Determinants of urban tree canopy in residential neighborhoods: Household characteristics, urban form, and the geophysical landscape

Abstract

The aesthetic, economic, and environmental benefits of urban trees are well recognized. Previous research has focused on understanding how a variety of social and environmental factors are related to urban vegetation. The aim is often to provide planners with information that will improve residential neighborhood design, or guide tree planting campaigns encouraging the cultivation of urban trees. In this paper we examine a broad range of factors we hypothesize are correlated to urban tree canopy heterogeneity in Salt Lake County, Utah. We use a multi-model inference approach to evaluate the relative contribution of these factors to observed heterogeneity in urban tree canopy cover, and discuss the implications of our analysis. An important contribution of this work is an explicit attempt to account for the confounding effect of neighborhood age in understanding the relationship between human and environmental factors, and urban tree canopy. We use regression analysis with interaction terms to assess the effects of 15 human and environmental variables on tree canopy abundance while holding neighborhood age constant. We demonstrate that neighborhood age is an influential covariate that affects how the human and environmental factors relate to the abundance of neighborhood tree canopy. For example, we demonstrate that in new neighborhoods a positive relationship exists between street density and residential tree canopy, but the relationship diminishes as the neighborhood ages. We conclude that to better understand the determinants of urban tree Urban Ecosyst (2012) 15:247-266 canopy in residential areas it is important to consider both human and environmental factors while accounting for neighborhood age.

Human and biophysical legacies shape contemporary urban forests: A literature synthesis

“…Alternatively, building age may capture differences in urban form or development patterns. When controlling for age of development, Lowry et al (2012) found that higher street density and connectivity in Salt Lake County, Utah were associated with greater tree canopy only in the short term (15 years), whereas the association between tree canopy and lot size became positive only in the long term (after 95 years). Also in Salt Lake County, older neighborhoods had higher numbers of trees and higher species richness, but with variation in effects for street and yard trees, and across income levels (Avolio et al in press).…”

Drivers of Vegetation Species Diversity and Composition in Urban Ecosystems

“…Wealthier neighborhoods tended to have greater species diversity than lower income neighborhoods, a pattern that they termed the "luxury effect." Complicating the relationship between socioeconomic status and diversity, however, is the legacy of past land-uses and the age of neighborhoods, which can interact with present conditions to influence relationships between neighborhood variables of interest (Luck et al 2009;Lowry et al 2011). In a study of neighborhoods in Baltimore, Maryland, tree canopy coverage increased with age of houses in neighborhoods (Grove et al 2006).…”

Land cover in single-family housing areas and how it correlates with urban form

“…One could suggest that the larger extent of tree cover on the rectangular parcels of the oldest neighbourhood (site A) could be explained simply by age of neighbourhood (Lowry et al 2012;Talarchek 1990), and the higher trees in site A than in the younger neighbourhoods supported this. However, if this was the only explanation, the number of trees would have been constant despite the age of neighbourhood, which is not the case, in that site A had more trees per m 2 of garden.…”

“…This resulted in comparable lower surface temperatures, higher infiltration rates and less surface runoff. After these studies, the potential ecological importance of gardens in such areas has been acknowledged by researchers across the world (Cook et al 2012;Davies et al 2009;Doody et al 2010;Gaston et al 2005;Goddard et al 2010;Rudd et al 2002;Troy et al 2007;van Heezik et al 2013), and several studies have tried to identify factors affecting land cover composition, most of all tree cover, in gardens (Boone et al 2010;Gaston et al 2005;Kim and Zhou 2012;Loram et al 2008;Lowry et al 2012;Mathieu et al 2007;Smith et al 2005;Stone 2004). Social factors, such as socioeconomic status, have been especially investigated, while less focus has been paid to physical factors related to the built environment (Lowry et al 2012).…”

“…the spatial pattern of urban features such as buildings, roads and sidewalks, has been known to affect land cover composition between urban zone and thus the ecological performance (Alberti 2005;Conway and Hackworth 2007;Sanders 1984;Tratalos et al 2007). Some studies point to physical factors like size and shape of gardens, which are related to urban form, to affect land cover at garden scale (Loram et al 2008;Lowry et al 2012;Smith et al 2005;Stone 2004). Hence, a difference in urban form of single-family housing areas would assumedly result in a difference in land cover composition at neighbourhood scale.…”