Parts of Any Human Ecosystem
There are four components of human ecosystems: biological, physical, social, and built. They are all necessary categories for human ecosystems, by definition. The one-word label for each is a convenient shorthand that cannot instantly convey all the richness embodied in each one.
The Parts have Parts
Take "social," for example. The comprehensive nature of the human ecosystem framework presented by Machlis et al. (1997) gives some sense of the variety of structures, processes, and relationships that are implied by the simple term "social." The familiar use of social-ecological conceptions in contemporary urban ecology have helped biophysical scientists appreciate some of the richness that simple term stands for. And of course those with biological or ecological training will immediately fill in the detail implied by the terms "biological" or "physical."
What Parts Exist in the Built Component?
Where subtlety may be missed in urban ecology is in what is commonly labeled the built component. To help expose some of that richness, perhaps "constructed" could be used to refer to the "fourth component" of urban ecosystems.
Why might an alternative term be useful for the built realm? Unfortunately "built" may make non-specialists think of buildings or edifices. Adding the idea of infrastructure helps, of course, since that term traditionally points to the connective tissue that people also build. Wires, pipes, ditches, drains, roads, streets, and rails are common features of urban infrastructure. Most of these will elicit thoughts of engineering.
|Human ecosystem model template, with linkages and specialized disciplines. Environmental components are described as either physical or constructed, to emphasize the extensive range of activities and artifacts that humans create in urban areas.|
But even extending the focus to built infrastructure may allow people to miss important material parts of ecosystems that humans design, shape, or unintentionally modify. The surface of urban land may be purposefully modified for many reasons. Landforms may be shaped to alter water flow or to improve the view. Low places are filled to provide more space for buildings and roads, and grading is a common part of highway and railroad construction. Cuts through hills and mountains also are a part of the constructed environment, as are borrow pits. The soil and subsoil excavated for cellars, and the masses of materials removed in making the deep basements of high rises, cisterns, tunnels, and subways are deposited elsewhere. Often the receiving sites are (former) wetlands, or coastal margins. In some urban situations, topsoil or turf is imported and installed over sterile or compacted fill.
|Baltimore in 1935, constructed shoreline in gray shading|
Not Missing the Construction For the Buildings.
Some of these activities and artifacts may be missed if one uses the term built and too easily sees only edifices. Even buildings may hide infrastructure or flows from view. For example, when one looks at a block of handsome Baltimore rowhouses from the 19th century, the housing residents is the obvious use. But the rowhouses are also part of a unified system of stormwater management. The roofs slope gently to the rear of the house, where gutters and downspouts convey the rainfall to the back yards, and thence to the alleys behind the houses. The alleys, with their central gutters, convey the stormwater to the streets, and in the streets, the water was guided by the curbs into storm drains. So buildings, whose principal intention was shelter (and social significance -- but that's another story) also participate in a larger system of construction with the goal of water management.
While we are thinking about constructed systems for stormwater management, it is worth pointing out that the 18th century stormwater system involving houses was different in some ways from the 19th century pattern noted above, and the current "on site" components of stormwater management are different still, with their rain barrels, disconnected downspouts, rain gardens, detention basins, and other water-sensitive design strategies that characterize more recent developments or retrofits.
Complexity in the Built - Seeing Construction.
The upshot of all this complexity is that the term constructed may be a more evocative term to use as the label for one of the main components of the human ecosystem. Each of the four components will suggest its own contributing structures and processes, just as the human ecosystem does so well for the constituent social systems, social-economic resources, and cultural resources. Substituting the term "constructed" for the term "built" may on the surface seem unnecessary, but the substitute term has value in immediately pointing to a broader array of activities and artifacts than the making of edifices. The alternative term helps expose equal detail in all four of the components of urban ecosystems, not just the ones that are familiar to biologists or to social scientists.
Cadenasso, M. L., S. T. A. Pickett, and J. M. Grove. 2006. Integrative approaches to investigating human-natural systems: the Baltimore ecosystem study. Natures Sciences Societes 14:4–14.
Machlis, G. E., J. E. Force, and W. R. Burch. 1997. The human ecosystem 1. The human ecosystem as an organizing concept in ecosystem management. Society & Natural Resources 10:347–367.