Research Spotlight: New Models Demonstrate the Role of Climate and Seed Production in Post-fire Forest Regeneration

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Large, severe fires are becoming more frequent in the Southwest. These fires can be extreme enough to kill the vast majority of trees over areas covering thousands of acres. Forest recovery may be limited because seeds must travel long distances to recolonize these burned areas. In addition, the seeds that do arrive may encounter unfavorably hot, dry conditions. Managers can respond by planting tree seeds and seedlings, and responses could be more effective with knowledge of when and where interventions are likely needed most.  

To meet this need, scientists from the USGS, in collaboration with the US Forest Service, UC Davis, and CalFire, developed forecast maps of likely areas of natural forest regeneration following fire. The forecast maps were derived from models of post-fire seedling establishment in California and use satellite imagery, forest structure, and climate to make predictions. The models allow users to adjust post-fire climate and seed production to see how forests are likely to regenerate under different scenarios. These forecast maps can help identify locations at high-risk for tree seedling failures that may be targeted for post-fire management – seeding or planting. 

The models were developed using field observations collected 5 years following fire in 1,234 study plots from 19 wildfires that burned from 2004–2012 in low elevation forests of California. Seed production data were estimated from more than 200 seed fall traps monitored over 18 years in permanent forest plots in the Sierra Nevada.

The models and forecast maps demonstrated how different climate scenarios, seed production levels, and tree species may result in different forest regeneration outcomes. Under expected future climates the models suggest that forest regeneration following large, high-severity will be less successful than it has been in the past, particularly in low-elevation forests that already experience frequent drought stress. The results also indicated that pines (e.g. ponderosa pine and sugar pine) and firs (e.g. white fir) respond differently to fluctuations in climate and seed availability.

The model results indicated that over 42% of the area of the 19 fires that burned between 2004-2012 were estimated to have had no natural conifer regeneration. Under a drier end-century (2070–2099) scenario, the models predicted that the percentage of burned area with no conifer recruitment could reach 49.4% (45.8% and 51.9% under high and low seed production scenarios). Conversely, under a wetter end-century scenario the expected percentage of burned area with no conifer recruitment could decrease to 31.3% (28.6% and 33.2% under high and low seed production scenarios). Projected declines in conifer regeneration under drought scenarios were especially pronounced in low-to-moderate-elevation coniferous forests.

These projected outcomes emphasize the need for postfire forest management (e.g. seeding or planting) if the focus is to maintain coniferous forests following large, high-severity fires. By providing managers with a range of postfire regeneration scenarios the models and forecast maps support improved postfire management planning.

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This research spotlight refers to the following publication:

Stewart, J.A.E., van Mantgem, P.J, Young, D.J.N., Shive, K.L., Preisler, H.K., Das, A.J., Stephenson, N.L., Keeley, J.E., Safford, H.D., Wright, M.C., Welch, K.R., Thorne, J.H. 2020. Influence of variable postfire climate and seed production on postfire conifer regeneration. Ecological Applications. https://doi.org/10.1002/eap.2280

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Read a press release about this study from UC Davis here.