Part I — Introduction to Urban Greening

This section introduces the ideas of the urban environment. This should provide a community group with a theoretical background to view the city and understand how the city affects both the local and global environment.

Table of Contents

 


Background  top of page

Some time in mid 1999 the United Nations made the observation that over 50% of the human population now lives in cities. In a matter of 200 years people of all races and backgrounds, representing all cultures on the planet had made the most massive migration in our history. The world is still reeling from this shock.

Our impact as an urban species is enormous. For the first time most of us rely of food that must be shipped from distant and remote places. We are dependent on polluting and scarce fossil fuels to bring us this food.

The change from country to city has come with such staggering speed that the earth has not had time to adapt to the demands that six billion people place on it. Traditionally even the most nomadic of people would only travel a few hundred of kilometers in a year to survive. Today the average molecule of food travels 3100km km to reach the mouth of the American consumer.

In short, 200 years ago humankind embarked on an experiment into the unknown. Without ever asking the question directly, we are testing whether we can replace nature's systems that emerged over the last earth five billion years with human ingenuity and technology.

So far we have much to boast of. There is also a lot to be alarmed by. On the positive side people live longer healthier lives today than they ever did in the past. Similarly, much of the world's population is literate, infant mortality and malnutrition are at an all-time low and for the last fifty years many countries have made serious steps to addressing the rights of women and minorities.

On the other side of the coin is the fact that we are living in a world where an unprecedented amount of wealth is concentrated in the hands of a small number of people. We live in a world where human technology has shifted the climate to such an extent that weather patters are changing unpredictably. We live in a world where tens of millions live in urban slums without the most basic of needs.

We live in a world where much has been accomplished yet much needs to be fixed.

Urbanization  top of page

Without a doubt, the most striking part of the modern world are the cities. Although humans still look the same today as our ancestors our lives are fundamentally different. Very few of us now must engage in producing or gathering food. Most of us use some form of money to acquire the things that we need to survive. Traditional communities and ways of life have broken down, and many of us live, paradoxically, in relative isolation being surrounded by complete strangers.

Urbanization and the Environment
One of the key differences between an urban world and a more traditional way of life is the distance which materials must travel to move from their source to the place where they are used. Food, fuel and building materials all must be imported to cities. In this way the modern urban development takes environmental resources away from remote areas. As a result the impact of the city is felt across the entire globe.

Some academics have described this by saying that the "urban ecosystem" has broken the "nutrient cycles" of "natural ecosystems." Other scholars have said that the city has an "ecological footprint" that is much larger than the actual space that a city takes up.

No matter what way you choose to describe this process, the city represents a very different type of system than the one that emerged in nature where resources usually travel a small distance, and at a slow rate before, being re-incorporated into the ecosystem. For example: when a tree dies, it decomposes, releasing nutrients. Depending on the mineral, these nutrients enter the ecosystem through the soil or into the atmosphere, and often are used very quickly by other living things. This is especially true in the tropics where hot humid temperatures provide ideal conditions for decomposition, and the year round growing season creates a continual demand for nutrients. The city, on the other hand, imports huge quantities of nutrients and stores them for a limited amount of time. The refuse instead of being recycled accumulates, usually in the form of landfill or excessive carbon in the atmosphere, and becomes a major problem.

The urban form, therefore, is inherently un-ecological and puts natural systems around the globe at risk.

Urbanizaton and the Developing World
One of the remarkable facts about our migrations from country to city is where this has occurred. At the turn of the last century almost all the largest cities were in the (so-called) developed world. Today most of the earth's mega-cities are in poor countries. This creates two problems: one social and one environmental.

First, the poorer countries have fewer resources to invest in services like sanitation, water, electricity, or housing. In Bangkok alone it is estimated that one third of all homes do not have water and most sewage ends up untreated in the canals that crisscross the city

Second, most of the world's poor countries are found in the tropics, an ecologically fragile area where most of the earth's species reside. When environmental damage occurs in these areas, the cost is extremely high.

In is into these delicate ecosystems that the urban population has exploded. Hundreds of millions have poured into places like New Deli, Mexico City, San Paulo, Bangkok, and Nairobi, creating human and environmental problems of epic proportions.

The modern city acts as a magnet, offering people opportunities. In some cases these opportunities are real, while in others, they prove to be an illusion. Whether or not the people are able to fulfill their dreams the city has taken its toll on the environment. The air is toxic, the water unfit to drink, wildlife habitat has been destroyed and people live in inhuman conditions — all in search of a better life than the ones that they had grown up in.

In many situation people end up moving from very poor rural environments to very poor urban environments.


Urban Environmental Management  top of page

To correct some of problems associated with the city it is useful to view it as an ecosystem. For example ecosystems recycle nutrients. Robust ecosystems also have high amounts of biological diversity, as this makes them flexible to changing circumstances. These two important characteristics are largely absent from today's metropolises.

When an urban area is managed like an ecosystem it is possible not only to address environmental problems but also improve the quality of life. In this way urban environmental management is a way of addressing social, environmental, health and economic problems in the city.

The key is to use grassroots community planning to conduct small-scale urban greening programs. By harnessing the energy of local communities, it is possible to create biologically rich green areas that also provide an economic return, foster community cohesion, and address public health issues.

