Question

American chestnuts were trees that once dominated forests of the eastern United States. A disease accidentally introduced to North America killed all but a small number of these trees. You don't have to know anything else about chestnuts to answer the following questions. a, Provide one explanation of how the change in species composition might have affected ecosystem function. b. Please provide one example of how the disappearance of these trees might have affected ecosystem function.

Answer 1

a)

North American infection

The chestnut blight was accidentally introduced to North America around 1904 when Cryphonectria parasitica was introduced into the United States from Japanese nursery stock.It was first found in the chestnut trees on the grounds of the New York Zoological Garden (the "Bronx Zoo") by Herman W. Merkel, a forester at the zoo. In 1905, American mycologist William Murrill isolated and described the fungus responsible (which he named Diaporthe parasitica), and demonstrated by inoculation into healthy plants that the fungus caused the disease.By 1940, most mature American chestnut trees had been wiped out by the disease.

Infection of American chestnut trees with C. parasitica simultaneously appeared in numerous places on the East Coast, most likely from Castanea crenata, or Japanese chestnut, which had become popular imports. Japanese and some Chinese chestnut trees have some resistance to infection by C. parasitica: the infection usually does not kill these Asian chestnut species. Within 40 years the nearly four-billion-strong American chestnut population in North America was devastated.—only a few clumps of trees remained in Michigan, Wisconsin and the Pacific Northwest. Because of the disease, American chestnut wood almost disappeared from the market for decades, although it can still be obtained as reclaimed lumber.

It is estimated that in some places, such as the Appalachian Mountains, one in every four hardwoods was an American chestnut. Mature trees often grew straight and branch-free for 50 feet and could grow up to 100 feet tall with a trunk diameter of 14 feet at a few feet above ground level. The reddish-brown wood was lightweight, soft, easy to split, very resistant to decay; and it did not warp or shrink. For three centuries many barns and homes near the Appalachian Mountains were made from American chestnut. Because of its resistance to decay, industries throughout the region used wood from the American chestnut for posts, poles, piling, railroad ties, and split-rail fences. Its straight-grained wood was ideal for building furniture and caskets. The fruit that fell to the ground was an important cash crop and food source. The bark and wood were rich in tannic acid, which provided tannins for use in the tanning of leather.Many native animals fed on chestnuts, and chestnuts were used for livestock feed, which kept the cost of raising livestock low.

Efforts started in the 1930s and are still ongoing, in Massachusetts and many other places in the United States, to repopulate the country with chestnut trees.Surviving American chestnut trees are being bred for resistance to the blight, notably by The American Chestnut Foundation, which aims to reintroduce a blight-resistant American chestnut to its original forest range within the early decades of the 21st century.Japanese chestnut and Chinese chestnut, as well as Seguin's chestnut and Henry's chestnut—have been used in these breeding programs in the US to create disease-resistant hybrids with the American chestnut.Chinese chestnut trees vary considerably in blight resistance. Some individuals are quite susceptible while others are essentially immune.

Hypovirulence is not widespread in the US and attempts to commercially introduce CHV1 have not been widely successful. Though CHV1 persists in the applied tree, it does not spread naturally as it does in Europe, preventing it from being an effective form of biocontrol.

b)

In less than fifty years after its emergence, C. parastica virtually eliminated American chestnut as a canopy species in 8.8 million acres (3.6×106 ha) acres of forest. The chestnut fruit was a major food source for animals in the low elevation Appalachian forests. This loss resulted in a drastic decrease of the squirrel population, the extinction of seven native moth species, and the slowed recovery of deer, Cooper's hawk, cougar, and bobcat populations. The effects of this disease also rippled further through the ecosystem, being linked to a decrease in the abundance of cavity-nesting birds and to a decrease in river water quality which negatively affected aquatic invertebrate populations.

In 1912, standing chestnut timber in just three states was estimated to be $82.5 million ($1.9 billion in current dollars) in value. Therefore, in addition to ecological impacts, C. parasitica potentially caused a devastating loss in economic welfare for communities dependent on the chestnut tree. Mountaineers, residents of Appalachian Mountain communities, had to drastically alter their life styles to cope with the effects of this disease.

Economic effects have also been considerable in Europe, particularly before CHV1 spreads naturally to a region. In Greece for example, the disease forced the migration of people who could not longer afford to live off chestnut trees. It has also lead to a 40% decline in Greek chestnut production