- What’s the difference between horse chestnuts and sweet chestnuts?
- Identifying your Chestnut Tree
- There used to be 4 billion American chestnut trees, but they all disappeared
- Tallest American Chestnut Tree Found In Maine
What’s the difference between horse chestnuts and sweet chestnuts?
Chestnut is one of the world’s most popular and unique nut-bearing trees. Fresh chestnuts contain vitamin C and are much lower in fat than other nuts and contain twice as much starch as a potato, earning the chestnut tree the nickname “bread tree” in some regions of the world. Chestnut acreage in the U.S. has increased substantially over the past 30 years and Michigan boasts the largest number of growers and acreage in the United States. Michigan residents can benefit from our region’s agricultural diversity and often find Michigan chestnuts seasonally at local grocery stores, in roadside stands and at farmers markets.
Chestnut trees are found naturally in the landscape, in green spaces as ornamentals and are also planted in orchards for nut production. Edible chestnut species found in Michigan include the American chestnut, Chinese chestnut, Japanese chestnut, European chestnut and chinquapin. Consumers should be aware that the term “horse chestnut” is sometimes used to describe an unrelated tree in the genera Aesculus; trees in this genus may also be referred to as buckeyes. Trees in the genus Aesculus produce toxic, inedible nuts and have been planted as ornamentals throughout the U.S. and are sometimes incorrectly represented as an edible variety.
Left, edible chestnut with spiny husk and pointed tassel on tip. Center, fleshy husk of horse chestnut. Right, rounded toxic horse chestnuts without a tassel. Photos by Erin Lizotte (left) and Virginia Rinkel (center and right).
Edible chestnuts are easy to tell apart from unrelated toxic species like horse chestnut or buckeye. Edible chestnuts belong to the genus Castanea and are enclosed in sharp, spine-covered burs. The toxic, inedible horse chestnuts have a fleshy, bumpy husk with a wart-covered appearance. Both horse chestnut and edible chestnuts produce a brown nut, but edible chestnuts always have a tassel or point on the nut. The toxic horse chestnut is rounded and smooth with no point or tassel.
Quality, curing and season
The value of a chestnut is based primarily on its size and most nuts are sold fresh in the shell. Smaller quantities are available peeled and frozen or in value-added forms like chips, flour and slices. Chestnuts require a two- to three-week curing process to achieve maximum quality and sweetness. Chestnuts purchased from the store should have already undergone the curing process and should be ready to eat. Stores should be holding whole chestnuts under refrigeration for maximum quality. If you are purchasing chestnuts from a roadside market, be sure to ask if they have been cured. If you are collecting at a u-pick operation, it will be necessary for you to cure them yourself.
Peeled and frozen chestnuts. Photo by Erin Lizotte, MSU Extension.
During the curing process, starches in the nuts convert to sugar, making the chestnut taste sweeter. The best way to cure the chestnuts is to take time and store them just above freezing (32-40 degrees Fahrenheit) in your refrigerator for a couple of weeks. This longer, refrigerated curing process will increase their storability. The quickest way to cure chestnuts is to store them at room temperature for a few days; however, room temperature conditions will also dehydrate the chestnuts and so they will need to be consumed in a timely manner.
When selecting cured chestnuts at the store or market, consumers should inspect them carefully for quality just you would inspect a banana or pear. A ripe chestnut should have a slight give when squeezed, indicating they have been properly cured. A rock hard chestnut may require more curing time. A chestnut shell with a great deal of give indicates it is past its prime and has become dehydrated or has internal disorder. Lastly, when purchasing chestnuts, be sure the store or market is storing them in a chilled environment for maximum quality.
Chestnuts properly stored in a produce cooler at the grocery store. Photo by Erin Lizotte, MSU Extension.
When you get your chestnuts home, keep them cold but do not let them freeze (Due to their sugar content, chestnuts do not freeze until 28 F or below.). Store them in the produce compartment of your refrigerator where well-cured chestnuts can last for a few weeks. Ideally, place them in a plastic bag with holes made with a fork or knife to help regulate the moisture levels. If nuts are frozen, use them immediately after thawing.
The most recognizable and simple method of chestnut preparation is roasting. Chestnuts may be roasted in the oven, over a fire or even in the microwave. To roast chestnuts, be sure to score through the shell to ensure steam can escape and to prevent a messy and loud explosion. Scoring halfway around the equator works very well. Generally, it takes around 20 minutes in a 300 F oven.
For microwaving, the time can be as little as 2 minutes. Cook times can vary by microwave and oven, so some trial and error may be necessary and wrapping several nuts in a wet paper towel before microwaving works well. You can also try roasting them over an open fire or grill—though technically nestling them in the embers is best to prevent scorching. Depending on the temperature of the embers, this process can take anywhere from 15-30 minutes.
Cooked nuts should be tender, sweet and peel easily. Be sure to allow the chestnuts to cool before handling.
