flowers, also focused toward the North American export market. Latin American
growers supply much of the U.S. floral market during the winter months.
The region known as thetierra friais found approximately from 6,000 feet to
12,000 feet, and represents the highest zone of significant human habitation. Popu-
lation densities here are much lower than in the two lower zones, due to the lack of
large-scale commercial agriculture, as well as the frigid temperatures, encountered
especially at the upper reaches of thefria. Frosts are common in thisregion,and
the growing season is much shorter than at lower elevations. The natural vegetation
at this level consists mostly of hardy evergreens at the lower elevations, and brush,
grasses, and stunted trees at the top of thetierra fria. The growing season at the
lower end of thefriais frequently long enough to allow for the cultivation of wheat
or barley, and highland pastures at this elevation often support sheep, or indigenous
livestock such as llamas or alpacas. In the Andean countries of South America,
indigenous peoples make up a high percentage of the population of thetierra fria.
Lying between 12,000 and 15,000 feet, thetierra heladarepresents a harsh
environment of sparse settlement and restricted activity. This is the highest level
of permanent human occupation, with the majority of villages clustered along
the lower margin of the zone. Few crops can be grown at these extreme elevations,
and animal husbandry is limited almost exclusively to hardy indigenous animals
adapted to the cold temperatures and thin atmosphere, like the llama, alpaca and
vicuna, although sheep can be raised in some locations in the lower part of the
helada. Crops are restricted to those that may be grown underground such as
tubers, or in some instances fast-maturing varieties of grains at the lower end of
the zone. Only subsistence agriculture is found at this elevation, as the climate is
too cold to support any commercial crops.
The highest zone is thetierra nevada, found only in the Andean region of South
America. Located above 15,000 feet, thenevadais an environment dominated by
snow pack and glaciers, and does not support any permanent human settlement.
Agriculture is nonexistent, and even animals adapted to high altitude do not sur-
vive for extended periods in the extreme conditions of thetierra nevada. Although
of no direct economic importance to the countries of South America, thenevada
plays a vital role as a supplier of water to the rivers and streams of the Andean
region, providing a crucial resource to agricultural production down slope.
Anticyclones
First conceived by Sir Francis Galton in the 1860s, anticyclones are, in some
senses, the opposite of cyclones. Where cyclones are associated with the world’s
Anticyclones 13