Making trees in fire-maintained forest less susceptible to drought

Recently published research from a Ph.D. graduate from the biology department at The University of New Mexico finds that frequent fires have the potential to reduce tree water stress. Kevin Willson, a postdoctoral researcher with the Forest Service, found that fire-maintained forests had fewer trees with increasingly less water stress than fire-excluded forests.

"Restoring frequent fire to these forests reduces forest density and competition for water, increasing the amount of water available per tree, which can improve tree response to drought," said Willson. "As forests have become more flammable and prone to drought effects, determining how frequent fires affect tree response to drought is necessary to forecast how forests will function in response to future disturbances."

To assess tree response to drought following frequent-fire, Willson and his team compared tree growth and water stress before, during, and after two multi-year droughts (1996-2018) in fire maintained forests of the Gila Wilderness, where fires have been allowed to burn since 1975, and nearby areas that have not experienced a fire since at least 1909.

They found that frequent fires do not inhibit tree growth during drought but reduce forest density, which increases water availability for the remaining trees. Therefore, the reintroduction of frequent, low-severity fire regimes has the potential to moderate some effects of droughts on forests as climate change intensifies.

"This work demonstrates that there is value beyond just hazardous fuels reduction from restoring frequent fire in ponderosa pine forests. It demonstrates that regular fire can increase tree resilience to drought," said UNM biology professor Matthew Hurteau.