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Out on a limb — endangered plants and their protectors

Ten percent of the plants in the Arnold Arboretum are now endangered in the wild. The staff is working with other botanical institutions around the world to provide a safe harbor against loss.

Paperbark maple (acer griseum) at the Arnold Arboretum.Michael S. Dosmann

“They took all the trees, put ’em in a tree museum

And they charged the people a dollar and a half just to see ‘em.”

Joni Mitchell, “Big Yellow Taxi,” 1970

It’s hard not to think of Joni Mitchell’s prescient lyrics when standing amid the majestic living collection of 15,000 trees and other plants at the Arnold Arboretum, assembled from 60 countries over nearly 150 years. Of course, one significant difference is that no one charges people to see these trees: The 280-acre park is free and open to all. But the idea of the Arboretum as a tree museum is a poignant one, especially since its most recent annual audit found that fully 10 percent of its plants are now endangered in the wild. “We’re in a race against time,” said Arboretum director William “Ned” Friedman.


Conservation has always been a major part of the Arboretum’s mission, but now there’s a new urgency, as staff horticulturists work with other botanical institutions around the world collecting seeds and cuttings to provide a safe harbor against loss. “We are parking what little genetics we can get,” Friedman said, “not just at the Arboretum but everywhere.”

Among the threatened plants are familiar species: maples, yews, conifers, even one variety of the famed Arboretum lilacs. They are menaced by climate change, habitat loss, and international trade, which can introduce pests and diseases. Globally, one-fifth of all plant species are threatened with extinction, including one of every five maples and one of every three oaks. The percentage of endangered plants in the Arboretum has been creeping up with every census, but that’s partly because of the park’s increasing focus on collecting threatened species. In this sense, the Arboretum is not so much a museum as a kind of Noah’s Ark.


I recently toured the Arboretum in the company of horticulturist Michael Dosmann, whose poetic title is Keeper of the Living Collections. We began at the visitor center, where a pretty flowering plant called the Arkansas blue star (Amsonia hubrichtii) graces the entry. It’s a familiar plant, for sale at garden centers, but it is vulnerable to extinction in the wild. According to NatureServe, a nonprofit network of biodiversity scientists, there are just a few dozen populations of this blue star variety growing wild, and their numbers are declining.

But if I can buy blue star at any garden center, what does it matter if it is threatened in the wild? Dosmann explains that most commercial plants are propagated or cloned, limiting their genetic diversity and their value to researchers. Indeed, we stopped to admire another threatened species — the cinnamon-colored paperbark maple (Acer grisium) — which botanist Ernest Henry Wilson introduced to the Arboretum as a seedling from China in 1901. Virtually every commercially available paperbark maple is a descendant of Wilson’s seeds. Cloned and propagated plants are fine for ordinary gardeners, but without genetic diversity they can become less resilient over time.

In 2015, Dosmann traveled 2,200 miles across China to collect samples from the remaining wild paperbark maples. His group included faculty from the Chengdu Institute of Biology, and the expedition resulted in a trilateral conservation agreement including the Huanglong National Nature Reserve, a UNESCO heritage site in Sichuan. Today, Dosmann’s Chinese seed collection is growing in the Arboretum’s nursery.


Not surprisingly, getting the public to care about endangered plants is harder than mounting campaigns to save charismatic animals like elephants or the giant panda. Humans suffer from so-called plant blindness, an inability to appreciate the greenery in our midst. It’s not our fault, exactly: Dosmann said it’s in our DNA to be more acutely aware of things that move. “A plant probably isn’t going to eat you,” he noted.

So the Arboretum’s challenge is to get humans to have empathy for organisms that are not like us. For director Friedman, this respect extends to human diversity as well. “People can be so uncaring if they perceive ‘someone is not like me.’ To learn to be able to care about plants is the beginning of being able to care about something ‘not myself,’ and that’s a very important human value.”

In fact, plants may be more like us than we realize. Recent science shows that trees can communicate danger and even have a sense of smell. The line between self and other is actually quite porous. That is a lesson nature will teach us, if only we can see the forest for the trees.

Renée Loth’s column appears regularly in the Globe.