Species of the Month: Eastern Hemlock
Eastern Hemlock (Tsuga canadensis) is one of the most gorgeous, and ecologically fascinating of Ontario’s native coniferous trees. Hemlock is evergreen, retaining its needle-like leaves throughout the winter. Needles are ~1.5cm long, arranged opposite to each other, giving young twigs a flattened appearance. Seed cones are 2.5cm long, and similar in appearance to spruce (Picea sp.). Hemlock is a member of the pine family (Pinaceae), being most closely related to Balsam Fir (Abies balsamea) of any other native tree species.
With a mature height of 30m or more, Eastern Hemlock is one of Ontario’s larger tree species. Although rare in Norfolk County, large Hemlock specimens are common in northern Ontario and Michigan’s upper peninsula, where some of the largest concentrations of older-growth Eastern Hemlock trees occur in North America. Ecologically, Hemlock is considered a late-successional species as it dominates older-growth forests, thriving in shaded areas and contrastingly, not tolerant of major disturbance, such as wildfires.
Eastern Hemlock has a very distinctive growth form – a pyramidal crown with weeping branches. This is an ecological adaptation to the heavy snowfall in the areas where Hemlock is most abundant.
Hemlock obtained its name similarly to the crushed foliage of poison hemlock (Conium maculatum), a poisonous, European forb. There are also several closely-related species to the European poison-hemlock native to Norfolk County, the most common being water-hemlock (Cicuta maculatum), which is a common understory plant in deciduous swamps (typically dominated by Silver Maple, Acer saccharinum). All poison-hemlocks are members of the carrot family, Apiaceae.
In much of the Carolinian Life Zone (southernmost Ontario), Eastern Hemlock is a regionally uncommon species: attributable to the prevalence of hardwood species, warm microclimates, and a history of forest disturbance / deforestation, which suppresses Hemlock growth. However, it is more common in southern Norfolk County, where varied terrain creates favourable habitats for Hemlock, especially moist, cool microclimates. Hemlock is most abundant on north-facing slopes, and moist bottomlands. It is also common in moist hardwood forests (dominated by Sugar Maple, Acer saccharum and Beech, Fagus grandifolia), usually as scattered specimens.
In the southern Great Lakes region, Hemlock is threatened by the introduced Hemlock Woolly Adelgid (Adelges tsugae), a sap-sucking insect that feeds on Hemlock foliage, originally introduced from Japan. In the southern Appalachians, Hemlock Woolly Adelgid has caused extensive Hemlock mortality. Currently, large populations are restricted to Haldimand and Niagara Regional Municipalities in Canada. Hemlock Woolly Adelgid is currently not present in Norfolk County, but future spread is likely.
Biocontrols for Hemlock Woolly Adelgid have been approved in both Canada and the United States. Two of the most widely-utilized biocontrol insects for Hemlock Woolly Adelgids are Laricobius beetles and Leucotaraxis silver flies. When utilizing these biocontrol insects, the hope of conservationists is to reduce Woolly Adelgid populations below the mortality threshold for Eastern Hemlock.
A well-known strand of mature Eastern Hemlock can be found within the eastern portion of Backus Woods. LPBLT also protects substantial populations of Hemlock on a substantial proportion of its properties, including the Hammond Hemlock Slough, Jackson-Gunn Old-Growth Forest, Stackhouse Forest Sanctuary and Arthur Langford Nature Preserve.
Written By:
Matthew Palarchio, Honour’s BSc in Environmental Science candidate, Western University
