Old-growth forests 101

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 and dying trees. But any enlightened 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 depending on the forest type. 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 or dying trees important?

Dead trees greatly influence, in a positive way, the ecological structure and composition of the forest. They provide habitat for wildlife both as standing stems and as logs on the ground. And when trees die there are always saplings waiting in the shadows to take their place.

“This helps us understand how a forest will naturally respond to disease and natural disturbances such as fire or tornadoes,” 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, ON (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 1,154-hectare (2,851-acre) forest is the most intact example of mature sugar maple and beech forests characteristic of 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 302 hectares (747 acres) protected so far, hopefully the Happy Valley Forest will have a chance to become truly old-growth in the years ahead.”