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Individual Highlight

Forests transformed by fire exclusion help us understand climate resilience

Photo of This large Douglas-fir died in 2012 and is surrounded by many smaller Douglas-fir, white fir, and Southwestern white pine that recruited during fire exclusion. Stand density in mesic mixed conifer forests increased during fire exclusion.
This large Douglas-fir died in 2012 and is surrounded by many smaller Douglas-fir, white fir, and Southwestern white pine that recruited during fire exclusion. Stand density in mesic mixed conifer forests increased during fire exclusion. Snapshot : Fire exclusion can cause rapid changes to forest species composition and structure. These changes can make a forest more susceptible to drought, insects, and extreme fire. By restoring fire as an ecosystem process to some forests, we may be able to reduce their vulnerability to these conditions. 

Principal Investigators(s) :
Lynch, Ann M. O'Connor, Christopher D.
Research Location : Pinaleño Mountains of southeast Arizona?
Research Station : Rocky Mountain Research Station (RMRS)
Year : 2018
Highlight ID : 1512

Summary

Background Frequent surface fires in western forests fostered resistance to drought, insect outbreaks, and extreme fire-weather conditions. Fire exclusion in the 20th century resulted in abrupt shifts in tree abundance and species composition. For example, relatively sparse ponderosa pine-Douglas fir forests were transformed into high-density forests that include fewer ponderosa pine but orders of magnitude more Douglas-fir and a massive influx of white fir. This altered state maxes out the site capacity and is susceptible to high-intensity fire and insect outbreaks. Many forests are already at their biological limits for productivity and climate projections suggest a warmer, drier future; making them vulnerable. Research Dendrochronology (tree-ring) studies of pre-fire exclusion forest species composition and structure and of changes over the past century help identify those forests most likely to benefit from restoring fire as an ecosystem process. These studies can also indicate where restoration is unlikely to influence vulnerability to future disturbances. Prioritizing management actions based on the ability to promote resilience in these altered forests can help avert forest die off from drought, insect outbreaks, and unprecedented extreme fire behavior.  Future studies could look at management actions that can be taken to mitigate climate impacts in forests that have always been constrained by site productivity. Key Findings -Fire exclusion can and has produced rapid changes to forest species composition and structure. -Restoring disturbance-adapted species composition and structure to forests most changed by fire exclusion may buffer them against future drought, fire, and insect outbreaks. -Forests that have not experienced much change as a result of fire exclusion have fewer management options to promote adaptation to future disturbances.

Forest Service Partners

External Partners

  • Craig P. Wilcox, Lincoln National Forest
  • Donald A. Falk, University of Arizona School of Natural Resources and the Environment Thomas W. Swetnam, University of Arizona Laboratory of Tree-Ring Research.