Tree mortality response to drought-density interactions suggests opportunities to enhance drought resistance
John. B. Bradford, Robert K. Shriver, Marcos D. Robles, Lisa A. McCauley, Travis J. Woolley, Caitlin A. Andrews, Michael Crimmins, David M. Bell
Climate Change, Forest Restoration Benefits
A future of hotter temperatures and less precipitation under climate change could increase tree mortality under drought conditions in dry forests across the western U.S., causing large-scale tree die offs. Restoration projects that reduce densities of overgrown forests can result in lower competition for scarce water resources and is one of the few ways in which forest managers can potentially minimize tree mortality and increase forest resilience. This study evaluated the climate and tree density conditions that best explained tree drought mortality in ponderosa pine stands across the western U.S. A key objective of the study was to determine where and how much reducing tree density can help sustain dry forests projected to undergo future drought. We found that basal area, a measure that represents the number and size of trees, was the most important factor that explained ponderosa pine tree mortality from over 3,000 stands monitored by the U.S. Forest Service. Specifically, higher density stands had higher mortality. We also found that mortality was higher in stands that experienced hotter and drier than conditions. However, an unusually wet period could reduce mortality in a stand. Our results suggest that a 50% reduction in forest basal area could reduce tree mortality from 20% – 80% even under adverse climate conditions. This study shows that large-scale forest restoration projects designed to reduce wildfire risk, that are currently being implemented across the West, can also reduce tree mortality from drought.
Aerial view of the Parks West restoration site overseen by TNC. Taken March 16, 2020.
Conservancy staffers, Dale Turner and Amanda Rebore, helping to map the Sabn Pedro River in Arizona. They use a GPS unit to denote the end of the water flow on the LowerSan Pedro River. They hiked through the Conservancy’s San Pedro Preserve.
Our Approach to Science
The Nature Conservancy’s conservation science program in Arizona engages stakeholders and expertise in applied science and policy to develop new information, ideas, and tools that can help solve some of our most pressing challenges affecting people and nature
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We are working with partners and stakeholders to accelerate the pace and scale of forest restoration for a healthy Arizona
Mapping the Status of River Streams
Wet/dry mapping provides a low-cost, river-wide snapshot of hydrologic conditions for rivers with interrupted perennial surface flows.
Every June groups of volunteers walk the entire 170 mile length of the San Pedro River and record where it is wet and where it is dry during the hottest, driest time of the year. Twenty years’ worth of data on summertime surface flows in the San Pedro River within the San Pedro Riparian National C[…]
Arizona, Geo Region
Forest Restoration Benefits, Topic
Jamie L Peeler, Lisa McCauley, Kerry L Metlen, Travis Woolley, Kimberley T Davis, Marcos D Robles, Ryan D Haugo, Karin L Riley, Philip E Higuera, Joseph E Fargione
Identifying opportunity hot spots for reducing the risk of wildfire-caused carbon loss in western US conifer forests
As both the climate and wildfire crises intensify and investments are made to dramatically increase the pace of forest restoration across dry forests in the western U.S. through the Wildfire Crisis Strategy, an understanding of where Nature-Based Solutions are the most optimal in lessening climate i[…]
Arizona, Colorado River Basin, Western U.S.
Climate Change, Forest Restoration Benefits
Collaboration, USDA ARS
Ravindra Dwivedi, Joel A. Biederman, Patrick D. Broxton, Kangsan Lee, Willem J.D. van Leeuwen, Jessie K. Pearl
Forest density and snowpack stability regulate root zone water stress and percolation differently at two sites with contrasting ephemeral vs. stable seasonal snowpacks
Much of the western United States depends on high elevation snowpack in forested watersheds for water supply, wildlife habitat, and recreation in both adjacent and downstream communities. The forest-snow-water relationship is well studied in areas with stable – that is, cold – seasonal s[…]