Journeys in ancient and old growth forests
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Eastern hemlock: Ontario’s forest cathedrals

When we think of old-growth forest in Ontario, we tend to think of white pine, or ancient cliff-growing cedars – but we should probably be thinking about hemlock forest. Eastern hemlock is a very long-lived climax species that is common in old-growth forests south of the boreal (map below). Because it doesn’t recover well after disturbance, hemlock is often found in areas that have been continuously forested since before European settlement hundreds of years ago.

Although it has declined in southern Ontario, in parts of central Ontario hemlock is still a relatively common dominant tree, and the trees are often much older than we realize. In Algonquin Park alone there are more than 20,000 hectares of hemlock dominated forest aged over 180 years old, and hemlock trees over 400 years old have been found in widely disparate corners of the province, including the Niagara Gorge, Burnham Woods near Peterborough, and several places in Algonquin Park. We will probably find many more if we look for them; old hemlock trees are often overlooked because they may not be that large. Trees over 300 years old are commonly under 80 cm diameter, and may be less than 50 cm!

Eastern hemlock is a tree of shorelines and river valleys. It shades the north slopes of the ravines and waterfalls of the Niagara Escarpment, and is an iconic tree of Muskoka and Algonquin Park shorelines. Hemlock is known as a foundation species, because it exerts such a strong influence on ecosystems where it grows. The dense shade of hemlock groves cools streams throughout the summer – streams that run through hemlock valleys average about one to two degrees Celcius cooler than in nearby hardwood forests, creating important habitat for cold-water fish species such as brook trout. Hemlock also helps maintain summer water levels in streams by holding spring snowpack longer, and reducing summer evaporation. If you’re not sure how to recognize eastern hemlock, the Morgan Arboretum has a great post to help you.

Hemlock is threatened by a sucking insect that kills trees called hemlock woolly adelgid – keep an eye out for it while hiking, because early detection can help save our hemlock forests. The eastern hemlock project aims to document remnant hemlock forests in southern Ontario and encourage citizen engagement in their stewardship. In the spring of 2017 Michael Henry, author of Ontario’s Old-Growth Forests, will be on a speaking tour about eastern hemlock’s ecology, history, and future.

Find a hemlock forest near you using the map below. Help us improve the map with new sites, information or photos. Join the Eastern Hemlock Project on inaturalist to upload locations of hemlock from your smartphone.