Remember, chestnuts aren’t just for roasting. Chefs around the world recognize their unique characteristics and produce delicious soups, pastas and spreads using this unique nut. Search online or in cookbooks to see how you can use this local food in your recipes!
For more information on Michigan produce, recipe ideas and preservation information, visit the Michigan Fresh page from Michigan State University Extension.
Roasted chestnuts on a street corner in France, where they’re called “marrons”.
Chestnuts roasting on an open fire: thus begins Nat King Cole’s classic Christmas song. One has to hope that they were true chestnuts (edible) and not horse chestnuts (toxic). And the nuts do look much alike, even though the trees they come from are very different. It may be wise to learn to tell the two part.
Two Trees, Two Different Families
First, the two trees are in no way related. The chestnut (Castanea) belongs to the Fagaceae, the beech and oak family. The horse chestnut (Aesculus), long in its own family, the Hippocastanaceae, was recently transferred to the Sapindaceae, the soapberry family. But the nuts of chestnuts and chestnut trees do look very similar. In the long distant past, someone began calling one plant “horse chestnut”, because its chestnutlike nuts could be used to treat horses of respiratory ailments, and the name stuck.
Edible or Toxic?
That was probably not a good idea, as the true chestnut (Castanea) is edible while the horse chestnut is toxic and in my opinion, there should be no possible confusion between edible and toxic plants.
Besides being roasted over open fires and sold as roasted nuts on street corners, the chestnut can be used as turkey stuffing or turned into chestnut cream.
The horse chestnut (Aesculus), on the other hand, is slightly toxic to humans and many mammals, although not to squirrels or deer. Like many poisonous plants, it can have useful medicinal properties when properly prepared.
In Your Garden
Chestnuts (Castanea spp.) are rarely used as ornamental trees.
Unless you’re a nut-grower, you’re unlikely to have a chestnut tree (Castanea) in your yard. Most species are big trees and are not considered terribly attractive. Besides, the very prickly burr (seed covering) is a major annoyance when it ends up on the ground in the fall. You certainly won’t want to step on it barefoot!
Also, in North America, the main native species, the American chestnut (C. dentata) was almost wiped out by chestnut blight (Cryphonectria parasitica), accidentally introduced from Asia in the early 20th century. As a result, many North Americans have never see a chestnut tree and their only encounter with chestnuts is likely to be through the roasted nuts offered on street corners or in supermarkets.
Europeans are more likely to have seen massive chestnut trees, as their own main native species, the common chestnut (C. sativa), grows widely throughout central Europe into Asia minor and was not decimated by the blight.
Their striking flowers make horse chestnuts popular ornemental trees.
In gardens, though, as well as along streets and in parks, the horse chestnut is widely grown as an ornamental tree in both North America and Europe. The common horse chestnut (Aesculus hippocastanum), with its upright spikes of white flowers dotted pink, is especially popular, as are hybrids with pink or red flowers that come from crosses between A. hippocastanum and other species.
Conkers is a popular kid’s game.
You may remember harvesting the nuts and using them to play conkers (a child’s game where they are hung on a string and banged together; the owner of the one that doesn’t break becoming the winner).
And there are other species of horse chestnut you sometimes find in gardens, notably Ohio buckeye (A. glabra), a medium-sized tree, and bottlebrush buckeye (A. pauciflora), a large shrub with white flowers. (The term “buckeye” is used for Aesculus species whose shell is spineless, as they are said to resemble deer eyes they split open.)
Telling Them Apart
Here’s an easy guide to telling chestnuts and horse chestnuts apart:
Entire toothed leaf.
Multiple spikes of yellowish white flowers.
Nuts (usually more than one) enveloped in an extremely spiny burr.
Compound leaf with 5 to 7 leaflets.
Single upright spike of attractive flowers.
One or two nuts in a capsule with or without short, widely spaced spines (variable according to species).
Identifying your Chestnut Tree
Almost all the chestnut trees in Louisville currently are Chinese chestnuts, including a large collection at Cave Hill Cemetery, and several groupings at Bernheim. There were previous examples of European chestnuts (C. sativa) at Yew Dell Botanical Gardens, but these were heavily blighted and have been removed. A map of Chinese chestnuts reported in Louisville and a slide show will be attached to this page.
|Leaf taper to stem||straight||curved||curved||curved||straight||Be aware that all chestnuts can cross-pollinate, so that the chestnut you are trying to identify may actually be a mix of two or more different types of chestnuts, known as a hybrid.
We can attempt to identify your chestnut, if you are unable to do so, by means of a leaf and twig sample.
Please press one or two fresh leaves between cardboard with a 4-6 inch twig. Do not use plastic unless it is perforated or the leaves will mold. Crushed and bent leaves will not be in good enough condition to positively analyze.
