About Hemlock Trees
Hemlock trees, from the genus Tsuga in the family Pinaceae, are found in North America, China and Japan, where they grow in cool, moist areas. In the southern range of their habitat, they prefer higher elevations. Most species are shade-tolerant, making them useful in landscape design. They are fairly long-lived trees, with some specimens recorded as over 400 years old. Does this Spark an idea?
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Geography
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The North American species include the Eastern Hemlock (Tsuga canadensis), the Carolina Hemlock (Tsuga caroliniana), the Mountain Hemlock (Tsuga mertensiana) and the Western Hemlock (Tsuga heterophylla). The Eastern Hemlock ranges from Eastern Canada south into Georgia and Alabama and west into Minnesota. The Carolina Hemlock is native to the Appalachian Mountains and is found at elevations of 700 to 1,200 meters above sea level in North and South Carolina, Georgia, Tennessee and Virginia.
The Mountain and Western hemlock are found in the same range from Alaska to northern California with some found in Idaho, Montana and British Columbia. Chinese hemlock (Tsuga chinensis), and Himalayan hemlock (Tsuga dumosa) grow in Asia, mainly in the mountainous regions in areas with cool, rainy environments. Japanese hemlock are divided into the Northern Japanese Hemlock (Tsuga diversifolia) and Southern Japanese hemlock (Tsuga sieboldii). Both species are located on the islands of Honshu, Kyushu and Shikoku, with the Southern version also found on Yakushima.
Uses
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Historically, hemlock trees were used in the leather tanning industry because the bark contains high levels of tannins. More recently, the timber industry harvested hemlock trees, for use mostly as a source of wood pulp. Hemlock trees of all varieties are used in the landscaping industry as an ornamental tree, and in hedges and privacy barriers. The needles and sometimes the bark can be used as a tea, or as a source of aromatic oils.
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Identification
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Hemlock trees are evergreen conifers with a cone-shaped, sometimes irregular crown and branches that commonly droop at the ends. The bark varies in color depending on the species but is usually scaly and furrowed with a gray to brown hue. The leaves are small and flat, sometimes slightly angled in the center approximately 5 to 30 mm long and 1 to 3 mm wide, with hundreds of leaves on each branch spiraling around the stem. The leaves are usually dark green on top and grayish-green underneath. The cones, which contain the seeds, are usually small, from 2 to 3 cm long, except the Mountain Hemlock, which has larger cones that are 3 to 8 cm long.
Misconceptions
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Hemlock trees are not the source of the notorious poison that killed Socrates, which was derived from a plant named poison hemlock (Conium maculatum). The poison hemlock plant leaves resemble parsley and it has a white taproot that has been mistaken for wild parsnip. The poison contained in the poison hemlock is known as a conium alkaloid that affect the central nervous system.
Initial symptoms of hemlock poisoning include headache, unsteadiness, salivation, sweating and increased heart rate. This gives way to the depression of the central nervous system resulting in a slowed heart rate, paralysis and death. Water hemlock (Cicuta maculata), a plant growing in wet, swampy areas in North America and Europe, is also poisonous, containing a cicutoxin that also affects the central nervous system and causes abdominal pain, nausea, vomiting, tremors and seizures.
Considerations
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Recently, as of 2010, the hemlock woolly adelgid (Adelges tsugae) infestation in eastern North America is causing major die-back of hemlock stands with about 50 percent of the geographic range infested. This pest was introduced to western North America from Asia in 1924, showed up in Virginia in 1951 and has since become an ever-worsening problem. Infested trees usually die within two to four years, though some can last longer.
Hemlock trees in western North America are not as badly affected, because they seem to be more tolerant to the fluid loss and the pest has more natural predators in that region. Biological and chemical controls are in practice, though they are expensive and take time to have an effect.
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References
- Photo Credit hemlock forest in snow image by Jorge Moro from Fotolia.com
