332 ■ CHAPTER 18 General Principles of EcologyECOLOGY
A
n action or process is sustainable if it can be continued
indefinitely without causing serious damage to the
environment. The current human impact on the biosphere is
not sustainable.
Each of us can help build a more sustainable society.
We can advocate legislation that fosters less destructive
and more efficient use of natural resources, patronize
businesses that take measures to lessen their negative
impact on the planet, support sustainable agriculture, and
modify our own lifestyles. For example, we can increase our
use of renewable energy and energy-efficient appliances;
reduce all unnecessary use of fossil fuels (for instance, by
biking to work or using public transportation); buy seafood
from sustainable fisheries; use “green” building materials;
and reduce, reuse, and recycle waste. Experts estimate
that more than 200 million women around the world wish to
limit their family size but have no access to family planning.
Those of us who live in developed countries can support
aid efforts that provide education, health care, and family-
planning services in developing countries.
One measure of sustainability is an ecological footprint,
which is the area of biologically productive land and water
that an individual or a population requires to produce
the resources it consumes and to absorb the waste it
produces. Scientists compute an ecological footprint using
standardized mathematical procedures and express it in
global hectares (gha). One gha is equivalent to one hectare
(2.47 acres) of biologically productive space. Approximately
one-fourth of Earth’s surface is considered biologically
productive; this definition excludes areas such as glaciers,
deserts, and the open ocean.
According to recent estimates, the ecological footprint
of the average person in the world is 2.7 gha, which is about
60 percent higher than the 1.7 gha that would be needed to
support each of the world’s 7.4 billion people in a sustainable
manner. An ecological footprint can also be expressed in
Earth equivalents, the number of planet Earths needed to
provide the resources we use and absorb the wastes we
produce. Currently, the global population uses 1.6 Earth
equivalents each year (as shown at the bottom of the figure
on the facing page).Overall, such estimates suggest that, since the late 1970s,
people have been using resources faster than they can be
replenished—a pattern of resource use that, by definition, is
not sustainable. As the world population grows, the amount of
biologically productive land available per person continues to
decline, increasing the speed at which Earth’s resources are
consumed.
The per capita consumption of Earth’s resources by
different countries is most directly related to energy
demand, affluence, and a technology-driven lifestyle. As
people in populous countries such as China and India
become wealthier, their ecological footprints are growing
rapidly.
What is your ecological footprint? If you are a typical
American college student, your footprint is probably close to
the U.S. average of 8.2 gha. It would take nearly five planet
Earths to support the human population if everyone on Earth
enjoyed the same lifestyle that you do (see the top row of the
accompanying figure). Your ecological footprint depends on
four main types of resource use:- Carbon footprint, or energy use
- Food footprint, or the land and energy and water it takes to
grow what you eat and drink - Built-up land footprint, which includes the building
infrastructure (from schools to malls) that supports your
lifestyle - Goods-and-services footprint, which includes your use of
everything from home appliances to paper products
If you drive a gas guzzler, live in a large suburban house,
routinely eat higher up on the food chain (more beef than
grains or veggies/fruits), and do not recycle much, your
footprint is likely to be higher than that of a person who uses
public transportation, shares an apartment, eats mostly plant-
based foods, and sends relatively little to the local landfill.
Most of us can significantly reduce our ecological footprint
with little reduction in our quality of life, while bestowing an
outsized benefit on our planet.How Big Is Your Ecological Footprint?
grassier savanna-like ecosystem (Figure 18.11).
“This could be the trigger for changing forest
to savanna,” says Balch. “The message is that
repeated disturbances, such as multiple fires or
drought and fire, cause forest to reach its tipping
point, to shift into grassland.”While Balch and her team observed changes
in plants after fire, ecologist Michael Coe inves-
tigated how fire affects its nemesis: water. “The
forest is an incredibly important part of the hydro-
logic cycle,” the circulation of water from the land
to the sky and back again, says Coe (Figure 18.12).