New England Regional Science Coordinator
Northern Research Station, US Forest Service
705 Spear Street
South Burlington, VT 05403
|Leaf taper to tip||straight||curved||curved||curved||straight|
|Teeth||1-3 mm, small, sharp, no hook||tiny, often only bristles, no hook||large or small, not pronounced or hooked||big, sharp or rounded, no hook||6 mm, big, sharp, and often curved (hooked)|
|Underside||sun leaves hairy||many large dots (glands), sun leaves hairy||sparse dots, sun leaves hairy||many small dots, sun leaves hairy on some specimens but not others||many small dots, sun leaves not hairy, long sparse hairs only on midrib|
|Twig||hair tips, purple||pink to light red, large white lenticels||hairy tips, tan to pea green, large elliptical yellow lenticels||stout, dark brown, small white lenticels||slender, smooth, hairless, reddish brown, small white lenticels|
|Bud||3 mm, downy dark red, pointed, longer than wide, sticks out from stem||glossy brown, as long as it is wide (rounded)||hairy, tan, dull brown to black, rounded and flat against stem||dark red, fat and globular||long 6 mm, smooth, reddish brown, pointed or longer than it is wide, sticks out from stem|
1/2 tip pointed with a round cross section
rounded hairy tip, sunburst pattern
pointed tip, top 1/3-2/3 downy, sunburst at base
This is an example of an American chestnut tree reaching its branches out in the sun over Flint Pond in Lincoln, MA. The long thread-like structures are male catkins, which are not yet showing anthers. When anthers appears the catkins become white and creamy yellow, and were called “summer snow” in the Appalachians. This is a cluster of spiny chestnut burs, with two nuts. The nut on the right is firm and full and delicious (pollinated) but the other is shriveled and hollowed out and will not sprout. In a fully pollinated bur, there are typically 3 full nuts. These are catkins fully developed with burs that are ready to be pollinated. The other native trees that bloom late in the year around the same time as American chestnuts are Black Locust and Sourwood. The flowers of Sourwood can be mistaken for chestnut at a distance. Chinese chestnuts bloom earlier than American chestnuts. Those backcross hybrid trees (15/16th hybrids) which leaf out and bloom earlier than native KY American trees are revealing that Chinese heritage.
This is a group of 20 year old pure American chestnuts planted by Welles Thurber (in front) in Maine. Notice the height of these young trees. They are covered with burs.
This is a large Chinese tree in Boston, Kentucky, one of two trees in the old cemetery.
Identifying Your Chestnut Tree:
- The first step in deciding whether your tree is a possible chestnut is to distinguish it from other trees which can be mistaken for chestnut trees. The chestnut genus “Castanea” is not the same as the horsechestnut family “Aesculus” or the beech genus “Fagus”.
- In a second step, you need to learn the differences between the common members of the Castanea family. In Kentucky, these are the American chestnut (Castanea dentata), the Chinese chestnut (Castanea mollissima), and the occasional Japanese chestnut (Castanea crenata). In addition, there are specimens of Chinkapin growing in Kentucky.
Beech – If your tree looks like this, then it is probably a beech tree. These trees have toothed leaves, and smooth gray bark. They also have long pointed buds. The leaf is wider and shorter than the American chestnut tree leaves. There are many giant old American beeches in Cave Hill Cemetery at the Grinsted entrance, and along Lexington Road, particularly at the entrance to Whitehall Historic Home. Horse Chestnut – If your tree has leaves like this, it is probably a horsechestnut tree. The leaves are “palmate”, radiating from the center, and are arranged in a spoke. The tree is often found planted in towns. It originated in Europe, and it is often what people think of when they hear about “chestnut” trees. It is in a separate family called “Aesculus”. The American buckeye trees are also in this family. The nuts can be confused with American chestnuts, since they have the same shiny rich brown appearance, but THEY ARE NOT EDIBLE. American Chestnut – If your tree has long toothed pendant leaves like this, it may be a member in the chestnut family. The American chestnut has long canoe shaped leaves with a prominent lance shaped tip, with a coarse, forward hooked teeth at the edge of the leaf. The leaf is dull or “matte” rather than shiny or waxy in texture.
Identifying Your Chestnut Tree – Step 2
Once you have decided that you have a Chestnut, the second step in deciding if your tree is American chestnut is to distinguish whether it is pure American, or if it has some non-American chestnut parentage.Over the past hundred years or so, European, Chinese, and Japanese chestnut trees as well as hybrids have been planted in the natural range of American chestnut, so remote location is not necessarily a guide to a tree’s parentage.
Most of established Chestnuts are Chinese, and they have a very distinctive apple tree shape, rounded with multi-stemmed trunk (see next column). The leaf is spade shaped, with a rounded bottom and is characteristically wider in the other third of the leaf. It is glossy and heavier than American leaves.
But fortunately, each species of chestnut as a pure species has a definite kind of glandular hair on the back of the leaf than can be seen with a good dissecting scope. This is generally the safest way to confirm identification of a pure species.
