What do people living in Boston, Baltimore, Miami, Minneapolis-St. Paul, Phoenix, and Los Angeles have in common? From coast to coast, prairie to desert - residential lawns reign.
But, according to a new study in the Proceedings of the National Academy of Sciences, beneath this sea of green lie unexpected differences in fertilization and irrigation practices. Understanding urban lawn care is vital to sustainability planning, more than 80% of Americans live in cities and their suburbs, and these numbers continue to grow.
The study was undertaken to test "the homogenization hypothesis." Peter Groffman, a scientist at the Cary Institute of Ecosystem Studies and one of the paper's authors explains, "Neighborhoods in very different parts of the country look remarkably alike, from lawns and roads to water features. This study is the first to test if urbanization produces similar land management behaviors, independent of the local environment."
Some 9,500 residents in the six study cities were queried about their lawn care habits. The research team, led by Colin Polsky of Clark University and colleagues at 10 other institutions, took into account differences in climate and neighborhood socioeconomics, both within and between cities. A focus was put on fertilization and irrigation, practices with potentially hefty environmental price tags.
Fertilizer is rich in nitrogen and phosphorus. This stimulates lawn growth, but when fertilizer washes into waterways, it causes algal blooms that degrade water quality and rob oxygen from fish and other aquatic life. According to the Environmental Protection Agency, landscape irrigation accounts for nearly one-third of residential water use nationwide.
Some 79% of surveyed residents watered their lawns and 64% applied fertilizer. Groffman comments, "These numbers are important when we bear in mind that lawns cover more land in the United States than any other irrigated crop. What we do in our suburban and urban yards has a big impact, for better or worse, on the environment."
Among the survey's findings: residents of Boston and Miami - cities with very different climates - had similar fertilization rates. And, perhaps unsurprisingly, in the study's two driest cities (Phoenix and Los Angeles) irrigation was positively correlated with affluence. But overall, local climate and social factors led to more lawn care variability than initially expected, both between and within cities.
Polsky notes, "One of the take-home lessons is that responding to lawn care-related environmental challenges may require locally-tailored solutions in more cases than we initially thought. Place matters, there is not a one-size-fits-all approach."
With Groffman adding, "The management of urban and suburban areas has a direct impact on water resources, carbon storage, and the fate of pollutants, like nitrogen and phosphorus. Yards are also where our environmental knowledge, values, and behavior are likely generated. The good news is that individual actions, on a yard-to-yard-basis, can make a difference."
The project was made possible through funding provided by the National Science Foundation's (NSF) MacroSystems Biology Program and Long-Term Ecological Research Program. It is part of a larger initiative that is investigating how urban homogenization can be used to understand carbon and nitrogen dynamics, with continental scale implications.
Henry Gholz, program director in NSF's Division of Environmental Biology notes, "Research on residential landscapes is critical to sustainability science. The approach in this study can be used to test other ideas about how people who live in cities decide to manage their yards. This should open a new phase in the field of urban ecology."