Jake Barker ^1,2* James Voorhis ³ Sinead Crotty ¹

• ¹ Carbon Containment Lab, New Haven, United States
• ² School of the Environment, Yale University, New Haven, Connecticut, United States
• ³ Kodama Systems, Sonora, United States

Pile burning of thinned residues is a critical tool to dispose of fuels and to reduce wildfire risk in overstocked, fire-prone forests globally. Cost estimates of pile burning are limited. In the Western United States, where fuel reduction and pile burning are key strategies to mitigate risk of severe wildfire, previous reports estimate that the average cost of pile burning after machine treatment is $457 ac-1 ($1,129 ha-1). There is, however, limited information on the costs of hand thinning and pile burning. In response, this study quantified the costs of cutting and yarding, piling, and burning residues via two pathways: the USDA Forest Service Activity Tracking System (FACTS) database, and interviews with 11 USFS fire management professionals from California, Oregon, and Washington. Interviews were reviewed to identify cost drivers, implementation constraints, and future opportunities. The average costs of piling and burning machine piles as determined from the interviews were $735±$464 ac-1 ($1,817±$1,146 ha-1; all mean±SD), 29% higher than reported in the FACTS database and 47% higher than previous reports. The average costs of cutting, piling, and burning hand piles as determined from the interviews were $1,570±$762 ac-1 ($3,880±$1,884 ha-1), 74% higher than reported in the FACTS database. Interview participants reported proximity to roads and terrain as key cost drivers, and described common practices, challenges, and constraints. Geospatial analyses supported interviewee-identified cost drivers, district road density (a proxy for accessibility) and district maximum elevation (a proxy for terrain). Simulations of direct emissions from pile burning on National Forests included in this study indicated annual emissions of 11,322 MT of particulate matter (PM), 8,029MT of PM10, and 6,993MT of PM2.5 across the study area. In addition, pile burning on these National Forests annually emits >1.7 million MT CO2, 61,515MT of carbon monoxide, 3,823MT of methane, and 3,211MT of non-methane hydrocarbons. Given the economic, human health, and climate implications of current pile burning practice, removing residues as feedstocks for carbon-negative utilizations is recommended as a near-term priority. Policy mechanisms, like feedstock production, transport, or offtake subsidies of similar magnitude to such avoided costs, could efficiently incentivize residue removal and support such climate-positive utilizations.