that prevent the warm oil from melting the permafrost and damage from seasonal
heave of the tundra. Currently, the cryosphere is noticeably shrinking.Global
warmingis causing ice caps, glaciers, seasonal and permanent snow, and seasonal
and permanent sea ice to decrease in area. For instance, Arctic Sea ice is decreas-
ing in both area and thickness with the maximum winter extent lessening by more
than 1.5 percent per decade. Similarly, the ice and snow on Earth’s surface modi-
fies temperatures.
Cultivation Regions
Sometimes called agricultural regions, cultivation regions are units of territory
associated with a specific type of agricultural activity. This activity can involve
the actual tilling of the land or can be some type of animal husbandry. Cultivation
regions emerge due to both cultural and environmental factors.
A region ofshifting cultivation, often labeled “slash and burn” agriculture, is
found in tropical and subtropical climates in Latin America, Africa, and Southeast
Asia. Fields are prepared here by killing the natural vegetation and then burning
away the dead material. The ash residue from the burnt vegetation helps to enrich
the tropical soil, which is typically tilled and planted by hand with food crops.
One type of crop is often planted between the rows of another crop, in a system of
intertillage. Once the soil is exhausted farmers “shift” to another location and repeat
the process.
Plantation cultivationis also associated with tropical or subtropical climates.
This system is focused on the production of a single commercial crop, such as cof-
fee, tea, palm oil, cotton, tobacco, or others. Historically, this form of cultivation
relied on abundant, cheap labor, but many modern plantations have incorporated
machinery into the production of their crops. Plantations are usually located close
to road, rail, or water transport, because much of the production is typically grown
for export. Crops may be refined or processed on the plantation before being sent
to markets.
Yet a third cultivation region found primarily in the tropics isrice paddy culti-
vation. This is a labor-intensive style of agriculture, and has been widely mecha-
nized only in areas lying outside the tropics, like Japan and the lower Mississippi
River valley in the United States. In the tropical climates of South and Southeast
Asia, fields are small and prepared using draft animals. Most rice production is
for subsistence in the tropics, and typically two crops are produced in a single year,
a practice calleddouble-cropping.
In many developing areas outside the tropics, a system of subsistence produc-
tion calledpeasant grain, roots, and livestock farmingis found. Also labor
Cultivation Regions 77