Paper: Drought, Tree Mortality, and Wildfire in Forests Adapted to Frequent Fire

Here is a fascinating paper by Scott L. Stephens and 8 other authors from BioScience, February 2018 (open access):

Drought, Tree Mortality, and Wildfire in Forests Adapted to Frequent Fire

Stephens is a professor of fire science in the Department of Environmental Science, Policy, and Management at the University of California, Berkeley. He’s director of the university’s Fire Science Laboratory.

The authors suggest that “For long-term adaptation to climate change, we highlight the importance of moving beyond triage of dead and dying trees to making “green” (live) forests more resilient.” The focus on the central and southern Sierra Nevada, but the paper also applies to other areas of the west.

The recent massive tree mortality has many implications for the future of FF forests [forests adapted to frequent fire] and the ecological goods and services they provide to society (recreation, wildlife habitat, water storage, timber, aesthetics, carbon storage, etc.). It could be surmised that because FF forests have seen such dramatic increases in tree density relative to historical conditions, the bark-beetle-caused tree mortality could be helping to produce more resilient forest conditions (we define resilience as the ability of a forest to maintain characteristic structural components, such as large trees, and broad functionality following disturbance and/or chronic stressors). The actual outcome, however, will likely be forests that are very different from their historically resilient condition.

Also interesting: a sidebar entitled “The contrasting impacts of drought: Frequent fire forests in the western United States versus northwest Mexico.” The forests of the Sierra de San Pedro Mártir (SSPM) “have not seen the dramatic tree densification as occurred in California FF forests from fire suppression and logging.”

After the drought ended, a wildfire burned in the northern SSPM in 2003, but only 20% of the trees in this forest died from the combined effects of a severe 4-year drought followed by a wildfire (figure 4; Stephens et al. 2008), demonstrating considerable resilience to drought, tree-killing insects, and wildfire. FF-adapted forests in California and elsewhere once likely possessed similar resilience, which has been lost in the last 100 years.

I agree with the authors’ conclusion:

Many of our FF forests have failed to receive the very management that could increase resilience to disturbances exacerbated by climate change, such as the application of prescribed fire and mechanical restoration treatments (Stephens et al. 2016). Recent tree mortality raises serious questions about our willingness to address the underlying causes. If our society doesn’t like the outcomes from recent fires and extensive drought-induced tree mortality in FF forests, then we collectively need to move beyond the status quo. Working to increase the pace and scale of beneficial fire and mechanical treatments rather than focusing on continued fire suppression would be an important step forward.


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