Chapter 28: Urban Environments

City Life

• In the past, the emphasis of environmental action has most often been natural landscapes outside cities.

• Now it is time to turn more of our attention to city environments.– Cities were thought of as polluted, dirty, lacking in

wildlife and native plants, and artificial.

– Majority of people live in cities and have suffered directly from their decline.

City Life

• The NSF has added two urban areas, Baltimore and Phoenix, to its Long-Term Ecological Research Program– Program that supports long-term monitoring of,

as well as research on, specific ecosystems and regions.

City Life

• Today approximately 45% of the world’s population live in cities.– Economic development leads to urbanization;

• 75% of people in developed countries live in cities

• But only 38% of people in the poorest developing countries are city dwellers

City Life

• Megacities– Huge metropolitan areas with more than 8 million

residents

– In 1950, the world had only two: New York City and nearby urban New Jersey (12.2 million residents altogether) and greater London (12.4 million).

– By 1975, Mexico City, Los Angeles, Tokyo, Shanghai, and São Paulo, Brazil, had joined this list.

– By 2002, 30 urban areas on the list.

The City as a System

• Must maintain a flow of energy, provide necessary material resources, and have ways of removing wastes.

• City ecosystem maintained by transportation and communication with outlying areas.– Not a self-contained ecosystem– Takes in raw materials: food, water, wood, energy,

mineral ores.– Produces and exports material goods and ideas,

innovations, inventions, and art.– Cannot exist without a countryside to support it

The City as a System

• The average city resident produces large amounts of waste each year.– If exported w/o care, they pollute the

countryside, reducing its ability to provide necessary resources for the city.

• With such dependencies and interactions between city and surroundings, relationships between people in cities and countryside have often been strained.

The City as a System

• Ways must be found to – Make urban life healthy and pleasant

– Keep the cities from polluting the very environment that their dense human population in theory frees for other uses.

• City planning has a long history– Defense and beauty

– Connecting cities in environmentally and aesthetically pleasing ways with surrounding mountains or water.

Site and Situation: The Location of Cities

• Cities are not located at random but develop mainly because of local conditions and regional benefits. – They grow up at crucial transportation locations

(situation).– Can be readily defended, with good building

locations, water supplies, and access to resources (site).

– Primary exceptions are for political reasons.

Site and Situation: The Location of Cities

• A good site includes – A substrate suitable for buildings– Nearby supplies of drinkable water– Nearby lands suitable for agriculture and forest– Easier to build a city where climate benign

• An excellent and important situation can compensate for a poor site– I.e. New Orleans

New Orleans - Poor site, important situation

New York City - Good site and situation

Site and Situation: The Location of Cities

• Environmental situation strongly affects the development and importance of a city.– Before railroads, automobiles, and airplanes,

cities depended on water for transportation. – Most early cities were located on or near

waterways.• major ocean harbors or at the fall line on major

rivers

Site Modification

• Site is provided by the environment, but technology and environmental change can alter a site for better or worse.

• Changes in a site over time can have adverse effects on a city.– E.g. Bruges, Belgium

City Planning and the Environment

• A danger in city planning is the tendency to transform a city center from natural to artificial features.– To replace grass and soil with pavement,

gravel, houses, and commercial buildings.

City Planning for Defense and Beauty

• City planning– Formal, conscious planning for new cities.– Two dominant themes have been defense

(fortress cities) and beauty (park cities).

The City Park

• Parks have become more and more important in cities.

• A significant advance for US cities was the 19th –century planning and construction of Central Park in New York City,– The first large public park in the US.– Designed by Olmsted– Example of “design w/ nature”

The City Park

• Olmstead also worked on projects in Boston– The result of his vision was a control of water

that was also an aesthetic addition to the city.– Blending of goals made the development a

landmark in city planning.

The City Park

• An extension of the park idea was the garden city.– City and countryside should be planned

together.– Surrounded by a greenbelt.

• The idea was to locate garden cities in a set connected by greenbelts, forming a system of countryside and urban landscapes.

The City as an Environment

• A city changes the landscape, and because it does, it also changes the relationship between biological and physical aspects of the environment.

• Many of these changes were discussed in earlier chapters as aspects of pollution, water management, or climate.

The Energy Budget of a City

• The city exchanges energy with its environment in the following ways: – (1) absorption and reflection of solar energy– (2) evaporation of water– (3) conduction of air– (4) winds (air convection) – (5) transport of fuels into the city and burning of fuels

by people within the city – (6) convection of water (subsurface and surface stream

flow)

The Urban Atmosphere and Climate

• Cities affect the local climate; as the city changes, so does its climate.

• Generally less windy than nonurban areas because buildings obstruct the flow of air. – But buildings also channel the wind

• Receives less sunlight than the countryside– Because of the particulates in the atmosphere

over cities.

The Urban Atmosphere and Climate

• In spite of the reduced sunlight, cities are warmer than surrounding areas.

• Form heat islands for two reasons: – Increased heat from the burning of fossil fuels

and other industrial and residential activities. – Lower rate of heat loss, partly because

buildings and paving materials act as solar collectors

Solar Energy in Cities

• Passive solar energy– Used in Greece, Rome and China to heat

household.– Overlooked in America and Europe because of

cheap fossil fuels.– Importance beginning to be appreciated again.

• Photovoltaic devices now seen in many cities.

Water in the Urban Environment

• Paved city streets and city buildings prevent water infiltration, most rain runs off into storm sewers.