Other chestnut identification sites to improve your eyes…
- The American Chestnut Foundation identification pages
- USDA Plants Database
Other chestnut identification resources
“We’re just going to walk up the ridge,” Don Leopold tells me, leading me along a trail through Whiskey Hollow, a 14-hectare nature reserve about 20 minutes outside Syracuse, N.Y. “It’ll be a good stretch of the legs.”
It’s a chilly, slightly cloudy September day. Leopold and I have traveled here hoping to find a rather elusive species—one that used to be so abundant it was impossible to take a walk in these woods without seeing dozens of its kind, if not several hundred. There is no guarantee we will find the creature today, however. Although not extinct, the organism we seek has been dwarfed in size and number, maintaining an unassuming existence in the understory instead of dominating the forest as it once did.
We stomp off the trail, down a gentle slope and stop beneath a young skinny tree maybe 4.5 meters tall with gray bark and serrated leaves like giant arrowheads. To most people the tree would be entirely unremarkable. But to Leopold, a forest ecologist, the sapling is a rare and beautiful sight—a living descendant of the formerly mighty American chestnut.
Before the early 1900s one in every four hardwood trees in North America’s eastern forests was an American chestnut. Together, chestnuts and oaks predominated in 80 million hectares of forest from Maine to Florida and west to the Ohio Valley. Every spring so many chestnut trees erupted in white blossom that, from a distance, the hills appeared to be draped in quilts of snow.
The American chestnut once provided copious food and shelter for animals and people alike. Bears, deer and all manner of small mammals and birds feasted on fallen chestnuts, which sometimes piled so high on the forest floor that people would scoop them up with shovels. Reaching heights of 40 meters and growing two meters around the middle, American chestnuts were home to squirrels, chipmunks, blue jays and scores of benign burrowing insects. People, too, constructed their lives around chestnut. Lightweight, rot-resistant, straight-grained and easy to work with, chestnut wood was used to build houses, barns, telegraph poles, railroad ties, furniture and even musical instruments.
In the late 1800s a hitchhiker that would ultimately devastate the country’s chestnut forests arrived in America for the first time. A New York City nurseryman named S. B. Parsons imported Japanese chestnut trees in 1876, which he raised and sold to customers who wanted something a little exotic in their gardens. Other nurseries in New Jersey and California soon did the same. One or perhaps all of these shipments concealed the pathogenic fungus Cryphonectria parasitica, which chokes chestnut trees to death by wedging itself into their trunks and obstructing conduits for water and nutrients. Asian chestnut trees had long evolved resistance to C. parasitica, but their American relatives—which had never encountered the pathogen before—were extremely susceptible to the fungal disease known as chestnut blight.
First discovered in New York State in 1904, chestnut blight was soon spotted in New Jersey, Connecticut, Massachusetts and Pennsylvania. Within 50 years, C. parasitica killed nearly four billion chestnut trees. Now, few if any large trees remain in the chestnut’s native range. Because the species has a resilient root system, however, the American chestnut survives here and there in the form of living stumps, which sometimes send up young, skinny treelings like the one Leopold and I found. Although a credit to the chestnut’s persistence, such saplings are mere gestures at the glory and girth of their predecessors and almost always succumb to blight by their teens or 20s, never getting old enough to flower and reproduce.
Humans are both responsible for the demise of America’s chestnut forests and the only species on the planet that can do something about it. Since the 1980s several generations of Leopold’s colleagues at the State University of New York College of Environmental Science and Forestry (S.U.N.Y.–ESF) have toiled to restore the American chestnut to its native habitat. One semisuccessful strategy has been mating American chestnut with blight-resistant but much smaller Chinese chestnut, selectively breeding the hybrids to achieve a tree that is as genetically and physically similar to an American chestnut as possible, yet still resilient. Genetic engineering has offered another even more successful route to restoration. By taking genes from wheat, Asian chestnuts, grapes, peppers and other plants and inserting them into American chestnut trees, William Powell of S.U.N.Y.–ESF and scores of collaborators have created hundreds of transgenic trees that are almost 100 percent genetically identical wild American chestnut yet immune to C. parasitica. The scientists hope to get federal approval to begin planting these trees in the forest within the next five years (See “The American Chestnut’s Genetic Rebirth” in the March 2014 issue of Scientific American).
To predict how a new generation of American chestnut trees will modify the forest in the coming decades we need to examine how this one species defined the forest in the past. Doing so is difficult, however. C. parasitica wiped out nearly all mature American chestnut trees before forest ecology became the rigorous science it is today, so most of the pre-1950s data about the species comes from observational studies rather than controlled experiments. Still, by drawing on historical records and recent research on remaining chestnut trees, we can piece together a portrait of this magnificent tree’s role in the forest ecosystem. In its prime the American chestnut determined the physical structure and microclimate of the forest, creating specific and stable environmental conditions on which many other creatures depended. When the American chestnut fell, the whole forest shuddered.
