Eastern Hemlock
(Tsuga canadensis: Pinaceae)
Description: Hemlocks are conical conifers with long, slender, drooping branches. They generally grow to between 60 and 70 feet tall, and have small pendent-like cones that are about three-fourths of an inch long. The state tree of Pennsylvania, they have very distinguishable needles, which are flat and flexible. The dark green and glossy needles are about a half inch long and spread in two rows from short leaf stalks. Young Hemlocks have flaky gray-brown to red-brown bark which becomes thick and roughly grooved over time. Eastern hemlocks are the most shade-tolerant of the eastern conifers.
Geographic Range: Hemlocks are distributed across Canada, (Nova Scotia, New Brunswick, through Quebec, and Ontario) and extend south to Delaware. They are found along the mountains into Georgia and Alabama, and to the west in Michigan and Minnesota. In Michigan specifically, they are found thoughout the sate except in the southeast. Greater numbers are found in the west than the east side of the state.
Habitat Requirements: Hemlocks occur widely in cool moist areas, often with acidic soils. They are extremely shade tolerant trees. These conifers can be seen in wooded areas as well as along rock outcrops, and are known to be found largely in hillside and ravine environments.
Distribution and Density on Hope Property: The Hemlocks found on the Hope property are found all over but have different abundances in certain areas. Very few were found on the northern side of the property, near Kelly Lake. The average density of the trees was measured to be 4.23 trees per 400 m^2, but this ranges from 0 to 65 trees per 20m square quadrat (as measured in the spring of 2001).
Status on the Preserve: The Hemlock size distibution shows that the species is replacing itself. This is shown that of the 342 trees censused, over half were less than 8 cm dbh. This is a much higher density than the larger, older trees. Not all the younger trees will survive but we predict that there will be enough trees to sustain themselves on the property.
Most important threats: In the last two decades, substantial estern hemlock have been observed throughout its range. Widespread hemlock defoliation mainly due to an exotic woolly adelgid, an aphid-like invader from Japan has decimated the species in the Appalachians. However the adelgid has yet to reach SW Michigan. Forest fires have also been shown to greatly affect Hemlock numbers. A low-severity ground fire killed 93% of saplings, while 60% of the mature trees died or were badly injured.
Sources:
Illinois State Academy of Science. http://www.il-st-acad-sci.org/trees/hemlock.html
USGS. http://ael.er.usgs.gov/groups/gis/hemlock/
Contributors: Spencer Bacon, Anna Kievit, Gregory Town