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Although the standing inventory of hardwood and softwood tree species in the United States has increased continually over the last 50 years, foresters remain concerned about deforestation -- the destruction of forests or a severe reduction in their overall health. Most people are familiar with the issue as it relates to tropical rainforests, but it's a serious problem in forests globally. You can read more about the causes and effects of deforestation in How Deforestation Works, which focuses primarily on human impact.
Unfortunately, human activity isn't the only danger to forests. There are three other important causes of tree mortality: insects, diseases and invasive plants.
Several native and nonnative insects have wreaked havoc on U.S. forests (see table, below). One of the most devastating is the gypsy moth, a Eurasian native that arrived in North America in the late 19th century. In its larval form -- a caterpillar -- it consumes the leaves of hardwood trees. It prefers oak but will feed on many different species of trees. Since 1930, the gypsy moth has defoliated more than 80 million acres (32 million hectares) of forests in the East [source: USDA Forest Service]. Several eradication strategies have prevented the insects from spreading to western states.
Tree Species Targeted
Hemlock wooly adelgid
Eastern and Carolina hemlock
Half of hemlock forests across 11 states infested
Western spruce budworm
Western conifers, including Douglas firs, white firs, blue spruces and western larches
The most widely distributed and destructive defoliator of western coniferous forests
Mountain pine beetle
Lodgepole, ponderosa, sugar and western white pines
Caused tree death on more than 3 million acres (1.2 million hectares) in 2005
Southern pine beetle
Loblolly and shortleaf pine
Affected 2.7 million acres (1.1 million hectares) in 2004
Aside from insects, diseases, too, can take their toll on forests. Sudden Oak Death, or SOD, is a relatively new but serious threat to American forests. The disease, which is caused by the pathogen Phytophthora ramorum, was first reported in California in 1995. Since then, it has killed 1 million oaks, primarily coast live oak, California black oak, shreve oak and tan oak [source: Alvarez]. It also has infected several other types of plants, such as rhododendron. Scientists are trying to decipher the biology of the disease, but they still don't know how it spreads. One concern is that SOD will infect oak forests of the eastern United States.
Lastly, about 1,400 invasive plant species pose significant threats to American forests, according to the USDA Forest Service. Most aren't native to the United States and have no natural predators. As a result, these plants grow uncontrollably, overwhelming and displacing other plants. Mile-a-minute weed is a great example. Introduced from Asia, this climbing vine grows unchecked across the Mid-Atlantic. It prevents natural forest regeneration by crowding out seedlings, which jeopardizes future timber harvests. It also destroys habitats, mostly in the forest shrub layer, in which birds and mammals live.
Controlling these threats and others, such as wildfire, is vitally important, as is decreasing our consumption of wood and paper. If we don't, we risk losing more biologically diverse forestland and the timber resources we rely on for the hundreds of wood-based products we use every day.
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More Great Links
- Abundant Forests Alliance
- U.S. Forest Service
- Forestry on the Food and Agriculture Organization of the United Nations
- Project Learning Tree
- A Guide to American Hardwood Species
- Weyerhaeuser Growing Ideas Microsite
- Alvarez, Mila. "The State of America's Forests." Society of American Foresters/Abundant Forests Alliance. January 2007. (Sept. 28, 2008)
- Bowyear, Jim L. "Forest products." World Book Multimedia Encyclopedia. 2004.
- Doyle, Rodger. "By the Numbers: Forest Density in the U.S." Scientific American. April 1998.
- Doyle, Rodger. "By the Numbers: Global Forest Cover." Scientific American. November 1996.
- Food and Agriculture Organization of the United Nations. "Forest cover." (Sept. 28, 2008)
- Food and Agriculture Organization of the United Nations. "Forest and the economy." (Sept. 28, 2008)
- International Paper: Learning Center. "How Paper is Made." (Sept. 28, 2008)
- International Paper: Learning Center. "Sustaining Our Forests, Protecting Our Future." (Sept. 28, 2008)
- International Paper: Life of the Forest. "Waste Not." 2002. (Sept. 28, 2008)
- Johnson, James E. "Harvesting Your Timber? Factors to Consider to Ensure A Profitable and Healthy Forest." Virginia Cooperative Extension Publication Number 420-160. April 2004. (Sept. 28, 2008)
- Lillard, Richard G. "The Great Forest." Alfred A. Knopf. 1947.
- Logan, William Bryant. "Oak: The Frame of Civilization." W.W. Norton & Company. 2005.
- Maycock, Paul F. "Forest." World Book Multimedia Encyclopedia. 2004.
- Parker, George R. "Forestry." World Book Multimedia Encyclopedia. 2004.
- Shaffer, Robert M. "Farm Tractor Logging for Woodlot Owners." Virginia Cooperative Extension Publication Number 420-090. April 1998. (Sept. 28, 2008)
- Tudge, Colin. "The Tree." Three Rivers Press. 2005.
- USDA Forest Service. "America's Forests: 2003 Health Update." May 2003. (Sept. 28, 2008)
- USDA Forest Service. "An Analysis of the Timber Situation in the United States: 1989-2040." (Sept. 28, 2008)
- USDA Forest Service. "2000 RPA Assessment of Forest and Range Lands." February 2001. (Sept. 28, 2008)
- U.S. Department of the Treasury/IRS. "Hardwood Timber Industry." February 1998. (Sept. 28, 2008)