A Methodology for Assessing and Managing Biodiversity in Street Tree Populations: A Case Study

Abstract

As a consequence of compacted soils, impervious surfaces, heat irradiation, pollution, and other stresses, urban trees have an average expected service life of 10 to 25 years. Most public agency budgets for street tree replacement and maintenance are declining. Public tree managers need tools to prolong the service life of street tree populations while reducing the need for maintenance activities (including pruning and pest management). Many jurisdictions rely on "approved tree" lists, but these often contain large numbers of species generally unavailable in a given area, and filters for diversity are seldom part of these documents. To avoid catastrophic losses and pest outbreaks associated with virtual monocultures, the Maryland Department of Natural Resources has developed a methodology for assessing biodiversity in existing populations. An inventory is taken. The results of the inventory are broken down taxonomically by family, genus, and species; The results are then analyzed, with target levels established as follows: no more than 30% of any one family, 20% of one genus, or 10% of one species should be present. Based on the results of the assessment, recommendations are made as a tool for use in future replacement contracts to bring about the desired species composition.