Grasslands of the World.pdf - Disasters and Conflicts - UNEP

Grasslands of Patagonia 125
Mean annual temperatures range from 15.9°C in the north (Cippoletti) to
5.4°C in the far south of Tierra del Fuego (Ushuaia) (Soriano, 1983). Mean
temperatures of the coldest month (July) are above the frost mark, although
absolute minimum temperatures can be below -20°C (Paruelo et al., 1998).
Cibils and Coughenour (2001) reported a significant increase in mean annual
temperatures over the last 60 years of the twentieth century for Río Gallegos, a
town with one of the longest weather records, on the steppes surrounding the
Straits of Magellan. This trend is consistent with predictions of climate change
from Global Circulation Models simulating enhanced atmospheric CO2 concentration
(Hulme and Sheard, 1999), but conclusions from weather station
data analysis are still preliminary.
Strong, persistent westerly winds are an outstanding characteristic of
Patagonia ’s climate. Because there is relatively little land in the Southern
Hemisphere, westerlies between 40°S and 50°S gain impressive momentum,
with annual intensities of between 15 and 22 km/h and frequent gusts of over
100 km/h, mostly in spring and summer (MacArthur, 1972; Paruelo et al., 1998;
Soriano, 1983). Strong winds increase evaporation and can have a considerable
influence on sheep performance through chill (Borrelli, unpublished data;
Soriano, 1983).
Over half of Patagonia ’s soils are Aridisols (desert soils), with Entisols (soils
with little development ) and Mollisols (dark coloured, base-rich steppe soils),
respectively, as the second and third most important types (del Valle, 1998).
Over 70 percent of topsoil is coarse-textured, ranging from sand to sandyloam
(del Valle, 1998). Soil textures can explain a large portion of the variation
in dominant plant life form (grasses vs shrubs) across the region (Noy-Meir,
1973; Sala, Lauenroth and Golluscio, 1997). Small-scale spatial heterogeneity of
soils tends to increase with aridity (Ares et al., 1990); important differences in
leaching and salinity occur over short distances, possibly causing soils within a
taxonomic group to function differently (del Valle, 1998, and references therein).
Over 90 percent of Patagonian soils are degraded to some degree, mostly
because of improper land use; severe desertification affects 19 to 30 percent
of the region (del Valle, 1998). Some of the most dramatic erosion processes
occur in the form of sand macro-accumulations that, in the early 1970s, covered
approximately 85 000 km 2 (Soriano, 1983). Both aerial photography and
satellite imagery indicate that many of these accumulations are about 100 years
old, suggesting that the rate of wind-driven erosion has been accelerated by the
introduction of domestic livestock (Soriano, 1983).
Archaeological records from caves suggest that human occupation began
around 11 000 BP (Borrero and McEwan, 1997). Native peoples were huntergatherers,
although there are indications of limited agricultural activity in the
north (Villamil, 1997). Bifacial stone weapons suggest that people of south
Patagonia hunted guanaco (Lama guanicoe). The Mapuche tribe occupied the
northern reaches, the Tehuelches the southern mainland, and the Selknam,