Biology Reference
In-Depth Information
8.4 and 4.2 Ma (Ickert-Bond and Wojciechowski 2004). Explanations for
such disjunct distributions include long-distance dispersal and migration
along a former connecting corridor. There is little paleobotanical evidence
for a continuous or near-continuous arid corridor between the northern
deserts and the Monte, and the most parsimonious explanation for many of
the plants is long-distance dispersal by birds such as sparrows and plovers.
The latter move annually between North and South America in an enor-
mous migratory loop 2000 miles across and 8000 miles long.
The Gran Chaco, or “the green hell,” is a plain at a slightly lower el-
evation that covers 1 million km 2 between the Andes Mountains and the
Paraguay-Paraná rivers north to the Mato Grosso Plateau of Brazil, 17°S to
33°S (see, e.g., Oxford Atlas of the World , 150, or NASA's Earth Observatory
site). It is a dry shrubland/chaparral-woodland-savanna with commercially
valuable stands of Schinopsis balansae (breakaxe, or quebracho), one of the
hardest woods known, used for railroad ties, fence posts, and construction
timbers. Annual rainfall is lowest in the southwest (350 mm), and there is a
hot, tick-infested dry season lasting six months from April to September.
The pampas is a slightly more moist plain to the southeast, situated be-
tween 30°S and 40°S (e.g., from Córdoba to Buenos Aires) and covering
650,000 km 2 . It is bordered on the north by the Gran Chaco and on the
south by Patagonia. Pampas is a Quechua word for fl at, and it is a grassland,
supporting one of the world's leading cattle-producing regions and tended
by the picturesque gauchos. MAP is about 508 mm along the driest western
margin. The cool and dusty southwesterly summer wind meets warm air
from the north to produce the gales and rain storms called pamperos that
characterize the pampas.
The Cerrados and Caatingas
The cerrado—the Portuguese word means “closed”—is a savanna with
transitions to (1) low to medium dry shrubland or dense woodland that
is nearly impenetrable, and (2) to a more open community approaching
grassland (fi gs. 2.49 and 2.50). The MAT is 20°C-26°C, MAP is from 750
to 2000 mm, and the average elevation is 500-600 m. It is centered in
Brazil bordering the Amazon Basin and covers about 2 million km 2 , or
22 percent of the country. The cerrado is a diverse plant formation with
some 10,000 plant species, of which 4400 are endemic and represent about
1.5 percent of the Earth's vascular fl ora (Sano et al. 2008). One kind of cer-
rado, found on rocky substrate, is called the campo rupestre. Among the
notable features of this vegetation are the candelabra-like branching, cruci-
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