Tsuga canadensis

Scientific name: Tsuga canadensis (Linnaeus) Carrière 1855

Synonyms: Abies americana Mill., Abies canadensis (L.) Dum.Cours., Abies curvifolia Salisb., Abies pectinata Poir., Picea canadensis (L.) Link, Pinus americana (Mill.) Du Roi, Pinus canadensis L., Pinus pendula Sol. ex Salisb., Tsuga americana (Mill.) Farw.

Common names: Eastern hemlock, Canada hemlock, Pruche (French)

Description

Tree to 30(-50) m tall, with straight trunk to 1.5 m in diameter. Bark furrowed, scaly, cinnamon brown. Crown conical, shallow with age in dense stands. Twigs downy. Winter buds pointed, 1.5-2.5 mm long. Needles variable in length, 0.5-1.8(-2.0) cm long, tapering from the base to the tip, with tiny teeth along the edge, the bluntly pointed or rounded, the white stomatal bands beneath each with five or six lines of stomates. Pollen cones 3-5 mm long, yellow. Seed cones green before maturity, ripening light brown, 1.5-2.5 cm long, opening to 1-1.5 cm wide, the seed scales 8-12 mm long. Seed body 2-4 mm long, the wing 5-8 mm longer.

Eastern North America, from Nova Scotia south to northern Alabama, west to eastern Minnesota. Moist ridges, slopes, and valleys; 600-1,800 m. The climate is cool and humid, with annual precipitation between 700 and 1,500 mm.

Conservation Status

Red List Category & Criteria: Near Threatened

This very widespread and abundant species occurs in many forests and woods. In parts of its range, mainly the southwest, dieback that is caused by an invasive alien insect pest is spreading. This causes the flagging of this species as Near Threatened. Whether this pest is moving the species closer to extinction in the near future is uncertain as there is past (prehistoric) evidence of great fluctuations of Tsuga canadensis that were possibly caused by pest outbreaks, from which it recovered. Tsuga canadensis grows locally pure, but is usually mixed with other conifers and broad leaved trees: Pinus strobus, Pinus resinosa, Abies balsamea, Picea rubens, Picea glauca, Larix laricina, Betula spp., Acer saccharum, Quercus rubra, Fraxinus americana, Fraxinus nigra, Fagus grandifolia, Populus spp., and other species. It is very shade tolerant and allows very little vegetation to develop under its own canopy. An introduced insect pest, the Hemlock Woolly Adelgid (Adelges tsugae) is causing substantial dieback in many areas, expanding from Virginia where it was apparently introduced in 1951 to the north and east. It has not yet reached the main area of occupancy around the Great Lakes. Moderating temperatures associated with climate change could allow the spread of this pest into areas where it has so far been prevented from infesting due to low winter temperatures. The slow growing Eastern Hemlock produces lumber of good quality suitable for building (e.g. roofs, floors) and making crates or boxes, but until recently these kinds of use were completely overshadowed by its use in the paper pulp industry. Other former uses were to make telegraph poles and railway sleepers. In the past its bark was used in the tanning industry. Eastern hemlock is still in demand as an ornamental tree; it was introduced to Europe in 1736. In gardens and parks it often grows several trunks, but this is by no means a characteristic of the species in its natural habitat. A large number of cultivars has been produced, including variegated foliage plants and dwarf forms raised from cuttings, whereby the slow growth of this species is an obvious advantage over Western hemlock, of which few cultivars exist. Conversely, due to that slower growth Eastern hemlock is less preferred as a forestry plantation tree, giving way to Western hemlock. This species is present in many protected areas. Control of the insect pest Adelges tsugae is the main priority and is being researched. Pest control in wild populations is difficult because of negative environmental effects of spraying from airplanes with insecticides.

References

Farjon, A. (2010). A Handbook of the World's Conifers. Koninklijke Brill, Leiden.
Eckenwalder, J.E. (2009) Conifers of the World: The Complete Reference. Timber Press, Portland.
IUCN Red List of Threatened Species, International Union for Conservation of Nature and Natural Resources. Cambridge, UK /Gland, Switzerland

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