The city as man's habitat is a complex concept. It must include all of the elements necessary to man's survival—those elements that are necessary to his comfort, well-being, and security. But in addition, the city as habitat for man must include all the elements of man's technology—his industry, his work, his business.

The city habitat of man is not isolated, but forms a continuous environment with the surrounding countryside. Depending upon the climate, latitude, and physiography, the hinterland may be farmland, forest, mountain, desert, or any of the other conditions that prevail on the surface of the earth.

Wherever man builds cities he does so for the purpose of generating the wealth to be derived from natural resources, communications, knowledge, and information. The mass migrations from rural areas to the cities did not come about because the land could no longer support the people but because the cities beckoned with their increased economic opportunities. Since World War II, the natural reproduction processes have caused city populations to swell further.

Yet, even today, the sizes of the cities that man has created vary widely. Some remain quite small communities centered around a single industry or around one or a few mineheads. Others are enormous metropolitan complexes that contain many communities. But whatever the size—single-purpose city or multi-purpose megalopolis—each resident relates only to those areas that touch his daily life. For most people, these are the neighborhoods where they live and raise their families, the area where they work and earn their livelihood, and the area where they play and enjoy their hours of recreation. This is true no matter what the size of the city and differs only in that large cities offer a greater variety of employment opportunities, recreational facilities, and variety of housing than do small ones. Such differences are quantitative not qualitative.

If one considers the reasons for setting aside great national areas for parks as contrasted to cities, they are relatively simple but similar. First, with the Yellowstone Act came the concept of the preservation of ecosystem processes and public policy to preserve certain areas together with plant and animal communities in their natural state. Many parks have been established as a result of this policy, including most of the great national parks.

Following the establishment of Yellowstone National Park, many areas were added as parks because of their great scenic beauty or because they were outstanding examples of particular geological, plant geographical types, or because they were habitats for the vanishing animal populations of the continent. The National Park Plan is based upon the recognition of the desirability of having examples of all physiographic regions of the nation represented along with the plant and animal life.

Once these national area parks are established their maintenance depends upon an understanding of the ecological and environmental factors that produced them in the first place. It is axiomatic in the principles of ecology that natural ecosystems will come into equilibrium or balance with the totality of physical and biological factors that produced them.

Managing natural park areas is a matter of arranging those environmental factors that are most likely to produce the stable ecosystem that will preserve the natural state of the vegetation and the resident animal population. If one compares the basis of maintaining and managing the natural environment of man to that of the natural areas of national parks, there is a great deal of similarity.

Man lives in family units, and families, in turn, are gathered together into neighborhoods. These neighborhoods, together with the technological means for providing man's livelihood, form communities. The predominant organisms of this community are human beings at various stages of growth and development. The ecosystem of man may also include other plants and animals, the products of man's technology, and the means of operating that technology.

The ecosystem processes that operate in the community of man are the biological and physical ones that operate in natural ecosystems and which have essentially the same properties common to any natural ecosystem.

In man's ecosystem, the biological processes are those that occur without the aid of man as well as those that are created by his technology. As a matter of fact, the environment of man may have been modified and shaped extremely to accommodate his machines, although man himself and his biological requirements remain the most important element in his own ecosystem.

The principal technological influences in man's ecosystem are the houses and buildings that contain man and his machines and the development of a means of transportation. Ribbons of concrete and asphalt connect the places where man lives and the places where he works, and ribbons of concrete and rails of steel connect and transport people and goods to cities. The airlanes between the major ecosystems of man are virtually filled with transportation devices also carrying goods and people from city to city, i.e., from ecosystem to ecosystem. Rivers and harbors are dredged, engineering projects contain floods and create shipping channels, rivers are rechanneled to provide areas for development, and canals are dug to carry water for municipal and agricultural purposes or to transport manufacturers' goods.

In many respects, the biological properties of man have been only superficially accommodated to the machines he must use and with which he must live. The history of technology is replete with examples of man being used as a link between machines or as a human force of power to manipulate primitive, simple tools in the construction of complex engineering works.

Man may live in substandard housing, he may drive unsafe automobiles, or work in occupations that are hazardous or detrimental to his health or he may live, work, and play in the most salubrious environments, environments that are most conducive to the realization of his humanity. Regardless of the exact circumstances or details, the environment, together with man and his technology forms the ecosystem of man. The fact that some communities are dangerous or hazardous or inhuman simply points to the array of physical and biological factors that are driving the ecological balance away from that which is most favorable to man.

