Vol.:(0123456789) 1 3 Socio-Ecological Practice Research (2019) 1:197–208 https://doi.org/10.1007/s42532-019-00024-4 REVIEW ARTICLE McHarg’s theory and practice of regional ecological planning: retrospect and prospect Thomas Daniels 1 Received: 18 January 2019 / Accepted: 1 August 2019 / Published online: 9 August 2019 © Springer Nature Singapore Pte Ltd. 2019 Abstract Ian McHarg’s theory of regional ecological planning is a milestone in the history of planning and socio-ecological practice. The use of science—geology, physiography, soils, hydrology, and vegetation—to determine the appropriate locations for development marked a distinct departure from planning based on promoting economic growth. McHarg tested his theory in practice, most notably in three projects in the USA: The Metropolitan Open Space study of greater Philadelphia, The Plan for the Valleys in Baltimore County, Maryland, and The Woodlands, a new town outside of Houston, Texas. New challenges to regional ecological planning have arisen in the past 30 years: population growth, infrastructure needs, climate change, and social equity and environmental justice. McHarg’s emphasis on the integration of nature and the built environment is still valid, especially in urban/suburban areas, where the use of green infrastructure has gained popularity. McHarg advocated some separation of rural areas from urban/suburban areas to protect farmland and curb sprawl. But more separation is now necessary given America’s much larger and dispersed metropolitan populations. Also, greater emphasis is needed on social equity, environmental justice, and the sustainability of the built environment to provide more afordable housing and to produce more resilient, healthy, walkable, and mixed-use cities and suburbs that rely on mass transit to reduce greenhouse gas emissions. Keywords Carrying capacity · Ecological determinism · Plan for the valleys · Regional ecological planning · Socio- ecological practice · The Woodlands 1 Regional ecological planning as a response to unplanned sprawl Of the many contributions made by Ian McHarg to our understanding of ecology, physical design, and land use planning, his ideas on regional ecological planning have been the most challenging to implement. The decline of America’s industrial cities in the 1950s and 1960s often led to a fight of urban residents to the suburbs, and the suburbs sprawled across the landscape, turning felds and forests into shopping malls and housing subdivisions with little regard for nature (Ammon 2016; Anderson 1965). State and local governments enacted few laws and land use controls to control suburban sprawl (Healy and Rosenberg 1979), and the federal government had yet to adopt the Clean Air Act (1970) and Clean Water Act Amendments (1972) to regulate pollution emissions into the nation’s air and water or the National Environmental Policy Act (NEPA) to review the environmental impacts of federal projects (Anderson 1973; Freeman 1990; Portney 1990). This environmental legisla- tion was aimed at protecting public health rather than pro- moting good ecological design. The US Environmental Pro- tection Agency gave no directions on how to build cities or develop metropolitan regions that would meet air and water quality regulations and provide a healthy environment (Dan- iels 2014, p. 667). McHarg wrote his masterpiece, Design with Nature, to demonstrate how and where to develop sites, communities, and regions with a sensitivity to the environ- ment (McHarg 1969, pp. 55–65). McHarg’s fundamental ideas are: (1) Nature is a process consisting of physiography, hydrology, drainage, climate, soil, vegetation, wildlife habitat, and land use (Steiner 2006, p. xiv), and (2) it is desirable to plan and develop cities and metropolitan regions in concert with natural * Thomas Daniels thomasld@design.upenn.edu 1 Department of City and Regional Planning, School of Design, University of Pennsylvania, 127 Meyerson Hall, 210 South 34th Street, Philadelphia, PA 19104-6311, USA