The story of how the American chestnut once defined North America’s eastern forests—and how it might once again—begins in the last ice age. Between two million and 10,000 years ago, an epoch known as the Pleistocene, massive sheets of glacial ice covered Canada and the northern regions of what is today the U.S., repeatedly invading and retreating. Mammoths, mastodons, giant beavers and colossal sloths roamed New England, which at the time was a forested tundra filled with evergreen, needle-leaved conifers like spruce and pine as well as some hardwood, leaf-shedding trees such as birch, along with many grasses and shrubs. Around 10,000 years ago the ice sheets dwindled, the Gulf Stream moved north and climatic conditions much more similar to the recent past began to establish themselves. Conifers claimed the northern area of New England, hardwood species dominated its south and two kinds of trees shared its central region. A warming climate over the next 3,000 years allowed hardwoods like red maple, beech and hickory to migrate into northern New England. Between 1,500 and 2,000 years ago American chestnut followed this pattern, spreading across Connecticut and Massachusetts.
Over time North America’s forests became a dense patchwork of different sylvan communities, each characterized by a unique topography and climate. As a whole, the deciduous forest was home to many different tree species—oaks, beeches, maples, basswoods, hickories, chestnut, ashes, elms, birches and poplars—but different types of trees predominated in different regions. Between Maine and northern Georgia oaks and chestnuts prevailed.
Soon enough the eastern forests had to contend with a relentlessly invasive species with which they had never interacted before: people. Based on the latest geologic and archaeological evidence, early explorers from east Asia may have arrived in North America by water along the western coast and by land via an ice-free corridor as long as 16,000 years ago. Once settled in the east, Native Americans chopped down many trees for firewood and building materials and used fire to clear tracts of forest. Although it was by no means trivial, this first wave of human landscaping was nothing compared to what would come from across the Atlantic.
From the 1750s onward European settlers burned immense sects of forest, rapidly converting them into farmland. As much as 75 percent of forested areas became open fields. Yet this dramatic transformation was short-lived. By 1850, just before C. parasitica completed its journey from Asia to America, people began to abandon the vast majority of newly created farmland and move west, lured by the Louisiana Purchase, the California gold rush and improving transportation. As people left, trees moved in. Today, forest covers more than 80 percent of New England.
The American chestnut would surely have prospered as part of this renewal if only humans had not inadvertently infected the forests with a deadly fungus. Instead of reclaiming old forest sites like other tree species, the chestnuts shriveled into a meager existence, which in turn changed the whole ecosystem in which they were enmeshed. In areas where the blight had reduced a stand of chestnut trees to stumps, all available shade vanished, stunting plant species requiring shade to thrive. Sun-loving saplings, blackberries and greenbriers wrapped their nubile tendrils around the opportunity, tangling with one another in thick knots as they scaled toward the light. Oaks, maples and tulip trees became more numerous, claiming real estate that chestnut might have occupied.
These newly dominant tree species were not large enough to provide forest animals with as much food and refuge as the chestnut had once offered. Unlike oaks—which often flower too early to escape late frosts, losing what might have been a bounty of acorns to the bitter cold—chestnuts reliably bloomed after the latest frost and produced huge numbers of nuts, each of which was bigger than an acorn.
One of the most frequent diners at chez chestnut was the now extinct passenger pigeon. A swift and agile flier, highly social and twice the size of modern urban pigeons, the passenger pigeon was once the most common bird in North America. Scientists have estimated that as many as five billion passenger pigeons lived in America when Europeans first discovered the new land, comprising between 25 and 40 percent of all birds on the continent. In 1866 a cloud of 3.5 billion passenger pigeons 1.5 kilometers wide and 480 kilometers long took 14 hours to pass over southern Ontario. Such massive flocks routinely migrated from one breeding site to another, going wherever weather was most welcoming and food most plentiful. By the early 1900s, however, the passenger pigeon was pretty much nonexistent in the wild.
Although chestnut blight was not the sole or even primary cause of the passenger pigeon’s downfall, the fungal disease almost certainly hastened the bird’s extinction. At the same time that people were using nets, guns and pots of noxious sulfur to hunt pigeons on a massive scale for its meat and feathers, blight was knocking down the chestnut trees the birds needed to survive. Not only did the trees provide hoards of nuts, they also offered massive and sturdy branches on which the birds could safely roost and breed. Enormous flocks were notorious for breaking weaker branches with their weight.
Even the chestnut’s leaves were more nourishing to many animals than those of oak. Whenever leaves fall into streams or standing water they leach all their chemicals—a slower version of what happens to tea leaves in hot water. Chestnut leaves decay much more quickly than tougher, lignin-rich oak leaves, releasing plenty of nutrients for the aquatic larvae of various insects. A 1985 study found that crane fly larvae, for instance, prefer dining on American chestnut and maple leaves to eating oak leaves.
