What is an old-growth forest?

Sometimes we envision a tract of old-growth as an expanse of large, old trees. In fact, they have a complex, multi-layered structure, with trees of varying age and size.

Super-canopy trees are the tallest trees that poke through the canopy. The canopy itself is composed of mature trees that shade the understorey. Below these layers are shrubs and young saplings, growing in shade or under occasional openings in the canopy. On the forest floor are ferns and wildflowers, mosses, fungi, bacteria, and tree seedlings. Still lower is the important layer of organic litter—leaves, branches, and other dead plants and animals—that enrich the soil with nutrients and provide habitat for some species. Dead standing trees, called snags, are also an important part of the ecosystem, providing nesting and feeding habitats for insects, birds and mammals.

The former old-growth forests of southern Ontario were more diverse than most forests we see today. They had a greater variety of trees, shrubs, herbaceous plants, and mosses. These, in turn, supported many animal, insect and microbial species. Some of these species adapted specifically to large, undisturbed tracts of mature forest and the loss of these forests has led to population decline for those species.[1]

Here are some related sites if you are interested in learning more:

[1] The Old-Growth Forests of Southern Ontario. LandOwner Resource Centre, Ontario Extensions Notes. 1999.