Fjölrit RALA - 05.12.1999, Blaðsíða 45

OsvaldoA. Fernández et al.
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The deserts and semi-deserts were at the outer edge of the central Humid Pampas
which made those regions marginal and less important in economical terms when
compared with the productivity of cultivated crops such as cereals, sunflower, soy-
bean or cultivated pastures. Historically, political and government activities were ori-
ented towards development of the richer regions in the country. Agricultural experi-
mentation and training of technicians and university graduates were clearly focused on
the productivity of the humid regions.
The contrast between irrational exploitation of the land and its proper use starts to
be considered when signals of deterioration are clearly evident. It is in general a re-
sponse to a situation of ecological crisis which prevails today in about 70% of the Ar-
gentinean territory. Overall, the Argentinean rangelands have suffered less degrada-
tion than most other arid land regions of the world due to their low human population
density. Today the society appears to be aware of the magnitude and severity of the
problem, and that it will become worse if no adequate measures are taken.
A brief description of the environmental characteristics of each territory comprising
relief, soil, climate and vegetation follows. It includes discussion of the effects of past
and current rangeland utilization and assessment of desertification problems in these
regions.
Descriptton and use of major rangeland regions
Patagonia
This territory extends from latitude 40 to 55°S and from the Atlantic Ocean to the An-
dean piedmont in the west, and occupies nearly 60 million ha of the southem portion
of Argentina (Soriano 1983). Most of it is quoted by Cabrera (1976) as the Patagonian
Province. It is one of the few cold semi-arid rangelands of the world. The landscape
consists of a system of plateaus and hills of flattened surfaces. A noticeable feature
characterizing the plateau surfaces is the presence of Patagonic or "tehuelches" boul-
ders of glaciofluvial origin. These boulders form a desert pavement due to the strong
winds which prevents the deposition of material. Soil horizons at greater depth have
consisted of gravel in westem Patagonia, probably forming a continuous layer reach-
ing from the Andes into the eastem foothills which makes sub-surface flow of water
highly possible. The existence of ffee water at greater depth would be contributing to
the maximum rooting depth in the Patagonian arid region (Schulze et al. 1996). Soil
water was available at 2-3 m soil depth within a 140-km transec from Nothofagus
forest through grassland to desert in Patagonia, and roots reached this depth at all
these sites (Schulze et al. 1996). However, further research is needed to answer the
question of when and why roots of plant species in western Patagonia grow deep,
since various fronts of water coming from distinct rain events were not used to a
greater extent (Schulze et al. 1996). Soil water at greater depths originated fforn rain-
falls in the last or even prior to the last rainy seasons rather than water ffom recent
rain events (Schulze et al. 1996). The observed vegetation zonation in western Pa-
tagonia cannot be explained by using water balance alone (Schulze et al. 1996); seed-
ling establishment in the dry period may limit migration of species into drier habitats,
and light competition during the active growing period may limit migration of arid
species into wetter habitats. A detailed summary of the geology and soils, climate and
vegetation of Patagonia has been published by Soriano (1983).