Two-wing silver bell

What do water locust, Texas walnut, chalk maple, pyramid magnolia, two-wing silver bell, and butterbough all have in common? They’re among the U.S. tree species most vulnerable to climate change, according to a study by North Carolina State University (NCSU) and the U.S. Forest Service.

The Forest Service Forest Health Protection program sponsored the study, which was recently published in a special issue of the journal New Forests. The study builds on discussions at a 2014 workshop involving 25 U.S. Forest Service managers and scientists from across the country. They came together to reach consensus on a science-based and transparent process for identifying vulnerable tree species. Many species are facing genetic degradation due to rising temperatures, shifting moisture patterns, and related habitat changes. Project CAPTURE (Conservation Assessment and Prioritization of Forest Trees Under Risk of Extirpation) emerged from their discussion.

“If tree species have sufficient genetic diversity within and across populations, they may be more able to adapt to changing environmental conditions. Genetic degradation means the possibility of a significant reduction in the ability of a species to persist for the next century,” explains Kevin Potter. Potter, the study’s lead author, is an NCSU scientist cooperating with the Forest Service Eastern Forest Environmental Threat Assessment Center.

“Project CAPTURE provides a method, driven by data and expert opinion, to identify tree species that could be lost at the population level or altogether through widespread extinction. Our goal is to help scientists and managers target species and populations for proactive monitoring, management, and gene conservation.”

Potter, along with Forest Service Southern Region geneticist Barbara Crane and Eastern Threat Center research ecologist Bill Hargrove, used the Project CAPTURE framework to evaluate 339 native U.S. tree species.

The Forest Service Forest Inventory and Analysis program collected data on 333 of these species; researchers added six additional rare tree species to the study, including seaside alder, saguaro, Santa Cruz cypress, Gowen cypress, Arkansas oak, and Boynton oak.

The researchers analyzed the traits of each species and predictions of climate-related pressure, including each species’ exposure and sensitivity to the threat and its capacity to adapt to a changing environment. They then listed each species in one of seven vulnerability classes.

Thirty five tree species ended up in the highest vulnerability class, meaning that they are the most exposed and sensitive, have the least capacity to adapt, and therefore have the most immediate need for conservation action. Of these 35 species, 24 are mostly found in the southeast.

The second vulnerability class includes 43 species with high exposure and sensitivity and some ability to adapt, but probably require conservation assistance. The 69 species in the third vulnerability class have high threat exposure and moderate sensitivity but low adaptive capacity, and should be monitored closely. The remaining tree species are classified as currently not vulnerable. All species in the three vulnerability classes can be found at www.srs.fs.usda.gov/pubs/53942.

Chalk maple

Tree species are ranked within each vulnerability class, but researchers stress that scientists and managers should focus on species’ categorization in these classes—not necessarily their ranking—when planning monitoring, management, and gene conservation activities.

As climate and habitat changes, there are winners and losers among tree species. Some tree species may spread and thrive, some may persist at new altitudes or latitudes. However, others may be restricted to small patches, and others may simply disappear.

“The reality is that it’s impossible to conserve the genetic diversity of every species or population, so conservation practitioners need to apply rational, systematic, and defensible approaches to species prioritization and allocation of scarce budgets and resources,” says Potter. “As we continue to analyze additional tree species and updated climate projections, we expect that Project CAPTURE will guide conservation, restoration, and management decision making at a national level.”

Stephanie Worley Firley is a biological science information specialist at the U.S. Forest Service, Eastern Forest Environmental Threat Assessment Center, Asheville, N.C.

Researchers analyzed traits of 339 U.S. tree species and predictions of climate-related pressure, including exposure, sensitivity, and capacity to adapt to a changing environment, and then listed each species in one of seven vulnerability classes. View the full chart (pgs 291-292) here: http://bit.ly/vulnerable-trees
Chart courtesy of U.S. Forest Service/New Forests