the american chestnut (castanea dentata). american chestnut: range maine to georgia and west to ohio...
TRANSCRIPT
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The American Chestnut(Castanea dentata)
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American Chestnut: Range• Maine to Georgia and west to
Ohio and Tennessee. (Braun, 1950)
• Commonly made up 25% or more of mixed stands
• Formed pure stands on many dry Appalachian ridgetops and near densely populated areas.Historical Range of Castanea dentata
(Saucier, 1973)
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American Chestnut: Habitat
• Common on midslopes and other moderately dry soils
• Shared moist soils with many other species
• Tap root 4 to 5 ft down
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“Redwoods of the East”
• Mature chestnuts could be 600 years old and average up to five feet in diameter and 100 feet tall
• Many specimens of 8 to 10 feet in diameter were recorded
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American Chestnut: Ecological Importance
• Wildlife depended on the abundant crop of chestnuts
• Many species of insects fed on the leaves, flowers, and nuts
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American Chestnut: Economic Importance
• Throughout much of the range chestnut had the most timber volume of any species
– Half the standing timber volume of CT
• Was the major source of tannin for leather production (6-11 % tannin content)
• Chestnuts
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“From cradle to casket…”
• Fast growing – reached half ultimate height by 20th year
• Resistant to decay
• Straight and tall – often branch free for 50 feet
• Only white pine & tulip poplar could grow taller
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“From cradle to casket…”
• Posts & railroad ties
• Telephone poles (65 feet)
• Construction
• Fuel
• Fine furniture & musical instruments
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American Chestnut: Economic Importance
• Scientific forest management in the US was just getting started when the country lost its most important hard wood species (Smith, 2000)
• Foresters had begun to develop comprehensive plans for intensive management
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• Near densely populated areas Chestnut often formed nearly complete stands
– due to rapid growth from stump sprouts
– repeated coppicing for fuelwood
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Experts estimate that American Chestnut represented half the commercial value of all Eastern North American hardwoods
Pure stand of Chestnut in CT 90 years after clear-cutting, 1905.
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“… the most valuable and usable tree that ever grew in the Eastern United States.”
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Introduction of Cryphonectria parasitica
• American Chestnut produces a sweet but small nut
• Chinese chestnut produces a large but generally tasteless nut
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Chestnut BlightCryphonectria parasitica
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Introduction of Cryphonectria parasitica
• In 1904, Herman Merkel, a forester at the New York Zoological Garden, found odd cankers on American chestnut trees in the park
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Introduction of Cryphonectria parasitica
"rapid & sudden death of many branches stems & trees"
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Introduction of Cryphonectria parasitica
• Thomas Jefferson – imported European or Spanish chestnut (Castanea sativa)
– grafted it onto native root stocks at Monticello.
• In 1876, a nurseryman in Flushing, NY, imported the Japanese chestnut (C. crenata). – More were brought over in 1882 and 1886.
• Chinese chestnut (C. Molissima) was brought here from Ichang in 1900. – to hybridize for ornamentals and nut production
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Dispersal
• Animals and insects
• Ascospores are shot into the air after rain storms in the fall
• Rain (conidia)
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• Infects trunk and branches – Only above ground parts of trees
active growth & sporulation
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How does it kill the tree?
• Enters through fissures or wounds in the bark
• Grows in and under the bark, girdling the cambium.
• Kill the tree above the point of infection.
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• Causes swollen or sunken orange-colored cankers on the limbs and trunks of the chestnut trees.
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How does it kill the tree?
• The leaves above the point of infection die, followed by the limbs.
• Within two to ten years the entire tree is dead.
• Not uncommon to find many cankers on one tree
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How does it kill the tree?
The fungus has girdled the tree and is producing yellow conidia asexual spores
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Rate of Spread• Aggressive attempts to halt
the spread of the blight were made by PA and NY – removed chestnut over a large
area to halt southward spread
• In 1911-1913, the U.S. Congress appropriated special funds to enable foresters to study and control the blight
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Rate of Spread
• Horticulturalists, found a blight-free area in Pennsylvania and quickly imported trees to form an experiment station
– transported the blight and created a new epicenter – Accelerated spread in PA
• Cuts in funding for Chestnut blight research:
– With the onset of World War I in 1914 – The evident futility of control efforts
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• By 1926, fungus reported throughout native range
• By 1940, virtually all (an estimated 4 billion) were dead or infected with the blight
• Chestnut was the dominant wood processed at PA sawmills in the early 1920s, – salvage logging to make use of the dead and dying trees
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• “…a tragic loss, one of the worst natural calamities ever experienced by this nation”
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Cummulative Impacts
• Chestnut in Southern range was first affected by Phytophtera cinnamomum
• Now affecting hybrids
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Cummulative Impacts
• In 1974, the Oriental Chestnut Gall Wasp (Dryocosmus kuriphilus) was brought to the US
– Female lays eggs in chestnut vegetative buds – Galls suppress shoot elongation and reduce fruiting– Heavy infestations can kill the trees (afflicts both
American and Chinese chestnuts at the southern end of their ranges)
• Threatening complete extinction
(Anagnostakis, 1994)
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Current Status
• Reduced to a short lived sprouting understory tree
• Fungus can not survive below the ground. – roots continue to live and they send up stump sprouts.
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Current Status
• Stump sprouts grow until infected– the stump re-sprouts again
• Little chance for resistance to evolve – sprouts typically killed before they become
sexually mature
– sexual reproduction rare
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Last remaining stand of American Chestnut
• Trees were blight free due to isolation until a canker was found in 1986
• Now over 1600 cankers are present on 530 trees.
• Virus was introduced in 1992 – not successful
• Largest living (>3 ft dbh) about 20 miles east of La Crosse, WI.
•10 chestnuts planted in 1885
• Seeds propagated around 50 acres and more than 3000 trees
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Where are we now?• Upper slopes – scarlet oak,
hickory, black gum
• Mid slopes – red and white oak, red maple, & hickory
• Coves – Poplar, hard maple, beech
• Understory - American chestnut sprouts still persist, however they become infected between 1-12 yrs of age.
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American chestnut resistance
• Breeding programs
– Scions were grafted into chestnut rootstocks to
establish seed orchards
• Seeds and seedlings have been distributed that have
low levels of blight resistance by artificial inoculation
with a standard virulent strain