McHarg’s theory and practice of regional ecological planning: retrospect and prospect
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 affordable housing and to produce more resilient, healthy, walkable, and mixed-use cities and suburbs that rely on mass transit to reduce greenhouse gas emissions.
KeywordsCarrying 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 flight of urban residents to the suburbs, and the suburbs sprawled across the landscape, turning fields 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 legislation was aimed at protecting public health rather than promoting good ecological design. The US Environmental Protection 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 (Daniels 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 environment (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 features and so maintain ecological processes and services that benefit both humans and nature (McHarg 1964, p. 24; McHarg 1970, p. 63; Ndubisi 2002, p. 45). This latter concept became known as “ecological determinism,” which McHarg tested in practice throughout his career (McHarg 1966, p. 34). McHarg unified his ideas into a regional ecological approach to planning and design that stressed beginning with a scientific inventory and analysis of a region, understanding its suitability and carrying capacity to accommodate development and then formulating a plan and implementation techniques for the location of development and open space (ibid.).
McHarg tested his ideas on regional ecological planning through practice as a landscape architect and planner. Three projects in the USA demonstrate the evolution of McHarg’s thinking and work: (1) The Metropolitan Open Space study for greater Philadelphia completed in 1963 (McHarg 1963a, 1969, p. 57; University of Pennsylvania 1963); (2) The Plan for the Valleys in Baltimore County, Maryland, written with David Wallace in 1964 (Wallace-McHarg Associates 1964); and (3) The Woodlands, a new town 28 miles north of Houston, Texas in 1974 (Wallace et al. 1974; McHarg and Sutton 1975). This paper evaluates: (1) the accuracy and scale of McHarg’s analyses; (2) the implementation of the drafted plans; (3) the effectiveness of implementation techniques that McHarg proposed and those that have built upon McHarg’s ideas; and (4) the outcomes of the projects. The paper then presents new challenges that suggest some further evolutions of McHarg’s regional ecological planning model.
The Metropolitan Open Space study for greater Philadelphia was an early application of regional ecological analysis, but it did not result in an actual regional plan (McHarg 1969, p. 65). Today, there is a need for metropolitan regional plans that address not only ecological issues, but the infrastructure of the built environment and social issues of environmental justice and affordable housing. The Plan for the Valleys was a sub-regional analysis and plan for locating a large amount of development amid a sub-region of 44,000 acres of mostly open land, but the plan was not implemented (Avin 2013, pp. 21–22; Bunster-Ossa 2014, p. 7; Ndubisi 2002, p. 47). The plan raised issues about the degree to which urban development can be integrated within a rural environment (Hundt Jr. and Daniels 2018, p. 15). The plan did lead to a strong growth management effort in Baltimore County, Maryland, featuring the separation of rural and urban areas to control sprawl. And controlling sprawl remains a major challenge for metro areas today (Burge et al. 2013, p. 235). The Woodlands was another sub-regional analysis and large site planning exercise on 29,000 acres. Here, McHarg was successful in fitting development within the constraints and opportunities of the environment (McHarg et al. 1979, p. 262). However, further development of The Woodlands did not reflect McHarg’s ecological principles and exceeded the carrying capacity of the area (Yang et al. 2015, pp. 781, 784; Yang 2019).
2 McHarg’s theory of regional ecological planning
McHarg’s six steps in ecological determinism.
Source: McHarg (1966, p. 34)
1. Ecosystem inventory
2. Description of natural processes
3. Identification of limiting factors (water, slope, soils, etc)
4. Attribution of value (i.e., ecological services)
5. Determination of prohibitions and permissiveness to change
6. Identification of indicators of stability or instability
Eight natural landscape features, from least to most suitable for development.
Source: McHarg (1969, p. 57)
1. Surface water
6. Steep slopes
3. Flood plains
7. Forests and woodlands
4. Aquifer recharge areas
8. Flat land
3 The open space study for metropolitan Philadelphia
McHarg tested his theory of regional ecological planning through on-the-ground projects. For each project evaluated in this paper, I assess the regional ecological analysis, the subsequent plan, implementation techniques that emerged from McHarg’s ideas, and the outcomes and challenges that suggest some revision to McHarg’s regional ecological planning model.
