158 CHAPTER 7 Climate and Terrestrial Biodiversity
7-3 How Have We Affected the World’s Terrestrial
Ecosystems?
CONCEPT 7-3 In many areas, human activities are impairing ecological and
economic services provided by the earth’s deserts, grasslands, forests, and
mountains.▲
Humans Have Disturbed
Most of the Earth’s Land
The human species dominates most of the planet. In
many areas, human activities are impairing some of
the ecological and economic services provided by the
world’s deserts, grasslands, forests, and mountains
(Concept 7-3).According to the 2005 Millennium Ecosystem
Assessment, about 62% of the world’s major terrestrial
ecosystems are being degraded or used unsustainably
(see Figure 3, pp. S24–S25, and Figure 7, pp. S28–S29,
in Supplement 4), as the human ecological footprint
intensifies and spreads across the globe (Figure 1-10,
p. 15, and Concept 1-3, p. 12). This environ-
mental destruction and degradation is increas-Deserts Grasslands Forests MountainsNATURAL CAPITAL
DEGRADATION
Conversion to
croplandRelease of CO 2 to
atmosphere from
burning grasslandOvergrazing by
livestockOil production and
off-road vehicles in
arctic tundraClearing for agriculture,
livestock grazing, timber,
and urban developmentConversion of diverse
forests to tree plantationsDamage from off-road
vehiclesPollution of forest streamsAgricultureTimber extractionMineral extractionHydroelectric dams and reservoirsIncreasing tourismUrban air pollutionIncreased ultraviolet radiation from ozone
depletionSoil damage from off-road vehiclesLarge desert citiesSoil destruction by off-road
vehiclesSoil salinization from
irrigationDepletion of groundwaterLand disturbance and
pollution from mineral
extractionMajor Human Impacts on Terrestrial Ecosystems
Figure 7-20
Major human
impacts on the
world’s deserts,
grasslands, for-
ests, and moun-
tains. Question:
Which two of
the impacts on
each of these
biomes do you
think are the
most harmful?