Wildflower is published quarterly by the Wildflower Center. Its content is national in scope with articles about the conservation and use of native plants as well as news from the Wildflower Center. A subscription is provided to Wildflower Center members as a benefit of membership.
Perfect Trees - Fall 2010
Native hardwood trees are American icons
By Mariellé Anzelone, Virginia Barlow, Sheryl DeVore, Susan Freinkel and Sandra Lynn
American elm (Ulmus americana L.).
Photo by Andy and Sally Wasowski.
“If a man walks in the woods for love of them half of each day, he is in danger of being regarded as a loafer. But if he spends his days as a speculator, shearing off those woods and making the earth bald before her time, he is deemed an industrious and enterprising citizen.”
— Henry David Thoreau
This is ever more true today than in Thoreau’s time. Or is it? The optimist in each of us would hope instead that oil-slicked mangrove roots and fall foliage claimed by climate change has altered the collective unconscious toward thinking it’s high time that trees are allowed to stand their ground.
After all, perhaps more than anything in the landscape, trees equal shelter, nourishment and sense of place. The Wildflower Center will honor these gifts at the Mollie Steves Zachry Texas Arboretum, made possible by a donation of nearly $1.4 million from an anonymous fund of the San Antonio Area Foundation at the request of Mollie Steves Zachry. Set on 16 acres that boast the Center’s deepest soils and biggest trees, the arboretum will be the spot in Texas to see native Texas trees and will be home to the Center’s tree-related educational programs and events.
Because autumn is many a tree lover’s favorite season, we asked five authors to discuss some of the most iconic North American native hardwood trees and their greatest threats.
American chestnut (Castanea dentata)
“Under the spreading chestnut tree/The village smithy stands;/The smith, a mighty man is he,/With large and sinewy hands;/And the muscles of his brawny arms/Are strong as iron bands.” —Henry Wadsworth Longfellow
Adapted from “American Chestnut: The Life, Death and Rebirth of a Perfect Tree” by Susan Freinkel, University of California Press, 2007.
In 2006, a wildlife biologist hiking a little-used trail on Pine Mountain in Warm Springs, Georgia, made a startling discovery. Not far from the trail he spotted a small stand of American chestnuts – rare surviving members of a near-extinct species. The biologist had never seen an American chestnut, but he recognized the trees at once: They were “just shining there, almost impossible to miss,” he said. The find made national headlines, for what the fabled ivory-billed woodpecker is to birders, the American chestnut is to tree lovers: a vanquished species that continues to haunt their dreams.
The American chestnut once was one of the country’s most populous and important trees, a soaring pillar of wood that ruled East Coast forests from Georgia to Maine. Many considered it the “perfect tree.” Chestnut timber had a value and versatility unmatched by any other hardwood, while the nuts sustained wildlife and humans alike. Those qualities were particularly appreciated in the heart of the chestnut’s historic range, the southern Appalachians, where generations of mountain farmers counted the tree a vital ally in their struggle to survive. The American chestnut “was our icon,” says Appalachian folk historian Charlotte Ross. “We loved that tree.”
American chestnut (Castanea dentata (Marsh.) Borkh.)
Photo by Andy and Sally Wasowski
But in the early 20th century, the perfect tree met its perfect foe: a virulent pathogen unwittingly brought to the U.S. on chestnut trees imported from Asia. The chestnut blight, as it came to be known, spread with unprecedented ferocity. Over the course of 40 years, the disease rampaged along the Atlantic seaboard, destroying almost every mature American chestnut – more than 3 billion trees in all. To this day, the blight persists in the forests, attacking new chestnuts that dare to sprout.
Though mostly gone, the tree was not forgotten. Fond memories and enduring love for the chestnut have sustained rescue efforts for decades. Scientists have used classical breeding methods as well as cutting-edge tools of biotechnology to beat the blight and restore the chestnut to American forests.
The foremost restoration program, the American Chestnut Foundation (www.acf.org), in partnership with the U.S. Forest Service, recently began planting test plots of hybrid chestnuts, products of a 25-year-long program to breed blight-resistant trees. Although it’s too soon to say if the effort will succeed, some of the trees are thriving – even flowering. If successful, it will be a powerful demonstration that sometimes we can redress the ecological wrongs that we have wrought. If the day comes when our descendants can venture with wonder into chestnut forests, we will have regained more than a perfect tree. We will have gained a new reason for hope.
Susan Freinkel is the author of “American Chestnut: The Life, Death and Rebirth of a Perfect Tree,” winner of a National Outdoor Book Award in 2008. A San Francisco-based writer, her work has appeared in a variety of publications including The New York Times and Real Simple. Her book “Plastic: A Toxic Love Story” will be out next March.
Sugar maple (Acer saccharum)
“And you, how old are you?/I asked the maple tree:/While opening one hand, he started blushing.”
