Landscape, vegetation characteristics, and group identity in an urban and suburban watershed: why the 60s matter

Urban landscapes are heterogeneous, a patchwork of built and vegetation land covers, multiple land uses, and social groupings. Because urban landscapes are highly managed, it follows that the patchwork of cities should reflect the characteristics, preferences, resources, efforts, and influences of their managers, including homeowners. Existing research shows that the distribution of trees and grassy lawns in cities are, like most urban characteristics, uneven, and that those patterns are related to social characteristics of neighborhoods.

As one would expect, scarcity of tree and grass cover is typically a function of population density. As population densities increase, vegetation cover tends to decline as built-residential uses out-compete non-built land uses (Nowak et al. 1996; Iverson and Cook 2000). However, population density alone cannot explain the variation in vegetation cover in cities. Suburbs usually contain more green cover than downtown cores, but within urban areas, the leafiest and greenest areas are often also the wealthiest (Talarchek 1990; Martin et al. 2004; Jensen et al. 2004; Mennis 2006). This association between wealth and vegetation has been observed for cities in the United States and elsewhere (Escobedo et al. 2006; Kirkpatrick et al. 2007; Conway and Hackworth 2007). These findings suggest that greater wealth provides residents and neighborhoods with more resources to plant and take care of vegetation, and the greenness of wealthy communities may be self-reinforcing, as it attracts more wealthy residents. Trees and green spaces also increase property values, which increases tax bases for planning and maintenance of public spaces, and may attract further high-income buyers to the neighborhood.

Although income is an important predictor of vegetation, other social characteristics such as education and ethnicity are strongly associated with greenspace in cities. A study of urban forest canopy cover in 60 cities in central Indiana, for instance, found that tree cover was significantly and positively correlated with percent of persons holding a college degree (Heynen and Lindsey 2003). Landscapes also reflect dominant cultures. In a study of vegetation characteristics and ethnicity in Toronto, homeowners of British heritage were more likely to have shade trees on their properties than persons of Chinese ancestry (Fraser and Kenney 2000).

Others have pointed to lifestyles, typologies of neighborhoods or individuals based on a combination of socioeconomic and housing characteristics, as key determinants of vegetation. In a study of vegetation on private property parcels in Baltimore, Troy et al. (2007) found that lifestyle categories were strongly correlated with what they term realized stewardship, or the percent of potential pervious surface on properties that is vegetated. Specifically they found that a well-educated but less wealthy lifestyle category has 52% less realized stewardship than the well-educated and higher income lifestyle group. Even though the population densities are similar, the first lifestyle group tends to be younger and more likely to live in rental or multi-unit housing than the second lifestyle group. Other studies have found that renters live in areas with lower urban tree canopy cover than homeowners (Emmanuel 1997; Perkins et al. 2004). Renter is a social class and a housing characteristic, both of which tend to result in less commitment to long term property maintenance, short-term or temporary timelines for residents, and relatively weak political power to demand city services, such as street trees.

Vegetation characteristics of properties are also the result of a neighborhood effect. Property owners often mimic the landscaping practices and preferences of their neighbors (Zmyslony and Gagnon 2000). Grove et al. (2006) describe this phenomenon of mimicry as an ecology of prestige, the phenomenon in which household patterns of consumption and expenditure on environmentally relevant goods and services are motivated by group identity and perceptions of social status associated with different lifestyles (Grove et al. 2005; Law et al. 2004). This theory suggests that a household’s land management decisions are influenced by the desire to uphold the prestige of its community and outwardly express its membership in a given lifestyle group. Conceptions of luxury and prestige, however, are highly variable, even within the same income or demographic group. Lifestyle variables may only be weakly correlated with socio-economic status, such as family size, marriage status, and life stage. However, lifestyle can play a critical role in determining where households choose to locate and how they manage their properties (Timms 1971; Knox 1994; Short 1996; Gottdiener and Hutchinson 2000; Kaplan et al. 2004).

In newly-built suburbs, the vegetation cover may be an expression of the current social and housing characteristics of the resident or neighborhood, although it is more likely the perception of what the developer believes will satisfy buyers. Newly-built neighborhoods are also more likely to have new vegetation, such as small saplings, especially if the land was formerly agricultural or the developer clears forests for construction. In long established neighborhoods, where residents have come and gone, existing vegetation may reflect the tastes and wishes of past residents. People moving into older homes thus inherit past social preferences of landscapes. Even in newly-built suburbs, legacies from past land uses, such as woodlands or agricultural fields, may put their stamp on current landscapes (Dow 2000). A central question of this research is whether past social and housing characteristics are better predictors of woody and herbaceous vegetation than current social and housing characteristics. Some prior research, though limited, suggests that past inhabitants and age of housing are significant predictors of current vegetation in urban areas (Heynen and Lindsey 2003; Martin et al. 2004). In a pioneering study, Grove (1996) found that 1970 social characteristics were the best predictors of 1990 vegetation in the Gwynns Falls Watershed of Baltimore. Using a parcel-level analysis, age of housing was also found to be an important predictor of vegetation abundance in Baltimore City (Grove et al. 2006; Troy et al. 2007). Amount of realized stewardship, or percent cover of potentially vegetated surface per parcel, shows an inverted-U relationship with age of housing, peaking in 1950 (Troy et al. 2007). This article builds on Grove’s (1996) analysis of the Gwynns Falls Watershed by using an updated and high resolution land cover layer of vegetation, census data from 2000, and by examining, in addition to demographics and housing, the association between lifestyle and vegetation cover. Group identity, we argue, is a powerful force in defining neighborhood characteristics, including its vegetation.

Group identity can be expressed in a number of material ways, from gang colors, to uniforms, to flags. It can also be manifest in the landscape, as generations of social scientists have shown (Sauer 1925; Cosgrove 1998). The study of the cultural landscape is well established, albeit with a bias toward the rural rather than urban. A trained scholar can pick out remnants of past cultures, even from very fragmentary evidence; the shape of a barn, the construction of a fence, or shards of pottery are used to identify folkways that bind together individuals into groups through a common way of doing something (Anderson 2001). When studying the urban environment, making the linkage between the legacies of culture, or group identity, and landscape can tell us more about the dynamics of urban ecology compared to purely contemporary associations (Dow 2000; Cadenasso et al. 2006). In this paper we argue that group dynamics are key to understanding behavior that impacts landscape management at the neighborhood level.

Identifying what constitutes a group is a difficult endeavor, something that has kept legions of social scientists busy for decades (Côté and Levine 2002). Single variables like race, income, or education can go a long way in teasing apart the elements of group identity, but given their colinearity, a number of methods have been derived to search for the bundle of variables that tell us what makes groups different and separate from one another. Part of group identity is defined by where people live (Weiss 2000). Similar individuals or households cluster geographically. These clusters may be self-reinforcing by attracting similar people to certain neighborhoods, strengthening a sense of neighborhood or group identity, and at the same time shunning those that do not share that group’s identity (Massey and Denton 1993). Cities are, however, dynamic places and such patterns can shift over time. Every reader can think of a neighborhood that has changed in social characteristics, sometimes slowly and sometimes surprisingly quickly. On the other hand, many neighborhoods and the characteristics of people who inhabit them can remain remarkably stable. In neighborhoods there is a high amount of fixed, social, and even emotional capital, sometimes referred to as attachment to place. Such investments will be carefully guarded and defended, in extreme cases through violence and intimidation. In subtler ways neighborhoods retain their identity because the sense of group membership is so strong that few outsiders feel welcome. As disagreeable as clustering (or put another way, segregation) may seem to some, it is a powerful force that shapes patterns and processes of urban landscapes.