The Forest Family: Relationships among Tree Species

Conifers, such as these longleaf pines, tended to be more distantly related than expected by chance. Photo by David Stephens, courtesy of
Conifers, such as these longleaf pines, tended to be more distantly related than expected by chance. Photo by David Stephens, courtesy of

Like all species, forest trees have their own web of relationships among themselves. Studying these evolutionary ties is the main focus of phylogenetics, and can assist in forest health assessment.

“Understanding relationships among tree species can show how they interact with each other and with the environment,” says North Carolina State University scientist Kevin Potter. “Phylogenetics can be used to assess forest health from the perspective of biodiversity and resilience to stress.” Potter, a research cooperator with the Forest Service Southern Research Station (SRS) Eastern Forest Environmental Threat Assessment Center, is lead author of a new study that analyzes forest phylogenetics across the entire United States. The study was coauthored by SRS scientist Frank Koch, and was recently published in Forest Science.

Potter and Koch studied forest trees across a network of more than 100,000 plots across the United States. The plots are part of the Forest Inventory and Analysis Program, which provides a continual census of forest status and trends.

Over most of the ecoregions studied, the researchers found that trees – except conifers – were more closely related than could be explained by mere chance. “This can mean that many of the trees in that particular environment are able to co-exist because they have similar adaptations to the environmental niches there,” says Potter.  “At the same time, tree species that are closely related can be susceptible to similar threats, whether insect infestations, diseases, or climate change.”

In some areas, including in the Rocky Mountain region, tree species were more distantly related than expected. These results can be somewhat more difficult to interpret, because there are two processes that can lead forest communities to consist of tree species that are more distantly related. First, competition between closely related species for similar resources can result in the survival of only one of them. Second, distantly related species sometimes have evolved similar traits that allow them to be adapted to similar environmental conditions. “The ecological integrity of such communities may be less at risk because they may encompass a wider variety of evolutionary adaptations,” says Potter.

The researchers also found patterns of relatedness along environmental gradients. In harsh environments, such as at high elevations or in dry areas, tree species tended to be more distantly related than expected. In more favorable environments, tree species tended to be more closely related. “These results have implications for broad-scale forest health monitoring,” says Potter. “The relatedness of forest tree species may be connected to their susceptibility to threats such as climate change, nonnative plant invasion, and insect and disease infestation.”

Read the full text of the article.

For more information, email Kevin Potter at

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