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Arboretum Offers Hope for Threatened American Trees

When a single decrepit oak tree was found in May in a remote canyon in West Texas, it was a sign of hope for The Morton Arboretum’s efforts to preserve threatened trees in the United States and around the world.

A team of searching scientists identified the tree as a lateleaf oak (Quercus tardifolia), a rare and poorly known species that they feared had vanished from the earth. The last known lateleaf oak had died in 2011.

The expedition, supported by the United States Botanic Garden, was combing the Chisos Mountains of Big Bend National Park for rare oak species. The tree the scientists found was fire-scarred and fungus-infected, but it was alive. The lateleaf oak might not be extinct after all—at least not yet.

In a recent assessment led by the Arboretum of all 881 tree species in the contiguous 48 states of the United States, Quercus tardifolia was one of 17 oak species listed as in danger of extinction out of the total of 85 oak tree species.

“In many regions of the world, oaks serve as an ecological anchor, cleaning air, filtering water, sequestering carbon dioxide, and supporting countless fungi, insects, birds and mammals,” said Murphy Westwood, PhD, vice president for science and conservation at the Arboretum. “When one oak species is lost, we don’t know what else we might permanently lose in its wake.”

Arboretum scientists are still investigating at the molecular level whether the surviving tree is, in fact, a lateleaf oak, and not a hybrid of the many other oak species that grow in the Chisos Mountains. But the possibility of the discovery that at least one threatened species was not lost was greeted as good news around the world, from Texas to Russia, in publications such as the Washington Post, the Hindustan Times in India,, and Science Times. Yet even finding a lone lateleaf oak would not mean that this rare species is saved.

Instead, it has kicked off a concerted conservation effort. More expeditions are planned to seek other living specimens that could be used to confirm the genetic identity of the species, cultivate the species elsewhere, and eventually restore it in its native habitat.

The Arboretum’s leadership and experience with conservation of other threatened tree species has provided the necessary knowledge, expertise, and a growing network of partners to put behind the effort to save this and other threatened trees.

The recent U.S. assessment, led by the Arboretum’s Global Tree Conservation Program in partnership with Botanic Gardens Conservation International and other partners, provides a baseline. “We realized that there was no checklist to guide our work, so we set out to create one,” Westwood said. The study found that 11 to 16 percent of native U.S. tree species–between 94 and 135 species–are threatened with extinction, yet only eight species have the protection of the U.S. Endangered Species List.

The major threats to trees include invasive pests and diseases, such as the emerald ash borer that threatens most American ash species with extinction; climate change; logging; and the loss of habitat to farming and other development.

Oaks and hawthorns, groups that include the most tree species, also include the most that are threatened. The majority of at-risk trees are native to Texas, California, and the southeastern states, where heat, drought, and severe storms brought by climate change are a growing threat.

Because oaks are so widespread and ecologically important, they are a major focus of science and conservation at the Arboretum. The Arboretum-based Global Conservation Consortium for Oak is already working with partners to conserve threatened oaks such as the bluff oak (Quercus austrina) in the Carolinas, the Boynton sand post oak (Quercus boyntonii) in Alabama, and the Georgia oak (Quercus georgiana) in Georgia.

A recently announced $1 million grant from the Walder Foundation will allow the Arboretum to expand on its work with local scientists and conservationists in Mexico and Costa Rica to preserve and replant threatened oaks. It will support the development of an Arboretum-based hub for assessment, planning, and action for threatened trees in the Americas and Asia.

The role of the Arboretum and other botanical gardens is critical to conserve species if their native habitats are threatened. Many rare trees, including oaks, can only be preserved as living trees; their seeds can’t be preserved in a seed bank. The Arboretum actively encourages planting trees in protected spaces such as public gardens, national parks, and university campuses, but the recent U.S. assessment found 17 threatened species that are not yet safeguarded in any living plant collection.

Planting trees, even in safe, protected spaces such as arboreta, will not always be easy. For Quercus tardifolia, for instance, not a single mature acorn has been found since the species was first described in the 1930s. That’s why the Arboretum is exploring other methods of reproduction, such as grafting and tissue culture, while also studying the genetic relationships of threatened trees to make sure conservation efforts capture their unique genetic diversity.

The discovery of a single lateleaf oak tree raises hopes that this species, and others, can be saved through The Morton Arboretum’s unique combination of scientific expertise, growing partnerships, on-the-ground conservation skill, generous donors, and space to plant trees where they can live for decades or centuries.

“Everyone who supports the Arboretum is supporting the future of trees and biodiversity in the United States and throughout the world,” Westwood said.