—Georges Bonneau, “La Sensibilité Japonaise”
The exhilaration that sweeps the Northeast when the warm spring sun first coaxes the temperature above freezing is due largely to the sugar maple (Acer saccharum). For a few weeks, many of us – including those who never have made maple syrup and never will – evaluate each day on the basis of how the sap is running. Sugar-makers may appear calm but are beholden to the weather forecast. Temperatures during sugaring season determine the amount of syrup they make, and spring weather is known to be fickle. Huge investments in equipment are part of the quest to produce the superior untainted syrup that sophisticated urban shoppers demand. Even in Vermont, most people don’t have pancakes for breakfast every day, and marketing efforts now involve more than the “Maple Syrup for Sale” sign that hangs by most sugar-makers’ mailboxes.
About when the evaporators used to boil sap into syrup go cold, another sugar maple phenomenon is getting underway beneath the trees. The sugar maple seeds that fell in autumn germinate, and seedlings appear early – often before the snow is gone. The ideal temperature for germination is 34 degrees F, the lowest of any known forest tree. A solid carpet of deep-green shade-tolerant seedlings adds to the beauty of many a sugar maple forest.
Sugar maples dominate rich, moist soils in the Northeast, where their towering crowns of dense green leaves create the coolest shade. A stand of northern hardwoods may lack ash or beech or yellow birch but are never without sugar maple.
Sugar maple (Acer saccharum).
Photo by Andy and Sally Wasowski.
This year, sugar maples at Vermont’s Proctor Maple Research Center opened their buds 13 days earlier than the 20-year average date because of exceptionally warm weather in March and April. For a while, tacking nearly two weeks onto the growing season looked like one of the few good things to be said for climate change. Then, on May 11 a hard frost – quite common in a normal year – killed the half-opened leaves on 200,000 acres of higher-elevation northern hardwoods. The blackened leaves fell and another crop of green ones were unfurling within a month, but such a loss is clearly hard on a tree’s balance sheet.
The tree that provides our best syrup, timber and autumn color may be in for a rough patch. Over the long term, expectations may be high for that lovely carpet of sugar maple seedlings. May they have the resilience and diversity to survive under whatever new conditions come our way.
Virginia Barlow is a cofounder of and writer and editor for Northern Woodlands magazine. She works as a consulting forester at Redstart Forestry, also in Corinth, Vermont.
Oak (Quercus spp.)
“The creation of a thousand forests is in one acorn.”
—Ralph Waldo Emerson
Wherever a mature oak grows, its fruits – the acorns – often can be found scattered on the forest floor. Because rarely does an oak tree produce more than a few acorns before age 20 and since it can take as many as 100 years for a tree to reach peak acorn production, acorns symbolize perseverance and patience. Able to live 150, 200 or even 500 years, oaks tie Americans to their heritage like no other tree species.
At least 90 native oak species grow in the United States – from the California black oak (Quercus kelloggii) in the West to the escarpment live oak (Q. fusiformis) in Texas. In the Midwest, white (Q. alba), bur (Q. macrocarpa), northern pin (Q. ellipsoidalis) and red oak (Q.rubra) trees dominate native savannas.
The king of them all is the bur oak, which can grow 120 feet tall with a 10-foot diameter. At Oak Openings Nature Preserve near Grayslake and Libertyville, Illinois, bur oaks spread their thick, gnarly branches above bottlebrush grass, native goldenrod and sedges. Invasive plants such as European buckthorn have been removed from the preserve so that sun can reach oak saplings and other native plants. On a hot summer day, Eastern wood-pewees sing their names from oak tree perches.
Oaks have provided shelter and sustenance to wildlife for as long as they have grown in the nation’s landscape. Passenger pigeons once built their nests in various oak species, dining on their acorns. Today, other birds and mammals do the same. The eastern screech owl, for example, uses a natural cavity in the oak to raise its young, and squirrels build leaf nests in the canopy. A study from 2004 showed that many migratory birds in Illinois, including some warblers, prefer oaks to other tree species. The birds keep the insect population living in the tree’s leaves in check so that the oak can remain healthy.
Insect pests, disease and lack of fire, however, are threatening the survival of some oak species. The non-native gypsy moth troubles the eastern part of the United States and is spreading to the Midwest, including Chicago suburbs. Larvae feast on the undersides of oak leaves, defoliating the tree, which can rob the plant of chlorophyll. Land managers debate whether to spray oaks with a safe substance to curb the moths or wait out an infestation.
Even more worrisome are oak wilt, which kills thousands of oaks each year in the eastern United States, Wisconsin, Minnesota and Texas, and sudden oak death, which claims oaks in the western states. Protecting the oaks means that animals that depend upon the trees for sustenance may thrive and that the ecosystem in which these trees live will not be disrupted. To remain mighty, the oak now needs help from humans, who have revered it for centuries.
Sheryl DeVore, an author of three published books on nature, is a reporter and website producer for the Chicago Tribune’s TribLocal.com. She has written for many nature-oriented organizations including Chicago Wilderness, National Audubon Society and Outdoor Illinois.
American elm (Ulmus americana)
“Old Elm that murmured in our chimney top/The sweetest anthem autumn ever made” —John Clare
American elm (Ulmus americana L.).
Photo by Andy and Sally Wasowski.