Desirable and/or human communities, on the other hand, are also the result of ecological factors that promote the desirable or favorable balance or equilibrium. Cities act no differently from natural communities in responding to the inevitability of achieving a balanced equilibrium among all the forces that impinge upon them. Change in the equilibrium point, that is, where improvement or deterioration of community conditions occurs, is always accompanied by a mix in the ecological factors. Thus, the management of cities differs in no conceptual way from the management of any ecosystem.

To achieve this goal, the habitat of man, in common with all habitats, should incorporate appropriate environmental constraints and environmental management practices in order to create ecosystems that promote the common weal.

It is in the city that most people spend most of their time. It is here that man earns his living and seeks his recreation. The city is a biological community or a collection of biological communities; it is the ecosystem of man and must be managed in much the same way that we manage any natural resource.

But in the management of city ecosystems, as with any other, we must first establish goals. Once that management judgment is made, the methods of achieving the goals are no different from the management of any natural ecosystem.

Man lives in and makes use of environments that are a continuum from the city to the wilderness. The main factor in differentiating the elements of this continuum is population density and man's impact upon his environment. In a city, man's influence is at its peak, whereas in the great natural area parks and wilderness man has the least impact. Between these two extremes, man's impact is felt to varying degrees in cultivated agricultural land, in the managed timber forests, in the grazing lands, and in the rivers, estuaries, and waters of the continental shelf. Man's influence, principally through his technology, is present everywhere.

The great natural area parks have many urban-like properties, and many of them are steady-state communities in their own right. Yosemite National Park, for instance, is a steady-state city of 50,000 people during the height of the season. It has a mayor in the form of a superintendent, a chief of police, street maintenance personnel, grocery stores, and sewage disposal plants. In fact, it has all the elements and requirements of a city of 50,000 inhabitants. The people who inhabit the park change from day to day, but this shifting population requires essentially the same services that would be required by a static community.

Moreover, cities have many features in common with natural areas, including natural vegetation and wildlife, and many cities are situated on the banks of rivers and streams.

Man seeks out those places in the cities that are of interest and where there are other people and pleasing activity. A part of the charm of cities is the extent of diurnal and nocturnal activity. Places in the city that are most enjoyable are often those where people are on the streets anywhere from 12 to 18 hours each day. The most hazardous areas in cities are those that are in use only during the working hours of the day and which are deserted the rest of the time.

The most popular cities are those populated by people of diverse ethnic backgrounds, where cultural opportunities abound, and those that offer that variety fabled to be "the spice of life."

San Franciscans live in the areas of greatest activity and make maximum use of their public places. The trend to single-purpose, highrise buildings in San Francisco will probably adversely effect this—a price San Francisco will pay for keeping up with its more modern sister cities. One day, San Francisco will be viewed in historical context as the way to build a very pleasant city before the advent of single purpose, highrise buildings.

In exactly the same way that natural ecosystems with great diversity are stable, cities with great diversity are stable. In the same way that ecotypic interchangeability leads to diversity and stability, so it is that many competing entities produce greater economic stability in cities.

If we set aside great areas of the natural landscape to preserve the natural ecosystems and call these places parks, we can and must look at our cities as great natural ecosystems and make provisions for their preservation—not only preservation of the relics from our heritage, essential as that may be. We must also preserve the processes that produce stable, wealth-producing cities that provide the basic elements of comfort, well-being, and security. To that we must add pleasure, recreation, and the full range of ecosystem interactions necessary to man. Such a city is, in fact, a park by all the standards we have defined.

To bring about these changes requires not wealth (that is generated by the growth of the city itself), but direction. Much has been done already and a growing public awareness of ecosystem interactions suggests that the trend will continue. We look forward to a period of great development during which the form and function of future cities will be determined. Will they be ecologically sound?

Our present population of 200+ million will increase to 260 million by the year 2000. How will this growth be accommodated in our present urban structure? Will we build more cities? Rebuild the ones we have?

Whatever the choice, the thrust and force of the future is at our backs. In making the choice, we can begin with the premise that man is more comfortable and more at ease in a living environment. Man needs cities that are viable communities, with safe and pleasant streets, adequate transportation, and a minimum of pollution. Economics and aesthetics demand that our cities be made livable again. There is no alternative, for we cannot desert them and we are not about to perish in them.

—Theodore W. Sudia