Tsuga canadensis, also known as Eastern 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 ranges from northeastern Minnesota eastward through southern Quebec to Nova Scotia, and south in the Appalachian Mountains to northern Georgia and Alabama. Scattered outlier populations occur in several areas east and west of the Appalachians. It is the state tree of Pennsylvania.
The eastern hemlock generally reaches heights of about 30 metres (100 feet), but exceptional trees have been recorded up to 53 metres (173 feet). The diameter of the trunk at breast height is often 1.5 metres (5 feet), but again, outstanding trees have been recorded up to 1.75 meters (6 feet). The trunk is usually straight and monopodial, but very rarely is forked. The crown is broadly conic, while the brownish bark is scaly and deeply fissured, especially with age. The twigs are a yellow-brown in colour 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 (0.05 to 0.1 inches) in length. These are usually not resinous, but may be slightly so.
The leaves are typically 15 to 20 mm (0.6 to 0.9 inches) in length, but may be a short as 5 mm (0.2 inches) or as long as 25 mm (1 inch). They are flattened and are typically distichous, or two-ranked. The abaxial surface of the leaf, or underside, is glaucous with 2 broad and clearly visible stomatal bands, while the adaxial surface, i.e. the upper-side, is a shiny green to yellow-green in colour. The leaf margins are very slightly dentate, or toothed, especially near the apex. The seed cones are ovoid in shape and typically measure 1.5 to 2.5 cm (0.6 to 1 inch) in length and 1 to 1.5 cm (0.4 to 0.6 inches) in width. The scales are ovate to cuneate in shape and measure 8 to 12 mm (0.3 to 0.5 inches) in length by 7 to 10 mm (0.3 to 0.4 inches) in width. The apex is more or less rounded and is often projected outward. 24 diploid chromosomes are present within the tree's DNA.
It is found primarily on rocky ridges, ravines and hillsides with relatively high levels of moisture.
The eastern hemlock grows well in shade and is very long lived with the oldest recorded specimen being at least 554 years old. The future of the species is currently under threat due to the hemlock woolly adelgid (Adelges tsugae), a sap-sucking bug accidentally introduced from East Asia to the United States in 1924. The Adelgid has spread very rapidly in southern parts of the range once becoming established, while its expansion northward is much slower. Virtually all of the hemlocks in the southern Appalachian Mountains have seen infestations of the insect within the last five to seven years, with thousands of hectares of stands dying within the last two to three years. Attempts to save representative examples on both public and private lands are on-going. At exceptionally important project named "Tsuga Search", funded by the Great Smoky Mountains National Park, is being conducted to save the largest and tallest remaining Eastern Hemlocks in the Park. It is through Tsuga Search that Hemlocks have been found with trunk volumes of up to 44.8 m³ within the Park, making the it the largest eastern evergreen conifer, eclipsing in volume both Pinus strobus (Eastern White Pine) and Pinus taeda (Loblolly Pine). The tree is currently listed as a least concern species in the IUCN Red List, but this is based largely on its wide distribution and the fact that the adelgid populations have not reached the northern areas of its range.
Trunk volume is the third dimension to receive attention by ENTS. The largest Eastern Hemlock has been calculated to be 44.8 m³. This makes the hemlock the largest natural evergreen conifer in the eastern United States. But recent research by ENTS places the hemlock in the first position. Many eastern hemlocks have been modeled to over 30 m³ trunk volume. The center of maximum size development for the species is the southern Appalachians and within that region, the Great Smoky Mountains.
It was introduced to British gardens in 1736. In the UK it is encountered frequently in gardens both large and small, as well as some parks and is most common in the eastern areas of the country. It is sometimes employed as a hedge, but is considered inferior for this usage compared to Tsuga heterophylla (Western Hemlock); it is not well adapted to the UK climate and as a consequence there often has a poorly developed, forked and sinuous trunk. In Germany it is the most frequently seen hemlock in cultivation and is also used in forestry.
Over 300 cultivars have been selected for use, many of them being dwarf forms and shrubs. A partial list of popular cultivars includes:
Terrain and Landform Influence on Tsuga canadensis (L.) Carrière (Eastern Hemlock) Distribution in the Southern Appalachian Mountains
Mar 01, 2010; ABSTRACT We examined the relationships between hemlock distribution and abundance and terrain attributes for the Coweeta Basin in...
Water use by eastern hemlock (Tsuga canadensis) and black birch (Betula lenta): implications of effects of the hemlock woolly adelgid.
Oct 01, 2007; Abstract: Eastern hemlock (Tsuga canadensis (L.) Carr.) is a coniferous evergreen species found across the northeastern United...
Effects of nitrogen supply and wood species on Tsuga canadensis and Betula alleghaniensis seedling growth on decaying wood.
Nov 01, 2006; Abstract: Eastern hemlock (Tsuga canadensis (L.) Carriere) and yellow birch (Betula alleghaniensis Britt.) in primaryMichigan...