A study of 10 Northeastern urban forests shows no sign that there is a common urban park plant complex, but does show that population levels affect both native and nonnative species diversity, according to a Penn State study.
"Less than 1 percent of species were common among all 10 parks," says Robert Loeb, associate professor of biology and forestry at Penn State's DuBois Campus. "This is evidence that common urban park flora does not exist and demonstrates that a diverse flora can be maintained in urban parks."
The parks studied were in Boston, New York, Philadelphia, Baltimore and Washington. All of the parks are more than 100 years old except for the three parks in the Gateway National Recreational Area, New York -- Breezy Point, Jamaica Bay, and the Wildlife Refuge which are all less than 60 years old. The other parks are Middlesex Fells, Boston; Pelham Bay and Van Cortland, The Bronx, New York; Pennypack and Wissahickon Creek, Philadelphia; Oregon Ridge, Baltimore and Rock Creek, Washington, D.C.
Loeb looked at populations of native and nonnative vascular plants in existing surveys of these parks and reported on his work in a recent issue of the Journal of the Torrey Botanical Society.
While all the parks have some fresh water habitat, four Pelham Bay, Breezy Point, Jamaica Bay and Wildlife Refuge have salt marsh and seashore environments. Loeb suggests that the long history of plantings in the parks appears to have resulted in greater species similarity among the parks in Baltimore, Washington, D.C. and The Bronx than among the parks in the Gateway National Wildlife Refuge, New York and Bronx, New York.
Dividing the 13 species found in all the parks into native and nonnative, 7 were native and 6 nonnative. The native species included red maple, yellow oxalis, and Virginia creeper. The nonnative species, all considered invasive species in the area, included dandelion, Japanese honeysuckle and tree of heave
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