid environmental change is an essential scientific frontier, particularly given the threat of climate- and land use-induced changes in disturbance regimes. In western North America, recent widespread insect outbreaks and wildfires have sparked acute concerns about potential insect–fire interactions. Although previous research shows that insect activity typically does not increase wildfire likelihood, key uncertainties remain regarding insect effects on wildfire severity (i.e., ecological impact). Recent assessments indicate that outbreak severity and burn severity are not strongly associated, but these studies have been limited to specific insect or fire events. Here, we present a regional census of large wildfire severity following outbreaks of two prevalent bark beetle and defoliator species, mountain pine beetle (Dendroctonus ponderosae) and western spruce budworm (Choristoneura freemani), across the US Pacific Northwest. We first quantify insect effects on burn severity with spatial modeling at the fire event scale and then evaluate how these effects vary across the full population of insect–fire events (n = 81 spanning 1987–2011). In contrast to common assumptions of positive feedbacks, we find that insects generally reduce the severity of subsequent wildfires. Specific effects vary with insect type and timing, but both insects decrease the abundance of live vegetation susceptible to wildfire at multiple time lags. By dampening subsequent burn severity, native insects could buffer rather than exacerbate fire regime changes expected due to land use and climate change. In light of these findings, we recommend a precautionary approach when designing and implementing forest management policies intended to reduce wildfire hazard and increase resilience to global change.

Citation

Meigs, G.W.; Zald, H.S.; Campbell, J.L.; Keeton, W.S.; Kennedy, R.E. 2016. Do insect outbreaks reduce the severity of subsequent forest fires? Environmental Research Letters. 11(4): 1-10.

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