Trees in Transition

Kevin Potter collects cones from a Fraser fir. Photo courtesy of North Carolina State University.

In forests as in life, the only constant is change. Forest species are ever adjusting to changing conditions resulting from seasonal fluctuations in temperature and precipitation, disturbances such as storms and wildfire, and interactions with other species.

But typical temperature and precipitation patterns are now also changing; in some areas, climatic changes are occurring rather rapidly, which could pose a severe threat to forest trees. Whether tree populations adapt onsite to changing habitat conditions, shift their ranges to new suitable locations, or simply die out, the forests we know today—and the genetic makeup of the species within them—could be very different by the middle of the 21st century.

Now researchers from the Eastern Forest Environmental Threat Assessment Center (EFETAC) are asking the question: In a future with a different climate, where will trees be?

With support from the Forest Service Forest Health Monitoring Program, EFETAC ecologist Bill Hargrove and North Carolina State University cooperating scientists Kevin Potter and Frank Koch are collaborating to develop Forecasts of Climate-Associated Shifts in Tree Species (ForeCASTS). Using projections of future climate in combination with the concept of ecoregions—land areas that share similar environmental characteristics such as soils, topography, and climate variables—the researchers are developing maps that show future suitable habitat ranges for tree species in North America.

ForeCASTS maps can help scientists, land managers, and policymakers target tree species for monitoring and management activities by pinpointing locations where climate change pressures are likely to be most intense.

“The Forest Service has a long history of understanding that the seed source makes a huge difference in tree growth and performance,” says Hargrove. “ForeCASTS maps can ultimately be used to assess the risk to genetic integrity of North American forest tree populations.”

So far, the researchers have developed maps for 213 tree species under varying climate models and scenarios for the years 2050 and 2100, including minimum required movement” maps that show the distances between existing habitat that may become unsuitable in the future and the nearest future suitable habitat.

“The general trend, as we would expect, is for tree ranges to expand at least a little bit to the north, and to drop off at least a little bit at their southern edges,” says Potter. “Looking at species with ranges that include the Southern Appalachians, the ForeCASTS maps show nearly all species decreasing their overall suitable habitat area.”

The ForeCASTS maps are still provisional. As the project unfolds, the researchers refine the available map products and add additional species to the queue. They plan to identify closest “lifeboat” areas for tree species that may migrate from multiple locations as well as areas where certain species may thrive in the future.

Recommended reading:

Potter, Kevin M.; Woodall, Christopher W., 2012. Trends over time in tree and seedling phylogenetic diversity indicate regional differences in forest biodiversity change. Ecological Applications 22(2):517531.

Potter, K.M.; Hargrove, W.W.; Koch, F.H. 2010. Predicting climate change extirpation risk for central and Southern Appalachian forest tree species. In: Rentch, J.S.; Schuler, T.M., eds. Proceedings from the

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