Woodpecker-snag interactions: an overview of current knowledge in ponderosa pine systems

Standing dead trees (snags) with cavities are a critical ecological component of western coniferous forests. These structures provide foraging, roosting, and nesting habitat for numerous species of invertebrates, amphibians, reptiles, birds, and mammals. Snags may be created through a variety of interrelated processes including wildfire, drought, insects and disease. However, dead trees containing excavated cavities are primarily the result of nest excavation by woodpeckers. While the specific factors leading to cavity generation in certain snags is not well understood, the manner in which a tree dies likely plays a significant role. We provide an overview of woodpecker-snag interactions in relation to the major modes of tree mortality in ponderosa pine. Of particular interest is the effect of mortality agent on the temporal patterns of snag decomposition, woodpecker foraging use, and woodpecker cavity excavation. Generally, snags created by bark beetles, and/or fire decay fastest, and experience the greatest foraging and nesting use by woodpeckers. Consideration of these interrelationships may aid in snag management.