Geoscience Reference
In-Depth Information
Extensive midlatitude grasslands occur in South Africa,
eastern Europe, central Asia, and central North America (see
Figure 10.6). In South America, grasslands are known as the
Pampas
(Figure 10.15a), whereas in North America they are
most closely associated with the
Great Plains
(Figure 10.15b).
In Russia, grasslands are referred to as the
steppe
. Although it
may not look like it, the biomass in these areas is quite high, with
a nearly continuous cover (except in the drier places) of grass
and flowering plants that have an extensive root network. Most
grasses are perennials that lie dormant through the winter and
sprout in spring. This landscape is also adapted to fire, which
usually occurs during the summer dry season. The common re-
currence of fire historically contributed to the lack of trees and
woody shrubs in this region, as did grazing by large animals such
as bison (also known as “buffalo”) in the Great Plains. Given that
fire is suppressed by humans in many grasslands today, forest
vegetation is actually expanding into the fringe of these areas.
Desert Biomes
Desert biomes occur in areas where average annual precipita-
tion is less than 25 cm (10 in.) and cover about one-fifth of
Earth's land area. Although deserts most commonly occur in
low latitudes, they also appear in colder regions such as in
Nevada and Utah in the western United States and in portions of
western Asia. Two major subdivisions within the desert biome
are recognized: (1) the hot and dry desert biome, and (2) the
semi-arid and cold desert biome.
Hot and Dry Desert Biome
The hot and dry desert biome
occurs in the subtropical regions and is centered on 30° latitude
(see Figure 10.6). Major deserts of this kind include the Sahara
in northern Africa, the Kalahari Desert in southern Africa, and
the Mojave and Sonoran Deserts in the southwestern United
States. Another large area of hot and dry desert occurs in central
Australia. These areas are associated with the hot low-latitude
desert climate (
BWh
), which is dominated by the STH Pressure
System. Average annual precipitation can be less than 2 cm
(0.8 in.), and average monthly temperature is greater than 18°C
(64°F). As a result of the combined low rainfall and high tem-
peratures, these areas often experience chronic moisture deficits.
The vegetation in the hot and dry desert consists of bare
ground that grades into
xerophytic plants
, including cacti, low-
growing shrubs, and scattered clusters of grass (Figure 10.16).
(a)
Xerophytic plants
Plants in very dry places that have a num-
ber of survival mechanisms in response to prolonged periods
of drought.
(b)
Figure 10.15 The midlatitude grassland biome.
(a) The
Pampas of Argentina is one of the great grasslands on Earth.
(b) Mixed grass prairie in the central Great Plains. Note the
combination of short and midlevel grasses on this landscape.
Such a mix of grasses occurs because this region lies on the
eastern part of the Rocky Mountain rain shadow, with annual pre-
cipitation of about 63 cm (25 in.). Grasses are taller to the east
and shorter to the west of this area.
Figure 10.16 Example of the hot and dry desert biome.
The
Sonoran Desert in the southwestern United States features tall,
columnar saguaro cactus, as well as a variety of smaller cacti and
hard-leaved shrubs.