The world’s best-known plant disease came to the United States by accident. In 1930 a shipment of logs carrying Dutch elm disease from Europe arrived at an Ohio furniture company. Eighty years later, it is still difficult to comprehend the subsequent losses: more than 100 million dead trees, dramatically defoliated urban streets and the disappearance of living historic monuments.
Under normal circumstances, American elms (Ulmus americana) can survive several human generations. They bore witness to historic events and were celebrated and culturally revered, especially in the Northeast. While American elm’s natural range is the eastern half of North America, it is a quintessential New England tree. Towns such as New Haven, Connecticut, and Portland, Maine, proudly cultivated their “elm town” status by lining nearly every block with the stately tree.
The tree’s exalted status comes from its classic architecture, the “V” formation of the trunk. The only native elm with a vase-like canopy, American elm gave rise to awe-inspiring suburban vistas. The species is also fast-growing, hardy and tolerant of various ills. All in all, it is the ideal street tree. Ironically, this was to be its downfall.
In the U.S., two species of fungi are responsible for Dutch elm disease (so named because the causal agents were identified in Holland). Native to Asia, the pathogens are highly virulent and work quickly, entering the tree as spores through the burrowing and feeding of bark beetles. To fight the infection, the elm creates scar tissue that eventually inhibits the flow of water and nutrients. Sick plants develop wilted, yellowing leaves, leading to branch loss and eventually plant death.
The creation of foliar cathedrals exacerbated the problem since the contiguous canopy cover necessary to achieve the look meant planting trees close together. They were so close as to cause their root systems to fuse, facilitating fungal movement through this underground network. Simultaneously, the bark beetles aided and abetted the disease by feeding on the branches above and easily traveling down the street through the canopy.
Unlike trees in a forest, planted urban trees are cultivated varieties. These cultivars are clones, with identical genetic makeup. Only a handful of cultivars were used by municipalities on thousands of streets in hundreds of towns, creating miles and miles of monoculture that is as a rule more vulnerable to disease. The resultant epidemic illustrates the importance of genetic diversity within a species when creating makeshift populations.
While still present as a minor forest tree and although Dutch elm disease-resistant cultivars of American elm are available, the glory age of American elms in the urban landscape is preserved today only through written words and photographs.
Mariellé Anzelone is a botanist, urban conservation biologist and native plant landscape designer with her company, Drosera. She is also co-founder and executive director of NYC Wildflower Week, which connects urbanites to the nature in their backyards through free cultural programming.
Bur oak (Quercus macrocarpa)
Photo by Damon Waitt
Quaking aspen (Populus tremuloides)
And the wind, full of wantonness, woos like a lover/The young aspen-trees till they tremble all over.
—Thomas Moore, “Lalla Rookh/The Light of the Harem”
The names sprinkle the map of the western United States – Aspen Grove, Aspen Vista, Aspen Acres, Aspen Cove and, of course, the famous Colorado mountain resort known simply as Aspen. TV stations and newspapers begin in September predicting the best routes and weekends for aspen viewing, guaranteeing traffic jams on mountain roads and trails. Populus tremuloides is beloved in the West, where it paints the mountainsides yellow. But in recent years the ritual tours to view this colorful display have been tainted with worry and even dismay. A tree that is truly iconic – deeply rooted, both literally and figuratively, in the geography and culture of the region – is dying, quickly and in large numbers.
The aspen is not just a mainstay of the West; in fact, it is the most widely distributed tree in North America. But to many, it signifies the lure of the high mountain country, and it is in the West that its decline is most obvious and ominous. In 2004, observers in Colorado began to report sudden die-offs of aspen, and the mysterious phenomenon had spread by 2009 to a half-million acres. Similar areas of rapid mortality are occurring in Arizona, Utah and Wyoming and are likely to spread.
The phenomenon has been tagged SAD, Sudden Aspen Death. The acronym is grimly appropriate. Sadness is what people will feel when contemplating a summer without the whispering flutter of aspen leaves, an autumn without their sparkle or a winter without the spare elegance of their black-and-white trunks amid snow. But many plants and animals would feel their loss as well, since aspens provide a richer habitat than the surrounding conifers.
Because aspens are deciduous and even their leafed-out canopies admit a great deal of sunlight, an understory of grasses, wildflowers and shrubs flourishes beneath them. This ground cover and accumulated leaf litter tend to retain moisture.
Aspens readily populate an area devastated by fire but are often, though not always, eventually replaced by conifers, whose seedlings benefit from habitat provided by the aspen grove. However, SAD is not just the replacement of aspen in the process of succession. The causes of SAD are not known, but forest ecology researchers hypothesize that mature aspen stands that date from a time when natural wildfires occurred more often have been weakened by recent drought accompanied by higher temperatures, especially those on south-facing slopes at lower elevations. Unfortunately, these dying aspens are not regenerating as they normally would by means of new trees sprouting from the clonal root network.
When aspens disappear, mountain forests lose both valuable habitat and spectacular beauty. So the prospect of increasingly dry, warm Western mountains graced by aspens in name only is sad indeed.
Sandra D. Lynn lives in Albuquerque, New Mexico, where she writes and publishes poetry, essays and articles, often about native plants. She is working on a book about the natural and cultural history of poplars in the Southwest and the threats to their future.