Are all home gardens the same?

Here’s a fun fact: residential lawns cover more of the United States than any other irrigated crop, and that includes the corn and soy that blanket the Midwest. Common knowledge was once that no matter the underlying climate, a lawn in Charlotte, North Carolina would be more or less indistinguishable from a lawn in San Francisco, California. On the surface, that appears to be true. The diversity of plant species, the relative presence of nutrients in soil, and the extent of surface water seem to be identical among cities, even in different climates. But new research published last week in Proceedings of the National Academy of Sciences suggests that there’s more lawn diversity than at first it may seem.

The homogenization hypothesis holds that urbanization generates similar lawn care practices across cities and that, in turn, results in similar environmental outcomes. But that assumption has not yet been subject to empirical testing. It’s entirely possible that the opposite is the case. The researchers, led by Colin Polsky of Clark University, point out that it could take different behaviors (not similar ones) in order to produce similar landscapes, given the different underlying ecology. “Producing the same English manor-style yards from the native landscapes in Phoenix and Boston would require different activities (adding or removing trees, respectively) due to the differing initial conditions,” they write. By the same logic, similar activities (such as adding trees) could have different environmental outcomes, depending on the local ecology.

Polsky and his colleagues put the question to the test. Would the homogenization hypothesis hold up to scientific scrutiny? Phone interviews were given to 9,480 people living in six very different US cities and their adjacent suburban and rural counterparts: Boston, Baltimore, Miami, Minneapolis, Phoenix, and Los Angeles. They focused on just two behaviors relevant to lawn care: irrigation and fertilizer use. In general, they found more differentiation than they expected. But in some cases, they were actually surprised to find homogeneity.

For example, Los Angeles and Miami are both differentiated within the city: urban homeowners are least likely to use fertilizer, with suburban and rural homeowners fertilizing their lawns at roughly the same rates. However, across cities, LA and Miami are homogenous. That is, the urban parts of the two cities are statistically indistinguishable from eachother, as are the suburban and rural parts, respectively.

Some more findings: both in Phoenix and LA, irrigation varies according to socioeconomic status. Wealthier folks are more likely to water their lawns. Like Miami and LA for fertilizer use, Phoenix and LA are statistically indistinguishable when comparing the cities as a whole for water use. That makes sense, since they’re the two driest cities assessed by the researchers. On the other hand, “it is not intuitively apparent,” the researchers say, “why self-reported fertilization practices are statistically indistinguishable by life stage,” for Boston and Miami, which have very different climates.

It isn’t the specific findings themselves that are important; instead, it’s the statistical methodology that the researchers used to compare within and between cities. The comparison matrix that they describe allow these researchers and others to combine both geophysical data and social data in order to better – and more empirically – understand the relationships between human behavior, the underlying climate, and ecological outcomes. This will become increasingly important as the effects of human behavior on the landscape become more pervasive in a world undergoing dramatic climate change.

In addition, the findings reveal an important message for activists, governments, science communicators, and other organizations that advocate for sustainability and environmental awareness. Before they began their study, Polsky’s group assumed that all Americans managed their lawns the same way, with lots of water and fertilizer. But their findings were contrary to the homogenization hypothesis, once accepted by researchers and activists as a given. “Responding to lawn-care related environmental challenges may require locally-tailored solutions in more cases than we thought,” Polsky said. – Jason G. Goldman | 19 March 2014

Source: Polsky C., Grove J.M., Knudson C., Groffman P.M., Bettez N., Cavender-Bares J., Hall S.J., Heffernan J.B., Hobbie S.E. & Larson K.L. & Assessing the homogenization of urban land management with an application to US residential lawn care, Proceedings of the National Academy of Sciences, DOI:

Header image: shutterstock.com

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