Hemlock

Early colonists believed that sleeping on a pillow of fresh needles from the eastern hemlock ( Tsuga canadensis ) could dispel hay fever.

Pennsylvania's state tree, the eastern hemlock is a species of cool ravines, mountain stream valleys, wetlands and north-facing slopes throughout the state. This species provides dense shade and cover for wildlife throughout the year and is a major component of forest ecosystems throughout the eastern U.S.. It so defines and punctuates the landscape of the state that it is hard to imagine what it would be like without the hemlock. Unfortunately, the spread of an insect known as the hemlock wooly adelgid ( Adelges tsugae ) is threatening just such a possibility.

This insect was introduced into the U.S. from Japan in the early 1950's and first observed in Virginia. It has spread steadily north and westward and, in Pennsylvania, the front of infestation lies near the center of the state with most western Pennsylvania counties still adelgid-free. The insect feeds by sucking sap from the twigs of the tree, limiting nutrients to the needles which consequently yellow, die and drop from the tree. After several years of heavy infestation, the tree will succumb.

Biological controls (other insects that feed on the adelgid) have been introduced to help control current infestations and slow the spread to non-infested areas. The USDA Forest Service as well as numerous state forest agencies are working to develop and implement plans to control the wooly adelgid. Perhaps the best approach that any one person can take is to watch for signs of infestation (small cottony clusters beneath the twigs), take care not to spread infested material, and stay aware of programs and efforts in your area.

For more information on the hemlock wooly adelgid, visit the USDA web site: www.fs.fed.us/na/morgantown/fhp/hwa/hwasite.html

Today's photo by Robert Ruschak features several snow-covered hemlocks below Frank Lloyd Wright's Fallingwater.

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