Composition, structure, and sustainability of hemlock ecosystems in eastern North America

Abstract

Across its natural range in North America, eastern hemlock (Tsuga Canadensis (L.) Carriere) is an important resource for people and wildlife, but it is seriously threatened by the hemlock woolly adelgid (HWA) (Adelges tsugae Annand). From 10 to 20 percent of the hemlock resource is found in the Canadian provinces of New Brunswick, Nova Scotia, Ontario, Prince Edward Island, and Quebec. In the United States, hemlock is found across a wide range of forest types and stand conditions. There are 2.3 million acres of hemlock-dominated stands, but this species also is a common associate in many other forest types. The total net volume of live hemlock trees in the United States is 8.4 billion cubic feet, or 2 percent of the total inventory in states within its natural range. The existing hemlock resource is in a mature condition dominated by large-sized stands and trees. Young stands of hemlock are uncommon. Currently, hemlock mortality is low compared to other species within its range, but this would change if the HWA continues to expand. Hemlock is growing at a rate three times faster than it is being removed by harvesting and changes in land use. Long-term sustainability will depend heavily on the degree that hemlock is favored in future management practices, the future spread of the HWA, and the ability of forest managers and policymakers to control the HWA.