Arboriculture & Urban Forestry 44(3): May 2018 Arboriculture & Urban Forestry 2018. 44(3):133–145 133 The Influence of Abiotic Factors on Street Tree Condition and Mortality in a Commercial-Retail Streetscape Camilo Ordóñez, Vadim Sabetski, Andrew A. Millward, James W. N. Steenberg, Amber Grant, and James Urban Abstract. It is challenging to successfully grow trees in highly-urbanized areas, such as downtown commercial-retail districts. As part of a streetscape revitalization project, initiated in 2010, 133 London planetrees (Platanus × acerifolia) were planted in structural soil cells along the downtown, commercial district of Bloor Street in Toronto, Ontario, Canada. Aſter most trees experienced severe decline, with many dying, all trees were removed and replaced in 2015. This research reports on an investigation of multiple abiotic factors that may have contributed to the decline and mortality of the Bloor Street trees. Researchers collected cross-sectional data on soil texture, soil compac- tion, soil chemistry, built-environment characteristics (e.g., proximity to road intersections, pit or bed planter), sunlight availability, and historic data on tree condition and mortality, and analyzed them with multivariate statistical techniques (e.g., correlation, MANOVA, contingent, and ANOVA tests) to investigate the potential for relationships to tree mortality (mortality rate of 46.6% before removal) and tree condition. Results indicate that trees that were alive and demonstrated better structural and foliar condition before removal in 2015 had significantly lower levels of soil salinity and alkalinity, sunlight exposure, and signs of physical damage, suggesting co-occurring and cumulative impact of these variables on tree performance. Modification to streetscape design can ameliorate tree decline in the long term, while education targeted at raising awareness about de-icing salt application and irrigation practices will lessen tree stressors immediately. Key Words. De-Icing Salts; London Planetree; Platanus × acerifolia; Structural Soil Cell; Sunlight Availability; Toronto; Urban Soils. North American cities are setting goals to increase the number of trees in urban spaces (e.g., City of Toronto 2012), particularly in downtown com- mercial areas where trees can increase the aesthet- ic appeal of streets, enhance retail activity (Wolf 2005), and provide environmental benefits, such as moderating ambient heat (Greene and Millward 2017). Growing trees in these areas, however, is a significant technical challenge, as trees frequently face high rates of decline and mortality (Jim 1997). Incorporating trees in these spaces usually neces- sitates the adoption of techniques that can improve soil quality and water availability conducive to tree- root development (Bassuk and Whitlow 1987). Underground structural elements, such as struc- tural soil cells, have the capacity to significantly improve growing conditions for trees (Grabosky et al. 2001; Bartens et al. 2010; Day et al. 2010; Brockbank and Slater 2016). Structural soil cells, an underground framework that contains pre- scribed soil conditions, are designed to support tree growth and provide a system of passive irrigation to the trees, while also collecting, absorbing, and infiltrating surface water runoff (Page et al. 2015). Structural soil cells were installed along Bloor Street, located in a downtown shopping district in Toronto, Ontario, Canada, and notably one of the most important commercial-retail streets in the country. This tree installation was part of a multi-million-dollar street-revitalization project, finalized in 2011, which had the goal of improv- ing tree-growing habitat to maximize survi- vorship and enhance growth, thus ensuring a consistent flow of aesthetic and environmental benefits. Despite significant consideration for tree growing conditions, and substantial invest- ment in underground soil infrastructure, many of the 133 trees originally planted fared poorly ©2018 International Society of Arboriculture
May 2018
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