Tsuga canadensis, also known as eastern hemlock,[3] eastern hemlock-spruce,[4] or Canadian hemlock, and in the French-speaking regions of Canada as pruche du Canada, is a coniferous tree native to eastern North America. It is the state tree of Pennsylvania.[5] Eastern hemlocks are widespread throughout much of the Great Lakes region, the Appalachian Mountains, the Northeastern United States, and Maritime Canada. They have been introduced in the United Kingdom and mainland Europe, where they are used as ornamental trees.
Eastern hemlock populations in North America are threatened in much of their range by the spread of the invasive Hemlock woolly adelgid, which infests and eventually kills trees. Declines in population from hemlock wooly adelgid infestation have led to Tsuga canadensis being listed as Near Threatened on the IUCN Red List.
Eastern hemlocks are long lived trees, with many examples living for more than 500 years. They can grow to heights of more than 30 metres (100 ft), and are tolerant of shade, moist soil, and slopes. Hemlock wood is used in construction, and for railroad ties. Historically its bark was an important source of tannin for the leather tanning industry.[6] Eastern hemlocks are popular as ornamental trees, thanks to their tolerance of a wide variety of soil and light conditions, as well as their characteristic drooping branches.
Description
The eastern hemlock grows well in shade and is very long lived, with the oldest recorded specimen, found in Tionesta, Pennsylvania, being at least 554 years old.[7] The tree generally reaches heights of about 31 m (102 ft),[5] but exceptional trees have been recorded up to 53 m (174 ft).[8] The diameter of the trunk at breast height is often 1.5 m (4 ft 11 in), but again, outstanding trees have been recorded up to 1.75 m (5 ft 9 in).[9] The trunk is usually straight and monopodial, but very rarely is forked.[10] The crown is broadly conic, while the brownish bark is scaly and deeply fissured, especially with age.[5] The twigs are a yellow-brown in color with darker red-brown pulvini, and are densely pubescent. The buds are ovoid in shape and are very small, measuring only 1.5 to 2.5 mm (0 to 1⁄8 in) in length. These are usually not resinous, but may be slightly so.[5][10]
The leaves are typically 15 to 20 mm (0.59 to 0.79 in) in length, but may be as short as 5 mm (0.20 in) or as long as 25 mm (1 in). They are flattened and are typically distichous, or two-ranked. The bottom of the leaf is glaucous with two broad and clearly visible stomatal bands, while the top is a shiny green to yellow-green in color. The leaf margins are very slightly toothed, especially near the apex. The seed cones are ovoid in shape and typically measure 1.5 to 2.5 cm (5⁄8 to 1 in) in length and 1.0 to 1.5 cm (3⁄8 to 5⁄8 in) in width. The scales are ovate to cuneate in shape and measure 8 to 12 mm (3⁄8 to 1⁄2 in) in length by 7.0 to 10 mm (1⁄4 to 3⁄8 in) in width. The apex is more or less rounded and is often projected outward. Twenty-four diploid chromosomes are present within the trees' DNA.[5][10]
