At right: a maple snag in a Guelph, Ont., city park.
In 1987 I visited one of Canada's few remaining old-growth temperate rainforests in Pacific Rim National Park. What impressed me was the prevalence of death in a forest untouched by loggers or developers. The sylvan landscape was strewn with fallen giants: Western red cedars and Western hemlocks that had lain rotting for decades or centuries. Their carcasses would present insurmountable obstacles to anyone venturing off the trail, further complicated by the dense tangle of shrubs like salal. (View an image gallery from Canadian West Coast temperate rainforest.)
Around Southern Ontario I frequently encounter forest plantations, most often red pine, established to replace woodlands clear-cut for lumber decades ago. These tracts are characteristically uniform: monocultures containing one tree species and few other plant forms. They are unattractive as habitat to most wildlife species.
The woods around my cottage in Central Ontario was destroyed by fire 90 years ago, a relatively short period of time in forest progression, and yet it has recovered to the point that dead trees play a significant role. Fallen Eastern hemlocks look like miniatures of the behemoths I saw on the West Coast in 1987. We frequently observe pileated woodpeckers, a species dependant on large dead trees.
In the past 40 years wildlife ecologists have gained greater knowledge of what constitutes good forest management. With forest cover in many regions drastically reduced over the past two centuries, the practise must not only provide a sustainable resource, but also build habitats that foster species diversity. One important principle is to avoid removing all dead wood. One bibliography identifies 57 species of birds and mammals that live in standing dead trees in Oregon and Washington.
When a tree dies it goes through several different phases of decay. A standing dead tree is called a snag. Depending on tree species and the soundness of the wood, the snag may be described as hard or soft. As decay progresses, the tree attracts different organisms. Eventually, rotting and falling to the ground, it performs yet other important functions in the ecosystem. Fallen trees in advanced stages of decay are known as nurse trees.
Some of the organisms that benefit include:
- Insects and other arthropods. Many species, from beetle larvae to carpenter ants, spend all or part of their life cycles living in and feeding on dead wood. Others hibernate or otherwise take shelter under loose bark. While some of these species can pose a threat to commercial forestry, their presence in dead trees attracts
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