Which Tree Species are Most at Risk in a Changing Climate?

Carolina hemlock (Tsuga caroliniana), which grows on high-elevation slopes and ridges, is expected to lose areas of suitable habitat in a changing climate. Photo by Will Cook, www.carolinanature.com.

A walk in the woods or a stroll on a tree-lined street could be a very different experience just a few decades from now. Higher temperatures, altered precipitation patterns, and longer growing seasons predicted for the future could require that some tree species will have to move – or be moved – into new areas where habitat will be more suitable. Some tree species may be able to stay in place by adapting to new conditions, yet others may succumb to the pressures of climate change if they are unable to adapt. Researchers with the U.S. Forest Service Eastern Forest Environmental Threat Assessment Center are developing measures to predict which tree species are most at risk.

Kevin Potter, a North Carolina State University scientist cooperating with the Eastern Threat Center, and Bill Hargrove, Eastern Threat Center research ecologist, collaborate on a project known as Forecasts of Climate-Associated Shifts in Tree Species, or ForeCASTS. In a recently published study, they used Forest Service Forest Inventory and Analysis data to identify where tree species presently occur and combined this information with statistical clustering—an approach that identifies and groups locations with currently suitable environmental conditions for each species based on soil, climate, and landscape conditions. Then, they projected where these suitable environmental conditions might be located in the year 2050 using a relatively conservative model of future climate based on lower levels of climate-warming greenhouse gas emissions.

Potter and Hargrove’s efforts resulted in projected habitat changes for 172 North American tree species in terms of the percent change in suitable habitat area, habitat range stability over time, minimum distance to the nearest suitable habitat required for survival, and species’ current occupation of suitable habitat given ecological limitations (which suggests whether species are more able to adapt to change). “Of all 172 tree species we analyzed, all but two are expected to lose suitable habitat by 2050,” says Potter. “These results may seem overwhelming, but this information can help land managers and decision makers prioritize tree species for conservation activities.”

Some tree species may already be responding to climatic changes with fluctuations in the timing of budburst and other seasonal events as well as movement to new locations. Though this ForeCASTS study presents results for just one point in time and one climate scenario, it contributes to a greater understanding of the risks posed by climate change. “Our emphasis with this study was to describe and illustrate measurements of climate change pressure rather than to present a range of potential climate change effects,” says Hargrove.

So which tree species are most at risk? “On average, species in the eastern United States are projected to lose more suitable habitat and have less habitat range stability compared to species in the West,” says Potter. September elm, delta post oak, Kentucky coffeetree, and Carolina hemlock are species of particular concern. See the published study for a complete table of results.

For more information, contact Bill Hargrove at whargrove@fs.fed.us.

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