Why are large woodlands important?

Woodlots in southern Ontario tend to be small and intersected by roads, farm fields, trails and urban and rural development. Just like a puzzle with missing pieces, a woodland ecosystem broken into small fragmented pieces does not function as a healthy forest should.

Large woodlands are those expanses of forest that still contain sheltered core areas, know as interior habitat. As a rule, the forest interior is that portion of a woodlot greater than 100 metres from the woodland edge, such as a field, road, or hydro corridor. To put this into perspective, a square 10 acre (4 hectare) woodlot measuring 200 metres by 200 metres and will contain only a fraction of 1 acre of forest interior habitat. A longer, narrower woodlot of the same area will contain no interior at all, since no part of the woods will be more than 100m from an edge.

Large woodlands are more diverse in every way. They containg more tree and shrub species (e.g. fruit and nut producing species such as oak, hickory, cherry), more opportunities for aquatic habitat – small wetlands, springs, streams, vernal pools – upland and lowland woodlands, old growth features such as super-canopy white pine, abundant cavity and standing dead trees, and usually more large and small woody debris on the forest floor. Larger woodlands also have a greater buffering capacity from the wind and sun that dries out the forest edges. Small woodlands are more exposed to sun and wind and tend to drier and warmer.

Only large woodlands with forest interior provide the habitat necessary for the survival of many increasingly rare forest species, particularly interior birds. Smaller patches of forest allow a great number of nest predators into the forest. Many forest interior bird species nest on the ground or in low-shrubs. Species such as the ovenbird have not evolved quickly enough to deal with the high numbers of raccoons or domestic and feral cats now frequenting our southern Ontario woodland edges. The brown-headed cowbird, a nest parasite, is also common along woodland edges. Cowbirds lay their eggs in the nests of other songbirds rather than raising their young themselves. The adopted parent then incubates the cowbird eggs to be raised as its own, often to the detriment of the other young.

While every little piece of woodland left is worth keeping, it is especially important to conserve and enhance large woodlands with forest interior.

For more information please read Conserving the Forest Interior: A Threatened Wildlife Habitat.