Fungus on the Paragon of Beauty

In his Essay on American Scenery, Thomas Cole shows an appreciation for biodiversity in a forest, writing, "it is a beautiful instance of the exhaustlessness of nature; often where we should expect unvarying monotony, we behold a charming diversity." He names several species of particular interest, calling the elm "that paragon of beauty and shade."

The tanning and lumber industries were devastating to the Hudson River Valley forests by the sheer number of trees cut down, but commerce in the region has hurt the forest in another, more subtle way. The introduction of foreign diseases has destroyed the elm and American chestnut populations of the Hudson River Valley and the East coast of the United States.

In the late 1800s, about 1 out of every 2 trees found in a northeastern hardwood forest was an American chestnut (Castanea dentata). These trees were treasured for their straight stems, massive size, umbrella canopies, and near perfect symmetry. They were valuable for their superior quality wood and the nuts that could be used as sustenance for both people and livestock. Patrons at the New York Zoo observed the death of these great trees beginning in 1904; the disease that was killing them spread rapidly from that time in all directions, sometimes as quickly as 50 miles per year. Zoo goers were witnessing the work of a fungus, called Cryphonectria parasitica, that infects stems, branches, and shoots of the trees, producing blisters of the bark called cankers. It is likely that these infections were ultimately a product of global trade; it appears to have come to America via a ship from Asia. By 1940, adult chestnuts were virtually impossible to find; any existing saplings could not live to reproductive age before being fatally attacked by the fungus. This devasting event in the history of the northeastern hardwood forest came to be called the great American chestnut blight and scientists predict that the forest will not recover from it for several hundred years, if ever.

Dutch elm disease hit the northeastern hardwood forests in the 1930s. This pathogen is also a fungus; called Ophiostoma novo-ulmi, it clogs the vascular tissue so the shoots and branches of the trees wilt and eventually die. Though the name would have you blame the Dutch, this fungus probably came from the Himalayas on infected wooden crates. The strategies to combat the Dutch elm disease, such as root grafts, fungicides, and pesticides to kill the carriers, have proved largely ineffective, expensive, or harmful to the environment in other ways.

The changes in the forest composition as a result of the introduction of exotic diseases would probably sadden Cole, who valued the Hudson River Valley forest for its "unrivalled variety." But how much is this biodiversity worth? Was the introduction of these diseases more or less harmful than the logging that was done by the timber and tanning industries? Would it have been worth the cost of stopping or regulating overseas trade if, somehow, the traders of the 19th and early 20th centuries could have forseen the consequences to the forests? The problem in answering these questions arises because different people put very different values on biodiversity and ecological preservation.

The information I used came from these websites and also the book The Dying of the Trees by Charles Little.

http://www.forestpathology.org/dis_chestnut.html

http://plantclinic.cornell.edu/FactSheets/dutchelmdisease/DED.htm