Much more recently, Aaron Stoler of the University of Pittsburgh and his colleagues re-created miniature ecosystems resembling forest wetlands by filling kiddie pools with water, gray tree frogs, plankton, snails, insects, bacteria and leaf litter from American chestnut and a range of other tree species. His experiments confirmed that chestnuts provide more nutrients more quickly than oak, but also underscored that a wetland thrives when it has a variety of leaf types—some that decompose slowly, others quickly, rather than just one kind or the other. In one case, red maple leaves decayed so quickly and stained the water so dark that they prevented plankton from producing oxygen through photosynthesis. As oxygen levels in the water sank, the frogs began to die, which would translate to less food for snakes, birds and other larger predators in the wild. A leaf falling into a stream might seem like an insignificant event, but it sparks a complex chain of interactions between countless living things that ultimately alter an entire ecosystem.
The same is true for falling twigs and branches. Resilient chestnut branches that plopped into brooks would have created more permanent underwater shelters and hiding spots for fish than more swiftly disintegrating oak wood. J. Bruce Wallace of the University of Georgia and his team discovered that 24 percent of large woody debris that had accumulated in a southern Appalachian mountain stream by the late 1990s was from American chestnut that had perished 50 years earlier.
Chestnut trees also undoubtedly changed the very soil in which they grew. Before the 1950s mature chestnut trees in their native range lived in a variety of soils—mostly well-drained acidic dirt—but also soils made from shale, sandstone and limestone. Of course, researchers cannot directly study how those trees altered soil chemistry—but they can get close. The largest remaining stand of mature American chestnut trees grows in West Salem, Wisconsin. In the late 19th century a Wisconsin settler named Martin Hicks planted about nine chestnut trees that quickly multiplied, escaping the brunt of the chestnut blight that swept the east. C. parasitica eventually reached even these trees, however, perhaps on the boots of visiting New England scientists. White, red and black oaks, as well as hickory, aspen and several more of the same hardwood tree species found in the chestnut’s native range grow around the stand in Wisconsin—in the same kinds of soils, too—creating a kind of eastern deciduous forest microcosm.
In 2002 Charles Rhoades of the U.S. Forest Service’s Rocky Mountain Research Station traveled to West Salem and gathered dirt and leaf litter from areas surrounding 20 chestnut trees and from 20 different spots where other kinds of hardwood trees grew. Later, in the lab, he analyzed the chemistry of these samples. Chestnut leaves had more nitrogen, phosphorus, potassium and magnesium than leaves from other species, and sandy soil beneath chestnuts had as much as 17 percent more carbon and nitrogen as well as a little more moisture. In sandy soils chestnuts were returning more nutrients and life-building molecules to the earth, where they would be available to numerous other plants, animals and microorganisms.
Just a year earlier, Ryan McEwan of the University of Dayton and his colleagues also visited West Salem and harmlessly drilled into the trunks of chestnut trees and eight other species, collecting more than 100 pencil-size wood samples. Tree-ring analysis confirmed that, as many ecologists had surmised over the years, chestnuts grow faster than most other hardwood trees and that the trees are tenacious, surviving in the understory as saplings until enough light breaks through the canopy for them to grow tall.
If S.U.N.Y.–ESF’s Powell and his colleagues succeed in planting young transgenic blight-resistant chestnuts in the wild, chances are good that the trees will successfully expand their domain—relatively quickly in some areas; slowly but surely in others. Over the decades this new generation of American chestnuts will change the forest from floor to canopy: Their uppermost branches will bring shade to areas that have too little; their quickly decomposing leaves will carpet the soil and drift into streams and standing water, staining the water with nutrients; their trunks will be home to billions of insects and mammals, their branches the foundations of nests; and, one day, when the trees are mature enough, they will drop scores of chestnuts for the first time in more than a century.
This past September, a day before taking a walk through the woods with Leopold in search of wild American chestnut, Powell gave me a tour of his laboratories. Linda McGuigan, one of the lab technicians, invited me to examine chestnut tree embryos under a microscope—clusters of rapidly dividing cells that have the potential to become an adult tree. In white light the embryos looked like clumps of sea salt. When Linda switched the light source to ultraviolet, some of the clusters glowed neon green. These were the transgenic embryos. Powell and his colleagues hitch the gene for blight resistance to one that makes a green fluorescent protein, so they can easily identify their successes.
Such naked embryos are not as hardy as seeds. You can’t just put them in soil, spritz them with water and wait for them to sprout. Instead, Powell and his colleagues have spent 15 years developing an elaborate growing regimen that simulates what would usually happen to an embryo within the protective husk of a chestnut seed buried in the forest floor. Once the embryos are large enough the scientists transplant them to glass cubes layered with nourishing translucent gels. They treat each one with a series of plant hormone cocktails that trigger the growth of roots and shoots at different times, carefully controlling light, temperature and humidity all the while. Whereas ordinary seedlings have a thin stem and a few large, floppy leaves, the plants inside the cubes are more like baby bonsai trees, producing adult structures in miniature.
