Snags and nurse trees
Beside the property where I grew up on the shore of Lake Erie stood a giant dead cottonwood, at least 25 metres tall, which weather had denuded and bleached to the colour of driftwood. Red-headed woodpeckers, an endangered species in Ontario, nested in its high branches. Once we spotted a bald eagle perched there, watching for fish in the water below. In those days Ontario had only a few nesting pairs of eagles (the species has since recovered dramatically). Imagine my family's grief and anger one day when we discovered that the neighbours, who owned the property but knew nothing of these birds, had cut down that venerable tree. Red-headed woodpeckers vanished from our neighbourhood and have rarely been seen since then.
A study of snags and nurse trees shows us that, in healthy ecosystems, dead and decaying organisms are just as important as the live ones. Woodlands benefit most from having snags of a variety of sizes and tree species, but one large snag can provide benefits to a several hectares. For more information about snags and how to conserve them, here are some articles for further reading:
Life After Death, by Scott Shalaway
Dead and Dying Trees: Part of a Healthy Forest, by Richard Harris and Bill Laudensayer