Baltimore Ecosystem Study Institute of Ecosystem Studies

2010 BES Annual Meeting Presentation and Poster Abstracts

Exurban Development in Carroll County, Maryland
Irwin, Elena
Co-Authors: Doug Wrenn, Wendong Zhang

Abstract: Low-density, scattered residential development is a dominant urban land use pattern in exurban areas of the U.S. located on the metropolitan fringes of urban areas. While only a small proportion of people live in exurban areas, the geographic extent of exurban areas is many times larger than that of urban and suburban areas combined. The expansiveness of the exurban footprint, combined with the scattered, non-contiguous pattern that is typical of exurban development, make land use patterns in these areas a primary environmental concern, e.g., in terms of their impacts on habitat loss, water quality and other ecosystem services. Efforts to protect and enhance urban ecosystem services must be guided by models that provide insights into the policy and other spatially heterogeneous factors that spur these types of land use patterns. In this set of papers, we focus on describing and explaining the evolution of scattered land development patterns in Carroll County, MD, an urban-fringe county in the Baltimore-Washington D.C. metro region. We use a micro-level panel dataset of land parcel conversion that was constructed from historical land records on subdivision development obtained from the Maryland State Archives. Using ArcGIS software, these data were used in conjunction with tax assessment data on land parcels from MD PropertyView to create a new spatial dataset that describes the entire history of the subdivision process in Carroll County from the 1920ís onward. Using these historical subdivision data, we first examine the extent to which residential subdivision patterns exhibit leapfrog versus infill development patterns over time. We find that, while the extent of scattered development associated with any given subdivision has diminished over time, substantial amounts of vacant land that could be developed and counted as "infill" development remain. For example, the average subdivision developed in the 1960s had an initial leapfrog measure of 0.8 associated with it, meaning that 80% of the developable land between the average 1960ís subdivision and either Baltimore or Washington D.C. was vacant when the subdivision was first developed. Over time, this measure has declined and by 2005 was 0.4. Second, we examine the role that the minor subdivision process has played in contributing to scattered leapfrog development patterns in Carroll County. Using historical data on residential subdivisions and agricultural land preservation and a number of other spatially heterogeneous variables, we apply a competing risks duration model to analyze which factors affect major versus minor subdivision development for a 15 year time period from 1993 to 2007. Empirically, we find evidence that the factors affecting the timing of minor versus major subdivision developments are different. Distance and access to road networks have less of an effect on minor over major developments, while surrounding preservation and the option to preserve has less of an effect on major subdivisions. Lastly, we examine the extent to which the option to develop a minor subdivision has influenced the choice to develop a major subdivision. Using a nested discrete choice model, we estimate the probability that a rural landowner chooses to sell her land for subdivision and, conditional on this choice, whether the land is developed as a major versus minor subdivision. Using the parameter estimates of this model, we examine how the choice to subdivide the land parcel would be predicted to change if the minor subdivision option were removed. In summary, our results provide concrete evidence of the evolution of scattered residential land use patterns in Carroll County and the role of the minor subdivision policy in promoting these patterns.