Efectos del pastoreo holístico sobre la estructura y composición vegetal en praderas naturalizadas de uso ganadero, provincia de Última Esperanza, región de Magallanes, Chile

Abstract

Naturalized grasslands in Magallanes are important but fragile agro-ecosystems that may change due to climatic variations and overgrazing. Holistic grazing (HG) has been introduced into Magallanes in 2013 as a new, management intensive technological alternative, that in principle would improve the health of grassland. Considering this, it is priority to generate scientific information and maintain a permanent follow-up on this type of management. The objective of this study was to analyze the effects on vegetation in order to assess whether holistic grazing degrades or improves the floristic structure and composition of naturalized grasslands. We compared three paddocks managed under grazing holistic (HG): La Campana, Lago Sofia and Parcela Tamara, with three equivalent areas under Semi-Intensive grazing (SIG), a traditional management in the area that includes rotations with short rests: Tres Pasos, Dos Lagos and Parcela Colonia Isabel Riquelme. All areas were ecologically equivalent and derived from substitution of nirre forests (Nothofagus antarctica (G. Forst.) Oerst.), and located in the province of Ultima Esperanza, with 389 mm annual rainfall. The study was conducted between 2014-18, with an average rainfall of 372 mm which is within normal for that area. The hypothesis was that the HG would increase the vegetation cover, palatable species cover and diversity. Vegetation and soil monitors were installed in three fields with HG and three SIG following the MARAS methodology. The results indicate that changes over the years were not significant in terms of cover (p>0.8450), but significant differences were observed in species richness (P 0.1710). In conclusion, plant cover increase was not detected for HG, but species dominance was rearranged, as palatable, exotic species, increased under HG. This is perhaps because grazing pressure decreased competition in the canopy, favoring naturalized exotic species such as white clover (Trifolium repens) that could not compete with invasive weeds like Achillea millefolium and Hieracium prealtum under SIG. Future trials should consider evaluating productive parameters such as forage availability, weight and animal health status.