Urban Soil Variability: How Can We Improve Soil and Site Management to Support Tree Growth?.

Street trees are essential to the urban environment because of the wide range of ecological, economic, and aesthetic benefits they provide. However, street tree growth, health, and longevity are jeopardized by inadequate planting sites and soil quality. As a result, trees in urban centers often only reach 7 to 10 years of age before declining and dying and can therefore fall short of supplying the benefits a mature tree could provide. Urban tree species must be selected to match soil conditions where they will be planted in order to thrive. However, assessing every tree planting site within a city is not resource effective. We evaluated street tree planting sites (defined as sites along roadways or parking lots surrounded on all sides by impervious surfaces) in Washington, DC and Jacksonville, FL for twenty soil properties known to influence tree growth. We measured available nutrients, organic matter content, and planting site dimensions to determine soil variability among these highly urbanized sites within and between cities. Results show that many soil properties, including most soil nutrients, varied considerably between cities. Within each municipality some soil property were relatively consistent and may not have to be measured at every site, such as soil texture, pH, and some plant available nutrients. This presentation will discuss urban soil property variability, its implication for urban tree management, and approaches for ranking site and soil variables to optimize their assessment. Soil amendment methods as tools to improve urban soil properties to support tree growth will also be discussed.