Sustentabilidad y el manejo de los pastizales en las estepas Patagónicas
Resumen
One hundred years of grazing by domestic herbivores hampered the ecological sustainability of the Patagonian steppes. We propose three management-related factors of such ecosystem degradation: (1) overestimation of carrying capacity of the rangelands, (2) inadequate distribution of animals in very large, heterogeneous paddocks, and (3) year-long continuous grazing. We suggest that these three management factors interact with the highly selective grazing habit of sheep generating a pattern of grazing heterogeneity at three scales: landscape, community, and population. Grazing differs in intensity among areas of the same paddock, among plant species, and even among individuals of the same species. As a consequence, the most palatable species within a patch are almost continuously subjected to a very high frequency of defoliation in the most preferred areas, which increases the mortality of the most preferred individuals of these forage species. We review the available ecological knowledge and range management technologies that may contribute to revert degradation. A quick assessment of both the availability and spatial heterogeneity of forage resources is now possible with the aid of remote sensing. Range assessment will allow to estimate the carrying capacity of each paddock, and separate different vegetation units. From information on the phenology of the different vegetation units it is possible to decide the timing of grazing and/or resting periods of single paddocks. Rotational grazing methods allow for a recovery of the most preferred species and for a reduction of the heterogeneity of defoliation at the three mentioned levels. Research efforts are needed to develop warning systems, improve the productivity and use efficiency of meadows, and design and evaluate grazing methods for the most arid areas of the region.
Citas
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Coughenour, M.B. 1985. Graminoid responses to grazing by large herbivores: adaptations, exaptations, and interacting processes. Annals of the Missouri Botanical Garden 72:852-863.
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Defing,J.K., M.I. Dyer and D.T.Winn. 1979. Net photosynthesis, root respiration, and regrowth of Bouteloua gracilisfollowing simulated grazing. Oecologia 41:127-134.
Dyksterhuis, E. 1958. Ecological principlesin range evaluation. Botanical Review 24:253-272.
Encuesta Nacional Agropecuaria. 1993. Ministerio de Economía de la Nación (Argentina). Secretaría de Agricultura, Ganadería y Pesca. Buenos Aires. 28 pp.
Evans, R.A. and R.M. Love. 1957. The step point method of sampling. A practical tool in range research. Journal of Range Management 10:208-212.
Golluscio, R.A., R.J.C. León and S.B. Perelman, 1982. Caracterización fitosociológica de la estepa del Oeste de Chubut; su relación con el gradiente ambiental. Boletín de la Sociedad Argentina de Botánica 21:299- 324.
Golluscio, R.A. and J.L. Mercau. 1995. Cambios en la biodiversidad ante distintos grados de desertificación provocada por el pastoreo. Pp. 60-71. In: Montes, L. y G.E. Oliva (eds.). Patagonia. Actas del Taller Internacional sobre Recursos Fitogenéticos, Desertificación y Uso Sustentable de los Recursos Naturales de la Patagonia.
Golluscio, R.A., J.M. Paruelo, J.L. Mercau and V.A. Deregibus. 1998. Urea supplementation effects on low- quality forage utilisation and lamb production in Patagonian rangelands. Grass and ForageScience 53:47- 56.
Heady, H.F. and R.D. Child. 1994. Rangeland ecology and management. Westview Press, Boulder. 519 pp.
Helman,M.B. 1965.Ovinotecnia.Tomo Segundo: Crianza-Mejora-Manejo y Administración. El Ateneo, Buenos Aires. 680 pp.
Hurlbert, S.H. 1984. Pseudo replication and the design of ecological experiments. Ecological Monographs 54:187-211.
Jobbágy, E.G. 1993.Relaciones vegetación-ambiente a la escala de paisaje en la estepa del Distrito Occidental de la Patagonia extra-andina. Graduation Thesis. Department of Ecology. Faculty of Agronomy. University of Buenos Aires. 61 pp.
Jobbágy, E.G., J.M. Paruelo and R.J.C. León. 1995. Estimación del régimen de precipitación a partir de la distancia a la cordillera en el noroeste de la Patagonia. Ecología Austral 5:47-53.
Jobbágy, E.G., J.M. Paruelo and R.J.C. León. 1996. Vegetation heterogeneity and diversity in flat and mountain landscapes of Patagonia (Argentina). Journal of VegetationScience 7:599-608.
Jobbágy, E.G., O.E. Sala and J.M. Paruelo. Patterns and controls of primary production in the Patagonian steppe a remote sensing approach. Ecology (in press).
Kennedy,P.1989.MonitoringthevegetationofTunisiangrazinglandsusingtheNormalizedDifferenceVegetation Index. Ambio 18:119-123.
Lauenroth, W.K., H.W. Hunt, D.M. Swift and J.S. Singh. 1986.Estimating above ground net primary productivity in grasslands: a simulation approach. Ecological Modelling 33:297-314.
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1998-12-01
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Golluscio, R. A., Deregibus, V. A., & Paruelo, J. M. (1998). Sustentabilidad y el manejo de los pastizales en las estepas Patagónicas. Ecología Austral, 8(2), 265–284. Recuperado a partir de https://ojs.ecologiaaustral.com.ar/index.php/Ecologia_Austral/article/view/1626
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