by MF Galvin
Journal of Arboriculture 25(3):124-1281999
Trees in urban areas provide many benefits, including carbon sequestration, reduction of building energy used for cooling and heating, and improvement of wildlife habitat and urban aesthetics. Unfortunately, urban trees have an average expected service life of 10 to 25 years due to pollution, compacted soils, impervious services, populations lacking species diversity, and other stresses. Although this situation indicates a need for significant maintenance and replacement funding to maintain street tree canopy in urban areas, most public agency municipal tree budgets saw a 40% reduction over an 8-year period from 1986 to 1994. Based on increased management needs and reduced funding available for management, public agency tree managers require tools that will allow them to prolong the service life of public street tree populations while reducing the amount of tree maintenance, removal, and replacement needed. This paper presents a methodology for assessing biodiversity in existing populations to circumvent substantial losses and pest outbreaks associated with virtual monocultures. This method involved the Maryland Department of Natural Resources inventorying street trees in Mount Rainier, Maryland, and recording information such as type, condition, and the surrounding environment of the trees. The data collected were then broken down by species, genus, and family to allow for specific recommendations regarding pest management and future species composition. The authors used previously established target levels for urban forests of no more than 30% of any one family, 20% of one genus, or 10% of one species to provide specific recommendations for future tree plantings. Use of this methodology allows public agency tree managers to apply these target levels to minimize management and replacement costs, and ensure the sustainability of their urban forests.