After weeks or months in a greenhouse and growth chambers that look like giant green refrigerators, the chestnuts are relocated to fields just on the edge of Syracuse. Here, fenced off from the forest, grow thousands of chestnut trees young and old. Some are Chinese chestnut; some are American-Chinese hybrids; and others are fungus-fighting transgenic American chestnut trees. Powell stoops beside a transgenic tree—one of the earliest he and his team created. He points to the base of one branch, where the bark is frayed and encircled by what looks like a band of rust. Moving our eyes along that branch, we see its leaves are yellowing and falling off. The earliest varieties of genetically engineered trees were not strong enough to fend off C. parasitica, but the newest transgenic trees in this field are very healthy. The risk of pollen from these trees carrying new genes to other plant species is incredibly low—the chestnut has few close relatives in its native range with which it is sexually compatible. If anything, the engineered trees might mate with wild chestnut, imbuing the latter with some much needed immunity.
Powell and his colleagues have also been comparing the transgenic trees with typical chestnuts in various ways, making sure that they both form the same kind of associations with beneficial bacteria and fungi; that the engineered trees are not in any way harmful to benign insects; and that the nut chemistry of transgenic trees matches that of ordinary ones. So far, everything syncs up.
Toward the end of our field trip, Powell, his colleague Andy Newhouse and I stop and look around. “Well, this is our program,” Powell says. “Anything else you think we should show him?”
“Not unless you want to look in the woods,” Andy says. “But the chestnuts around here are so small that there’s not a whole lot to look at. If you’re heading out with Don Leopold tomorrow, I think he’ll do a better job.”
The next day, after hiking for an hour and finding three American chestnut saplings total, Leopold and I have looped back to the beginning of the trail. He spots some wild sassafras—which was once used to flavor root beer—and cuts it so we can breathe in its spice. Before we leave, he decides to collect a few leafy American chestnut branches. We trek back to the first tree he spied.
“I want to show these to my students,” he says. “We don’t cover this species in class because it hasn’t really been relevant for the last 80 years. But I’m looking forward to including it again.”
Braun, E. Lucy. Deciduous Forests of Eastern North America. The Blackburn Press, 1950.
Freinkel, Susan. American Chestnut: The Life, Death and Rebirth of a Perfect Tree. Paperback. University of California Press, 2009.
Foster, David and John D. Aber. Forests in Time: The Environmental Consequences of 1,000 Years of Change in New England. Yale University Press, 2006.
There used to be 4 billion American chestnut trees, but they all disappeared
American chestnut trees once blanketed the east coast, with an estimated 4 billion trees spreading in dense canopies from Maine to Mississippi and Florida. These huge and ancient trees, up to 100 feet tall and 9 feet around, were awe-inspiring, the redwoods of the east coast, but with an extra perk — the nuts were edible. Chestnuts were roasted, ground into flour for cakes and bread, and stewed into puddings. The leaves of the trees were boiled down into medicinal treatments by Native Americans. The trees make appearances throughout American literature, like in Thoreau’s journal, where he considered his guilt over pelting them with rocks to shake the nuts loose while he lived in Walden woods, musing that the “old trees are our parents, and our parents’ parents, perchance.” Chestnut trees offered shade in town squares, were the wood of choice for pioneers’ log cabins, and were a mainstay of American woodcraft. In short, chestnuts were part of everyday American life. Until they weren’t.
Finding a mature American chestnut in the wild is so rare today that discoveries are reported in the national press. The trees are “technically extinct,” according to The American Chestnut Foundation. The blight that killed them off still lives in the wild and they rarely grow big enough to flower and seed, typically remaining saplings until they die. Essentially, the giant trees were reduced to shrubs by the 1950s.
The problem was a fungus imported from Asia that spread easily, attaching to animal fur and bird feathers. Spores were released in rainstorms and tracked to other trees through footsteps. The fungus infected trees through injuries to the bark as small as those created by insects. “It looks like a target filled full of small shot holes,” one Pennsylvania paper reported as the blight spread.
The first chestnut tree may have been infected as early as the 1890s, with blight first reported in 1904 when it was spotted on a tree in New York’s Botanical Garden. Panic over the blight was widespread by the 1910s. State commissions were formed. Farmers were implored to chop down trees with any signs of blight. “Woodman, burn that tree; spare not a single bough,” begged The Citizen, a paper from Honesdale, Pennsylvania, the heart of the chestnut tree’s range. Even the Boy Scouts pitched in to try and save the chestnuts, scouring forests for blighted trees as part of a multi-state effort to create an infection-free zone.
The combined powers of the public, scientists, and the governments weren’t enough to save the chestnuts. The loss was stunning, both financially and emotionally. “Efforts to stop the spread of this bark disease have been given up,” The Bismarck Daily Tribune resignedly reported in 1920. The paper estimated that the value of the trees was $400,000,000 as recently as a decade before.
