American chestnut

American chestnut Castanea dentata
American chestnut leaves and nuts
Scientific classification
Kingdom:	Plantae
(unranked):	Angiosperms
(unranked):	Eudicots
(unranked):	Rosids
Order:	Fagales
Family:	Fagaceae
Genus:	Castanea
Species:	C. dentata
Binomial name
Castanea dentata (Marsh.) Borkh.
Natural range of Castanea dentata

The American chestnut, Castanea dentata, is a large, monoecious deciduous tree of the beech family native to eastern North America. Before the species was devastated by the chestnut blight, a fungal disease, it was one of the most important forest trees throughout its range. There are now very few mature specimens of the tree within its historical range, although many small shoots of the former live trees remain. However, there are hundreds of large (2 to 5 ft diameter) trees outside its historical range, some in areas where less virulent strains of the pathogen are more common, such as the 600 to 800 large trees in northern lower Michigan.^[1][2]

Description

Castanea dentata is a rapidly growing deciduous hardwood tree, historically reaching up to 30 metres (98 ft) in height, and 3 metres (9.8 ft) in diameter. It ranged from Maine and southern Ontario to Mississippi, and from the Atlantic coast to the Appalachian Mountains and the Ohio Valley. It has several related chestnut species, such as the European sweet chestnut, Chinese chestnut, and Japanese chestnut, which are distinguishable from the American species by a few morphological traits, such as leaf shape, petiole length and nut size. C. dentata was once one of the most common trees in the northeastern US. In Pennsylvania alone, it is estimated to have comprised 25-30% of all hardwoods. The tree's huge population was due to a combination of rapid growth and a large annual seed crop in comparison to oaks which do not reliably produce sizable numbers of acorns every year. Nut production begins when C. dentata is 7–8 years old. The tree's survival strategy proved so successful that it may have ultimately become vulnerable to disease because of a near-monoculture in some locations. This natural event stands in comparison to other epidemics, such as Dutch Elm Disease and Emerald Ash Borer, caused by humans overplanting particular species of trees.

C. dentata can be best identified by the larger and more widely spaced saw-teeth on the edges of its leaves, as indicated by the scientific name dentata, Latin for "toothed". The leaves, which are 14–20 cm (5–8 in) long and 7–10 cm (3–4 in) broad, also tend to average slightly shorter and broader than those of the sweet chestnut. The blight-resistant Chinese chestnut is now the most commonly planted chestnut species in the US, while the European chestnut is the source of commercial nuts in recent decades. It can be distinguished from the American chestnut by its hairy twig tips which are in contrast to the hairless twigs of the American chestnut. The chestnuts are in the beech family along with beech and oak, but are not closely related to the horse-chestnut, which is in the family Sapindaceae.

The chestnut is monoecious, producing many small, pale green (nearly white) male flowers found tightly occurring along 6 to 8 inch long catkins. The female parts are found near base of the catkins (near twig) and appear in late spring to early summer. Like all members of the Fagaceae family, American chestnut is self-incompatible and requires two trees for pollination, which can be any member of the Castanea genus.

American chestnut male (pollen) catkins

The American chestnut is a prolific bearer of nuts, usually with three nuts enclosed in each spiny, green burr, and lined in tan velvet. The nuts develop through late summer, with the burrs opening and falling to the ground near the first fall frost.

The American chestnut was a very important tree for wildlife, providing much of the fall mast for species such as white-tailed deer and wild turkey and, formerly, the passenger pigeon. Black bears were also known to eat the nuts to fatten up for the winter. The American chestnut also contains more nitrogen, phosphorus, potassium and magnesium in its leaves when compared to other trees that share its habitat. This means they return more nutrient to the soil which helps with the growth of other plants, animals, and microorganisms.^[3]

Chestnut blight

Once an important hardwood timber tree, the American chestnut is highly susceptible to chestnut blight, caused by an Asian bark fungus (Cryphonectria parasitica, formerly Endothia parasitica) accidentally introduced into North America on imported Asiatic chestnut trees. The disease was first noticed on American chestnut trees in what was then the New York Zoological Park, now known as the Bronx Zoo, in 1904, by chief forester Hermann Merkel. While Chinese chestnut evolved with the blight and developed a strong resistance, the American chestnut had little resistance. The airborne bark fungus spread 50 mi (80 km) a year and in a few decades girdled and killed up to three billion American chestnut trees. Salvage logging during the early years of the blight may have unwittingly destroyed trees which had high levels of resistance to this disease and thus aggravated the calamity.^[4]

New shoots often sprout from the roots when the main stem dies, so the species has not yet become extinct. However, the stump sprouts rarely reach more than 6 m (20 ft) in height before blight infection returns.

