A policy paper by Adrian Dahlin.
By improving parks and implementing greenways around urban streams, we can create a network of natural space that will support greater biodiversity, protect urban habitat, preserve water resources, and provide vital ecosystem services.
Urban streams are perhaps the natural habitat most vulnerable in the face of development. Increased runoff from areas of reduced infiltration – including parking lots, roofs and manicured lawns – can effect urban waterways in several ways. Rainwater runoff from developed space can alter stream and wetland habitat by increasing sedimentation and by transporting motor oil, industrial chemicals, salt, and other toxins into streams. Within these waterways, plants and animals can die from deadly toxins or simply from changing temperature, pH, mineral content or oxygen content. These changes travel great distances downstream and reach large numbers of aquatic species. Thousands of species live in wetland ecosystems, and thousands of others in surrounding habitats depend on wetlands. Furthermore, the urban parks we see today typically consist of small plots of mowed grass and scattered trees. Such spaces support squirrels and pigeons, but not complex ecosystems.
Higher quality urban parks connected by greenways, or vegetated buffer zones, offer a simple way to shield waterways from harm. Greenways are patches of perennial vegetation allowed to grow on the borders of streams. A greenway should span at least several meters on either side of a waterway. To be most effective, greenways should connect with urban parks to create a substantial quantity of contiguous natural green space within a city.
City and state officials must build larger urban and suburban parks that will support a wide range of wildlife. These eco-friendly parks should lie adjacent to urban waterways and include more brush, native flowers and greater tree diversity. These parks will support much greater biodiversity, thereby mitigating the effect of development, and they will be more attractive for human use. To preserve sensitive habitat, some sections of these parks may be fenced off for limited use by humans. Schools in the community could then use these protected habitats to study flora and fauna at an easily accessible location.
Greenways significantly increase infiltration on the borders of streams, and greater infiltration means less runoff from impervious surfaces will reach urban waterways. Greenways also serve as natural filters for that water, preventing oils, salts, soaps, and other chemicals from contaminating the aquatic ecosystem. Furthermore, greenways combine with streams themselves to create complete ecosystems that allow for the interaction of aquatic and land-based organisms.
Community planners must cultivate greenways, improve the quality of parkland, and fit these changes into a form of development based on high-density construction and real protections for the environment. Only such a development model can meet the needs of a growing, increasingly urbanized world population. Because the 21st century residents of Los Angeles, Lagos, and Mumbai cannot live in nature and will not survive without it, they must find a way to live near it.
Boston’s Mystic River provides a great example of an unhealthy urban stream that would benefit greatly from a greenway. The EPA gave the river a grade of C- for its notoriously poor water quality. In some cities, like Somerville, bare patches of unused land flank the Mystic. These plots of land mostly consist of grass and dirt, and they are seldom used by humans or animals. If more forms of vegetation were allowed to grow here, and especially if this new habitat were fenced off from the recreational fields and roads that border it, a healthy ecosystem could flourish. This greenway would partially protect the Mystic against runoff from the many highways that cross its path.
HISTORY OF PARKS IN THE US
Trees and open space have been incorporated into urban development in the United States since New York’s Central Park was built in the 1850s. Originally, parks were not intended as real pieces of nature. “The naturalness of urban open spaces was antithetical to earlier landscape paradigms,” says historian Rutherford H. Platt (From Commons to Commons: Evolving Concepts of Open Space in North American Cities, 1994). Urban parks were first established as aesthetic touches and as a place “for fresh air and exercise”. They were thought to improve the health of the urban poor. In modern times, psychologists like John F. Dwyer, Herbert W. Schroeder, and Paul H. Gobster still connect park abundance with human health. They say trees promote comfort and relaxation, as well as mental and emotional health (The Deep Significance of Urban Trees and Forests, 1994).
Greenways and high-quality parks can be implemented by cities of all sizes. Virtually every community in the United States has room to increase the quality of its green space.
Cities can start by cleaning up open spaces around urban streams (like the Mystic River example) and allowing native vegetation to grow there. They should also assess which parks and grassy recreational areas are least used, and consider converting these to more natural spaces, especially when they sit adjacent to waterways and other natural areas. All new parks should be placed around streams and lakes, where they can connect with greenways. City governments should enact open space zoning laws that include several classes of parkland. These classes will vary in natural quality and practical purpose. One class should be almost completely left to nature, accessible only for educational and research purposes.
With more nature-friendly land use policies at the local and state levels, we will be able to enjoy beautiful urban parks, bolster the biodiversity of our urban ecosystems, preserve the health of our waterways, and meet our own needs with less harm done to the natural environment.