Fjölrit RALA - 05.12.1999, Side 50

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Arid and semi-arid rangelands of Argentina
poor forage species cover and carrying capacity, such as Larrea cuneifolia communi-
ties in this region (Passera et al. 1996). Since various mechanical shrub control meth-
ods have shown similar effects on carrying capacity on rangelands in the eastem foot-
hills of the Andes, Allegretti et al. (1997) recommended that less drastic methods,
such as hand-cutting and roller-chopping, should be favoured over extreme measures
such as root-plowing. Despite shrub control through different management altema-
tives can improve forage production in the Monte, rainfall appears to be the limiting
factor controlling rangeland productivity in any given year (Giorgetti et al. 1997). In
addition, cattle browsing has represented 48% of the relatively dry season overall diet
and 34.5% on an annual basis in the Monte rangelands (Guevara et al. 1997). Ade-
quate chemical composition of both herbage and browse species explain why stock
keep in good condition through the annual six-month dry season and supplemental
feeding is not necessary (Guevara et al. 1997). Thus, brush control should not be in-
discriminate nor excessive and íurther research should seek to find methods for selec-
tive brush control and evaluate their long-term consequences for the overall function-
ing and productivity of the ecosystem (Guevara et al. 1997).
Trees have also been cut as timber and/or fuel such as Prosopis spp., Acacia spp.
and Condalia mycrophylla. Hunziker et al. (1986) discussed the abusive exploitation
of the Prosopis woods in Argentina and the urgent need for genetic conservation of
the most valuable and promising species. They can provide human food, animal fod-
der, gums and tannins, and these species can be used by the parquet flooring and fur-
niture industry. They are also valuable for erosion control and can even be used for
alcohol and honey production. These species occur in most of the Argentine territory,
except for Southem Patagonia and Misiones, and the highest number of species occurs
in the phytogeographical Provinces of Monte, Espinal and Chaco (Cabrera 1976).
Since Argentina is the center of the greatest species diversity in America, Affica and
Westem Asia, the country should take a very active role in saving valuable germplasm
of these species (Hunziker et al. 1986).
Caldenal
The Caldenal lies in the ecotone between the Monte desert and the cultivated Humid
Pampa grasslands to the east. It corresponds to the southem subregion quoted by
Cabrera (1976) as the Espinal Province, where woody vegetation begins to replace
grasslands. We have identified this area as the Calden District. Recent papers have re-
viewed rangeland research and social and management aspects in this region (Morris
and Ubici 1996, Busso 1997).
The Caldenal is a level to gently undulating plain covered with recent loessic sandy
sediments of eolian origin. Dominant soils are Calciustolls with a petrocalcic hard pan
horizon (tosca) at a depth of 0.5 to 1 m. The climate is temperate semi-arid, and arid-
ity increases westward and southward. Precipitation varies between 350 and 550 mm
annually and is concentrated during spring and autumn. Annual potential evapostran-
spiration is 800 mm. Mean annual temperature is 15.3°C, and mean monthly tem-
peratures of the warmest (January) and coldest (June) months are 23.6°C and 7.4°C,
respectively. Absolute maximum and minimum temperatures have been 42.5°C and -
12.8°C.