Turfgrass revolution: measuring the expansion of the American lawn
Introduction
The ecology of urban growth has become a central concern for planners, bureaucrats, and geographers. The relationship of changes in urban form to increasing energy demands (Newman and Kenworthy, 1989; Anderson et al., 1996), problems of access and pollution (Newman and Kenworthy, 1996; Murray et al., 1998), and to declining green space (Tjallingii, 2000) are components of an emerging research program in urban ecology (Botkin and Beveridge, 1997).
Interest in such urban environmental concerns is itself accelerating, with recent research focusing on issues ranging from environmental justice (Cutter, 1995; Pulido, 1996), to urban garden and green space (Rocheleau, 1991; Bellows, 1996), and the prospect of sustainable cities (Capello and Nijkamp, 1998; Haughton, 1999). Little of this research, however, has taken a specifically Land Use/Cover Change (LUCC) approach to analyzing the processes that drive land cover transformations within a broader political ecology. LUCC approaches, previously used to good effect in non-urban environmental analysis, have been used to track the momentum behind deforestation and other global transformations (Turner and Meyer, 1991; Meyer and Turner, 1994). Directing the lens of LUCC onto cities might serve simultaneously to highlight ignored issues or problems in urban growth and better integrate the study of cities into larger scientific efforts that explore the human dimensions of global change (Turner et al. (1993), Turner et al. (1995)).
Specifically, an otherwise unexamined component of urban growth that is increasingly apparent when considered from an LUCC perspective is the expansion of high-input, monocultural, lawn landscapes. Much of the land cover in newly subdivided suburban lots may, in fact, consist solely of turfgrass and as suburbs begin to displace other land covers in the fringe belts surrounding US and Canadian cities, there is a parallel growth in the coverage of lawns. These bring with them inputs of insecticides, herbicides, and fertilizer, as well as expanded use of lawn maintenance tools, largely dominated by polluting two- and four-stroke engine equipment. So too, it means changes in soil profile, stormwater runoff, water consumption, micro-fauna diversity, energy use, air quality, and opportunities and constraints for terrestrial wildlife and nesting birds. Thus, suburbanization is less a process where “cultural” artifacts like roads, houses, and sewage lines expand into “natural” pastoral spaces, but rather a process where one produced nature, that of high-input agriculture, is replaced by another, that of high-input lawns (Smith, 1996). To begin to imagine and model the effects of such change, the specific rate and character of land cover change must be measured. What proportion of urban growth is turfgrass? Where does turfgrass make up the largest proportion of growth? What factors explain variation in the proportion of turfgrass in urban land cover?
Answers to these questions are currently unavailable, however, since no coherent measurement or rigorous estimate of urban and suburban lawn coverage exists and no index of lawn cover increase has yet been created. Aggregated estimates of lawn coverage in the United States fall between 10 and 16 million ha, surpassing that of some US food crops including barley (5 million ha), cotton (4.5 million ha), and rice (1.1 million ha), though less than major US crops like corn and soybeans (Bormann et al., 1993). No detailed municipal level figures and trajectories yet exist, however.
The research described here seeks to redress this problem by providing a methodological protocol for measuring the coverage of lawns in US cities and estimating their rate of growth, focussing on a case study from the US municipality of Columbus Ohio and its surrounding growth zone in Franklin county. The paper is divided into four sections. The first section describes the lawn as an ecological problem, summarizing the associated hazards that accompany this newly dominant land cover, introducing the central research questions of measuring and explaining lawn cover. The methods used in the study, specifically including the use of tax assessors’ data, census data, survey information, and aerial photography, are summarized in section two, where a technique for calculating lawn area is described and executed. The following section explores a model for explaining the uneven distribution of lawn coverage over municipal areas pointing to the accelerating coverage of lawns and the increase in the ratio of non-house area on residential lots, especially in recently constructed affluent subdivisions. The implications of this coverage are then discussed in terms of both chemical input hazards and the broader policy implications of suburban ecology. By laying the groundwork for measurement of land cover transformation, this work opens the door to more extensive modeling efforts aimed at better understanding the ecology of urban growth.
Section snippets
Why measure the lawnscape?
Throughout the United States, urban and residential land uses are large and growing. In the State of Ohio, for example, land under cultivation fell by 599,000 ha between 1992 and 1997, while urban land use grew by 365,000 ha (Natural Resources Conservation Service, 2000). Growth in developed land cover in the state grew at 4.7 times the growth rate of population (Ohio Farmland Preservation Task Force, 1999). The specific ecology of that transformation remains poorly understood, however. Increased
Calculating lawn area
To answer the previous questions it is necessary to create a universal technique that can be applied in municipalities throughout North America. Here, we utilize tax assessors’ data, calibrated with aerial photography to generate spatially specific measures of lawn coverage and proportion. We then use the resulting data to model the significance of localized income and housing age in explaining variation in lawn cover and distribution.
Compiling tax assessor data, we developed two measures of
Explaining lawn area
The degree to which PLA and PLR vary across municipalities is notable and unsurprising. Fig. 2, Fig. 3 show the distribution of mean PLA and mean PLR by census tract in Franklin County, OH. Both the total lawn area and proportion of lot under lawn appear to increase in growth areas of higher income and more recent construction.
PLA and PLR vary widely, as shown in Table 3. Mean PLA of each tract varied across the city, with some residential units showing high coverage of non-housing area,
Discussion: lawn cover growth and its implications
Drawing on these results, we can further estimate the total lawn area of the city and the relative rate of growth over time. Applying the calibrated estimate of PLA to calculate the lawn coverage in each the 205 available census tracts, produces a figure of approximately 21,000 ha of lawn. Total hectarage of the 205 tracts is 90,618 ha, making the coverage of lawn turfgrass, conservatively, 23% of the total land cover.
Moreover, we can also estimate turfgrass area growth. Using the unstandardized B
Conclusion
In summary, using the case of Franklin County, OH, we have demonstrated here that the proportion of total residential lots not under the house footprint has increased over the century, and that it continues to do so in the high-income areas of the urban periphery. This ratio of potential lawn area to total area, moreover, has increased despite overall national decreases in lot size and increases in house square footage. We have further demonstrated that state-wide and national trends in land
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