Urban, suburban and exurban ecosystems are important and increasing in the U.S. An apparent, but functionally untested result of urban land use change is homogenization across cities, where neighborhoods in very different parts of the country have similar patterns of roads, residential lots, commercial areas and aquatic features. This homogenization also involves ecological structure and functions relevant to soil and ecosystem carbon and nitrogen dynamics, with continental scale implications. Further, understanding urban homogenization provides a basis for understanding the impacts of urban land use change from local to continental scales. We sampled soils in similar urban, suburban and exurban neighborhoods across six metropolitan statistical areas (MSA) that cover the major climatic regions of the US (Phoenix, AZ, Miami, FL, Baltimore, MD, Boston, MA, St. Paul, MN and Los Angeles, CA) to determine if conversion of native to residential ecosystems homogenizes and alters (increase/decrease) soil microbial biomass carbon and nitrogen content, potential net nitrogen mineralization and nitrification, denitrification potential and microbial respiration.
Results/Conclusions
Conversion from native to residential ecosystems changes the magnitude of and homogenizes multiple ecosystem relevant to biodiversity, carbon and nitrogen cycling, microclimate, hydrography across the U.S. Variation in almost all variables was lower among residential than native ecosystems across the U.S., suggesting homogenization or convergence at the continental scale. Residential ecosystems had higher levels of several biodiversity and soil nitrogen cycle variables due to homeowner planting and fertilization activities. The increase in nitrogen variables was less than expected which may be linked to the maintenance of high levels of soil microbial biomass and carbon cycling, which act to conserve nitrogen and reduce losses to the environment (air, water). These results suggest that residential land use conversion has created a vast, relatively homogenous American Residential Macrosystem with significant changes in ecosystem processes. Some of these changes have positive effects on ecosystem services, while others raise concerns about water and air quality. The high levels of biological activity, e.g., the high soil carbon cycling, suggest that there is potential for adjusting design and management strategies to reduce the negative effects of these increasingly common ecosystems.