American chestnut

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American chestnut
American chestnut (Castanea dentata): leaf and nuts

American chestnut ( Castanea dentata ): leaf and nuts

Systematics
Rosids
Eurosiden I
Order : Beech-like (Fagales)
Family : Beech family (Fagaceae)
Genre : Chestnuts ( Castanea )
Type : American chestnut
Scientific name
Castanea dentata
( Marsh. ) Borkh.
Distribution area

The American chestnut ( Castanea dentata ) is a deciduous tree native to North America from the genus of the chestnut in the beech family (Fagaceae). It is not to be confused with the horse chestnuts , but is related to the sweet chestnuts found in Europe . It was once the most important forest tree in eastern North America.

description

Male inflorescences

The American chestnut is a stately, fast-growing deciduous tree that reaches heights of up to 30 meters with trunk diameters of up to 1.5 meters. (Other sources give heights of up to 45 m, tree canopy diameters of up to 30 m and trunk diameters of up to 3 m.)

The leaves of the American chestnut are 14–20 cm long and 7–10 cm wide and thus generally a little smaller and wider than the leaves of the sweet chestnut (16–28 cm × 5–9 cm). They can best be determined on the basis of the larger and regularly spaced teeth on the leaf margin, as the scientific name dentata - Latin for "toothed" - indicates.

The American chestnut forms a nut fruit , usually three nuts are contained in one fruit. They are covered with a brown velvety skin in a spiky green shell. The nuts develop in late summer. With the first frost in autumn, the shell opens and falls to the ground.

The number of chromosomes is 2n = 24.

distribution

The American chestnut is native to eastern North America . Their original range extends from Maine over southern Ontario to Mississippi and from the Atlantic coast to the Appalachians and Ohio Valley.

The American chestnut was of great importance in the animal and plant world, as the leaves and fruits served as food for many animals, such as the white-tailed deer , the turkey and the extinct pigeon . Also, American black bears are known to eat the nuts for their winter fat storage.

Chestnut Crab

Young tree in a natural environment

The American chestnut used to be an important supplier of wood . In 1904 the Asian bark fungus or " chestnut crab " (a hose fungus of the species Cryphonectria parasitica , syn. Endothia parasitica ) - to which the chestnuts are very susceptible - was accidentally introduced into the Bronx Zoo in America with a stock of seedlings from a Chinese ornamental chestnut . While the Chinese chestnuts could develop with cancer and are immune to it, the American chestnut is very susceptible to the fungal disease. The "chestnut crab" spread by transmission through the air about 80 km per year. In just a few decades, billions of American chestnuts were attacked in this way. The fungus grows in the cambium and in or under the bark of the tree, interrupting the absorption of water and thus the supply of nutrients. As a result of the infestation, the above-ground part of the tree withers. The tree stumps survive the disease because the roots are not attacked and develop new plant shoots. Also, the tree grows very quickly, and in many cases the canker does not break out until after the bark has become rougher, around the tenth year. By then, the tree has been able to fully develop its fruits for a few years. For these reasons, the species was saved from extinction , but the new plant germs on the tree stumps barely get more than 6 meters high before the fungus attacks them again.

It is estimated that the American chestnut accounted for a quarter of the tree population within its previous range, which corresponds to a total of around 3.5 billion specimens. Today there are only a few dozen mature trees left because of the fungus. It is believed that in the early years of the tree disease, panic felling also resulted in the unintentional destruction of trees that were immune to the disease, thereby preventing the development and selection of fungus-resistant variants. Most of western North America has so far been spared the fungus. American chestnuts thrive in the far north, for example in Revelstoke , British Columbia . The best-preserved trees can be found in Sherwood , Oregon . On May 18, 2006, a biologist with the Georgia Department of Natural Resources discovered a stand of approximately half a dozen trees near Warm Springs . One of the trees is 20-30 years old and 13 m high, and it is believed that this is the most southerly sighted chestnut tree that has the ability to produce flowers and fruits. It is believed that these trees do not belong to a fungus-resistant variety, but may have developed resistance due to the dry and rocky local climate or other influences from the environment in which they were found. American Chestnut Foundation employees will examine the trees and possibly pollinate them with fungus-resistant trees and vice versa. An unusually large (26 m high, 35 cm in diameter) "survivor" was found in Talladega National Park , Alabama in June 2006.

Young American chestnut tree in a field trial by the American Chestnut Cooperators Foundation

Several North American organizations are trying to grow American chestnuts that are resistant to fungi.

