Old-Growth Forests

As was noted previously, important habitat requirements of many species of wildlife relate to the numbers of dead trees in the forest, occurring as standing snags or as logs lying on the ground. These features are especially critical to some birds, which use the deadwood for nesting in excavated or natural cavities, as perches for hunting, resting, and singing, and as a substrate on which to forage for their food of insects and spiders. For example, a study in the northwestern United States found that up to 45% of the species of breeding birds are cavity nesters. These include various species of woodpeckers that actually excavate An old-growth Douglas fir forest in the Pacific Northwest. Photograph by Tom and Pat Lesson. National Audubon Society Collection/Photo Researchers, Inc. Reproduced by permission. cavities, as well as other species that are secondary users of those cavities, or that use natural hollows.

Unfortunately, modern forestry does not accommodate this habitat feature very well. Because forestry plantations usually have very few snags or other types of deadwood, cavity-dependent species of wildlife are at risk in these highly managed, secondary forests. As a result, forestry-related degradation of the habitat of these animals has become an important environmental issue in many areas. This concern is especially relevant to old-growth forests, because deadwood is such a prominent characteristic of this type of ecosystem. For example, as many as six woodpecker species can co-occur along with other cavity-dependent species in old-growth forests of the Pacific Northwest of the United States. It may be possible to accommodate most of these species, while still practicing forestry, if an appropriate system of integrated management can be developed. One study done in that region suggested that about 70% of the woodpecker Illustration by Hans & Cassidy. Courtesy of Gale Group. population could be maintained in selectively harvested old-growth forests, as long as at least four large snags remained per hectare on harvested sites.