An Ecological Perspective on Living with Fire in Ponderosa Pine Forests of Oregon and Washington: Resistance, Gone but not Forgotten
Merschel, A., Peter A Beedlow, D. Shaw, D. Woodruff, E Henry Lee, S. Cline, Randy L Comeleo, K. Hagmann, AND M. Reilly. An Ecological Perspective on Living with Fire in Ponderosa Pine Forests of Oregon and Washington: Resistance, Gone but not Forgotten. Trees, Forests and People. Elsevier B.V., Amsterdam, Netherlands, 4:100074, (2021). https://doi.org/10.1016/j.tfp.2021.100074
In the most recent decades, wildland fires (WLF) have become more severe in western forests resulting in greater impacts to society and ecosystems and dramatic increases in firefighting costs. Forests throughout the range of ponderosa pine (Pinus ponderosa Douglas ex P. Lawson & C. Lawson) in Oregon and Washington are most at risk by the interaction of a changing forest structure, a warming and drying climate, and an expanding Wildland-Urban Interface (WUI). Understanding the ecology of ponderosa pine forests and how restoring the ecosystem to withstand disturbance while maintaining its structure and ecological function is critical to learn how to live with fire. WED scientists in collaboration with the U.S. Forest Service reviewed the ecological setting and changes to forest structure and composition of the ponderosa pine ecosystem to illustrate how the historical disturbance regime and forest condition have been dramatically altered by 20th-century land management. Historically, ponderosa pine forests had a structural backbone of large old-growth ponderosa pine trees which persisted and were maintained by frequent low-severity surface fires prior to 1880. A key finding is 20th century land management practices of fire suppression, logging, and grazing have resulted in a shift from disturbance-resistant ponderosa pine dominated forest structures to denser, more homogeneous forests composed of less resistant tree species. A second key finding is the recent prolonged drought for the period 1980-2018 in the Pacific Northwest was unprecedented in the past 700 years based on dendrochronological and instrumental records. Third, more people are choosing to live in fire-prone ponderosa pine forests as indicated by a 41% increase in new houses in the WUI from 1990 to 2010. The densification and mesophication of PNW dry ecosystems in the 20th century, followed by an increase in frequency and severity of wildland fires, drought, and biological disturbance agents (BDAs), and a rapid expansion of the WUI pose serious ecological and socioeconomic challenges. We expect a continued increase in large and uncharacteristically severe WLFs along with increased tree mortality from drought and BDAs under a warming climate in the 21st century. The increasing trend in WLF events will have lasting impacts on ecosystem services, human health and property. Our work is important for filling in the gaps of knowledge in understanding the complex interactions of WLF, climate, biotic disturbance agents and humans on dry ecosystems in the PNW under climate change scenarios.
Wildland fires (WLF) have become more frequent, larger, and severe with greater impacts to society and ecosystems and dramatic increases in firefighting costs. Forests throughout the range of ponderosa pine in Oregon and Washington are jeopardized by the interaction of anomalously dense forest structure, a warming and drying climate, and an expanding human population. These forests evolved with frequent interacting disturbances including low-severity surface fires, droughts, and biological disturbance agents (BDAs). Chronic low-severity disturbances were, and still are, critical to maintaining disturbance resistance, the property of an ecosystem to withstand disturbance while maintaining its structure and ecological function. Restoration of that historical resistance offers multiple social and ecological benefits. Moving forward, we need a shared understanding of the ecology of ponderosa pine forests to appreciate how restoring resistance can reduce the impacts of disturbances. Given contemporary forest conditions, a warming climate, and growing human populations, we predict continued elevation of tree mortality from drought, BDAs, and the large high-severity WLFs that threaten lives and property as well as ecosystem functions and services. We recommend more comprehensive planning to promote greater use of prescribed fire and management of reported fires for ecological benefits, plus increased responsibility and preparedness of local agencies, communities and individual homeowners for WLF and smoke events. Ultimately, by more effectively preparing for fire in the wildland urban interface, and by increasing the resistance of ponderosa pine forests, we can greatly enhance our ability to live with fire and other disturbances.