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Individual Highlight

Mountain pine beetle effects on fire behavior

The telltale red needles of a mountain pine beetle attacked tree contain 10 times less water than those of a similar healthy green tree, and these low moisture contents cause the red foliage to ignite quickly and easily. This red-needle lodgepole pine tree was ignited from a single point source on its lowest branches; the entire tree was quickly consumed in flames. Forest ServiceSnapshot : Studies are shining light on how pine beetles affect wildfire.

Principal Investigators(s) :
Jolly, Matt 
Research Location : Rocky Mountain West
Research Station : Rocky Mountain Research Station (RMRS)
Year : 2011
Highlight ID : 395


Single-age stand conditions and warm climate patterns have led to a large-scale outbreak of mountain pine beetle (Dendroctonus ponderosae) throughout the Rocky Mountain West. Once infested, trees die, and their needles turn red. Scientists have debated the effect these beetle-killed trees might have on fire behavior, but little is yet known. For example, beetle-killed trees lose their needles over time, and once all the needles have dropped, crown fire danger largely disappears. But researchers currently do not know how long that process takes after infestation and thus how long the trees remain at risk for crown fire initiation and spread. Moreover, these red-needled trees have lower foliar moisture contents than un-attacked trees - leading to increased crown fire potential.

Initial findings on the time it takes for trees to lose their needles after a beetle attack indicate that some needles stay on trees for up to four years. Expanding the scope of the study, investigators are currently working with managers to quantify crown fuel changes over time. This will help managers identify how long beetle infested stands remain a crown fire hazard.

Researchers also investigated the moisture content of beetle-killed foliage prior to needle loss. They found that red needles have ten times less moisture than healthy foliage, and that red needles ignite four times faster than green needles. Consequently, forests with a large number of beetle-killed trees are at a significantly higher risk of surface fires igniting the crown. Such low fuel moistures could also result in beetle-killed trees spotting ahead of the fire.

This research provides insights into the potential use of fuel treatments in beetle-killed forests, increases firefighter awareness of dangerous situations, and assists managers in identifying areas at high risk for ignition and extreme fire behavior. The moisture-study research has not yet been published, but preliminary results have been presented at two fire management conferences and in an Associated Press article. For more information, see; new study shows beetle killed trees ignite faster [July 1, 2011], or contact Matt Jolly at or Russ Parsons at

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