  • One of them is the American Chestnut Cooperators Foundation , which grows all of the American chestnuts that have shown natural resistance to the fungus.
  • The Canadian Chestnut Council is a Canadian organization that is trying to reintroduce the trees in Canada, primarily in Ontario .
  • Another is the American Chestnut Foundation , which backcrosses fungus-resistant American / Chinese chestnut hybrids with native American chestnuts , with the characteristics and genetic structure of the American plant being recovered in order to ultimately cross the improved generations with one another and obtain a uniform fungus-resistant breed. The current goal is to bring the species back into the wild. In 2005, a hybrid tree with a high genetic content of the American chestnut was planted on the lawn of the White House , and it continues to thrive there to this day.
  • The United States National Arboretum is also showing interest in the American chestnut and using similar methods of crossing to find resistant hybrids. The species is believed to be ready for plant trials in the wild in about six years.
  • A group of researchers at the State University of New York's College of Environmental Science and Forestry was able to create transgenic seedlings that can produce an enzyme that is naturally occurring in wheat and that repels the fungus. In contrast to the backcrossings, these are pure chestnuts that are otherwise unchanged. The research team emphasized that this approach finds a certain acceptance even among people who otherwise reject genetic engineering, probably because only a human error is "corrected" because there is no profit intention and the team does not seek patenting of the breed. After the official approval is pending, the release into the wild could begin in 2019.

The intrinsic and economic value of reintroducing the American chestnut to its former range in the forests of the eastern United States cannot be estimated.

use

In the USA the nuts were once an important economic factor, where they were even sold on the streets in larger cities, as is still practiced in some places today during the Christmas season (usually roasted over an open fire so that the smell is widely recognized immediately) . Chestnuts can be eaten raw or roasted; however, they are preferred roasted. Instead of the American fruit, nuts from the European sweet chestnut are sold in many shops. In order to get to the edible yellowish-white substance inside, the brown skin is peeled off. They are to be distinguished from the poisonous horse chestnuts.

The wood of the American chestnut is a valuable hardwood , but it has largely lost its forestry importance due to the mass extinction caused by the “chestnut crab”. The heartwood has a straight grain and is tough like oak. Although easier to saw and split, it lacks the end grain from the center point found in most other hardwoods. The tree is particularly valuable for commercial use because the American chestnut grows faster than an oak. Rich in tannins ( tannins ), the wood is well protected against decay due to its long shelf life and was therefore used for a variety of purposes, e.g. B. for furniture production, cattle fences, clapboards , house building, flooring, railway sleepers , plywood , cellulose paper or telephone poles. Also tannins from the bark for the tanning of leather used. Although there are no longer any larger trees available for processing, a lot of chestnut wood from historic barns is incorporated into furniture and other accessories. The wood of "worm" chestnuts was damaged by insects . This wood was sawn off trees that had long since died from the fungal attack. The pattern of the wood resulting from the damage is popular because of its rustic character.

Web links

Commons : American chestnut ( Castanea dentata )  - Collection of images, videos and audio files

English language articles

Organizations:

Individual evidence

  1. ^ C. Frank Brockman: Trees of North America . Golden Press, New York, revised edition 1986
  2. ^ Castanea dentata at Tropicos.org. In: IPCN Chromosome Reports . Missouri Botanical Garden, St. Louis
  3. ↑ First breeding successes - Will the American chestnut soon be resistant to a deadly fungus? On: Wissenschaft.de from December 11, 2000.
  4. ↑ Lori Valigra: Back-Breeding Could Restore Chestnut Trees Ravaged by Blight . In: National Geographic News. December 29, 2005
  5. ↑ Elliott Minor: Rare American Chestnut Trees Discovered . In: Washington Post. May 19, 2006.
  6. ↑ Waldo: Talladega tree avoids blight Group seeks to pollinate, create offspring from rare tree; largest chestnut in state . In: Birmingham News (AL). June 20, 2006.
  7. ↑ William Powell: The Resurrection of the American Chestnut. In: Spectrum of Science January 2015, pp. 66–69 ( excerpt online , Spektrum.de).
    The enzyme is an oxalate oxidase. This destroys the oxalic acid that the fungal mycelium initially produces in order to penetrate the cortex. The team is trying to implement other defense mechanisms, including some presumably in the Chinese chestnut for resistance genes. These were not yet known at the beginning of the research, so foreign material was used.