Land fragmentation is a major concern in rapidly urbanizing cities of the Southwest, mostly caused by discontinuous, low-density development over the last few decades. It has negative consequences for socio-ecological systems through disconnecting habitat, destroying migration corridors, increasing costs of public service provision, and increasing transportation distances from home to work. A cross-LTER site research initiative has examined land fragmentation across the five cities and metropolitan areas associated with the Central Arizona-Phoenix (Phoenix, Arizona), Sevilleta (Albuquerque, New Mexico), Jornada (Las Cruces, New Mexico), Short Grass Steppe (Fort Collins, Colorado), and Konza Prairie (Manhattan, Kansas) Long Term Ecological Research (LTER) sites.
Central Arizona-Phoenix (CAP) researchers Abigail York and Christopher Boone have led the study with post-doctoral researcher Milan Shrestha, graduate student Sainan Zhang, and co-investigators from the other four sites. The research has focused on understanding both patterns and drivers of land fragmentation. Using the National Land Cover Database and a common land-use classification system for all five sites, the research team has analyzed land fragmentation trends from 1992 to 2001 along selected transects in each city.
They found that the amount of low intensity development increased for all cities between 1992 and 2001 (Figure 1). Low-density residential development increased land fragmentation on the fringes or peripheries at all research sites. Three general fragmentation patterns emerged from the analyses:
- Riparian: fragmentation along rivers (Las Cruces and Albuquerque)
- Polycentric: suburbanization and exurbanization in disaggregated cities (Manhattan and Fort Collins)
- Monocentric: rapid urban growth in a concentric ring pattern (Phoenix)
These patterns correspond to spatial differences in patch density among the five cities. High patch density indicates heterogeneity of land cover, which in wild land sites is associated with biodiversity. For this project, higher patch density is associated with more fragmented urban development. In the case of Las Cruces and Albuquerque, patch density declines with distance from the city center but remains relatively high along the river corridor. Manhattan and Fort Collins are cases of discontinuous urban development along transportation routes where patch density rises and falls relative to exurban and suburban development. Compared to the other four cities, Phoenix has a low patch density within the urban center, indicative of infill urban development, with higher patch density at the urban fringe.
Through gathering local expert opinions and reviewing the literature, the team also identified five relevant drivers of land fragmentation across the five sites:
- Water provisioning
- Urban population dynamics
A rich analysis of these drivers for each city using historical data revealed the relative importance of each for land use decision-making. Water emerges as an important driver across all sites, which have dammed major rivers for storage or flood prevention. In Phoenix, Las Cruces, Albuquerque, and Fort Collins, water provisioning is highly influential. All sites have been affected by the conversion of land from agriculture to urban uses, although the patterns of this development differ among sites. Las Cruces, Albuquerque, Fort Collins and Manhattan have experienced low density exurban development associated with homeowners seeking amenities in rural areas. Transportation routes have guided development in all cities. For example, historic rail corridors continue to influence observed patterns of urban growth in Fort Collins and Manhattan. Topography as associated with both barriers to growth (i.e. mountains) and amenities has played a role in the direction of development. Institutions, although varied across the sites, play a large role in shaping land-use decisions.
Additional results from this research will be published in an upcoming issue of Urban Ecosystems, and detailed analyses from specific sites are in preparation. The land fragmentation research also feeds into the work of an Urban Long Term Research Area Exploratory (ULTRA-Ex) grant that focuses on open space and ecosystem services in the Albuquerque, Las Cruces, and Phoenix areas.
York, A., M. Shrestha, C.G. Boone, S. Zhang, J. Harrington, T. Prebyl, A. Swann, M. Agar, M. Antolin, B. Nolan, J. Wright, and R. Skaggs. In press. Land fragmentation under rapid urbanization: A cross-site analysis of southwestern cities. Urban Ecosystems