Rings and scars reveal fire’s role in healthy forests

Large western larch survived a fire
Living biological legacies. Large western larch survived a fire that led to development of this dense lodgepole pine stand. Note the development of smaller subalpine fir beneath the pines. Photo: Robert Van Pelt.

Yes, fire is destructive but in forests and other landscapes it also can be part of the natural process of renewal that promotes biological diversity and healthy ecosystems. In the latest issue of Forest Stewardship Notes, DNR Forest Health Specialist Melissa Fischer points out that some plant species have not only adapted to fire but rely on it.

One example of this adaptation is lodgepole pine (Pinus contorta var. latifolia), a familiar tree of inland Washington but less common in lowland rain forests of state’s westside. Lodgepole pine cones are serotinous — seeds are released in response to fire or other environmental triggers. These trees retain their seed for long periods until a fire burns through the stand, causing them to releasing thousands of seeds as the resin seal enclosing the cones melts. This feature allows lodgepole pine to reproduce prolifically after a fire.

Burn scars in cross section of a giant sequoia
Burn scars (white arrows) in the cross section of a giant sequoia. The numbers represent the year each fire occurred. Photo: Tom Swetnam.

Fischer also notes that there are several fire regimes — repeated patterns — across the Pacific Northwest, from frequent surface fires of low intensity to infrequent high severity fires. The most common of these are:

  • High severity fire regimes, which generally occur in cool, wet environments at higher elevations where subalpine forests are found. These forests typically consist of subalpine fir, lodgepole pine, Engelmann spruce, and whitebark pine. Fire intervals can range greatly (100 to 300 years), and when large fires do occur they will typically destroy entire stands.
  • Moderate severity fire regimes, which tend to occur at mid-elevation zones where dry Douglas-fir forests remain. Other tree species in these zones include grand fir, subalpine fir, lodgepole pine, western red cedar, western hemlock and western larch. Moderate severity fires occur at intervals of 25 to 100 years and leave a mosaic of lightly burnt to severely burned areas.
  • Low severity fire regimes, which are characterized by fires that occur at frequent intervals (from 1 to 25 years apart). Because fuels like grasses have a limited time to accumulate in these areas, returning fires tend to be of low intensity. Ponderosa pine forests are an example of the low severity fire regime.

Unfortunately, those historic fire patterns have been disrupted by human interventions such as excluding all fire, replanting with different tree species after timber harvests, altering land uses and other actions. Add to that the projections of climate change that indicate higher average temperatures and earlier spring snow melt — all likely to increase the frequency and extent of wildfires. These projections suggest that to sustain forest landscapes forest managers must change their practices to help forests once again become adapted to wildfire.

Accumulated fuels in dry forests need to be reduced so that when fire occurs, rather than becoming a conflagration that destroys the entire stand, it is more likely to burn along the surface at low to moderate intensity. While such fires may consume many small trees, they also restore the forest’s resilience to future drought, insect and disease problems and wildfire.

Landowners can help by using combinations of thinning, slash treatments and prescribed burning to restore their forests to historic fire patterns. The Washington State Department of Natural Resources website has information about cost-share opportunities to help private landowners in eastern Washington with these tasks. Other efforts, like the federally funded Forest Stewardship Program administered in Washington state by DNR, provide advice and assistance to help small landowners manage their lands.

Most fires are human caused, often due to neglected campfires, sparks, irresponsibly discarded cigarettes and more often than not: debris burning. Significantly fewer fires may be started by taking greater caution. Check online for the current fire danger and outdoor burning restrictions in your county.

This post  is adapted from an article by Melissa Fischer, DNR Northeast Region forest health specialist regional extension specialist,  first appeared in Forest Stewardship Notes, a free quarterly e-newsletter published by DNR and the WSU Extension Forestry program.

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