'Mind the Gap' -Reforestation needs vs. reforestation capacity in the western United States Provisionally Accepted

Solomon Dobrowski^1* Matthew M. Aghai² Ariel Chichilnisky du Lac³ Rebecca Downer² Joseph Fargione⁴ Diane L. Haase⁵ Tyler Hoecker⁶ Olga A. Kildisheva⁴ Alix Murdoch⁴ Shaw Newman² Malcolm North⁷ Phil Saksa⁸ Matt Sjoholm⁸ Tom Baribault² Michele S. Buonanduci⁹ Marin E. Chambers¹⁰ Lisa Gonzales-Kramer² Brian J. Harvey⁹ Matthew D. Hurteau¹¹ Jonathan Loevner² Hugh D. Safford¹² Joshua Sloan¹³

• ¹University of Montana, United States
• ²Mast Reforestation, United States
• ³Oceans Department, Doerr School of Sustainability, Stanford University, United States
• ⁴The Nature Conservancy, United States
• ⁵Forest Service, United States Department of Agriculture, United States
• ⁶Independent researcher, United States
• ⁷Department of Plant Sciences, College of Agricultural and Environmental Sciences, University of California, Davis, United States
• ⁸Blue Forest Conservation, United States
• ⁹School of Environmental and Forest Sciences, College of the Environment, University of Washington, United States
• ¹⁰Colorado Forest Restoration Institute, Colorado State University, United States
• ¹¹Department of Biology, University of New Mexico, United States
• ¹²Department of Environmental Science and Policy, College of Agricultural and Environmental Sciences, University of California, Davis, United States
• ¹³New Mexico Highlands University, United States

Tree establishment following severe or stand-replacing disturbance is critical for achieving U.S. climate change mitigation goals and for maintaining the co-benefits of intact forest ecosystems. In many contexts, natural post-fire tree regeneration is sufficient to maintain forest cover and associated ecosystem services, but increasingly the pattern and scale of disturbance exceeds ecological thresholds and active reforestation may be warranted. Our capacity to plant trees, however, is not keeping pace with reforestation needs. This shortfall is uniquely apparent in the western U.S., where wildfire size and severity have increased in recent decades and long-term divestment in the reforestation supply chain has limited our ability to respond to existing needs. Here we present an analysis of key facets of both the supply and demand side of reforestation in the western U.S. and address six questions: 1) What is the current backlog of potential reforestation needs driven by highseverity wildfire?; 2) How will increasing wildfire activity through the end of the century affect potential reforestation needs?; 3) What is our capacity to meet current and future reforestation needs?; 4) How can we scale the reforestation supply chain to meet current and future demands?; 5) What approaches to reforestation can promote forest resilience to climate change and wildfire?; and 6) Where are opportunities emerging from recent policy initiatives, innovative public-private partnerships, and natural capital markets for scaling reforestation?Between 1984 and 2000, annual tree planting capacity met post-fire needs but cumulatively over the last two decades (2000 to 2021) it has fallen short of fire-driven needs by an estimated 1.5 million ha (ca. 3.8 million ac). We anticipate this gap will increase 2 to 3 fold by 2050. Scaling up reforestation efforts to close this gap will require increased investment across all facets of the reforestation supply chain, public-private partnerships, and novel approaches to reforestation that increase the resilience of western forests to drought and wildfire. We highlight emerging opportunities from recent policy initiatives and conservation finance for expanding reforestation efforts.