3.1 Regional ecological analysis
McHarg expected that the form of regional development integrated with natural areas would emerge organically: “If growth responds to natural processes, it will be clearly visible in the pattern and distribution of development” (McHarg, 1969, p. 161). That was the hypothesis. McHarg rejected the idea of simply creating a greenbelt–what today would be called a growth boundary—to fully separate natural areas from developed areas (ibid., p. 56). McHarg’s approach was to attempt to integrate development and natural areas. Yet, in retrospect, McHarg admitted that in testing his hypothesis “concentration on open space alone reduced the scope of the Philadelphia metropolitan study,” because the study did not focus as much on development needs for land (McHarg 1969, p. 127; Ndubisi 2002, p. 29).
Measuring open space without the benefit of GIS or remote sensing proved difficult. For example, in the case of agricultural land, McHarg and his team identified 11.7% of the region as agricultural land in 1963, which was far less than the 35 percent of the land base (808,000 acres) listed as agricultural land in the 1964 Census of Agriculture (U.S. Census Bureau 1964). The 1964 Census showed a total of 18.4% of the region as harvested cropland, the land easiest to develop as well as the most productive farmland (ibid.). The technology of landscape analysis has much improved in recent decades, enabling a fine-grained understanding of individual sites, landscape patches, and regional ecological systems (Ndubisi 2002, p. 28; Steiner 2017, p. 83).
3.2 Regional ecological principles rather than a plan
McHarg and his team did not propose a specific plan for greater Philadelphia, and hence no implementation techniques were recommended or tested. Instead, their analysis of the region offered a set of principles that McHarg and others would draw on in future work. McHarg approached metropolitan regional planning with a recognition of its limitations, stating, “[T]he metropolitan area occupies an area of land but constitutes the sum of many levels and forms of government. It is united neither by government, planning, nor an expression of these” (McHarg 1969, p. 153). Moreover, at the time, there was no ecological model of metropolitan areas. To try to overcome these limitations, McHarg called for a simple, yet powerful guiding principle: “certain lands are unsuitable for urbanization and others are intrinsically suitable” (ibid., p. 154). But in a region without a regional government, it was not realistic to expect hundreds of local governments to conduct analyses of development suitability. McHarg believed that “[a] structure for metropolitan growth can be combined with a network of open spaces that not only protects natural processes but also is of inestimable value for amenity and recreation” (McHarg 1970, p. 64). But to achieve that outcome would require a metropolitan regional government.
3.3 Outcomes for greater Philadelphia
The 1963 Metropolitan Open Space study without an accompanying plan was of little benefit to greater Philadelphia. Governance appears to be one of the major obstacles to an ecological plan for the region. For instance, although the Delaware Valley Regional Planning Commission has drafted regional land use plans, these plans are advisory. As David Rusk has pointed out, the greater the number of local governments, the more sprawl is likely to occur because of the hunt for property tax ratables (Rusk 1993, 2010). This hunt creates a bias in favor of development as opposed to ecological planning. Philadelphia is one of the most fragmented metro regions in the USA in terms of the number of local governments. Within the eight-county region, there are nearly 340 townships, cities, and boroughs (villages), each with control over planning and zoning (DVRPC 2018).
One indication of the loss of open space in the region since McHarg’s 1963 study is that by 2017, the amount of farmland had fallen by nearly half to 410,616 acres (USDA 2019). In the greater Philadelphia region, the eight counties had a total population of 4,342,897 in 1960. By 2010, the population was 5,259,684, an increase of 21%. Philadelphia County lost nearly 500,000 residents during these 50 years. The settlement pattern for the region was more dispersed in 2010 than in 1963 with Bucks, Burlington, Chester, Gloucester Counties more than doubling in population between 1960 and 2010 and Montgomery County adding more than 250,000 residents (U.S. Census Bureau 1970, 2018a, b).
