12 Dead Wood Management
Dead trees are the losers in density-dependent competition and a product of forest disturbance and disease. Considered by many to be a waste of wood fiber and a fire hazard, dead wood provides habitat for many animal species, nursery sites for germination of plants, and pathways for energy in a cellulose-based environment (Harmon et al. 1986). A large western redcedar may live to be 300 years old, and then may take another 300 years or more to decay (Embry 1963). Throughout its life, and after its death, a tree can play a role in contributing to habitat quality for a succession of organisms (Maser et al. 1979). Consider the pathway of energy following a natural disturbance that creates an early successional forest. Photosynthesis leads to allocation of energy to leaves, fruits, tree boles, and roots. In later stages of forest succession, most forest energy is stored in cellulose, and cellulose must be broken down into simpler molecules to allow the stored energy to become available to other organisms. Following an intense disturbance, that cellulose is abundant and can be decomposed to provide energy to other life forms. This process is the primary mechanism allowing energy flow through trophic levels in detrital-based systems. Cellulose is also the primary source of stored carbon in forest systems. Carbon is slowly released as CO2 during wood decomposition (Harmon et al. 1986). The decaying wood is also associated with nitrogen-fixing bacteria, which may contribute to the soil nitrogen, thereby influencing soil fertility in some forest types (Sollins et al. 1987).
The fungi and invertebrates responsible for decomposing and fragmenting the wood become the basis for energy flow into other organisms. The organisms responsible for decomposition can differ markedly between aquatic and terrestrial systems, often leading to slower rates of decay in submerged wood versus wood exposed to air. Further, dead wood can affect the function of terrestrial and aquatic systems. Dead wood adds complexity to forest floors, increasing ground-surface and below-ground heterogeneity. Trees and snags that fall into streams can have significant impacts on sediment deposition and scouring within the channel, leading to a more complex channel structure than would be present without these logs (Bisson et al. 1987).