Structure, Evolution and Growth
Human habitations undergo and evolutionary process. The first stage is generally the provision of habitat for single family units, primarily for shelter against the elements, and for defence. As groupings of shelters increase, village situations develop. These are basically characterised by a collection of habitations with some cohesion and centralisation. Villages tend to focussed around an area where natural resource exploitation is possible, close to a source of freshwater, and a food source such as a forest or coastline. Development of agriculture also takes place in areas adjacent to and surrounding the village.
As population grows, by reproduction and/or immigration, towns develop. Towns tend to have houses closer together and greater degrees of centralisation. Services develop, which reduce the need for location at a water source. Centralised shopping develops, reducing the reliance on in-situ food production. The functions of the system are controlled by the development of administrative centres, community meeting areas, hospitals and schools, within the framework of the town.
Eventually a town grows to the stage where it becomes a city. Cities are more urbanised, and tend to be more extensively zoned into specific commercial, administrative, residential, recreational and other areas. Water and food are usually "imported" into the urban systems from locations remote to the city.
The specific boundaries of cities are designated, formalising the "management unit" of the urban administration. This places limits in the short-term, on urban growth; however, "edge-effects" tend to occur at the boundaries. Residential areas often develop on the fringes, just outside the city limits. The residential areas often develop their own centralised facilities, mainly shopping areas. As such, further urbanization occurs on the fringes of the cities, eventually becoming encompassed by the city administration. This allows a dynamic growth, restricted by physical barriers (such as mountains) or existing land use designations (which can be changed).
Ecological Character
The "ecological character" of an urban system refers to the processes, functions, components and interactions of the city or town. As such, it must take into account the resident population and habitations, the administrative and commercial functions, communication systems, transportation, green spaces and city fauna, pets and adapted species (e.g., rats, cockroaches and mosquitos). There are also, a number of humans not directly or permanently associated with the urban system (commuters), who make use of the urban ecosystem (e.g., for employment or accessing services), but return to other systems for habitation, such as other towns, villages or residential developments (satellite cities).
A city is not a self-contained, closed-cycle system. There are inputs to the system, including energy, materials, food and water. The functions, processes and living components, also result in waste product output, including sewage, solid waste and some hazardous materials (oils, solvents, etc.). This leads to problems of disposal, and requires additional infrastructure, such as sewage treatment plants, landfills and hazardous waste sites, frequently outside of the city (there is usually little recycling in cities). In the case of a rural village, the natural resources and surrounding ecosystems are part of the ecological character of the village; however, in the case of a city, these are supplied from a remote location, and as such, are not direct components of the system, but are inputs. Food is imported into the city, and hence urban systems have fragile trophic relations.
The development of infrastructure associated with cities has environmental implications. Roads and sidewalks are paved, reducing the permeability of the city surface. This leads to an increase in run-off of storm water. The stormwater contains large amounts of nutrients and sediments. Drainage systems such as streams are often also paved, and no longer have riparian vegetation. The drainage canals and streams can no longer deal as efficiently with nutrified water, as the diversity of biota is decreased, and eutrophication tends to take place. Fish and other stream biota can no longer be supported by the deoxygenated water, exacerbating the problem. Water quality deteriorates affecting surrounding natural and agricultural ecosystems, which provide food and services to the city.
Cities are characterized by heavy subsidies of energy. The evolution of human habitation is accompanied by progressively moving from subsidised solar-powered systems to almost 100% artificially-powered systems. Cities are powered by hydrocarbons, coal and internal combustion engines, all of which have environmental impacts. The removal of natural vegetation also affects surface albedo, with the paved surfaces reflecting more solar radiation, increasing local-area temperatures (within the city). Other sources of urban heat are power plants, machinery, vehicles and large concrete buildings (urban heat islands). Cars and other vehicles, as well as light industries tend to have atmospheric impacts. The emissions can often affect areas outside of the city boundaries.
The large numbers of humans in close proximity to each other also has implications for the spread of diseases. The structure of urban ecosystems also encourages the colonisation and adaptation of rats, cockroaches and mosquitos, which have food, shelter and few natural predators in the city. These species are frequently disease vectors.
Urban environments also include "green spaces", such as urban parks, receation grounds, campuses and cemeteries. These are more closely related to natural environments, and although the integrity of the park ecosystems may be limited, they can provide habitats for birds, insects, reptiles and a variety of plants. Urban parks are important in the overall characteristics of urban ecosystems.
Urban Sustainability
The development of cities, as man-made ecosystems, present problems in the sustainability of their functions and component support, primarily as a result of the heavy subsidies required by their processes. This often leads to urban decline - increases in pollution, immigration from surrounding areas (including those impoverished by the city), unregulated / spontaneous settlements (squatting) on the city periphery, unemployment (as there are limits to the number of individuals that a city's processes and fucntions can support), increased crime, social decay, and further stresses on the natural resources of surrounding areas.
The goals of urban ecosystem management should include mechanisms to deal with, or mitigate such problems. As in any system, sustainability is the factor of fundamental importance, it is important that the infrastructure of a city can adapt to the dynamic character of urban systems. Some degree of ecological modelling is required, of the organization, structure, individual and group behaviour, and studies of the dynamics of populations and communities, in the context of the circumstances which led to a city developing at its particular location. Some solutions to urban sustainability in the long and short term include:
- Planting of trees throughout urbanised areas; expanding and/or intensifying "green space" ecosystems;
- Recycling of municipal waste water, and other waste materials (plastic, glass, metals, etc.), therby reducing the need for inputs and outputs to the system (more "natural" ecosystem);
- The use of "cleaner" technologies, and increasing the utilisation of solar energy, i.e., reducing the need for energy subsidies and inputs;
- Comprehensive management strategies, including limits to growth. Inclusion of "source" areas (for food and water) and "sink" areas (waste disposal) in the overall management plan, as they represent the urban "forcing functions";
- Analysis of patterns in urban ecosystem processes and functions, to monitor adverse changes, and ensure the continued viability of the human components and related systems.
Related Articles:
http://tropicalenv.conforums.com/index.cgi?board=manmade05&action=display&num=1215920280
0 comments:
Post a Comment