Sustain Our Nation's Forests and Grasslands

Effect of protected areas on tree rarity, evolutionary distinctiveness

Close-up of the needles of a Florida yew.
Florida yew is endemic to a 10 square kilometer area in northern Florida, making it one of the rarest trees in the world. Its bark contains a compound that has been used to treat certain cancers. Photo courtesy Richard Carter, Wikimedia Commons.

NORTH CAROLINA—Conservation goals range anywhere from aesthetics to survival. Among the most important of those is ensuring that an ecosystem is resilient to disturbances and provides as many different functions as possible. According to an assessment by a USDA Forest Service cooperating researcher, those qualities can be quantified using two metrics: rarity and evolutionary distinctiveness.

Rarity is a measure of how frequently a species occurs and evolutionary distinctiveness is a measure of how closely related a species is to its relatives and ancestors. These species are likely to possess similar traits and thus function similarly within an ecosystem. Rare species are often important to ecosystem function, but they are also quite vulnerable to disturbances and extinction. This makes them a priority for conservation.

In a recent study, NC State University research associate professor and USDA Forest Service collaborator Kevin Potter assesses the rarity and evolutionary distinctiveness of tree species throughout the United States using data collected from approximately 130,000 forest inventory and analysis plots.

The results, Do United States protected areas effectively conserve forest tree rarity and evolutionary distinctiveness?, were published in Biological Conservation. Potter identifies “hotspots” and “cold spots” where there are especially high or low concentrations of rare or evolutionarily distinctive tree species.

In this assessment, Potter asks if tree rarity and evolutionary distinctiveness are higher or lower within the nation’s designated protected areas than outside of them. In other words, are we doing a good job of protecting our forests’ genetic resources?  

Hotspots of a combined rarity–evolutionary distinctiveness metric are located throughout the southern region and along the west coast. Effective conservation is urgently needed in those areas because if they are lost, the biodiversity is more likely to be irreplaceable.

However, when it comes to rarity and evolutionary distinctiveness as separate metrics, the map changes. Hotspots of rarity are often cold spots of evolutionary distinctiveness. Therefore, managers should be aware of where they are situated within the regional variation.

The biggest unanswered question still remains—are we protecting those hotspots? Potter’s analysis reveals a number of interesting answers to that question.

For one, multiple-use protected areas—like national forests—are better at conserving evolutionary distinctiveness and the combined rarity–evolutionary distinctiveness metric than those that are restricted-use, like national parks and wildlife refuges.

Secondly, although protected areas tend to be better at conserving evolutionary distinctiveness, unprotected areas tend to be better at conserving rarity and the combined rarity–evolutionary distinctiveness metric. Exceptions to this trend include the protected areas in the southern region—there, evolutionary distinctiveness needs more attention.

Reviewing information about tree rarity and evolutionary distinctiveness will help managers maintain that biodiversity in their forests and strengthen their insurance policy against any disturbances that come along.