Drivers of planted tree seedling performance
Engelmann spruce seedlings were planted after the 2020 Cameron Peak Fire on the Roosevelt National Forest, Colorado.
In forests across the western United States, large, severe wildfires have created millions of acres of treeless patches that are unlikely to reforest naturally due to a lack of seed sources and a warming environment. Tree planting is increasing in pace and scale to address the large reforestation need. However, planting trees in and of itself does not address the reforestation need; the planted seedlings must also survive and thrive.
Two recently published research studies uncovered some of the key factors that drive tree seedling performance in sites planted after wildfire. These studies leveraged volumes of USDA Forest Service tree planting records obtained from managers throughout the Agency. One study focused on factors affecting the first-year survival of ponderosa pine and Douglas-fir seedlings planted after Colorado wildfires. The other study focused on factors affecting the first-year survival of all conifer seedlings planted after wildfires across 10 interior western states, as well as factors affecting remotely sensed estimates of longer-term forest growth. Together, the two studies found that average planting site climate, post-planting weather, and seed lot sources were among the factors that had particularly meaningful impacts on planted tree seedling performance. Specifically, sites with cooler and wetter average climates and sites planted in wetter-than-average years tended to have elevated seedling survival and/or forest growth. Also, in Colorado where seed lot transfer was examined, sites planted with seedlings grown from lower elevation seed lots had higher seedling survival.
The findings of the two studies not only inform expectations of planting outcomes, but also suggest that there may be a variety of management strategies that could be employed to bolster the success of reforestation programs. For example, managers could consider selecting cooler and wetter planting sites, and selecting seed lots collected from sites that are lower in elevation than the planting site. Managers could also consider spreading planting out over time to hedge their bets for favorable post-planting weather conditions.