The influence of collaborative fuel reduction treatments on cross-boundary wildfires east of the Cascade Range in Washington State, USA

Abstract

A warming climate and anthropogenic alterations in fuels has resulted in an increase in the average area burned during wildfire events in the Western US. This has led to an increase of cross-boundary wildfires, fires that burn across multiple landowners. As a result, the past decade has seen several programs implemented to support and fund collaborative restoration across landscapes. When trying to create climate and fire-resilient landscapes, forest managers and collaborative groups need to understand how wildfires move across multi-ownership landscapes and the influence collaborative management may have on fire behavior. We simulated a series of jurisdictional boundary fuel reduction treatments of various intensities and widths across a landscape east of the Cascade Range near Cle Elum, Washington. Our study area encompassed a historically moist-mixed conifer, mixed-severity fire regime that is highlighted as an area of concern for potentially large and destructive wildfires. Two wildfire models (Randig and FARSITE) were used to quantify the transmission factor between landowners and the influence of fuel reduction treatments on burn probability, fire size, fire spread, flame length and fireline intensity. Collaborative treatments significantly altered predicted fire size and spread compared to individual landowner treatments but were also influenced by the presence of legislative management restrictions. A clearcut with prescribed burn reduced predicted fireline intensity and flame length to the greatest extent and under extreme weather conditions reduced average flame length to heights at which active suppression could occur. Fuel reduction treatments with canopy cover reductions ranging from 30% - 60% resulted in similar decreases of fire severity metrics relative to each other, supporting findings that intensive management may not result in larger decreases in fire metrics compared to moderate management. Fuel treatments were modeled for widths ranging from 50 meters to 500 meters with reduction in fire metrics stabilizing between 300 meters and 400 meters. Proportional to ignitions, the greatest amount of outgoing fire was found for the Bureau of Land Management and Fish and Wildlife while incoming and self-burning fire tended to be concentrated on the US Forest Service and Teanaway Community Forest. However, dominant wind direction was found to influence fire exchange between the US Forest Service and Teanaway Community Forest with results varying substantially between the different fuel reduction treatments and treatment widths.