Coconino National Forest, Arizona
U.S. Forest Service photo by Deborah Lee Soltesz
Increasing aridity as a result of climate change is expected to exacerbate tree mortality. Reducing forest basal area—the cross-sectional area of tree stems within a given ground area—can decrease tree competition, which may reduce drought-induced tree mortality. However, neither the magnitude of expected mortality increases, nor the potential effectiveness of basal area reduction, has been quantified in dryland forests such as those of the drought-prone Southwestern United States.
David Bell, a scientist at the Pacific Northwest Research Station and his colleague John Bradford with U.S. Geological Survey used thousands of repeatedly measured forest plots to show that warm and dry forests experienced high tree mortality rates and that mortality is positively related to basal area. Those relationships suggest that although increasing high-temperature extremes forecasted by climate models may lead to greater tree mortality during the 21st century, future tree mortality might be partly ameliorated by reducing stand basal area. These results suggest that basal area reduction may be most useful in the relatively near term, potentially providing forest managers with a window of opportunity to promote species and genotypes that are more appropriately adapted to emerging climatic conditions.