14 redevelopment process provides a private property management opportunity for the city government and allowed us to examine and assess the efficacy of one tree cover ordinance (cited in City of Falls Church 2008) as it applied to individual lots. According to the ordinance, landowners are required to retain or plant enough trees for 20% canopy cover on their property in 10 years. The ordinance is implemented through a site-specific redevelopment plan for each lot that must be approved by the city arborist and other city officials. Each carefully crafted plan is a legal docu- ment that addresses the architecture, drainage, sewer, utilities, and landscape of a proposed residential rede- velopment and includes a tree inventory: a list of trees, by species, to be preserved, cut, and planted; diameter of those to be preserved and cut; and gener- ally a sketch of tree locations on the lot’s architectural map(s). The city arborist has two years beginning at redevelopment to enforce the plan; after two years, the homeowners—like any other homeowners—can do anything they wish to property landscaping and trees. Key to enforcement is knowing how long it takes various tree arrangements to reach 20% cover, but implementation guidelines provided by the city (City of Falls Church 2008; see especially pp. 6–9), partially based on nursery industry standards for open- grown tree species, lack documented scientific sup- porting information. Therefore, the Falls Church city arborist asked us to compare redevelopment plans to a current inventory to determine if tree arrangements approved under current guidelines are achieving the 20% goal and to develop a more scientific basis for projecting percent tree cover for future development. Our study focused on comparing Falls Church redevelopment plans to current tree inventories on sampled lots where existing houses had been replaced by larger ones. The study objectives were to (1) deter- mine if City of Falls Church urban forest manage- ment guidelines result in 20% canopy cover on a lot within 10 years after residential redevelopment, as mandated by ordinance, and (2) develop a lot-scale model framework for canopy growth projection after redevelopment using data from preserved and planted trees as input. We also explored the more traditional forestry metrics of basal area and quadratic mean diameter as complements to the canopy cover metric, because measurements and calculations for these metrics are simple and they appear to have potential for use in urban forestry (Kershaw et al. 2017). ©2020 International Society of Arboriculture Chojnacky et al: Redevelopment Effects on Urban Forest METHODS Study Area The City of Falls Church is located within the Pied- mont forest vegetation zone (Farrell and Ware 1991). Prior to development, white oak (Quercus alba) was probably the most abundant species, followed by other oaks, hickory (Carya spp.), tulip poplar (Lirio- dendron tulipifera), black gum (Nyssa sylvatica), and red maple (Acer rubrum); the latter three would have been more abundant on poorer acidic soils. Recover- ing Piedmont forests on about 100 plots in the sur- rounding counties are currently sampled by the Forest Inventory and Analysis Program (FIA 2015). These plots are mostly nonindustrial private ownerships, with some local, state, and federal government ownerships; none are managed for timber. The FIA-sampled for- est plots are dominated by Quercus (mostly white oak), Pinus (mostly Virginia pine, P. virginiana), Acer (mostly red maple), Carya (mostly mockernut, C. tomentosa, and pignut hickory, C. glabra) and tulip poplar. Although a complete inventory of public and pri- vate trees in Falls Church is lacking, a 2003 street tree inventory (on file with the City of Falls Church) shows the dominant genera are Acer (mostly red maple), Quercus (mostly red oak, Q. rubra, and willow oak, Q. phellos), Cornus (dogwood), and Prunus (cherry). Sampling Overview Two inventory datasets were compared: initial mea- surements from redevelopment plans and current remeasurements. Because redevelopment included the entire lot, we used the entire lot as the sample unit (i.e., basis of per-area statistics). Two types of lot- scale metrics were calculated and compared: a can- opy cover metric and traditional forest stand metrics based on basal area and trees per hectare. These met- rics were used for assessing canopy cover after rede- velopment and to develop a framework for predicting canopy cover growth. Twenty-one residential lots were selected from a list of more than 300 properties redeveloped in the City of Falls Church since 1994 (Figure 1). Random sampling was done within 6 classes that were defined by construction date to more heavily select lots with older construction dates and thus obtain more long- term growth data. Construction occurred between 1994 and 2011. Data from the initial redevelopment
January 2020
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