Series No. 7
Approach in Environmental Management
Issues Requiring Innovative Sollutions >
D. Cities as Sustainable
Cities are pollution sources and people living in them utilize resources
and generate waste. Due to inadequate systems and poor planning, cities are
disproportionately driving global warming, deforestation, and increasing water
scarcity. The world’s cities take up just two percent of the Earth’s
surface, yet account for roughly 78 percent of the carbon emissions from human
activities, 76 percent of industrial wood use, and 60 percent of the water
tapped for use by people.
Cities import resources and export pollutants, but have limited carrying
capacities. If the carrying capacity of a city is eroded, it becomes increasingly
difficult, if not impossible, to achieve sustainable development goals. For
example, the trucking of garbage to landfills outside of a city becomes increasingly
costly, the further from the city the landfills are located. Also, the importation
of fresh water to replenish a city's depleted aquifers becomes increasingly
costly, the greater the distance the water must be piped. One of the challenges
for the future will be our ability to reform urban systems so that they mimic
the metabolism of nature. Rather than devouring water, food, energy, and processed
goods, and then belching out the remains as pollutants, cities need to align
their consumption with realistic needs, produce more of their own food and
energy, and put much more of their wastes to use.
The concept of “Cities as Sustainable Ecosystems”,
or CASE, provides a framework for examining and understanding the interactions
of urban activity
and the environment and how these can be transformed into a sustainable relationship.
CASE is the multidisciplinary study of urban and economic systems and their
linkages with natural systems. CASE provides a conceptual framework upon which
understanding and reasoned improvement of current practices can be based. One
area where phytotechnologies can contribute to the objective of CASE involves
biodiversity in cities. In preserving biodiversity, cities can exercise two
strategies – they can enhance and reinforce biodiversity throughout their
domain, and they can promote the conservation of threatened species.
The presence of nature within the city can take many forms. Natural systems
tend to persist in the urban setting where strong geological features (i.e.,
rivers and geological contours) and land unsuitable for building exist. The
initial concepts instrumental in guiding the construction of the city are also
important factors, given that the density of buildings and infrastructure leaves
either more or less room for nature. In certain cities, zoning regulations
call for plenty of open space, which is usually developed as green space. There
are typically two types of green space within cities – the natural systems,
in which human intervention has been minimised, and which are composed of a
high proportion of indigenous species; and the cultivated biological areas
deliberately created by humans to embellish the city, usually characterized
by introduced species or horticultural plantings requiring human intervention.
The distinction between these two types of green space is an oversimplification.
In reality, there is considerable overlap between spaces deliberately developed
by humans making use of indigenous species (i.e., the concept of the “natural” garden)
and introduced species adapting to the city and spreading without outside intervention.
This overlap is important as cities continue to evolve in ways that integrate
the natural and built environment. This is an area where phytotechnologies
can play a beneficial role.
The ecology and biodiversity in a city go hand in hand. In natural spaces
comprised of different types of vegetation, a natural urban ecosystem can function
and varied urban wildlife can flourish. Many horticultural species (e.g. conifers
or many-branched shrubs) are often well adapted to the microclimate of the
city, and can provide shelter for urban wildlife. Tall trees, particularly
if planted in belts, can have a positive impact on the local environment and
improve air and water quality. Urban biological diversity also plays an important
educational role in providing opportunities for observing wildlife. It sensitizes
humans to the green spaces and natural systems which balance the “inorganic” reality
of buildings and urban infrastructure.