3.4 Re-assessing McHarg’s greater Philadelphia study
The experience of greater Philadelphia over the past 55 years suggests the limitations of analyzing the land capability of the region to support development without tying that analysis to a regional plan and specific implementation techniques. Public planning and zoning have largely been ineffective in maintaining open space in the Philadelphia metropolitan region, in keeping with McHarg’s criticism that “present land use regulations do not recognize natural processes; the public benefits of environmental services and do not place responsibility on landowners and developers” (McHarg 1970, p. 83).
The settlement pattern of the “exploding metropolis” for greater Philadelphia and other metro areas has put environmental strain on a much greater geographic area and increased demands on rural lands for water and recreation (Daniels 1998; Demographia 2014). Limiting the spread of urban and suburban development into the countryside has become a higher priority than in the 1963 study (Chapin 2012; Daniels 2001, 2014). McHarg’s primary approach was to try to integrate nature and development through the suitability analysis process (Ndubisi 2002, p. 44; Bunster-Ossa 2014, p. 4).
One critic has even contended that McHarg’s suitability analysis facilitated the spread of suburbia across the American landscape (Bunster-Ossa 2014, p. xiv). But this criticism is misplaced. McHarg noted that for suburbs “the instinct to find more natural environments became the impulse that destroyed nature” (McHarg 1969, p. 154). But many other factors were also at work in greater Philadelphia. Population growth, the decline of manufacturing, the inability of the city to expand in size, racial and income divisions, cheap and plentiful energy, highway construction, abundant housing finance, and the fragmented local government structure led to the expansion of the suburbs (Gillham 2002, pp. 36–46; Jackson 1985; Rusk 1993, 2010; Squires 2002, p. 2). Also, suburban zoning that encourages commercial and residential development has played an important role in the expansion of metropolitan regions (Rusk 1993; Duany et al., 2000). In short, growth and development did not respond to natural processes as McHarg had predicted.
In sum, the Philadelphia Metropolitan Open Space study enabled McHarg to test his ideas about regional ecological analysis, but mainly from an academic approach. There was no clear plan, settlement strategy, or set of implementation techniques that resulted from the study. The drafting of a plan would come a year later in the famous Plan for the Valleys.
4 Regional ecological analysis and planning: the Plan for the valleys
The Metropolitan Open Space study laid the foundation for McHarg’s work with David Wallace on The Plan for the Valleys, in Baltimore County, Maryland in 1964 (Wallace-McHarg Associates 1964a, b). The interstate highways had recently been completed, placing the three valleys of northwestern Baltimore County within easy commuting distance of the City of Baltimore. A group of private landowners hired McHarg and David Wallace, a planning professor from the University of Pennsylvania, to conduct a plan for the future growth and development of the three valleys with the hope of avoiding haphazard sprawl (Hundt Jr. and Daniels 2018, p. 7).
4.1 Regional ecological analysis of the three valleys
The Plan for the Valleys drew on the general regional ecological analysis experience from the Metropolitan Open Space study for greater Philadelphia to understand where development would have the best fit. McHarg then added a more fine-grained analysis, based on a layer cake of scientific data about development suitability (Avin 2013; Hundt Jr. and Daniels 2018, p. 7; Wallace-McHarg Associates 1964a, b). It became clear that the valley floors should not be developed because of the sensitive hydrology and because they contained the best soils for agricultural production. McHarg and Wallace identified the hilly plateaus as the most appropriate sites for development. But how much development could the region absorb?
4.2 The plan and implementation techniques
To protect the valley floors, the plan recommended three techniques: a growth boundary to limit the extension of sewer and waterlines, low-density zoning, and a conservation area where conservation easements would be acquired to keep the land undeveloped (Hundt Jr. and Daniels 2018, p. 11). McHarg envisioned the creation of a syndicate of landowners to acquire what today would be called Transferable Development Rights (TDRs) to compensate valley landowners for not developing their property and moving the development potential to the plateaus (ibid.). However, the syndicate proved too complicated to implement.
