White trilliums, The Happy Valley Forest, ON (Photo by NCC)
White trilliums, The Happy Valley Forest, ON (Photo by NCC)

Old-growth forests 101

Haida Gwaii, British Columbia (Photo by Tim Ennis/NCC)

Haida Gwaii, British Columbia (Photo by Tim Ennis/NCC)

Why are old-growth forests important?

When thinking about healthy forests, it’s not often we include dead, dying or diseased trees. But any forest manager will tell you that they’re an essential part of a healthy forest ecosystem, and a key characteristic of old-growth.

Old-growth forests exist because they have not been subjected to a significant disturbance such as wildfire or clear-cutting for a century or more. However, it’s not easy to pin down an age at which a forest becomes “old,” because depending on the climate, geography and soil, a forest’s composition and lifespan will vary drastically. 

So what makes old-growth forests unique?

Old-growth forests contain trees in all phases of their life cycle, including:

  • saplings
  • mature trees
  • dead standing trees
  • rotting trees on the forest floor

These dead standing and rotting trees provide a home for many species of plants, fungi, invertebrates, salamanders and snakes. This makes old-growth forests hotspots for biodiversity and a refuge for many species at risk.

“Protecting old-growth forests means respecting the elders, letting them die a natural death and crash down, even if they’re diseased,” notes Mark Stabb, the Nature Conservancy of Canada's (NCC's) Central Ontario program manager.

Why are dead, dying or diseased trees important? 

Dead trees significantly change the structure and composition of the forest, but there are always saplings waiting in the shadows to take their place.

“This helps us understand how a forest will respond to disease and natural disturbances such as fire, tornadoes or earthquakes,” says Stabb.

What is an example of an old-growth forest? 

“There aren’t many old-growth forests left compared to a couple hundred years ago,” Stabb adds.

Upland forest in Happy Valley Forest, Ontario (Photo by NCC)

Upland forest in Happy Valley Forest, Ontario (Photo by NCC)

However, at more than 200 years old, the Happy Valley Forest (HVF) Natural Area in Ontario is a good example of a forest that is growing old. Located just 35 kilometres from Toronto, this 2,851-acre (1,154-hectare) forest is the most intact example of mature sugar maple and beech forests characteristic on the Oak Ridges Moraine.

The HVF provides critical habitat for more than 110 breeding bird species, including nationally significant Acadian flycatcher and cerulean warbler and amphibians like Jefferson salamander.

What is NCC doing?

Across the country, NCC is working to identify and protect important old-growth forests for conservation.  

Dr. Henry Barnett, whose land NCC helped protect in the HVF and who has been instrumental in convincing neighbours to put their land under conservation protection, remarks:

“With more than 547 acres (221 hectares) protected so far, hopefully the Happy Valley Forest will have a chance to become truly old-growth in the years ahead.”

(This article was published in the spring 2008 issue of The Ark. Donors who contribute $20 or more annually receive three issues a year.)

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