Urban greening is a general term for any sort of planting in or around a city. It can refer from everything from an individual who grows vegetables or flowers in a barrel on their balcony, to much larger community forest projects.



Some Basic Ecological Concepts  top of page

It is important to introduce some basic ecological concepts to guide the process of urban greening. When a community plans their urban green plan it is important to keep the following three ideas at the center of any plan.

Nutrient Cycling
Very simply almost all of earth’s living systems originate from the sun. The sun’s energy is turned into fiber by the plant community. In the process oxygen is released. This oxygen and the plant matter itself forms the building blocks on which the fish, animal and insect world is built. When these “higher” organisms die they emit carbon and return nutrients to the soil. The plant community then uses this carbon and nutrients and combines it with sunlight to grow. Most ecosystems evolved along these lines. It is only in the last two hundred and fifty years that human systems, specifically our industrial urban lives, have broken these systems. As a result carbon dioxide levels are much higher in the atmosphere, there are problems with nutrient depletion in parts of the earth where our food is produced, and we have major waste problems in our cities. In an urban greening programme, composting, recycling, and vegetable gardens can help restore the nutrient cycle that the city has broken.

Biological Diversity
Ecosystems that have evolved over the earth’s history have been forced to adapt to change. These changes could have come in many forms from climate variation, to species migration, to extreme weather conditions. Not all organisms are suited to all of these variables. As a result ecosystems that have a large number of different organisms are better able to adapt to change than those that are only made up of a few types of living beings. For example, the native North American prairie is made up of some grasses that are able to withstand dry conditions but do not thrive in wet conditions, as well as species that flourish with high moisture. In dry years the drought-tolerant species are better able to grow, while in years where there is a lot of rain, the other species do better. At any time, however, there are always a few individuals from each type of plant that survive. In this way the prairie ecosystem has adapted to changing rainfall conditions. Similarly, most plant pests and diseases will only affect a small number of species. An ecosystem with a diversity of species will be able to with stand pest outbreaks. In an urban greening programme planting a diversity of species that will thrive in different conditions can help ensure that no one pest will destroy an entire urban green space.

Local Species
Over the earth’s history ecosystems have evolved around communities of plants and animals. Each of these plants and animals has specific characteristics that ensure that it can survive in a given area. In the modern age, however, it is possible to introduce species from all over the world into an area. Sometimes introduced species have no natural predators and are able to out compete local species driving the local species into extinction. In North America, for example, a species of plant was introduced into people’s gardens because of its pretty flower. This species has now invaded wetlands around the province of Ontario, causing a huge ecological problem. Good urban green space planning, therefore, will focus on only planting local species that are adapted to the immediate environment.


The Benefits of Urban Greening  top of page

The very presence of plants in a city improves the environment. For example, all plants transpire water just like air conditioners and absorb atmospheric carbon, which is one of the most serious of atmospheric pollutants in modern cities. Plants also improve the atmosphere by reducing smog. When plants transpire water they reduce the temperature. Smog is largely made up of ground-level ozone that is created by a reaction between carbon dioxide and sunlight. This is why on hot sunny days there is a lot of smog. By blocking sunlight and reducing the temperature, plants reduce smog production.

Properly targeted, urban green can provide a huge range of benefits other than the ones cited above.

From an economic perspective, urban greening can provide a source of raw materials for small-scale commerce. In various parts of the world, people have planted bamboo, reeds or willow to prevent soil erosion along river banks. Once mature these shrubs then become the raw materials for local handicrafts. Similarly, the produce from urban gardens can be used for sale. In poor urbanareas where purchasing food makes up a large part of a house-hold's income urban agriculture has proven to be an effective way of reducing poverty. Also, by creating shaded cool, areas urban green space can also provide natural market places for vendors and customers seeking to escape from the heat.

Urban green space can also be an effective tool to improve people's health. A major health problem in urban areas is atmospheric pollution that is causing epidemic levels of respiratory problems amongst children in both the developed and the developing world. The leaf canopy from trees and plants is an effective filter that traps particulate matter.

Another major health problem in cities in the developing world is caused by flooding and the accumulation of stagnant water. Flooding causes sewer systems to overflow, bringing bacteria-rich refuse to the surface. Stagnant water provides a breeding grounds for malaria and dengue fever carrying mosquitoes. Flooding and stagnant water can both be reduced by establishing well drained green areas, where water is able to infiltrate the soil, and reach the water table without causing run-off or ponding.

One issue that is inevitably raised is the potential that green space has to attract crime. Generally it is feared that a park will attract criminal activity for two reasons. First, parks may become deserted at night, and provide a secluded venue for crime. Second, if green space is public, people from outside the immediate community may be drawn to an area, and bring with them undesirable elements.

In some situations, where a municipal government has created a park without the community's involvement green spaces have indeed become havens for drug deals and other such activities. On the other hand, if the community has been involved in the planning and implementation of green space, there is an increased community presence in the area. Especially if green space develops land that has been un-utilized crime may actually decrease, as a community takes ownership of an area.


 photograph copyright Karl Lenmann


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