Research directed by: Dr. Margaret M. Carreiro
 
 

My research program focusses on the ecology of natural habitats that are surrounded by urban and suburban land use where pollution inputs, habitat fragmentation and exotic species introductions are changing community dynamics and ecosystem functions. Urbanization is an important land conversion process affecting large areas of the world's surface. In the USA between 1960 and 1997 nearly 50 million acres of farms and natural areas like forests and wetlands were converted to urban and suburban land use in the United States. In the tri-state New York City Metropolitan Region, where I most recently worked, urban expansion consumes 36,000 acres of natural habitat and farmland per year. Despite this remarkable and continuing trend in land use change in the United States, there have been few major studies of the direct and indirect effects of dense human habitation on adjacent natural systems. Urban and suburban areas provide not only exciting research opportunities in basic ecology in the places where most Americans live, but also the opportunity to guide the management policies of parks, reserves, and nature sanctuaries surrounded by urban and suburban land use.

Undergraduate, Erin McHugh, uses a quadrat sampler to determine how plant communities change from the forest edge to the forest interior. Edge creation can allow the forest interior to be colonized by exotic plant species.

Research topics particularly relevent to the needs of these endangered natural ecosystems, metropolitan parks, and suburban reserves include studies of:

• effects of habitat fragmentation and isolation on local species extinctions and community integrity
• impacts of introduced, invasive species on native species survival and on ecosystem functions such as nutrient cycling
• effects of pollutants like ozone, nitrogen, and heavy metals on organisms and on ecosystem processes

Until recently, my study sites are oak forest stands located along an urban to rural land-use gradient extending from New York City through suburban Westchester County, NY to rural Litchfield, Connecticut. These sites allowed me to conduct comparative ecological research on forest soil and leaf litter microorganisms and the nutrient cycling functions they perform.   Atmospheric nitrogen deposition can often be greater in and around cities due to high rates of fossil fuel combustion.  Since nitrogen is a resource for plants and microbes, this increase in nitrogen loading can affect plant and microbial community composition and the processes they regulate like primary production and decomposition.  Therefore, I have also conducted experiments to determine the effects that chronic nitrogen addition can have on the decay of different leaf litter species , fungal and bacterial biomass dynamics, microbial extracellular enzymes, and nitrogen and phosphorus retention and loss from decaying litter.  In January 2001 I transplanted my research program to the University of Louisville and am excited to begin working to establish permanent plots in Louisville's natural areas for measuring precipitation chemistry, determining species composition of vegetation, and measuring processes that affect carbon and nitrogen mineralization and storage in soils.

Kate Rubin helps Jennifer Reichert extract ergosterol from leaf litter to quantify fungal responses to nitrogen addition in decaying leaves. Ergosterol is a component of fungal cell membranes and is therefore an indicator of fungal biomass.

Graduate student, Raymond Hsiao, collects soil from a suburban forest to study how exotic species of earthworms alter nitrification rates and nitrogen cycling pathways in forest stands.

In 1995 I received a Presidential Faculty Fellowship (PFF) from the National Science Foundation to start a program in Urban and Suburban Ecology at the Louis Calder Center, Fordham University's biological field station. The 5 years of funding from this grant has allowed me to expand my research activities and directions. With this award I have hired two post-doctoral fellows who conducted detailed studies of nitrogen-cycling in the forests along the urban-rural gradient to determine how forests near cities may be differentially affected by urban and suburban land use.

Graduate student, Betsy Brantley, examines mycorrhizal roots collected from oak stands in New York City forests. New York City has 5000 acres of secondary and old growth forests that are natural laboratories for studying the effects human-induced disturbances on ecosystems.

High school students, Jason Post and Kate Rubin, grind decaying leaves of Ailanthus altissima,an exotic tree, for subsequent nutrient analyses. Their studies show that Ailanthusleaves decay and release nitrogen more rapidly than native trees like red maple.

The PFF has also allowed me to offer two year-round, research assistantships to graduate students per year, and summer research internships to two undergraduate and two high school students. Recent examples of undergraduate and high school research projects were:

• Plant community changes from edge to interior in a suburban deciduous forest
• A comparison of changes in fungal biomass, enzyme activities, and mass loss during leaf litter decay of the exotic Norway maple, and native Sugar maple
• Patterns of herbivory on the exotic tree, Ailanthus altissima (the Tree-of- Heaven)
• Atmospheric nitrogen deposition in oak forests along an urban-to-rural gradient (jointly with G. Lovett at the Institute of Ecosystem Studies)

A previous undergraduate, Jennifer Reichert, uses a high pressure liquid chromatograph to quantify ergosterol extracted from decaying leaf litter

Most of my teaching activities are focussed on training and mentoring graduate, undergraduate and high school students, particularly during their summer research experience funded by the National Science Foundation. Some of these students (graduates and high school students) continue to work with me throughout the school year. Two of these high school students were recently semi-finalist in the National Westinghouse-Intel Science Competitions.

As part of the summer research program, I help the students choose appropriate research topics, discuss experimental design, train them on methods and equipment, and teach them computer data entry and analyses. The students' summer experience culminated with their giving 15-minute talks on their research to an audience of scientists, nature-preserve managers, and governmental agency representatives at a Colloquium on Urban and Suburban Ecology that I organized. I helped each of them prepare a talk outline and make slides using computer presentation software. I also hold group sessions so all students can practice their talks and learn to give and receive constructive suggestions on improving their presentation skills. During the summer I also took these students to visit ecological restoration sites in the area.
 
 

Staff and students in the 1996 Urban and Suburban Ecology Program. The group is standing in front of a precipitation collector which is one of a series placed in urban, suburban and rural sites in the New York City area. The rainwater was  analyzed for chemicals like sulfates, nitrates, ammonium, calcium and magnesium. Since auto exhaust and fossil fuel burning are sources of sulfates and nitrates in acid rain, we wanted to determine if inputs of these chemicals to urban habitats differ from those further from cities.  We did ultimately find that atmospheric nitrogen deposition to New York City's forests were two to three times greater than in the suburban and rural forests along the transect.