What did we learn from the 2018 fires in North-central Washington?

What did we learn from the 2018 fires in North-central Washington?

Conservation Northwest / Mar 18, 2019 / Wildfire

By George Wooten and Dave Werntz, Forest Field Program

Conservation Northwest tracks the impacts of large wildfires on habitat, particularly old growth. Recently, there have been valid concerns because the three largest fires of 2018 burned into important habitat for spotted owls, Canada lynx and other wildlife dependent on large, old trees and intact canopies. When fire results in killing all the trees in a stand, it is termed “severe”, and then our work sometimes requires pointing agencies toward better recovery options. But we found that the 2018 fires were well within their historical range of severity.

In 2018, the Crescent Mountain and McLeod wildfires burned 77,457 acres, with about half at middle elevations in mixed pine and Douglas fir, and about half at higher elevations.

40 percent of the Crescent Mountain Fire burned in mixed conifer forests outside of designated Wilderness Areas, while 55 percent burned in Wilderness at higher elevations where fire regimes are historically more severe.  Of the mid-montane forests, over 60 percent of the fire was in patches with better than half survival of the trees. The severity of the McLeod Fire was similar, with 55 percent of the fire having low severity with better than half survival and lying outside of Wilderness.

This amount of low severity fire is right in the middle of what would be expected based on historic fire Wbehavior (see map below). Historically, mid-montane forests in Eastern Washington burned in a patchy pattern with a range of 20 percent to 70 percent severe fire with high tree mortality. It is important not to confuse the mid-montane fire regime with that of low elevation ponderosa pine forests that historically burned with low severity.

This tells us that the 2018 Okanogan area fire severity was normal—not overly severe—and well within the historic fire regime for mid-montane forests. Both fires were good for the ecosystem in providing a diversity of wildlife habitats and forest ages that is sustainable over the next fire return interval.

Washington fire perimeters form 1984-2017 (this does not show the most recent large fires that includes Crescent Mountain, McLeod and Diamond (2017).
Map of Crescent Mountain Fire Severity given loss of “basal area”, a common way to describe stand density. In forest management, basal area usually refers to merchantable timber and is given on a per acre basis.
Crescent Mountain fire pattern in October, 2018, at the end of the Twisp River Road. Note higher severity patches in the background mountain.