Arboriculture & Urban Forestry 42(1): January 2016 to 1) intensity of the urbanization [e.g., single- family residential versus city center (Pouyat et al. 2007)], 2) the extent of land management activities required to maintain the landscape in its current urban land use (Fantroussi et al. 1999; Pouyat et al. 2007), and 3) the time elapsed since the initia- tion of the land-use conversion (Scharenbroch et al. 2005). Generally, changes to the soils’ physical and chemical properties are most pronounced in areas that support a high density of urban infra- structure (e.g., roads and buildings) or have recently undergone a significant land-use change. The process of urbanizing and the subse- quent maintenance of formerly rural landscapes are believed to negatively affect the soil biology (McDonnell et al. 1997; Kaye et al. 2005; New- bound et al. 2012; Xu et al. 2014). Unfortunately, the direct and persistent effects of urbanization on soil microbial communities remains largely unstudied when compared to the number of investigations involving the impact on the soils’ chemical or physical properties. Furthermore, there are no reports within the scientific literature that define the ideal or desired structure and com- position for a soil’s microbial community. Conse- quently, urban landscape managers attempting to mitigate or correct the effects of urbanization on soils’ biological communities, and the processes they regulate, lack essential baseline information upon which to make soil management decisions. Therefore, the goal of this study was to compare soil microbial communities across various urban landscapes and to identify key soil character- istics that may aid in evaluating the state of the biology in urban soils. It is hypothesized that the combination of changes in edaphic charac- teristics induced by the process of urbanization, associated landscape management activities, and the time elapsed since the initiating land-use con- version event will result in significant changes in the abundance, structure, and activity of the soils’ microbial community. Specifically, the objectives were to 1) determine if differences exist in bac- terial and fungal community composition, bio- logical activity, and the soil physical and chemical environment across five urban land uses, and 2) determine if differences in the bacterial and fungal compositions compare to differences in the soil’s physical and chemical characteristics. MATERIALS AND METHODS Experimental Design Study sites were located within a 12 km radius in metropolitan Milwaukee, Wisconsin, U.S. The soils within the Milwaukee area are typically deep, moderately well to well drained, and slightly al- kaline, consisting of fine textured loess deposits over alkaline glacial till. Common soil series in this area include Morley, Blount, Varna, and El- liot; however, a majority of the soil in the City of Milwaukee has not been classified as a result of anthropogenic influences (Soil Survey Staff). The urban land-use designations in this study were urban street side terraces [Streets (ST)], new (<5 years since development) residential land- scapes receiving intensive management [New Managed (NM)], old (>25 years since develop- ment) residential landscapes receiving intensive management [Old Managed (OM)], old resi- dential landscapes receiving minimal manage- ment [Old Unmanaged (OU)], and forested lands [Forests (FR)]. Intensively managed study sites received regular fertilizer applications and pesti- cide treatments over the last 25 years (OM) or 5 years (NM) (pers. comm.: Nick Crawford, Craw- ford Tree and Landscaping, April 2009), whereas the unmanaged properties have no record of receiving fertilizer or pesticide applications over the past 25 years (pers. comm.: property owners, April 2009). Based on exposure to anthropogenic influences (management level, vehicular traffic loads, and housing densities) and previous find- ings that soils recover from disturbances over time (Scharenbroch et al. 2005), the order of land-use designations from most- to least-urbanized, in this study, was assumed to be: ST > NM > OM > OU > FR. The vegetative communities in all loca- tions, with the exception of FR sites, consisted of turfgrass areas with landscape trees of various species. The FR sites had mixed hardwood veg- etation dominated by Quercus sp. >25-years-old with a leaf litter surface layer devoid of turfgrass. Five urban study sites were randomly selected for each land use from a pool of potential loca- tions, resulting in 25 urban sites. Each study site was subdivided into 25 m2 soil sampling areas. Within each study site, three soil cores (2.5 cm × 25 cm) were removed from the near center ©2016 International Society of Arboriculture 59
January 2016
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