4.3 Outcomes and challenges for the valleys
The development of the proposed new settlements never happened; the local residents simply did not want that much development. Even though McHarg and Wallace proposed to locate the development on the hilly plateaus, away from the mostly agricultural valley floors, the local residents feared that if sewer lines were extended to the developments on the plateaus that the valley floors would also become sewered and developed.
As in the case of greater Philadelphia, McHarg was attempting to integrate development and open lands. A lesson from The Plan for the Valleys is that separating development and nature is sometimes desirable and justifiable (Hundt Jr. and Daniels 2018, p. 15). Also, a key issue that continues to arise is: what is the compatibility of development and the local or regional ecology?
Baltimore County responded to The Plan for the Valleys in 1967 by adopting its famous Urban–Rural Demarcation Line, a growth boundary separating urban and suburban development from the rural areas. This was the second growth boundary adopted in the USA, after Lexington-Fayette County, Kentucky in 1958 (ibid.).
Starting in 1976, Baltimore County implemented very low-density Resource Conservation (RC) Zoning which now protects more than 135,000 acres of farmland. Since 1975, landowners in the County have preserved more than 64,000 acres of farmland and natural lands through the sale or donation of conservation easements (Baltimore County 2018, p. 1).
The combination of growth boundaries, natural resource zoning, and the acquisition of conservation easements has enabled Baltimore County to maintain an agricultural industry generating $67 million a year in sales within a metropolitan region (USDA 2019). This combination of growth controls has also become a hallmark of some of the nation’s leading counties in growth management, including Lancaster County, Pennsylvania; Lexington–Fayette County, Kentucky; and Sonoma County, California (Hundt Jr. and Daniels 2018, p. 11).
Of the three valleys, the Green Spring Valley has experienced a considerable amount of scattered residential development on large lots; yet, the Caves and Worthington Valleys are still much the same thanks to low-density zoning and the decisions of many farmland owners to sell or donate conservation easements on their land (ibid.). Moreover, an estimated 90 percent of the county’s population lives inside the URDL, on about one-third of the county land area (ibid.).
4.4 Re-assessing the Plan for the Valleys
The regional ecological analysis of The Plan for the Valleys shows an accurate evaluation of the appropriate location of development. The question arises here and in The Woodlands of how much development is ecologically sustainable as well as politically acceptable.
The Plan for the Valleys was not a true metro-regional plan. McHarg himself admitted that “the study of the Valleys existed in only a part of a metropolitan and physiographic region” (McHarg 1969, p. 127). Yet, writing in 1996, McHarg proudly noted that the Valleys “more than 30 years later still retain their pastoral beauty” (McHarg 1996, p. 177).
5 Regional ecological planning in a new town: The Woodlands
McHarg sought to integrate nature into development in his practice as a landscape architect, perhaps most notably at The Woodlands, a project he considered “the best example of ecologically based new town planning in the United States during the 1970s” (McHarg 1996, p. 325). The site covers 29,000 acres in the coastal plain mostly in Harris and Montgomery Counties, 28 miles north-northwest of Houston, Texas. The property was owned by George Mitchell, a successful oil and gas developer, and a pioneer of hydraulic fracturing. Mitchell wanted to build a master-planned new town of 180,000 residents that would fit in with the environment (Malone 1985). The new town would have commercial, industrial, and recreational developments along with thousands of homes and miles of roads. Mitchell hoped that the City of Houston would eventually annex The Woodlands into the city, but that never happened (ibid.).
5.1 Regional ecological analysis of The Woodlands
McHarg focused on the hydrology of the site (Forsyth 2003, p. 12; McHarg and Sutton 1975). He was quick to note that The Woodlands had several constraints. Impervious soils covered about one-third of the area. The land was generally flat, drainage was slow, and there was standing water. The forests and wildlife habitat would be needed both to help absorb stormwater runoff and enable the water to move rather than pond up; and development would have to avoid the 100-year floodplains which buffered the streams and covered about one-third of the site (Forsyth 2003, p. 12).
