Trees in Protected Areas

Rarity and Evolutionary Distinctiveness

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. Is the species found in one valley or across an entire continent? In what types of habitats is it found? How many individuals of that species can be found on a specific plot of land?

phylogenetic tree
In this phylogenetic tree, Species A is more closely related to Species B than it is to Species C. Species I is more genetically distinct than Species F. Image by Tylototriton, courtesy of Wikimedia Commons.

All three of these scales are important in making an informed management decision. For example, if a tree species is rare on your property, but very common everywhere else, it may not necessarily be a conservation priority. 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.

Evolutionary distinctiveness is a measure of how closely related a species is to its relatives and ancestors. On a family tree, species which split most recently from their common ancestor are related more closely with one another. These species are likely to possess similar traits and thus function similarly within an ecosystem.

However, those species which diverged longer ago are less related to others on their family tree and are more evolutionarily distinct. They might have traits that others do not, and therefore play a unique role within the ecosystem. This makes them, too, a priority for conservation.

In his 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 U.S. using data collected from about 130,000 Forest Inventory and Analysis plots.

The results were published in Biological Conservation. He identifies “hotspots” and “coldspots” where there are especially high or low concentrations of rare or evolutionarily distinctive tree species. According to him, paying attention to these species and locations is one way to get “more conservation bang for your buck.”

Listen to a brief audio clip by author Kevin Potter describing this publication. • Text Transcript

This study builds upon Potter’s previous work in the field of evolutionary biology, helping managers and scientists protect forests from threats like climate change and invasive species.

In this new work, he 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?

Examples of highly rare and evolutionarily distinct trees include the sequoia, the Florida yew, and the Florida torreya. Additionally, 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 they are where, if 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 coldspots of evolutionary distinctiveness. Therefore, managers should be aware of where they are situated within this regional variation.

Florida yes
Florida Yew is endemic to a 10 square km 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 by Richard Carter, courtesy of Wikimedia Commons.

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.

Part of the explanation behind those results is historical. “We’ve ended up in a situation,” says Potter, “where we have the bulk of our biodiversity here in the East where there are more people, and more of our contiguous protected areas in the West.”

The east coast is highly populous and industrial simply because this is where the colonies were originally established. Meanwhile, the sublimity of the western landscape won over the American imagination, allowing—along with the isolation, aridity and ruggedness of much of the region—for large areas to be protected. Though certainly deserving of conservation efforts as well, eastern forests contain far more plant biodiversity than western ecosystems.

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.

Read the full text of the article.

For more information, email Kevin Potter at kevinpotter@fs.fed.us.

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