Severe droughts cause widespread tree mortality and decreased growth in forests across the globe—even in areas with cooler climates. Mitigating the negative effects of climate change, in particular increased drought frequency and severity, poses a major challenge to forest managers. Managers are searching for strategies that minimize the negative effects of drought on forests (i.e. increase their resistance to drought) and maximize the ability of forests to recover after a drought (i.e. improve their resilience). Evidence suggests that forests with certain combinations of tree species, sizes, and stem densities are better able to withstand and recover from drought.
The goal of this study was to identify which forest management practices best minimize drought impacts for a range of forest types and climates in the U.S. Researchers used eight long-term forest management experiments that are already underway across the country to identify how different forest management practices can increase the resistance and resilience of forests to drought. Practices such as forest thinning, a technique in which certain trees are selectively removed to make room for others, have been shown in the past to help reduce the stress experienced by the remaining trees during drought and to increase recovery rates following drought. Results of this study do show that relative tree population density was negatively related to drought resistance and resilience, indicating that trees growing at lower densities were less vulnerable to drought. This result was apparent in all three forest ecosystems, and was consistent across species, stand age and drought intensity.
Taking action to protect forests from drought can have far-reaching implications, ranging from sustaining wildlife that rely on forests for habitat, to retaining the carbon storage capacity of forests, to maintaining the ability of forests to regulate water flow and soil quality. The findings of this work are expected to directly inform the natural resource management community as to which management practices will best safeguard forests in the face of a changing climate and increasing drought.