A broad scale analysis of tree risk, mitigation and potential habitat for cavity-nesting birds

Trees in towns and cities provide habitat for wildlife. In particular, cavity-nesting birds nest in the dead and decayed stems and branches of these trees. The same dead and decayed stems and branches also have a greater likelihood of failure, which, in some circumstances, increases risk. We examined 1760 trees in Baltimore, MD, USA and western MA, USA, assessing tree risk and, for a sub-sample, noting the presence of cavity nests excavated by birds. In Baltimore, most trees were in areas of frequent use and had no visible defects. In western MA, most trees were in areas of infrequent use and 70% had visible defects. The most common defect in both locations was dead branches and stubs between 10 and 51 cm in diameter. Trees with a cavity nest had a greater likelihood of failure than trees without a cavity nest. Our data provide an overview of tree risk assessment and mitigation, a baseline understanding of risk parameters for common street trees in the Northeast and Mid-Atlantic regions of the United States, and insight into whether a balance can be struck between tree risk and provision of wildlife habitat.