Ponderosa pines are the most widely distributed pine species in North America. To lower wildfire risk in ponderosa pine forests, land managers in the region often thin small trees, clear out debris, and use controlled burns to reduce the forest’s understory. While these methods are effective for reducing wildfire risk, their impact on natural tree regrowth is less clear.  

A team of scientists, funded in part by the Southwest CASC, examined 77 forest sites in the Southwestern U.S., each with different histories of forest management – from thinning and prescribed burns to no interventions at all. Working closely with local forest managers, the scientists combined field observations, meteorological estimates, and water balance modeling to evaluate how these management strategies and climate conditions shaped ponderosa pine regeneration in these forests over the past 20 years.  

Their study found that, despite increasingly unfavorable climatic conditions, managed forests generally had stronger natural regeneration of ponderosa pine, usually occurring 5-10 years after treatment due to a reduction in competition between plant species, a changing forest structure and overall improved environmental conditions. However, not all outcomes were ideal. In 21% of the managed sites, trees regenerated too well, meaning they regenerated to excessively high densities that could increase future fire risk and may require follow-up treatments. Regeneration success was also influenced by temperature and soil moisture, the density of competing tree species, the amount of understory litter and debris cover, and cone production by mature trees.  

The takeaway: forest management strategies like thinning and burning can support both wildfire prevention and forest regeneration. However, continued monitoring and modifications are needed to support effective management application.