Urban Development and Ecological Degradation – Part I. Introduction
As human population continues its logarithmic pattern of growth, it increases demand for ecosystem goods and services while consequent urban development is leading to degradation of the ecosystems that provide the goods and services.
Urbanization and Population Growth
Today 55% of the world’s population live in cities. 2050, this percentage will exceed 68% of the world’s population living in cities. The majority of growth occurring in Asia and Africa (UN 2018). As of 2020 there are 34 megacities in the world, cities whose population exceeds 10 million, and 987 smaller cities whose populations are greater than 500 thousand but less than 5 million (UN 2018). In the United States approximately 83% of the population live in urban areas. In Florida, approximately 88% of the state’s rapidly growing population live in urban areas.
Urbanization and population growth place extraordinary demands for natural resources and exceptional stress on natural systems. Annually over 32 million acres of forest land throughout the world are converted to agriculture, urban land use, and industrial forestry. This deforestation of complex native forest ecosystem significantly affects hydrologic systems and both aquatic and territorial habitats.
Water Quantity and Quality
When urbanization leads to engineered impervious surfaces that amount to greater then 10% it creates a condition called urban stream syndrome. The increase in storm runoff leads to the alteration of stream flow, channel morphology, water temperature, and water quantity and quality. In addition, leaky sewer lines and poorly maintained septic systems can contribute significant amounts of nutrients and organic contaminants such as pharmaceuticals, caffeine, and detergents. Ecologically, these stressors and contaminants significantly affect the quality of water in municipal water supply aquifers and reservoirs.
Terrestrial Habitat Alteration
Habitat loss, alteration and simplification are the greatest threats to biodiversity. Urbanization not only destroys and fragments habitats but also alters its structure and composition. For example, deforestation and fragmentation of larger parches of forest lands lead to the simplification of native plant compositional and structural diversity, and loss of forest interior habitat as well as creating forest edge habitat. These changes shift species composition and abundance from urban avoiders to urban dwellers. In addition, roads and other urban features isolate populations causing local extinctions, limit dispersal among populations, increase mortality rates, and aid in the movement of invasive species. Cities often have higher ambient temperatures than rural areas, a phenomenon called the urban heat island effect. The urban heat island effect alters precipitation patterns, increases ozone production (especially during the summer), modifies biogeochemical processes, and causes stresses on humans and native species
Planning With Nature
The negative effect of the expansion and urbanization itself can be minimized through proper planning and design. Planning with nature is not new (McHarg 1965) but it has only recently been recognized that human survival is predicated on coexisting with biodiversity and native communities. How and if cities apply recommendations for sustainability depends entirely on the people themselves.
United Nations, Department of Economic and Social Affairs, Population Division. 2018. The World’s Cities in 2018—Data Booklet (ST/ESA/ SER.A/417)
Ian L. McHarg 1969. Design with Nature. American Museum of Natural History Press. 197 p.
This series on the ecological impacts of contemporary urban development practices and urban expansion are drawn from a chapter I co-authored with Dr. Wayne Zipperer, USDA Forest Service and Dr. Michael Andreu, University of Florida School of Forest Resources and Conservation.
Zipperer, W., Northrop, R., & Andreu, M. (2020). Urban development and environmental degradation. In Oxford Research Encyclopedia of Environmental Science. Oxford University Press. doi: https://doi.org/10.1093/acrefore/9780199389414.013.97