From Rainforests to Ice Caps: The Geography of Climates - Geography - page 161

of Russian origin) dominates the natural vegetation. Indeed, for the most part these forests are intact
because the same chilly climes that discourage deciduous tree-growth also preclude agriculture. As a
result, thebroadbelt ofsubarctic climate that extends all acrossthenortherly portionsofNorthAmer-
ica and Eurasia represents the largest expanse of forest on Earth. Generally, however, these forests are
well removed from markets and mills and are therefore relatively untapped. On the whole, the subarc-
tic realm is lightly populated. Mining is locally important and accounts for most towns' economies.
Vertical zonation and “highlands climate”
Vertical zonation refers to the changes in climatic conditions and their associated veget-
ation that are observed between the base of a high mountain and its summit. To take
an example from East Africa, the base of Mount Kilamanjaro lies in tropical savanna cli-
mate. Its summit, however, which is 19,430 feet above sea level, is covered partly by
snow and ice. For all intents and purposes, therefore, a hike from the base to the summit
is tantamount to traveling from the tropics to the poles, experiencing enroute climate and
vegetation change that would normally require a journey of several thousand miles. On
some world climate maps, mountain ranges are shown as having highlands climate. This
refers to the presence of the multiple climates of vertical zonation, instead of a singular
climate type that is unique to mountains.
Dropping Below Freezing: Polar Climates
Cold temperatures are the dominant characteristic of polar climates. The average temperature
of the warmest month is less than 50° F, and most months typically average below freezing.
The very small doses of solar energy that occur at these polar latitudes, despite the long day-
light hours of summer, explain the frigidity. The resulting natural vegetation (if any) consists
of short grasses, mosses, lichens, and an occasional stunted tree or shrub. The two climates
that make up the geography of polar climates (see Figure 10-6) are tundra and ice cap.