Evaluating Urban Canopy Cover Before and After Housing Redevelopment in Falls Church, Virginia, USA

Abstract

Local governments have created regulations aimed to maintain and increase valuable urban tree cover. The City of Falls Church, Virginia, USA, requires each residential redevelopment to retain or plant enough trees for 20% canopy cover within ten years. To assess whether this goal is being met, we studied 21 Falls Church residential lots redeveloped between 1994 and 2011 where existing houses had been replaced with larger ones. Initial tree inventories and measurements prior to redevelopment were recorded in redevelopment plans. We remeasured preserved and planted trees in a ground survey and modeled tree canopy growth from a periodic tree diameter growth model linked to a model relating tree and crown diameters. Geospatial analysis was used to calculate nonoverlapping canopy cover within lots from crown diameter measurements and/or model predictions. We found that the City of Falls Church generally met its 20% canopy cover goal, but that the canopy cover metric alone is insufficient to fully describe urban forest recovery. Although canopy cover might recover rapidly from planting many small trees, recovery to the larger tree sizes that maximize ecosystem services can take much longer. Our modeling of lot-scale growth from field measurements showed the potential to manage forests using traditional diameter-based forest metrics that would relate results to canopy cover when needed. These forest stand metrics—based on basal area and trees per hectare—can account for tree size changes masked by the canopy cover metric.