News Release

Researchers find 'luxury effect' helps determine plant diversity in urban areas

Peer-Reviewed Publication

Arizona State University

TEMPE, Ariz. – Income level appears to have a major positive effect on plant diversity in urban and suburban areas of Central Arizona, according to a team of researchers that includes several Arizona State University scientists.

The higher the income level the more plant diversity, the researchers found. This "luxury effect" is so pronounced that plant diversity at sites in neighborhoods with incomes above $50,750 per year were on average twice that found in landscapes of less wealthy areas. The researchers present their findings in the current on-line issue of the Proceedings of the National Academy of Sciences.

"In human-constructed systems, it's as if money is just as important to plants as nutrients and water supply" said Diane Hope, a researcher in Arizona State's Center for Environmental Studies and lead scientist for the survey.

"It's not the money per se, because you don't go and pour money on the ground and plants grow," Hope said. "But rather it's the things that money enables people to do and the way that they live that affects the plant diversity in urban areas."

The findings are the result of a large field survey and analysis of data gathered in the Central Arizona-Phoenix Long-Term Ecological Research site, a major on-going study to investigate the ecological characteristics of the Central Arizona-Phoenix region and how urbanization is affecting that character. The survey also will provide a baseline of data for future monitoring of the same sites, as well as give an overview of plant diversity, soil chemistry and animal distributions.

The results provide a comprehensive "snapshot" of the ecological characteristics of the Phoenix metro area and surrounding agricultural and desert lands. The survey will be repeated in five-year intervals to monitor long-term changes.

Three general factors -- income level, age of a housing development and whether the plot of land had ever been farmed -- influence plant diversity, the researchers report.

Newer housing developments had greater plant diversity than older, well-established neighborhoods. This may owe itself to the fact that landscaping for houses built in the 1960s had a different purpose (mainly to provide shade) than landscaping for houses that rely on air conditioning for cooling, Hope said.

A third factor was if the land had ever been farmed.

"When a piece of land is farmed, the land is cleared and plowed," Hope said. "When people develop a housing site in that area, they re-introduce plants, but they never really seem to get plant diversity up to levels of land that was never farmed."

Reasons for this may be in the nature of the land itself. Farmland tends to be in low laying, alluvial areas that didn't have a lot of plant diversity to begin with compared to land higher up in the foothills that has never been farmed.

Yet among the three factors, income level stood out.

"The relationship between wealth and plant diversity would also appear to be similar to the link between socioeconomic status, species composition, and physical structure of vegetation in residential yards in several other cities, leading us to suggest that the relationship between wealth and plant diversity maybe characteristic of urban landscapes generally," the researchers reported.

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In addition to Hope, authors of the paper include Corrina Gries, Charles Redman, Nancy Grimm, Chris Martin and Ann Kinzig of Arizona State University; Welxing Zhu of State University of New York, Binghampton; William Fagan of University of Maryland, College Park; and Amy Nelson of Alliance Data Systems, Gahanna, Ohio.

Source:
Diane Hope, Center for Environmental Studies, di.hope@asu.edu
480-965-2887; 928-226-0356


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