5.2 The plan and implementation techniques
The plan for The Woodlands featured development design (McHarg and Sutton 1975). Unlike the Plan for the Valleys, there was no mention of land preservation or zoning. The design strategy was to keep development away from the highly permeable soils, retain as much forest as possible, and integrate open space for surface drainage (Yang et al. 2015, pp. 777–778). The opportunities were to place high-density development on the impervious soils, clear pine trees instead of hardwoods, which were less tolerant of disturbance, and match proposed development types and densities with appropriate locations (McHarg et al. 1979, p. 257). A financial benefit of the design of The Woodlands was that it avoided expensive engineering projects by emphasizing compatibility with nature (Forsyth 2003, p. 12).
5.3 The Woodlands plan and outcomes
The Woodlands was launched in 1974 in part with help from a $50 million HUD New Communities loan (Forsyth 2003, p. 11, 2005; Yang et al. 2015, p. 774). By 1979, there were 2,500 residents. Ownership of The Woodlands development company changed hands three times as the population grew to 93,847 in 2010. The following year, the Howard Hughes Development Corporation purchased The Woodlands and began additional development. In 2017, before the arrival of Hurricane Harvey, there were an estimated 114,625 residents. As of 2018, The Woodlands boasted 215 miles of hike and bike trails, 146 parks, 7790 acres of green space (over one-quarter of the new town), 10 villages, and some 500 acres of office, institutional, and industrial space (The Woodlands 2018).
Residents of The Woodlands are heavily dependent on cars for transportation in part because of the low-density design and large percentage of single-family detached housing (Forsyth 2003, p. 13). Transportation networks are largely overlooked in McHarg’s regional ecological planning approach (University of Pennsylvania 1963; McHarg and Wallace 1965; McHarg and Sutton 1975). Today, suburban and ex-urban development residents rely primarily on cars, and motor vehicles are a leading source of America’s greenhouses gases and air pollution in many metro areas (Daniels 2014, p. 535). The increasing population and the less green development after 1997 in The Woodlands have coincided with the explosive, sprawling growth of greater Houston (Forsyth 2003, p. 13; Yang and Li 2011; Yang et al. 2015, pp. 781, 784). For instance, between 1996 and 2001, the developed area of The Woodlands increased by 3500 acres and the forest shrank by more than 4000 acres; the newer development did not follow McHarg’s design with nature principles (Yang et al., 2015, p. 784; Yang 2019).
When Hurricane Harvey struck the greater Houston region in late August of 2017, it brought a record amount of rainfall. Up to 50 inches of rain fell on parts of greater Houston, causing widespread flooding, taking more than 50 lives, inundating 204,000 homes, and wreaking an estimated $125 billion in damage. The New York Times reported that in The Woodlands “recently constructed neighborhoods flooded at far higher rates than others” (Schwartz et al. 2017, p. 8). Among the older homes, about 215 out of 33,000 homes were flooded, a rate of less than one percent, whereas 331 out of 1450 new homes, or 23 percent, were flooded (ibid.).
5.4 Re-assessing The Woodlands
The regional ecological design proposed by Wallace, McHarg, Roberts, and Todd withstood the brutal test of Harvey. Their design also underscored the fragility and limitations of The Woodlands to accommodate an ever-increasing number of residents. Although the original design led to a financially successful project, the addition of more dwellings to The Woodlands after 1996 was bound to occur on less environmentally suitable land (Yang et al. 2015, p. 784). This tension between the real estate profit motive and the ecological fitness of development will continue so long as new developments are being built. When the two goals are compatible, then development can be beneficial. When they are not compatible, either a profitable development cannot be built, or the development will be especially vulnerable to natural hazards. Those outcomes are what McHarg had predicted from this regional ecological theory. Yet, few new towns on the scale and with the ecological sensitivity of The Woodlands appear possible (ibid.).