• Water in the soil also prevented from evaporating to the atmosphere.– A process that cools natural ecosystems;

– Adds to heat island effect.

• Chances of flooding increase both within the city and downstream.

New, ecological methods of managing storm water can alleviate problems.

Water in the Urban Environment

• Most cities have a single underground sewage system.– During times of no rain or light rain, this

system handles only sewage. – During periods of heavy rain, the runoff is

mixed with the sewage and can exceed the capacity of sewage-treatment plants.

– Causes sewage to be emitted downstream without sufficient treatment.

Soils in the City

• A modern city has a great impact on soils.• Soils are no longer replenished by vegetation

– Lose organic matter, and soil organisms die from lack of food and oxygen.

– The process of construction and the weight of the buildings compact the soil, which restricts water flow.

• City soils, are more likely to be compacted, waterlogged, impervious to water flow, and lacking in organic matter.

Soils in the City

• A kind of soil important in modern cities is the soil that occurs on made lands, – Lands created from fill.– Fill material is unconsolidated and not well

suited for building foundations.– Vulnerable to earthquakes

Pollution in the City

• In a city, everything is concentrated, including pollutants. – City dwellers are exposed to more

• toxic chemicals in higher concentrations

• and to more human-produced noise, heat, and particulates

– Lives are shortened by an average of one to two years in the most polluted cities in the US.

Pollution in the City

• Sources of urban pollution– Motor vehicles, stationary power sources, home

heating and industry.– The primary sources of particulate air pollution

are older, coal-burning power plants, industrial boilers, and gas- and diesel-powered vehicles.

Bringing Nature to the City

• A practical problem for planners and managers of cities is how to bring nature to the city.

• Evolved into several specialized professions, including:– Urban forestry, landscape architecture, city

planning, and civil engineering specializing in urban development.

Cities and Their Rivers

• Traditionally, rivers have been valued for transportation and waste disposal rather than their ability to make city life more pleasant or to help in the conservation of nature. – Rivers have been viewed as places to dump

wastes.

• View changing w/ projects like Hudson River Park in NYC.

Vegetation in Cities

• Plants fill different needs in different locations.– Trees provide shade.– In parks, vegetation provides places for quiet

contemplation.– Trees and shrubs can block noise, and their complex

shapes and structures create a sense of solitude. – Plants also provide habitats for wildlife, such as birds

and squirrels.

• Paris and London among the first cities to plant trees along streets.

Vegetation in Cities

• Trees are increasingly used to soften the effects of climate near houses. – Rows of conifers planted to the north of a house

can protect it from winter winds. – Deciduous trees to the south can provide shade

in the summer, yet allowing sunlight to warm the house in the winter.

Vegetation in Cities

• Vegetation in cities must be able to withstand stress.– Root systems lack access to water and air and are more

likely to suffer from extremes.

– Some species sensitive to air pollution (ozone).

– Dust interferes w/ gas exchange.

– Subject to physical damage.

• Lifetime of city trees usually short that rural counterparts.

Vegetation in Cities

• Cities have many recently disturbed areas,– Abandoned lots and corridors between lanes in

boulevards and highways.

• Wild plants that do particularly well in cities are those characteristic of disturbed areas and of early stages in ecological succession.

Wildlife in Cities

• We can divide city wildlife into the following categories:– (1) those species that cannot persist in an urban

environment and disappear– (2) those that tolerate an urban environment but do

better elsewhere– (3) those that have adapted to urban environments, are

abundant there, and are either neutral or beneficial to human beings

– (4) those that are so successful they become pests

Urban “Wilds”

• Cities provide homes for many forms of wildlife.– E.g., Cooper’s hawks in Tucson

• Population is increasing

Urban “Wilds”

• Cities can provide all the needs, physical structures and necessary resources, for many plants and animals. – We can also identify ecological food chains in cities

• For some species, cities’ artificial structures are sufficiently like their original habitat to be home. – E.g., Chimney swifts

• Cities can be home to rare or endangered species– E.g. Peregrine falcons

Urban “Wilds”

• City environments can contribute to conservation of wildlife in a number of ways. – Urban kitchen gardens can be designed to

provide habitats for endangered hummingbirds. – Rivers and their riparian zones, ocean

shorelines, and wooded parks can provide habitat for endangered species and ecosystems.

– Urban drainage structures can be designed as wildlife habitat.

Animal Pests

• Most common city pests are cockroaches, fleas, termites, rats, and pigeons.

• Pests compete with people for food and spread diseases. – Before modern sanitation and medicine, such

diseases played a major role in limiting human population density in cities.

– Bubonic plague spread by fleas found on mice and rats in cities caused the Black Death.

Animal Pests

• An animal is a pest to people when it is in an undesired place at an undesirable time doing an unwanted thing.

• Animals that survive best in cities have certain characteristics in common. – Generalists in their food choice– High reproductive rate – Short average lifetime

Controlling Pests

• We can best control pests by recognizing how they fit their natural ecosystem and identifying their natural controlling factors.

• Often assumed that the only way to control animal pests is with poisons.– Early poisons generally toxic to people and pets – Another problem is that reliance on one toxic

compound can cause a species to develop resistance, which can lead to rebound.

Controlling Pests

• One of the keys to controlling pests is to eliminate their habitats. – For example, the best way to control rats is to

reduce the amount of open garbage and eliminate areas to hide and nest.