Fungi in the Environment

What two major United States tree species have been adversely affected by a fungus?

Two major tree species have been devastated by fungus in the United States—the American chestnut and the elm. The two species have been devastated by the chestnut blight and the Dutch elm disease. The American chestnut once made up almost half of the population of hardwood forests in central and southern Pennsylvania, New Jersey, and southern New England. In its entire range, the species dominated deciduous forests, making up almost one-quarter of the trees. By the mid-1900s, the fungus Cryphonectria parasitica caused a disease commonly known as chestnut blight and destroyed nearly every mature specimen of the American chestnut tree in the United States. The blight most often attacks older trees, infecting a tree’s layers of living bark and the adjacent layers of wood; this often creates cankers that cause the bark on the trunk to crack. The fungus continues to kill the cells that carry the food made in the leaves to other parts of a tree, and nutrients are not able to reach various parts of the tree. Although the fungus leaves the roots unaffected, allowing a tree to send up new sprouts and saplings, within a number of years, the “older” bark and wood of those trees can also become infected.

The other major fungal disease attacked elms—trees that are susceptible to the fungus Ophiostoma novo-ulmi and Ophiostoma ulmi, which causes Dutch elm disease. The fungus spores (carried by bark beetles) enter the cells in the outermost wood of trees. As the fungus grows, the tree’s cells become plugged, and water and nutrients are not able to move from the roots to the top of a tree—eventually causing the tree to die. Dutch elm disease is believed to have originated in the Himalayas and traveled to Europe from the Dutch East Indies in the late 1800s. It emerged in Holland just after World War I and was first identified in 1930 in Cincinnati, Ohio—thought to have been carried on elm logs imported from Europe. By 1940, the disease had spread to nine states; by 1950, it was found in seventeen states and had spread into southern Canada. Today it is found wherever elm trees grow throughout North America.


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