Collections of Collections Give Hope for Trees

The Morton Arboretum is a big place, spanning more than 1,700 acres. But its world-renowned tree collections are also part of something bigger: they fit together with other institutions’ collections to improve the future for endangered tree species.

For example, the Arboretum is home to a group of maple-leaved oaks (Quercus acerifolia), an extremely rare tree species. In the wild, this tree grows in only four small populations in the Ouachita Mountains of western Arkansas and is severely threatened by loss of habitat and the changing climate.

The Arboretum’s conservation grove is one lifeboat for this rare species. But as leader of the Global Conservation Consortium for Oak (GCCO), the Arboretum also coordinates with maple-leaved oak collections elsewhere, such as the Stephens Lake Park Arboretum in Columbia, Missouri. Together, these plantings form part of a “metacollection”—a collection of collections. It’s like a fleet of lifeboats.

A metacollection’s goal is to capture and preserve more genetic diversity in more trees than any one institution may have space or capacity to hold. “We’re essentially storing the genetic diversity of the wild population, for potential restoration in its native range or nearby,” said Amy Byrne, manager of strategic partnerships for the Arboretum’s Global Tree Conservation Program.

Genetic diversity—the variety of individual genes among different trees within a species—is important because more diversity provides more opportunities to respond to future threats or to adapt to changed habitats, such as a warming world. For that reason, data about trees in metacollections is carefully collected and tracked to make sure they represent the full range of differences within a species, like the many differences among humans.

For extra insurance, “You want to make sure that plants of concern are represented at a variety of sites,” Byrne said. That way, no local disaster—flash flood, drought, tornado—could take them all out. Trees planted in different places also might turn out to be able to survive in a wider range of conditions beyond their native ranges.

As the lead organization for the GCCO, the Arboretum works with other institutions and partners to collect acorns of rare oak species and grow them as parts of a metacollection. Some of these species won’t grow at the Arboretum. “Not every oak can be grown in every site,” she said. In southern California, there’s a metacollection for the endangered Engelmann oak (Quercus engelmanii), native to the dry foothills from Los Angeles south to Baja California, Mexico. Its partner collections include the San Diego Zoo Wildlife Alliance; the San Diego Botanical Garden; The Huntington Library, Art Museum, and Botanical Gardens; the Los Angeles County Arboretum and Botanic Garden; and the Viejas Band of Kumeyaay Indians, a sovereign nation that is growing the trees on its lands near San Diego.

It’s not just oaks. Trees in the Arboretum’s highly respected Magnolia Collection are part of a metacollection organized by the Global Conservation Consortium for Magnolia.

The term “metacollection” is fairly new, but it captures a kind of work the Arboretum has been doing for a long time, according to Kim Shearer, director of collections and curator. “We were doing metacollections before there was a word for it,” she said.

Back in 1991, the Arboretum was a founding member of the North America-China Plant Exploration Consortium, which makes sure that rare plants collected from the wild in both regions are spread across collaborating public gardens both in China and throughout North America.

The Arboretum also is part of the Plant Collecting Consortium, which includes many institutions in the U.S., Canada, and the United Kingdom. “We do expeditions in places like Azerbaijan, and the plants that are collected are shared out to gardens for planting,” she said.

The strong support of its caring donors is what makes it possible for The Morton Arboretum to be a leader in wide-ranging, long-term conservation work such as developing metacollections. Their continuing generosity connects institutions around the world to preserve the genetic diversity of threatened trees.