By Jessica Sanders and Jason Grabosky
New Brunswick, NJ (January 28, 2014) – 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. This research looked at a variety of tree species grown in parking lots and found that reductions in tree size were consistently associated with reduced apparent soil access.
Researchers studied five tree species (Acer rubrum, Prunus serrulata, Pyrus calleryana, Quercus pallustris and Zelkova serrata) in northern New Jersey that were grown in parking lots. The trees ranged from 18 to 23 years old. 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. Reduced growth expectations are important to understand, because they affect design choices for the urban tree canopy, particularly as required by legislative mandate.
A previous study from Florida was used for comparison of regional data, permitting conclusions on canopy reductions, relative to specification of design space for tree establishment.
Source: “20 Years Later: Does Reduced Soil Area Change Overall Tree Growth?” Urban Forestry & Urban Greening