Arboriculture & Urban Forestry 43(1): January 2017 Arboriculture & Urban Forestry 2017. 43(1):1–14 1 Street Tree Diversity in Three Northeastern U.S. States F.D. Cowett and Nina Bassuk Abstract. Street tree diversity is widely viewed as a key component in the resilience of street tree populations to pests, diseases, and climate change. Assessment of street tree diversity is considered integral to sustainable street tree management and preservation of the ecosystem services and social benefits that street trees provide. This paper assesses street tree diversity in three northeastern U.S. states— New Jersey, New York, and Pennsylvania—by analyzing municipal street tree inventory data stratified by the 2012 USDA Plant Hardi- ness Zones. Despite the lesson learned from the historical devastation of overplanted American elms (Ulmus americana) by Dutch elm disease, and awareness of the contemporary threats posed to ashes (Fraxinus spp.) by the emerald ash borer (Agrilus planipennis) and to maples (Acer spp.), and other tree genera by the Asian longhorned beetle (Anoplophora glabripennis), results presented here indi- cate a current concentration of street trees among a relatively small number of species and genera, and in particular the dominance of maples as street trees. Results also show a positive relationship between street tree diversity and warmer average minimum winter temperatures. Consequently, there is a clear need in all three states for greater species and genus diversity in statewide and munici- pal street tree populations. However, meaningful impediments exist to increasing street tree diversity, especially in the short term. Key Words. Acer spp.; Diversity Indices; Ecosystem Services; New Jersey; New York; Pennsylvania; Resilience; Street Trees. Biological diversity at the species level has been associated with the stability and productivity of non- urban vegetated ecosystems (Bezemer and van der Putten 2006; Tilman et al. 2006; Cadotte et al. 2012), including non-urban forest ecosystems (Thompson et al. 2009). Urban forest ecosystems differ meaning- fully from non-urban forest ecosystems, since factors typically found in urban environments, including but not limited to buildings, impervious surfaces, anthropogenic soils, pollution, and the urban heat is- land, may not be found in non-urban environments or at least not to the same degree (Nock et al. 2013). Despite these differences, however, and similar to the non-urban forest, urban tree diversity has been associated with the stability and productivity of the urban forest and with continued provision of ecosys- tem services and social benefits (Manes et al. 2012). Street trees growing in public street rights-of-way typically comprise a minority of the urban forest and the services and benefits they provide (Dwyer et al. 2000). Nevertheless, they have received special atten- tion and have been a focus of urban forestry due to their public function (Clark et al. 1997; Cumming et al. 2008). Because of the devastation wrought many years ago by Dutch elm disease on American elms (Ulmus americana) (Campanella 2003) and more current threats, such as those posed to ashes (Fraxinus spp.) by the emerald ash borer (Agrilus planipen- nis) (Poland and McCullough 2006) and to maples (Acer spp.) and other genera by the Asian long- horned beetle (Anoplophora glabripennis) (Smith and Wu 2008), diversity in street tree plantings is widely viewed as a key component in the resilience of street tree populations to pests, diseases, and cli- mate change, and assessment of street tree diversity is considered integral to sustainable street tree man- agement (Raupp et al. 2006; Sjöman et al. 2012). Street tree diversity has been assessed at a vari- ety of geographic levels. It has most commonly been assessed at the level of the individual municipality from data collected in a complete or sample street tree inventory (Clark et al. 1997). In Syracuse, New York, U.S., for example, Sanders (1981) assessed street tree diversity for the city as a whole and for 17 city neighborhoods from a complete inventory of 32,517 street trees. In Davis, California, U.S., Maco ©2017 International Society of Arboriculture
January 2017
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