A Grove of Possibilities

As part of each year’s Arbor Day celebration, employees of The Morton Arboretum plant trees on the grounds. This year, they did more: They helped plant a whole grove of trees as the latest move in the Arboretum’s decade-long effort to save an endangered species.

With help from staff who took turns digging to get them in the ground, more than 30 saplings of paperbark maple (Acer griseum) now grow along a trail in the far reaches of the Korea Collection. They are too young to display the handsome copper-colored peeling bark that makes the species a popular ornamental tree in gardens, but this fall they are sure to drop some red, orange, or bronzy leaves. “Give them a decade, and they’ll be spectacular,” said Kris Bachtell, vice president of collections and horticulture.

What makes these particular trees extra special is hidden in their genes. They are a conservation grove, a group of trees planted to preserve the range of genetic diversity of trees that grow in the wild. They represent new hope for a tree species that, common as it may be in gardens, is listed as endangered in its native habitat in Asia.

Bachtell and his partners at the Arboretum and other institutions in the United States and China have been working since 2013 to improve the odds for this species. All the Arboretum’s strengths—its global reach, farsighted view, history of plant collecting, cutting-edge science, and century of horticultural expertise—stand behind these slender trees.

The Arboretum has several handsome mature paperbark maples, as do many other public and private gardens around the globe. It may seem paradoxical, then, that such a common tree still needs saving. The problem is that the trees in cultivation are too much alike. As the researchers discovered through analyzing DNA collected from specimens in public gardens, nearly all paperbark maples in the United States and the United Kingdom are descended from just a handful of individual trees.

It was E.H. Wilson, a famed explorer who conducted several expeditions in Asia at the turn of the last century to collect plants for introduction in Western horticulture, who brought the paperbark maple to the West. “We found that nearly all the paperbark maples in cultivation come from samples he collected in 1901,” Bachtell said. They are all genetically very similar—too similar to provide an adequate genetic backup for the diminishing number of these trees in the wild, threatened with loss of habitat, climate change, and other challenges.

Every species of plant or animal needs genetic diversity to survive and adapt. The more diversity there is among the individuals of any species, the greater the chance that some will be able to thrive in challenging circumstances. “If you lose genetic diversity, you lose possibilities,” he said.

To capture a greater range of possibilities for the paperbark maple, Bachtell and his American and Chinese colleagues set out in 2015 to collect seeds and cuttings from wild plants on remote hillsides in China. Then they spent years developing and testing a technique to graft the cuttings onto a vigorous rootstock from another maple species. The saplings in the Arboretum’s new conservation grove were propagated that way.

Other public gardens are also planting these more genetically diverse paperbark maples, including the Arboretum’s partners in the project: The Morris Arboretum of the University of Pennsylvania, the Arnold Arboretum of Harvard University, and the Beijing Botanical Garden.

At the Arboretum, the paperbark maples are among several conservation groves that have been planted or are planned. “By planting these groups of trees, we’re helping to create a worldwide bank of genetic diversity,” Bachtell said.

The Morton Arboretum can lead such conservation efforts not just because it has space in its collections for entire new groves of trees, but because of its strong base of philanthropic support. Employees contributed by planting these paperbark maples. The far-sighted donors who contribute funds to support the work of the Arboretum, from scientific research into the need for genetic diversity to collecting tree specimens from the wild to caring for tree collections through the decades, are truly making a long-term investment in the future of trees.