Page 117 - Environment: The Science Behind the Stories

(a) Desert 300 (a) Tundra 80

Mean monthly temperature (ºC) 40 conditions 80 Mean monthly precipitation (mm) Mean monthly temperature (ºC) –10 0 40 Mean monthly precipitation (mm)
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Time of year (Northern Hemisphere)
Time of year (Northern Hemisphere) 0 –20 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
(b) Cairo, Egypt (b) Vaigach, Russia
Figure 4.25 Deserts are dry year-round, but they are not Figure 4.26 Tundra is a cold, dry biome found near the
always hot. The temperature curve is consistently above the pre- poles. Alpine tundra occurs atop high mountains at lower latitudes.
cipitation curve in this climatograph for Cairo, Egypt, indicating that Climatograph adapted from Breckle, S.W., 2002.
the region experiences “dry” conditions all year. Climatograph adapted
from Breckle, S.W., 2002.
seasonal variation in temperature and day length results from
daytime, but heat is quickly lost at night. As a result, tem- this biome’s high-latitude location, angled toward the sun in
peratures vary greatly from day to night and across seasons summer and away from the sun in winter.
of the year. Desert soils can be quite saline and are sometimes Because of the cold climate, underground soil remains
known as lithosols, or stone soils, for their high mineral and more or less permanently frozen and is called permafrost.
low organic-matter content. During the long, cold winters, surface soil freezes as well.
Desert animals and plants show many adaptations to deal When the weather warms, the soil melts and produces pools
with a harsh climate. Most reptiles and mammals, such as rat- of surface water, forming an ideal habitat for mosquitoes and
tlesnakes and kangaroo mice, are active in the cool of night. other insects. The swarms of insects benefit bird species that
Many Australian desert birds are nomadic, wandering long dis- migrate long distances to breed during the brief but produc-
tances to find areas of recent rainfall and plant growth. Desert tive summer. Caribou also migrate to the tundra to breed, then
plants tend to have thick, leathery leaves to reduce water loss, leave for the winter. Only a few animals, such as polar bears
or green trunks so that the plant can photosynthesize without and musk oxen, can survive year-round here.
leaves, minimizing the surface area prone to water loss. The Most tundra remains intact and relatively unaltered by
spines of cacti and other desert plants guard them from being human occupation and development. However, atmospheric
eaten by herbivores desperate for the precious water these circulation patterns (p. 473) bring our airborne pollutants to
plants hold. Such traits have evolved by convergent evolution this biome, and global climate change is heating high-latitude
in deserts across the world (see Figure 3.3b, p. 69). regions more intensely than other areas (p. 521). Climate
change is melting sea ice, altering seasonal cycles to which
Tundra Nearly as dry as desert, tundra (Figure 4.26) animals have adapted, and melting permafrost, releasing
occurs at very high latitudes in northern Russia, Canada, and methane gas that further worsens climate change.
Scandinavia. Extremely cold winters with little daylight and Tundra also occurs as alpine tundra at the tops of tall
summers with lengthy days characterize this landscape of mountains in temperate and tropical regions, where high ele-
116 lichens and low, scrubby vegetation without trees. The great vation creates conditions similar to those of high latitude.

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