When I look at the paperbark maple tree outside my window, I see a choice ornamental plant whose peeling, cinnamon-colored bark will only get more beautiful with age (sort of like me, ha-ha).
When Tony Aiello looks at his home-garden specimens, he sees the giant panda of the plant kingdom.
Like the panda, this species is running out of individuals in its native habitat in central China, and it may come down to those in our little plant zoos - that is, mine, Tony’s and yours, if you have one - to help bring the wild Acer griseum back from the brink.
No one is knocking on my door for pollen or seed at the moment, but the idea that I’m growing a tree that is imperiled is sort of exciting and decidedly unexpected.
“When I tell people it’s endangered in China, they’re very surprised,” said Aiello, director of horticulture at the Morris Arboretum in Philadelphia.
The paperbark maple was introduced to the West more than a century ago by the intrepid plant collector E.H. Wilson, but it has remained a fairly uncommon garden plant, in part because Wilson started with only about 100 seedlings. It is hardy in zones 5-8. Much of southern Idaho is zone 7.
I suspect my maple started life in the Salem, Ore., nursery of Mark and Jolly Krautmann, Heritage Seedlings. (Nursery trees generally go through two or three growers before reaching a retail nursery.) The Krautmanns have been propagating as many as 40,000 paperbark maples annually since 1985 from seeds they collected in China or had shipped to them. “We also collected from a tree here in Oregon that was very fertile,” Mark Krautmann said.
Part of its rarity - in commerce and in nature - is due to the fact that it sets very few fertile seeds. Another major problem is that cuttings don’t root, so the nursery keeper has to make new plants from a limited number of seeds.
In recent years, its availability has increased substantially, but the tree is still mostly found in the gardens of connoisseurs. It doesn’t have the flamboyant floral display of, say, a magnolia or dogwood, and its chief ornament, the peeling red bark, requires a more refined appreciation. It deserves wider use.
It can grow to 50 feet in the wild, but in the garden it tends to be a much smaller tree that lends itself to use by a walkway or patio. Mine was planted that way about four years ago to replace a stewartia that was sickly from the start.
Aiello and colleagues at other botanical gardens are seeking to increase the diversity of paperbark maple, and last year they visited five Chinese provinces to collect DNA samples and some seed from wild specimens. Populations have become isolated from one another as forest land has been lost to agriculture and other human pressure. “It was a very interesting way to see what it means to be an endangered species, because it took us a day to drive between different” stands, Aiello said. The tree’s distinctive bark - at times a coppery orange - made it easy to find the survivors. “The Chinese call it the blood-bark maple, and people could generally direct us to it,” he said.
The team, organized under the North America-China Plant Exploration Consortium, began its conservation project in 2013 and includes plant scientists from the Morton Arboretum in Lisle, Ill., the Arnold Arboretum in Boston and the Beijing Botanical Garden.
From samples collected in the wild and plant collections, Aiello and his colleagues are testing approximately 125 trees for their DNA. This will create a gene pool for future conservation efforts. “We are trying to get an understanding of what’s in cultivation and what’s in the wild, and then try to work with our Chinese colleagues to work at the conservation end of things,” he said.
As with pandas, the aim is to have enough diversity to ensure the survival of the species even if it becomes extinct in the wild. “The ultimate goal is to preserve it in its native habitat but as a backup preserve it in cultivation,” he said.
In horticulture, plant hybridizers also need a diverse genetic pool to tweak a species for desired traits, which include disease resistance, size and habit, vigor and cold hardiness.
The paperbark maple has not been extensively bred for new traits, but the Krautmanns are about to release an upright columnar form, as yet unnamed, that will be grafted onto rootstock.
Many ornamental tree species, particularly from Asia, were introduced in the United States a century ago or longer, and our current stock may not have the genetic diversity that it needs for its long-term security.
In that respect, the paperbark maple is “something of a poster child” for all trees that need the intervention of scientists to ensure their future, said Paul Meyer, executive director of the Morris Arboretum.
And the idea of a tree in horticulture preserving one in the wild has precedence, the native Franklinia tree being the obvious example. Collected in Georgia by Philadelphia botanist John Bartram in 1770, it is now found in botanical gardens and a few private ones but hasn’t been seen in the wild since 1790.
Today, species of oak and magnolia are facing the same conundrum, Mark Krautmann said.
If you are seeking to plant a tree as a piece of living sculpture this fall, consider the paperbark maple. It has clean, deep green leaves that turn a showy deep red-orange in the fall. But it is during the winter when its decorative, glossy and exfoliating bark stands out the most. Precious, in all its meanings, seems the word to use.
As Michael Dirr, America’s woody-plant guru, has written: “No finer tree could be recommended.”