Young tree in natural habitat

The total number of chestnut trees in eastern North America was estimated at over three billion, and 25% of the trees in the Appalachian Mountains were American chestnut. The number of large surviving over 60 cm (24 in) in diameter within the tree's former range is probably fewer than 100. Huge planted chestnut trees can be found in Sherwood, Oregon, as the Mediterranean climate of the West Coast is not conducive to the spread of the fungus, which relies on hot, humid summer weather. American chestnut thrives as far north as Revelstoke, British Columbia. Although large trees are rare east of the Mississippi River in contemporary times, it exists in pockets of the blight-free West, where the habitat was agreeable for planting: settlers brought seeds for American chestnut with them in the 19th century. At present, it is believed that survival of C. dentata for more than a decade in its native range is almost impossible. The fungus utilizes Northern red oak as a host, and while the oak itself is unaffected, any American chestnuts nearby will quickly succumb. In addition, the hundreds of chestnut stumps and "living stools" dotting Eastern woodlands may still contain active pathogens.

American chestnut field trial sapling from the American Chestnut Cooperators Foundation

Several organizations are attempting to breed blight-resistant chestnut trees. One of these is the American Chestnut Cooperators Foundation, which breeds surviving all-American chestnuts, which have shown some native resistance to blight. The Canadian Chestnut Council is an organization attempting to reintroduce the trees in Canada, primarily in Ontario. Another is The American Chestnut Foundation, which is backcrossing blight-resistant Chinese chestnut into American chestnut, to recover the American growth characteristics and genetic makeup, and then finally intercrossing the advanced backcross generations to eliminate genes for susceptibility to blight. The goal is eventually to restore the species to the eastern forests of North America. Backcrossed trees were first planted back into the forest for testing in 2009. In April 2012, another batch of trees were planted at an old mining site.^[5] In 2005, a hybrid tree with mostly American genes was planted on the lawn of the White House.^[6] A tree planted in 2005 in the tree library outside the USDA building is still very healthy seven years later; it contains 98% American chestnut DNA and 2% Chinese chestnut DNA. This tree contains enough Chinese chestnut DNA that encodes for systemic resistance genes to resist the blight. This is essential for restoring the American chestnut trees into the Northeast.^[7] The Northern Nut Growers Association (NNGA) has also been active in pursuing viable hybrids.^[8] From 1962 to 1990, Alfred Szego and other members of the NNGA developed hybrids with Chinese varieties which showed limited resistance. Other researchers, such as those at the State University of New York (SUNY), are trying to attack the blight with viruses or are creating trees that are genetically modified (GM) to resist the fungus. This is done by inserting wheat, Asian chestnuts, grapes, peppers or other plant genes into the American Chestnut genome (see cupin superfamily).^[9] In 2014, they hoped to get government permission to start planting these trees in the wild in the next five years.^[10] If this happens, they could be the first GM forest trees released in the wild in the United States.^[11][12]

Surviving specimens

• About 2,500 chestnut trees are growing on 60 acres near West Salem, Wisconsin, which is the world's largest remaining stand of American chestnut. These trees are the descendants of those planted by Martin Hicks, an early settler in the area. In the late 1800s, Hicks planted less than a dozen chestnuts. Planted outside the natural range of chestnut, these trees escaped the initial onslaught of chestnut blight, but in 1987, scientists found blight in the stand. Scientists are working to try to save the trees.^[13]
• Two of the largest surviving American chestnut trees are in Jackson County, Tennessee. One, the state champion, has a diameter of 61 cm (24 in) and a height of 23 m (75 ft), and the other tree is nearly as large. One of them has been pollinated with hybrid pollen by members of The American Chestnut Foundation; the progeny will have mostly American chestnut genes and some will be blight resistant.
• On May 18, 2006, a biologist with the Georgia Department of Natural Resources spotted a stand of several trees near Warm Springs, Georgia. One of the trees is approximately 20–30 years old and 13 m (43 ft) tall and is the southernmost American chestnut tree known to be flowering and producing nuts.^[14]
• Another large tree was found in Talladega National Forest, Alabama, in June 2005.^[15] It is 26 meters (85 ft) tall with a diameter of 35 centimeters (14 in).
• In the summer of 2007, a stand of trees was discovered near the northeastern Ohio town of Braceville.^[16][17] The stand encompasses four large flowering trees, the largest of which is about 23 m (75 ft) tall, sited among hundreds of smaller trees that have not begun to flower, located in and around a sandstone quarry. A combination of factors may account for the survival of these relatively large trees, including low levels of blight susceptibility, hypovirulence,^[18] and good site conditions. In particular, some stands may have avoided exposure thanks to their being located at a higher altitude than blighted trees in the neighboring area; the fungal spores are not carried to higher altitudes as easily.^[19]
• In March 2008, officials of the Ohio Department of Natural Resources announced a rare adult American chestnut tree had been discovered in a marsh near Lake Erie. The officials admitted they had known about the tree for seven years, but had kept its existence a secret. The exact location of the tree is still being held secret, both because of the risk of infecting the tree and because an eagle has nested in its branches. They described the tree as being 89 feet (27 m) tall and having a circumference of 5 feet (1.5 m). The American Chestnut Foundation was also only recently told about the tree's existence.^[20]
• An 80-year-old, 50-foot (15 m) tree was discovered in Adair County, Kentucky, in 1999.^[21]
• In June 2009, a mature American chestnut was discovered in Farmington, New Hampshire.^[22]
• In rural Missaukee County, Michigan, a blight-free grove of American chestnut trees approximately 0.33 acres (0.13 ha) in size with the largest tree measuring 128 in (330 cm) in circumference (40 in (100 cm) diameter) has been located. It is believed to be the result of nuts planted by early settlers in the area. The American Chestnut Council, located in the local town of Cadillac, Michigan, has verified the identity and existence. Efforts have been initiated to protect the property from logging and development.
• In Lansing, Michigan, Fenner Nature Center is home to a grove of blight-free American chestnuts descended from the aforementioned grove in Missaukee County.^[23]
• Hundreds of healthy American chestnuts have been found in the proposed Chestnut Ridge Wilderness Area in the Allegheny National Forest in northwestern Pennsylvania.^[24] Many of these trees are large, measuring more than 60 ft (18 m) in height. These trees will be protected from logging if the wilderness area, proposed by Friends of Allegheny Wilderness, is passed into law.
• The Montreal Botanical Garden has the American chestnut among its collection of trees and ornamental shrubs.^[25]
• Three of Portland, Oregon's heritage trees are American chestnuts, along with three Spanish (European) chestnuts.^[26]
• At least two American chestnuts live on the side of Skitchewaug Trail in Springfield, Vermont.^[27]

