Biology Reference
In-Depth Information
Miocene. There is a broad fl oodplain along the Orinoco River between the
Cordillera de Mérida and the Guiana highlands called the Llanos Orien-
tales. It is a low rolling landscape about 1.1 million km
2
in area with more
than 2300 shallow lakes. Forests grow along the rivers and lake margins,
and Latin America's largest savanna, the Gran Sabana, is located in the ad-
jacent Guiana highlands.
Páramo
Biologists say climate change may already be af ecting high-mountain ecosys-
tems around the world, where plants and animals adapted to cold, barren condi-
tions now face higher temperatures and a surge of predators and competitors.
—KEVIN KRAJICK,
“All Downhill from Here?”
2004
A distinctive plant formation of the Andean highlands is the treeless vegeta-
tion between 3500 m and the permanent snow line at 5000 m (fi g. 2.42).
Temperatures during the day may range from
3°C to 12°C, and the MAP
from a dry 500 mm to over 3000 mm. In the drier parts a prominent bunch-
grass is
Calamagrostis effusa
, and in the humid páramo it is the bamboo
grass
Chusquea tessellata
. There are also giant rosettes of
Puya
(fi g. 2.43).
The páramo consists of 4000 species of plants and, surprising to many
temperate-trained biologists, includes 22 genera of orchids. The rosaceous
shrubs
Acaena
and
Polylepis
are common as fragmented populations at high
altitudes from Ecuador to Argentina, and their pollen is found in Quater-
nary deposits in the Andes Mountains, preserving a record of presettlement
fi res, human activity (the wood is gathered for fuel and for making char-
coal), and shifts in tree line with changing climates (chap. 8).
The páramo has been highly disturbed through fi re, grazing, cultivation,
and lumbering of the adjacent high-altitude forests. This will become in-
creasingly signifi cant in the future because, compared to most mountain-
ous countries of the Earth where cities are located in the lowlands and at
midelevations, in the Northern Andes most of the population lives in the
highlands—50 percent in Ecuador, 70 percent in Venezuela, and 75 percent
in Colombia. The páramo is the principal water catchment, fi ltration, and
regulation system for cities such as Bogotá and its 7 million people. Under-
standing the páramo as an ecosystem is essential for formulating sustainable
management practices. Part of that information is preserved in the plant
fossil record, which provides insight into the pace and extent of Quaternary
climatic changes and their effect on the vegetation of the High Andes. At
the LGM, the lower limit of the páramo was at about 2000 m, a downward
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