6 Current planning challenges and revisions to McHarg’s regional planning model
Current planning challenges present obstacles to implementing McHarg’s regional ecological planning principles. They are also broader in scope than McHarg’s focus on ecology and require some revisions to McHarg’s model. The first challenge includes population growth, the growth of metro regions, and the location of development within those regions. In response, greater integration of nature in cities and suburbs will be needed to: (1) remediate the built environment; (2) enable an increase in the density of development; (3) make new development more resilient to natural disasters; and, (4) reduce the emphasis on greenfield development.
A second challenge is that the separation of rural and urban areas is needed to minimize sprawl; attempts to integrate urban development with rural lands have generally led to sprawl and the loss of rural lands. A third challenge is the lack of regional governments which has undercut the effectiveness of regional plans and the implementation of regional ecological planning. A fourth challenge is climate change from greenhouse gas emissions generated by humans now poses serious threats to a region’s natural environment and built environment, and to nature on earth (Steiner 2017, p. 81). Adapting to the effects of climate change with the help of green infrastructure will be needed as well as more careful investment in the built environment. Finally, social issues, such as equity, environmental justice, and affordable housing have become as important as environmental and economic issues in the triple bottom line of sustainability (Bunster-Ossa 2014, pp. 33, 35).
6.1 Population growth and the dominance of metropolitan regions
Population levels and population growth affect the carrying capacity of a region to support development without major negative environmental impacts. There are now 328 million Americans, an increase of more than 100 million compared to when McHarg conducted his regional planning work in the 1960s and 1970s. The stresses on natural resources are much greater today because of the larger population and the effects of climate change (Daniels 2014, p. 661; Steiner 2017, p. 81). The looming challenge is how to accommodate a projected 70 million additional Americans by 2051 (Colby and Ortman 2015, p. 1). While McHarg recognized the urgency of regional ecological planning, the sheer scale and urgency of regional planning work have only become more critical.
Much of McHarg’s regional work involved where to put development on greenfield sites, such as in The Plan for the Valleys and The Woodlands (Ndubisi 2002, pp. 47, 75–76). Writing later in life, McHarg noted that how and where to integrate nature and the built environment remained a challenge: “We observed that the greatest problem lies not with data, but with integration” (McHarg 1996, p. 363). A key factor in that integration is adequate infrastructure, and McHarg tends to overlook the cost and development-inducing effects of transportation and central sewer and water systems (McHarg 1968; McHarg and Sutton 1975). Infrastructure has become very expensive in accessing new areas for development. When cities and suburbs push into the countryside, mass transit systems are slow to expand. The preferred mode of transportation is cars and trucks, which means road construction and road widenings. In his study of where to locate highways, McHarg did not make the connection to greenhouse gas emissions, which are of critical concern today (IPCC 2018; McHarg 1968). In the Plan for the Valleys, the local residents did not embrace the proposal for large developments on the plateaus because they feared the extension of sewer and water lines would lead to the development of the valley floors (Hundt Jr. and Daniels, 2018, p. 10).
To accommodate tens of millions more Americans and to reduce greenhouse gas emissions, development must be concentrated on reviving cities, infill development, and the adaptive re-use of urban and suburban sites and buildings (Calthorpe 2010). McHarg’s concept of integrating nature and the built environment has value in helping to revitalize cities and densify suburbs, rather than aiding the further expansion of metro areas. Planners and designers have promoted green infrastructure from the site-specific to the regional scale to reduce stormwater runoff—a major source of water pollution, mitigate the urban heat island effect, provide recreation opportunities, connect wildlife hubs and migration corridors, and to guard against natural hazards, such as flooding and storm surges (Benedict and McMahon 2006; Daniels 2014, pp. 29–31). In sum, the installation and maintenance of green infrastructure in existing cities and suburbs will need to become the primary application of a design with nature approach.
6.2 Separating urban and rural areas
The difficulty in integrating urban and rural land uses is well-documented. The loss of farmland to urban development has been a national concern for almost 40 years (NALS 1981). Millions of people who live in the wildlands–urban interface in the west are at a high risk of exposure to forest fires (Theobald and Romme 2007, p. 352). And the primary cause of wildlife decline is the loss of habitat to human development (Daniels 2014, p. 308).
