Tsuga canadensis | Threatened Conifers of the World (en-GB)

Pinaceae

Tsuga canadensis (L.) Carrière

This very widespread and abundant species occurs in many forests and woods in North America. In parts of its range, dieback is caused by an invasive Hemlock Woolly Adelgid (Adelges tsugae). This has resulted in an asessment of Near Threatened.

Distribution

Recorded from eastern North America: occurs from Nova Scotia to northern Georgia, westwards to Minnesota. The extent of occurrence and area of occupancy are well in excess of the thresholds for any threatened categories.

Country Occurrence: Canada (New Brunswick, Nova Scotia, Ontario, Prince Edward I., Québec); United States (Connecticut, Georgia, Indiana, Kentucky, Maine, Massachusetts, Michigan, Minnesota, New Hampshire, New Jersey, New York, North Carolina, Ohio, Pennsylvania, Rhode Island, South Carolina, Tennessee, Vermont, Virginia, Washington, Wisconsin)

Habitat and Ecology

Tsuga canadensis occurs from near sea level (Nova Scotia) to 600 m in N Michigan, in the southern Appalachians between 600 and 1,500 m above sea level. The soils are of glacial, fluvio glacial, alluvial, or colluvial origin, podzolic and usually highly acidic (pH 3-4). The climate is cool and humid, with annual precipitation between 700 and 1,500 mm. T. canadensis grows locally pure, but is usually mixed with other conifers and broad leaved trees: Pinus strobus, P. resinosa, Abies balsamea, Picea rubens, P. glauca, Larix laricina, Betula spp., Acer saccharum, Quercus rubra, Fraxinus americana, F. nigra, Fagus grandifolia, Populus spp., and other species. It is very shade tolerant and allows very little vegetation to develop under its own canopy.

Human Uses

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.

Conservation Status

Global assessment

Near Threatened

Global rationale

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 (close to qualifying under criterion A4ae). 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.

Global threats

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.

Conservation Actions

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 and further reading

Burns, R.M. and Honkala, B.H. 1990. Silvics of North America. USDA, Forest Service, Washington, DC.
Eckenwalder, J. 2009. Conifers of the World: The Complete Reference. Timber Press, Portland, Oregon.
Farjon, A. 2010. A Handbook of the World's Conifers. Koninklijke Brill, Leiden.
Farjon, A. 2013. Tsuga canadensis. The IUCN Red List of Threatened Species 2013: e.T42431A2979676. http://dx.doi.org/10.2305/IUCN...
Heard, M.J. and Valente, M.J. 2009. Fossil pollen records forecast response of forests to hemlock woolly adelgid invasion. Ecography 32: 881-887.
Jetton, R., Whittier, W.A., Dvorak, W. and Potter, K. 2008. Status of ex situ conservation efforts for Carolina and Eastern Hemlock in the Southeastern United States. B. Onke and R. Reardon (compilers) Fourth Symposium on Hemlock Woolly Adelgid in the Eastern United States, February 12-14, 2008, Hartford Hilton Hotel, Hartford, Connecticut: 81-90.
Krapfl, K.J., Holzmueller, E.J. and Jenkins, M.A. 2011. Early impacts of hemlock woody adelgid in Tsuga canadensis forest communities of the southern Appalachian Mountains. Bulletin of the Torrey Botanical Club 138(1): 93-106.
Oswald, W.W., Doughty, E.D., Foster, D.R., Shuman, B.N. and Wagner, D.L., 2016. Evaluating the role of insects in the middle-Holocene Tsuga decline. The Journal of the Torrey Botanical Society, 144(1), 35-39.
Rentch, J. and Schuler, T. (eds.). 2010. Proceedings of the Conference on the Ecology and Management of High-Elevation Forests in the Central and Southern Appalachian Mountains Proceedings of a Conference held at Snowshoe Mountain Resort, Slatyfork, WV, May 14-15, 2009. U.S. Forest Service, Newtown Square, PA.