•Around 300 to 500 trees were spotted in the George Washington National Forest near Augusta county Virginia in 2014. Over one dozen trees were at least 12 inches in diameter with several measuring nearly 24 inches in diameter. Only one of the larger trees was a seed and pollen producer with numerous pods and pollen strands laying on ground. Unfortunately the site had a high presence of the chestnut bark blight, although the seed producing tree and several other large ones were relatively blight free with minimal to no damage.

American chestnut leaves, late spring

• Two trees were planted 1985 in Nova Scotia, at Dalhousie University, Sexton Campus and are thriving. Donated from saplings grown in Europe, away from the blight. They have 16" diameter trunks and are approximately 40 feet high.

Uses

The January 1888 issue of Orchard and Garden mentions the American chestnut as being "superior in quality to any found in Europe."^[28] The nuts were once an important economic resource in the US, being sold on the streets of towns and cities, as they sometimes still are during the Christmas season (usually "roasting on an open fire" so their smell is readily identifiable many blocks away). Chestnuts are edible raw or roasted, though typically preferred roasted. Nuts of the European sweet chestnut are now sold instead in many stores. One must peel the brown skin to access the yellowish-white edible portion. The unrelated horse-chestnut's seeds are poisonous without extensive preparation.

The wood is straight-grained, strong, and easy to saw and split, and it lacks the radial end grain found on most other hardwoods. The tree was particularly valuable commercially since it grew at a faster rate than oaks. Being rich in tannins, the wood was highly resistant to decay and therefore used for a variety of purposes, including furniture, split-rail fences, shingles, home construction, flooring, piers, plywood, paper pulp, and telephone poles. Tannins were also extracted from the bark for tanning leather. Although larger trees are no longer available for milling, much chestnut wood has been reclaimed from historic barns to be refashioned into furniture and other items. "Wormy" chestnut refers to a defective grade of wood that has insect damage, having been sawn from long-dead, blight-killed trees. This "wormy" wood has since become fashionable for its rustic character.

This tree is not considered a particularly good patio shade tree because its droppings are prolific and a considerable nuisance. Catkins in the spring, spiny nut pods in the fall, and leaves in the early winter can all be a problem. These characteristics are more or less common to all shade trees, but perhaps not to the same degree as with the chestnut. The spiny seed pods are a particular nuisance when scattered over an area frequented by people.

See also

• Central and southern Appalachian montane oak forest

References

External links

Wikimedia Commons has media related to Castanea dentata.

• Flora of North America
• RangeMap:
• The American Chestnut Foundation
• American Chestnut Cooperators Foundation
• Canadian Chestnut Council
• American Chestnut Research and Restoration Center, SUNY-ESF
• National Geographic article
• Castanea dentata images at bioimages.vanderbilt.edu
• Rare American Chestnut Trees Discovered (Washington Post, May 19, 2006)
• American Chestnut Restoration Breakthrough: The Tale of a Tree (GreenXC.com, June 28, 2011)
• The Chestnut Resurrection