Arboriculture & Urban Forestry 46(1): January 2020 Arboriculture & Urban Forestry 2020. 46(1):27–43 URBAN FORESTRY ARBORICULTURE Scientific Journal of the International Society of Arboriculture & Street Tree Diversity in Massachusetts, USA By F.D. Cowett and Nina L. Bassuk Abstract. Pests, disease, and climate change pose major challenges to street tree survival, and diversity in tree species and genera is widely considered to promote the sustainability of municipal street tree populations. Conversely, the lack of sufficient diversity in street tree popula- tion was judged a contributing factor in the death and removal of thousands of street trees in Worcester, Massachusetts, that state’s second most populous city, due to an infestation of the Asian longhorned beetle (ALB, Anoplophora glabripennis). Therefore, reducing the dominance of prevalent street tree species and genera and increasing tree species and genera diversity are considered vital to sustainable street tree manage- ment and to the preservation of the ecosystem services and social benefits that street trees provide. This paper assesses street tree diversity in Massachusetts by analyzing a nonrandom sample of collated municipal street tree inventory data stratified by plant hardiness zones. Consis- tent with results previously found for Connecticut, New Jersey, New York, and Pennsylvania, results in Massachusetts indicate that a relatively small number of species and genera dominate the composition of most municipal street tree populations, including in particular Acer spp. (maple), one of the ALB’s favorite host genera. There is accordingly a need for greater species and genus diversity in municipal street tree pop- ulations statewide. While there may be a trend towards increased street tree diversity and reduction in the dominance of Acer spp., consider- able work remains to be done. Keywords. Acer spp.; Asian Longhorned Beetle; Diversity Indices; Ecosystem Services; Worcester. INTRODUCTION Massachusetts, one of the original thirteen states that declared independence from Great Britain in 1776, has played a unique role in the history of urban and community forestry in the United States. The first official public shade tree in the American colonies was planted there in 1646 (Steiner 2016). To upgrade the appearance of the Boston Common following the construction of municipal buildings around it, double rows of trees were planted on all sides in the mid-19th century to create formal promenades for strolling, one of the first examples of trees being used for that purpose (Favretti 1982). In 1899, as a response to widespread woodland clearing, the Massachusetts state legislature passed a law requiring each munici- pality to appoint a tree warden responsible for the care and protection of community trees, acknowledg- ing the importance of urban forest management (Ricard 2005). More recently and far less propi- tiously, in 2008, the Asian longhorned beetle (ALB, Anoplophora glabripennis), native to China and Korea and one of the world’s worst invasive species (Sim- berloff and Rejmánek 2011), was found in Worcester, the state’s second most populous city. Although the ALB had been found previously in Europe, the north- eastern United States, and Canada, the Worcester infestation was of particular concern due to its prox- imity to the surrounding closed-canopied temperate forests extending from central New England west to southeastern Canada and the Great Lakes region, and because Acer spp. (maple), its primary host genus, was a prevalent and economically important compo- nent of those forests (Dodds and Orwig 2011). The ALB infestation in Worcester raised concerns about insufficient tree diversity. Species and genus diversity are considered significant contributors to the resilience of urban trees to stressors such as pests, disease, and climate change and their continued pro- vision of ecosystem services (Manes et al. 2012). Conversely, a vulnerability to stressors related to a lack of diversity can result in large numbers of trees requiring removal in a short period of time, which may not only impair streetscape aesthetics, but also strain municipal budgets and those departments responsible for tree management (Ball et al. 2007; MacDonagh 2015). However, competing with the ©2020 International Society of Arboriculture 27
January 2020
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