A dying chestnut tree photographed in 1916 in North Spencer, New York. (Cornell University)
The end of the trees marked the end of a “conspicuous and beautiful feature of the landscape in this country,” and the Daily Tribune predicted with incredulity that “schoolboys of the future who read the poem of the village blacksmith will ask, What is a chestnut tree?” (the allusion was to the first line of a Longfellow poem). The traumatic loss of the chestnut tree finally spurred federal laws to protect native plants from diseases they can’t resist.
Though the trees are long gone from the forest canopies of the east coast, efforts to find a cure for the blight continue. In fact, they haven’t stopped since the trees started dying. Some scientists are crossing American chestnuts with Chinese chestnut trees, which are resistant to the blight, and then backcrossing the hybrids with pure American trees. Others are infecting trees with other viruses to kill the blight. Still more are taking a cutting edge approach and sequencing the DNA of the American chestnut and the fungus that causes blight, in part to guarantee that any trees reintroduced into the wild are truly blight resistant.
The century-long drive to save the chestnut tree isn’t just about nostalgia or a funny manifestation of American exceptionalism. The American chestnut is distinct from other varieties for both its size and how quickly it grows, which is why it was historically such a valued source of wood. And given the starring role the nuts played in American cuisine until the trees died, they tasted pretty good too.
Tallest American Chestnut Tree Found In Maine
A century ago American chestnut trees dominated the eastern woodlands from Georgia to Maine. Growing straight and tall they were prized for timber. Wildlife depended on the nuts they provided every year.
People ate the chestnuts, too, scooping them up by the sackful every Fall. Then came an exotic blight accidentally introduced from Asia and the species was virtually wiped out.
That’s why scientists are excited by a recent find in western Maine, a record-breaking find that is raising their hopes for the future.
The unusual discovery was made from the air. Dr. Brian Roth, a forest scientist with the University of Maine was surveying areas most likely to have habitat conditions favorable for chestnut trees and – voila! Flying over some woods in Lovell he saw a telltale sign.
“In July, when nothing else is blooming, this tree will have a large amount of white flowers in its crown,” says Roth. “The old timers talk about the hillsides in the Appalachian Mountains being covered in flowers as if it was snow and so we were able to key in on the particular weeks that these were blooming and did find this tree.”
This is not just any tree. This is an American chestnut tree worthy of the record books. And this week, a gaggle of reporters, photographers and members of the American Chestnut Foundation, trudged out on a rainy December day to see Brian Duigan of the Maine Forest Service confirm some crucial measurements.
Listen Listening… / 4:21 Susan Sharon reports on the tallest American chestnut tree in North America. Shane Duigan of the Maine Forest Service measuring the girth of the tallest chestnut tree in North America in Lovell, Maine. Credit MPBN/Susan Sharon
“I have 16.1 inches,” Duigan says.
As girth goes, this chestnut tree is not so impressive. It’s on the skinny side. And most people wouldn’t pick it out as distinctive in a forest lineup. But when it comes to height, this American chestnut reigns supreme.
“We think it’s around one hundred years old,” says Roth. “It’s over 100 feet tall, which makes it the tallest tree that we know of in North America.”
One hundred and 15 feet tall to be precise. But beyond its size, Roth and members of the American Chestnut Foundation are interested in this hearty chestnut because of its ability to survive. Surrounded by a cluster of equally tall pine trees, this particular tree has escaped the fungus that has killed or stunted most of the rest of its species.
“And so we’re quite interested in these native trees, one for getting them into the population, our breeding program, as well as where do these trees grow?” Roth says.
The North Carolina-based American Chestnut Foundation is devoted to restoration of the American chestnut to its historic range. And over the past three decades the non profit organization has attracted a loyal following, six thousand chestnut enthusiasts who help run a complex breeding program to transfer genes from the Asian chestnut, which is resistant to the fungus, to the American chestnut, which is not. Dr. Jared Westbrook is the American Chestnut Foundation’s geneticist.
“We have an orchard of trees, chestnut trees, in Meadowview, Virginia and so I’m working on developing strategies for breeding and selecting the most blight resistant trees,” Westbrook says.
He says more than 60,000 chestnut trees have been planted so far. To help them out, the group is using a virus that infects the chestnut fungus and makes it weaker. But Westbrook says only 500 trees, the toughest and the best of the bunch, will ultimately be selected for reintroduction to the wild.
“To do that is not as simple as inoculating the trees with the blight and picking the ones with the least amount of disease,” Westbrook says. “There’s still a lot of cryptic variation so you have to extract DNA, do DNA sequencing and figure out which ones are the strongest.”
If successful, recovery of the American chestnut through breeding and biotechnology could be a model for protecting other tree species from Dutch Elm disease, hemlock woolly adelgid and the emerald ash borer. Lisa Thomson president and CEO of the American Chestnut Foundation says there’s a lot of hope riding on the little chestnut.
“We see real promise of the future to bring the species back and how often can you bring a species almost on the brink of extinction which the chestnut was?” says Thompson.
Thomson says she and her volunteers won’t see a cathedral of chestnuts in the forest in their lifetimes but their grandchildren will and that’s enough of a vision to keep them all going.