Coarse Woody Debris: #1 What is it?

Often neglected or overlooked, coarse woody debris is an integral element of the forest community. As a major structural feature within the terrestrial and stream ecosystems, it provides habitat for numerous organisms; contributes to the formation of soil, nutrient cycling, and water retention; and influences sediment transport and storage (Harmon et al. 1986).

Coarse woody debris (CWD) describes a variety of non-living materials. These include snags and dead and down woody materials that vary in size, texture and degree of decay. Snags are commonly defined in forestry as standing dead trees that lack most of their branches and leaves. For this blog we will consider a snag to have a minimum diameter of 4 inches at breast height, and a minimum height of 6 feet. This definition is based on the minimum diameter and height of dead trees used by birds for nesting (Thomas, ed. 1979).

Dead and down woody material may consist of logs, wood chunks (disintegrated snags) large branches and coarse roots. We can consider dead and down woody materials having a minimum diameter of one to three inches (Harmon et al. 1986).

CWD is habitat for many species, including autotrophs and heterotrophs. Snags provide a portion of the habitat needs of many plants, invertebrates, birds and mammals (Thomas ed. 1979). Invertebrate dependence on snags and dead logs has long been appreciated (Lang and Forman 1978). Decomposer bacteria, ectomycorrhizae, and various other forms of fungi utilize CWD as an energy and nutrient source, as well as a habitat (Franklin et al. 1982; Swift 1977a).

CWD has a significant influence over geomorphic processes in stream and river systems (Swanson et al., 1982a, b). Woody structures regulate sediment transport through the dissipation of energy and capture and storage of sediment. They also provide a diverse array of structural elements to habitat within streams that influence biological productivity (Franklin et al., 1982; Sweeney, 1993). CWD is an energy and nutrient source for forest streams. It captures forest litter and organic matter in streams until they can be used by aquatic organisms (Bilby and Likens, 1980; Cummins, 1979).

In the next blog in this series I will talk about how coarse woody debris is typically produced and retained within the forest. Later blogs in the series will discuss the role of coarse woody debris in the semi-tropical forests of west-central Florida and its potential role in the conservation of biodiversity within urban forests.

For a recent review of the scientific literature pertaining to the Southestern United States go to:

Ecology of Dead Wood in the Southeast