If cities and suburbs are to accommodate more people, then protecting the countryside from sprawling development will take on greater importance. Peter Calthorpe and William Fulton put forth the idea that the city is now the region (Calthorpe and Fulton 2001). The challenge is to design the regional city for human scale by combining a pleasant, efficient, and relatively dense built environment with green space. But inherent in the regional city concept is the existence of a growth boundary, separating the city from the countryside, rather than attempting to integrate the city and the countryside.
McHarg, however, rejected the greenbelt or growth boundary approach to rural land protection and metropolitan planning (McHarg 1969, p. 56). Even so, growth boundaries that separate urban from rural land have become popular on the West Coast (California, Oregon, and Washington) and examples exist in the South (Florida and Tennessee) and the Mid-Atlantic states (Pennsylvania and Virginia). A growth boundary can promote a compact, relatively dense development pattern, and an increase in the use of mass transit, walking, and biking, which help to reduce greenhouse gas emissions (Nelson et al. 2004). Implementing greenbelts/growth boundaries to separate urban and rural areas is a good application of designing with nature.
6.3 The lack of regional governments and regional ecological planning in practice
Metropolitan regions now contain four-fifths of America’s population and most Americans live in suburbs (Frey 2012). However, the USA has few, if any, examples of regional ecological plans that have been implemented at the metropolitan level. A primary reason is that there are very few regional governments with the power to plan and zone land. Even Metro of greater Portland, Oregon, the nation’s only elected regional government, must balance its planning with those of three counties and 24 municipalities (Metro 2018). Metropolitan regions consist of dozens, if not hundreds of local governments, each with control over planning and zoning. Coordinating local planning into a metropolitan regional plan has proven elusive.
Much of the metropolitan planning today is remedial and reactive in regions that are largely built-out, rather than proactive planning and designing for mostly undeveloped sub-regions as in the Plan for the Valleys and The Woodlands. More than 300 Metropolitan Planning Organizations (MPOs) are limited to transportation planning and have no zoning powers. Similarly, regional planning commissions in metro areas (nearly all of which also serve as the region’s MPO) can draft regional plans, but these plans are advisory and the regional planning commissions do not have zoning powers to implement their plans (Seymour 2011, p. 227).
McHarg pointed out that traditional land use planning did not integrate the limitations and services of nature and as a result traditional planning resulted in sprawl and ugly development that destroyed nature (McHarg 1970, p. 83). But McHarg did not fully appreciate that to draft and implement a metro-regional ecological plan requires a regional government. Metropolitan regional governments did not exist and still do not exist in greater Philadelphia, Baltimore, or Houston. Metro-regional comprehensive plans with a strong ecological element are needed. To implement these plans will require such measures such as urban growth boundaries to enforce compact development, restrictive zoning, and land preservation in the countryside to limit sprawl; inside the growth boundaries, there must be adequate infrastructure, density, and a mix of land uses and greenspace to accommodate the large majority of new development (Calthorpe 2010).
6.4 The challenge of climate change
To place McHarg in his historical context, it is important to note that climate change has become the leading environmental issue only within the past 20 years, well after McHarg formulated his theory of regional ecological planning (Calthorpe 2010). In 2018, the Intergovernmental Panel on Climate Change (IPCC) reported that the world has only 12 years in which to reduce greenhouse gas emissions to keep global temperatures from rising less than 1.5 °C since the start of the Industrial Revolution (IPCC 2018). Climate change and greenhouse gas emissions from the burning of fossil fuels were not prominent issues for regional ecological planning in the 1960 s and 1970 s.
Compact urban and suburban development that can be serviced by mass transit, walking, and bicycling options can help to reduce greenhouse gas emissions (Calthorpe 2010). Separating urban and suburban areas from rural areas will limit sprawl, vehicle miles traveled, and greenhouse gas emissions.
