20 years later: Does reduced soil area change overall tree growth?

Urban conditions have been thought to affect tree growth, but there is little conclusive evidence as to the severity of those influences or how various species respond differentially to urban stress. Reduced growth expectations are important to understand, because they affect design choices for the urban tree canopy, particularly as required by legislative mandate. Five tree species (Acer rubrum, Prunus serrulata, Pyrus calleryana, Quercus pallustris and Zelkova serrata) grown in parking lots ranging from 18 to 23 years old in central and northern New Jersey, USA were studied. Tree height, diameter at breast height (DBH), and canopy radius were measured, as was apparent plant available soil (nonpaved planting zone area). Tree DBH, commonly recorded for many municipal inventories, was found to be a useful predictor of canopy area. Data were normalized within site, to facilitate multiple site analysis. Across different parking lots, reductions in tree size were consistently associated with reduced apparent soil access. A previous study from Florida, USA was used for comparison of regional data, permitting conclusions on canopy reductions, relative to specification of design space for tree establishment.