Eastern Hemlock

Appearance

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. The tree generally reaches heights of about 31 meters, but exceptional trees have been recorded up to 53 metres. The diameter of the trunk at breast height is often 1.5 metres, but again, outstanding trees have been recorded up to 1.75 meters. 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 in length. These are usually not resinous, but may be slightly so.

The leaves are typically 15 to 20 mm in length, but may be as short as 5 mm or as long as 25 mm. 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 colour. 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 in length and 1 to 1.5 cm in width. The scales are ovate to cuneate in shape and measure 8 to 12 mm in length by 7 to 10 mm in width. The apex is more or less rounded and is often projected outward. Twenty-four diploid chromosomes are present within the trees' DNA.

Distribution

"T. canadensis" occurs at sea level in the north of its distribution, but is found primarily at elevations of 600 to 1800 metres. It ranges from northeastern Minnesota eastward through southern Quebec and into Nova Scotia, and south in the Appalachian Mountains to northern Georgia and Alabama. Disjunct populations occur in the southeastern Piedmont, western Ohio and into Illinois, as well as eastern Minnesota. In Canada, it is present in Ontario and all provinces to the east except Newfoundland and Labrador. In the USA, it is found in all states east of and including Minnesota, Wisconsin, Indiana, Kentucky, Tennessee and Alabama, but excluding Florida. Its range completely overlaps that of the closely related "Tsuga caroliniana".

It is found primarily on rocky ridges, ravines and hillsides with relatively high levels of moisture.

Habitat

"T. canadensis" occurs at sea level in the north of its distribution, but is found primarily at elevations of 600 to 1800 metres. It ranges from northeastern Minnesota eastward through southern Quebec and into Nova Scotia, and south in the Appalachian Mountains to northern Georgia and Alabama. Disjunct populations occur in the southeastern Piedmont, western Ohio and into Illinois, as well as eastern Minnesota. In Canada, it is present in Ontario and all provinces to the east except Newfoundland and Labrador. In the USA, it is found in all states east of and including Minnesota, Wisconsin, Indiana, Kentucky, Tennessee and Alabama, but excluding Florida. Its range completely overlaps that of the closely related "Tsuga caroliniana".

It is found primarily on rocky ridges, ravines and hillsides with relatively high levels of moisture.The mid-Holocene decline of hemlock populations is a much-studied phenomenon. From its foundation in the early Holocene in what is now the southeastern US, "T. canadensis" expanded rapidly and successfully into its potential range. However, palynological analyses show the hemlock population experienced a pronounced decline approximately 5,500 BP that lasted for about 1,000 years. Continued research points to other, though less dramatic, dips in Holocene hemlock populations. Pathogens, insects, and climatic change, and a combination of these, have all been proposed to explain these anomalies. The eastern hemlock increased again after the major decline, but did not recover its former place as a dominant species.