Green is the New Black: Outcomes of Post-Fire Tree Planting Across the US Interior West

Abstract

Reforestation activities such as tree planting are important management tools to offset carbon emissions and restore forest ecosystem integrity. Severe wildfire activity, a key driver of forest loss, is increasing throughout the western United States (US) and creating an immense backlog of areas needing reforestation. Major financial investments and recent policy changes are expected to accelerate rates of tree planting, yet the broad-scale impact and efficacy of post-fire planting activities remain poorly understood. We quantified the outcomes of recent (1987-2022) post-fire plantings in the US Interior West using remotely sensed estimates of forest cover change and in-situ survival records (69,245 seedlings) spanning 297 unique fire events. Overall, planted areas gained forest cover 25.7% more rapidly than environmentally similar, unplanted sites in the same fires, and planted seedling survival averaged 79.5% (SD = 23.2%) after one growing season. However, the effects of planting were highly variable over time and across environmental gradients. Forest cover gain and planted seedling survival were typically highest in cold, wet areas and when planting was followed by wetter-than-average years. Planting season also shaped outcomes, with late summer or fall plantings performing best on warm, dry sites, and spring plantings performing best in cold, wet areas. Forest cover gain was fastest in planting units that burned at low to moderate severity and had > 20% post-fire forest cover in the surrounding area. Nearly half of all plantings were completed in such areas, where natural regeneration processes are most likely to promote forest recovery even without intervention. Here, we demonstrate that tree planting can enhance post-fire forest recovery rates at broad scales, though its effects are dependent on a range of environmental and operational factors. Our results help inform realistic expectations of planting outcomes, an issue of global relevance as such projects expand to achieve restoration and climate mitigation goals.