Drought kills trees directly or by making them more vulnerable to pests and pathogens. Although reduced precipitation defines drought, high temperatures lead to increased evaporative loss from plants and soil that amplifies drought stress (called “hotter drought”). Many state and federal land-management agencies in the Southwest support large prescribed fire programs aimed at reducing understory fuels and forest density. Resource managers also assume that prescribed fire reduces competition among the surviving trees, making them more resistant to drought and other stressors. This project uses the ongoing, severe drought across the Southwest as a natural experiment to determine whether prescribed fire in fact helps trees survive drought stress. The researchers compared drought-related tree mortality in burned and unburned sites in Kings Canyon, Sequoia, and Yosemite National Parks to see whether the trees in the burned sites were more resistant to drought stress.
Early results show that current prescribed-fire practices did in fact increase forest resistance to drought. Managers at Sequoia and Kings Canyon national parks have used these results to expand prescribed fire operations. The researchers are continuing to work with forest managers across the region to help guide forest management practices to increase forest resistance to the hotter droughts that the region is likely to experience in coming years and decades.