The concept of design with nature has taken on added urgency because of the threats posed by climate change: sea level rise, more frequent and intense storms, rising average temperatures, more frequent and larger wildfires, arid places experiencing prolonged drought, and humid places experiencing more intense rain events. The need to adapt to climate change is clear (ibid.). Engineered interventions, such as building levees and sea walls, are hugely expensive, do not work with nature, and are not long-term solutions. Identifying areas vulnerable to climate change-induced disasters and directing development away from those areas is essential. For example, McHarg identified the coastal plain as an area suitable only for limited development (McHarg 1969, pp. 7–17); this is a region where development is already becoming increasingly vulnerable. Maintaining natural features such as floodplains, dunes, and marshes will help to absorb rising sea levels, flood waters, and storm surges, thus protect human health and safety.
6.5 Social issues
Social issues hold great importance as part of the triple bottom line of sustainability; these include environmental justice, social equity, and affordable housing. Yet, McHarg was known for a lack of interest in social issues (Herrington 2010, p. 8). As America continues to add population, decisions about siting locally unwanted land uses, the protection of vulnerable developments, and the provision of affordable housing will be paramount, especially for lower income communities within a metro region. Since Design with Nature was published, America has grown by more than 120 million people, and land has become scarcer as measured by the increase in inflation-adjusted real estate prices (US Census Bureau and US Department of Housing and Urban Development 2019). Access to safe and affordable housing continues to be a fundamental need. Moreover, environmental justice, the right to a safe and healthy environment for an increasingly diverse population, is an issue that did not gain prominence until after McHarg left the academic world (Bullard et al. 2001). Regional ecological planning must be married to environmental justice if such planning is to reflect maximum public benefit.
7 The evolution of McHarg’s regional ecological model
Ian McHarg’s theory of regional ecological planning evolved from a Metropolitan Open Space study for greater Philadelphia to a plan for a sub-region of Baltimore County to a plan and built design in The Woodlands new town in Texas. The theory has stood the test of time in on-the-ground practice but requires some adjustment to meet new and broader planning challenges. Regional ecological analysis has become the basis for several county comprehensive plans and large-scale master-planned communities but has not resulted in metropolitan regional ecological plans. McHarg’s layer cake ecological analysis underlies a widespread green infrastructure movement in urban planning and design and has spurred the application of innovative planning and design techniques to protect open lands and better integrate the natural environment and the built environment.
The lack of metropolitan regional governments has hindered the application of regional ecological planning. Metropolitan regional plans are mainly limited to MPO transportation plans and the advisory plans of regional planning agencies, and the agencies do not have control over zoning to implement those plans. Metropolitan regions, such as greater Philadelphia, are an amalgam of dozens if not hundreds of municipal governments, many of which are motivated toward the expansion of the property tax base through development, rather than the protection of natural areas and open space. Sub-regional planning, such as at The Woodlands and The Valleys in Baltimore County, appears easier to do.
The integration of the built environment and green infrastructure must concentrate on making existing cities and suburbs denser and more sustainable to adapt to climate change. The separation of cities and suburbs from rural areas is needed to reinforce compact development and to limit the emission of greenhouse gases. Yet, population growth poses a threat to environmental carrying capacity. Since Design with Nature appeared in 1969, America has added more than 120 million people to reach 328 million. Environmental impacts increase along with population growth. This is one of the lessons of The Woodlands. The new town became more vulnerable as less environmentally fit lands were developed after 1997 (Yang et al. 2015, p. 781; Yang 2019). And then Hurricane Harvey struck. The older, better situated homes suffered much less flooding.
Today, the model of the triple bottom line of social, economic, and environmental sustainability gives equal weight to these concerns. The McHarg regional ecological model must also be consistent with the social goals of environmental justice and equity and economic goals of the efficient use of resources and cost-effective infrastructure.
Finally, one of the most valuable ingredients that McHarg added to the planning process was a sense of urgency. He wrote, “Can we hope that man[kind] will be able to change the physical environment to create a new ecology in which he is a primary agent, but which will be a self-perpetuating and not a retrogressive process?” (McHarg 1963a, b, p. 7). That urgency for sustainable regional ecological planning has only increased and will continue to do so.
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