Abstract

GAITAN, Juan José; LOPEZ, Carlos Rodolfo  and  BRAN, Donaldo Eduardo. Grazing effects on soil and vegetation in the Patagonian Steppe. Cienc. suelo [online]. 2009, vol.27, n.2, pp.261-270. ISSN 1850-2067.

More than 100 years of sheep breeding has caused profound changes to ecosystems and is one of the main causes of desertification in the Patagonian steppe. The aim of this study was to evaluate sheep grazing effects on soils and vegetation, applying a modified version of the «Landscape Function Analysis» methodology developed in Australia. The study was carried out in seven sites with different levels of degradation caused by overgrazing in the Pilcaniyeu area (northwest of Río Negro province): three of the sites are closed to grazing (CLA), three are under moderate grazing (PM) and one is under heavy grazing (PI). We evaluated indicators of floristic composition and vegetation spatial structure, soil surface status on interpatches, integrated into three Indices of Function (Stability-EST-Infiltration-INF-and Nutrient cycling -NUT-), and soil organic carbon stock (CO). With increasing grazing intensity, a reduction in vegetation basal cover was observed (47.4, 23.2 and 17.4% in CLA, PM and PI, respectively), vegetated patches were more distant from one another (61.9, 117.9 and 181.7 cm), coverage of palatable grasses dropped (26.3, 3.4 and 2.1%) and that of non-palatable grasses increased (4.4, 15.8 and 17.6%). The Soil Function Indices (EST: 43.0; 42.3 and 36.2; INF: 48.3, 41.7 and 36.2; NUT: 33.1, 23.5 and 18.1) and CO (33.8, 26.5 and 7.9 t/ha) showed a downward trend with increasing grazing intensity. Further studies and more experimental data are required to be able to adapt this methodology to Patagonian conditions and to test whether the indices adequately reflect the processes and functions of these ecosystems.

Keywords : Soil health; Overgrazing; Arid and semiarid zones.

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