Biodiversity in Urban Environments

Katie Maginnis for TEI

Housing high concentrations of people, cities often develop negative reputations associated with traits such as traffic jams, high crime rates, and fewer green spaces.  However, Professor Paige Warren in the Department of Natural Resource Conservaton has a plan to shape urban areas into more pleasant habitats for both humans and wildlife.  As Warren suggests, “people need access to nature.  They need nature in their daily lives.  They need wildness around them.”  How does one create a sense of “wildness” in areas that are so highly populated with humans already?  By studying the relationships between human activities and wildlife populations, Warren hopes to improve the ecosystem functioning of cities, so that biodiversity within them may increase. 
           
More specifically, Warren focuses her work on bird populations and behavior in urban environments.  One of her ongoing projects involves studying the effects of urbanization on predation patterns of birds in Phoenix, Arizona.  Research conducted by her graduate student, Susannah Lerman, has indicated that birds in the city are not as concerned about predators as the birds living in the natural desert environment.  To study this phenomenon, the researchers prepare food for the birds then display the food in places that are either wide open to predators (where eating the food would typically prove more risky for them), or places that are more secluded (where they could eat without the added danger of watching their backs for predators).  These studies have revealed that birds in the natural desert areas spend more time eating in the secluded spots, whereas birds in the city spend equal amounts of time in both open and secluded places.  This suggests that the threat of predators is lower for birds in urban areas; and in fact city environments may actually be safer for some wildlife than their natural habitats.  Warren and her team continue to study this phenomenon to discover its root causes. 

While predators may not pose as great a threat to bird populations in developed areas, lack of habitat does present a danger.  This can be seen in another of Warren’s projects, involving woodpeckers in the town of Amherst, Massachusetts.  Many species of woodpecker prefer to make their nests in snags, or dead trees.  However, snags are often viewed as a hazard to people; their rotting branches can fall on top of houses or cars, causing property damage.  For this reason, many snags in populated areas are removed, which reduces the available woodpecker habitat.  In collaboration with her colleague Brian Kane, Warren strives to find a balance between removing snags that are potentially hazardous to humans and simultaneously maintaining adequate habitat for woodpeckers.  Warren’s research methods involve locating trees in which woodpeckers choose to build their nests, and comparing these to the trees the woodpeckers ignore.  In terms of the danger they pose to humans, the snags used by woodpeckers generally display a higher hazard rating than other trees.  However, Warren’s data also indicate that some trees with a high hazard rating are not being used by woodpeckers at all, and some of the trees the woodpeckers do choose have a much lower hazard rating.  Warren continues to work with members of a local tree care business, as well as town tree wardens, to gain a more thorough understanding of the hazard rating process and the ways decisions are made regarding the removal of snags. 

How is it that a town such as Amherst – with a population density of about 500 people per square kilometer – can be considered an urban environment in the ranks with the city of Phoenix, whose population density is roughly twice that of Amherst?  As Warren explains, the definition of “urban” remains fairly flexible: “There’s a gradient, so the cutoff point may be determined, in part, by what you’re interested in.  If you’re studying what [human] populations have an effect on stream quality due to runoff, that cutoff point might be different from what you’d use if you’re studying a bird species.”  This flexibility may be necessary on a small scale, but Warren points out that, when expanding to a larger scale, it would be useful to develop an average benchmark that can apply to any species or ecosystem. 

In the future, Warren hopes to incorporate issues of social justice into her research.   For instance, Baltimore, Maryland recently received a federal mandate to clean up the Chesapeake Bay, which resulted in a number of research groups getting involved with the issues of tree cover, impervious surface area, and wildlife populations within the city.  While working on this project, Warren has witnessed firsthand the correlation between poverty and lack of biodiversity.  In general, the areas with the lowest amount of tree canopy cover and the lowest diversity of bird species are also the neighborhoods with the lowest income.  This trend represents a larger problem that Warren would like to alleviate with her work.  As she explains, “that’s one of the really important things: to pay attention to equity issues for people as we try to enhance urban environments.” 

Overall, Warren has contributed substantially to the idea of increasing biodiversity in urban areas.  Until recent years, much of the research in this field consisted of quantitative, descriptive data such as which species are living in cities and how many are there?  While this is pertinent information, it is also necessary for researchers to explore the larger questions:  How do the actions of humans and urban development affect the wildlife populations in these areas?  Warren aims to weave these two fields of research together to generate a more holistic understanding of urban environments.  Ultimately, this represents a key factor in creating urban environments that will support a diversity of species while enhancing the quality of life for people as well.