Tuesday, November 28, 2017
The "Eastern Hemlock" - Tsuga Canadensis
The "Eastern Hemlock" - Tsuga Canadensis is a very unique evergreen/conifer, this is because it's terminal leader often droops instead of giving the tree a typical pointed top like most in the Pine family. It's natural range begins to the North in Nova Scotia and continues South through Wisconsin and Minnesota, throughout the Alleghany Mountains and South through Georgia and Alabama. It is native to every state along the East Coast with the exception of only Florida in the far South. It is very common in the Mountains of Pennsylvania and Ohio, it is the only Hemlock variety that is native to Ohio. It's hardiness zone is 4-7. In the Southern range it is found only where there is moist air, rocky ridges, valleys, ravines lakeshores and hillsides. In the Northern range it is found in a wider variety of locations including on low rolling hills and even glacial ridges. It most commonly grows in mixed stand settings along with White Pine, Red Oak, Sugar Maple, American Beech, White Ash, and Yellow Birch.
Image Citation: Paul Bolstad, University of Minnesota, Bugwood.org
In Eastern North America the Eastern & Carolina Hemlocks are greatly threatened by the Hemlock Woolly Adelgid. Trees infested with Hemlock Woolly Adelgid can be easily identified by visable egg sacs, which resemble small tufts of cotton clinging to the underside of hemlock branches. Once infested trees generally become a grayish-green instead of there rich healthy green color. This pest feeds on the phloem sap of tender hemlock shoots, and may also inject a toxin while feeding. The resulting desiccation causes the tree to lose needles and not produce new growth. In the northern portion of the Hemlock's range, death typically occurs four to ten years after the initial infestation. Trees that survive the direct effects of the infection are usually weakened and may die from secondary causes. This pest has been identified as active in 11 states within the Hemlocks growth range causing major concern for the future of these majestic trees.
Image Citation: USDA Forest Service Southern Research Station , USDA Forest Service, SRS, Bugwood.org
The Eastern Hemlock does not begin to produce cones until about the age of 15. The brown cones are relatively small only 1/2-1 inch in length and usually not more then a 1/2 inch wide. Once the cones begin production they come in high volume and for many many years, some specimen have been found producing cones even at 450+ years old. Seed viability is generally low, even though there are a large number of cones produced. The Hemlocks seed is easily damaged by drying. They regenerate best on exposed decomposing layers under 70-80% crown cover, in rotten logs or stumps or mounds where the temperature is warmest among the forest floor.
Image Citation: Rob Routledge, Sault College, Bugwood.org
The Eastern Hemlock grows in an upright primarily conical fashion with long branches that often droop at the ends. At full maturity they can average 100 feet tall but have been found growing as tall as 170+ feet. The bark is brown, scaly and fissured . The bark was once used commonly as a source of tannin or the leather industry. The needles are evergreen and flat, usually 5-25 mm long and set on each branch with peg like projection.
Image Citation: Pennsylvania Department of Conservation and Natural Resources - Forestry , Bugwood.org
The wood is not of a high enough quality furniture making. It is used for light framing material, boxes, crates and even pulping. It is not considered an important timber tree in today's market. Commercial stands have been greatly reduced by prior harvesting and lack of replanting.
The Eastern Hemlock can be used as a specimen tree, planted in groups for screening, or even trained/sheared over time into formal evergreen hedgerows. It is tolerant of full shade and has a natural open growth habit.