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Still standing: Snagfall the first decade after severe bark beetle infestation

Date: July 27, 2020

Post bark beetle outbreak snagfall dynamics create a multiple decade legacy that will persist longer in high-elevation compared to lower-elevation forests.


A fallen tree. The tree bole remains attached to exposed roots and soil mound.
Tip up occurs when the tree bole remains attached to exposed roots and soil mound. Tip ups represented a third of the overstory snagfall and were the most common cause for understory subalpine fir snagfall.

Mountain pine beetle (Dendroctonus ponderosae) attacks began in 2003, peaked by 2006, and killed 78% of overstory lodgepole pine in 133 plots distributed across a range of stand and site conditions on the Fraser Experimental Forest. The attacks have caused one of the most dramatic changes in forest condition in western North American forests in more than a century. The outbreaks affected lodgepole pine forests from Colorado to British Columbia and resulted in tree mortality in excess of 75% in many forests. The severity and extent of mortality prompted efforts to salvage dead timber, reduce canopy fuels, and regenerate new forests.

The persistence and fall rate of snags (standing dead trees) generated during bark beetle outbreaks have consequences for the behavior, effects, and suppression of potential wildfires, hazard tree and timber salvage operations, wildlife habitat, and numerous ecosystem processes. However, post-beetle snagfall dynamics are poorly understood in most forest types.

Chuck Rhoades, a Research Biogeochemist with Rocky Mountain Research Station (RMRS), and his team studied watersheds on the Fraser Experimental Forest in northcentral Colorado in order to understand the dynamics of snagfall across a range of forest conditions typical of high-elevation forests affected by severe bark beetle outbreaks. "We tagged standing live and dead lodgepole pine (Pinus contorta), subalpine fir (Abies lasiocarpa), and Engelmann spruce (Picea engelmannii) following the peak of a recent mountain pine bark beetle outbreak.  We then sampled snagfall 10 and 12 years later. We were surprised at how few of the MPB-killed pines that we tagged at the beginning of the outbreak have actually fallen (< 20% in the first decade since the outbreak)."

This study provides new insights regarding lodgepole pine snag dynamics and refines expectations regarding post-outbreak ecological conditions and commercial opportunities. Based on observations at Fraser Experimental Forest and other high-elevation lodgepole ecosystems, we estimate that one-half of the beetle-killed trees will fall within about 15–20 years after the peak of the outbreak. The findings will help develop projections of post-MPB surface and standing fuels, snow and water yield, harvest possibilities, cavity and coarse wood wildlife habitat, stand regeneration, and Carbon storage.

Key Findings

  • Bark beetle attacks killed 78% of overstory lodgepole pine in 133 plots distributed across a range of stand and site conditions on the Fraser Experimental Forest. Of those snags, only 17% fell in the first decade since the peak of the outbreak.
  • Post bark beetle outbreak snagfall dynamics create a multiple-decade legacy that will persist longer in high-elevation compared to lower-elevation forests.
  • Based on our findings and previous research, we estimate that one-half of the beetle killed lodgepole pine in high-elevation forests such as those at Fraser may fall within 15–20 years of beetle infestation, but that some pine snags are likely to persist for decades longer.

Featured Publications

Rhoades, Charles C. ; Hubbard, Robert M. ; Hood, Paul R. ; Starr, Banning J. ; Tinker, Daniel B. ; Elder, Kelly J. , 2020


Principal Investigators - External: 
Paul R. Hood - University of Wyoming
Daniel B. Tinker - University of Wyoming