Degradation of Patagonian ecosystems of Argentina by grazing. A regional approach.

BERTILLER, MB; CARRERA, AL; BISIGATO, AJ; SAIN, CL

Lima, Perú

Simposio; Simposio Internacional: Environment and Sustainable Use of Natural Resources in Latin-America: Challenge for Interdisciplinary Cooperation.; 2001

Patagonia covers an area of more than 780.000 km2, representing 28% of continental Argentina. Plant communities are characterized by a low vegetation cover (10 to 60% in extreme arid and semiarid ecosystems, respectively), dominated by two main plant functional groups: shrubs and perennial grasses. Domestic grazing, introduced at the beginning of the past century, led to an overall reduction of plant cover, species replacement and deletions along with soil degradation and losses in the size and diversity of soil seed banks. In areas with more than 250mm, vegetation may be degraded from grass steppes to dwarf shrub-lands with high losses in primary production and ecosystem functions. Conversely, in areas with less than 250mm annual precipitation, changes in vegetation are less marked from shrub-grass steppes to dwarf shrub steppes with lower losses in primary productivity and other ecosystem functions relative to more humid areas. The replacement of plant functional groups (grasses for shrubs) involve changes in the mechanisms of N conservation in vegetation affecting the rates of litter decomposition, soil nutrient availability, nutrient losses and nutrient cycling. Thus, the intrusion of shrubs (a more xeric plant functional group) following grazing impact represents the crossing of a threshold both in vegetation and soil structure and functional properties affecting ecosystem sustainability and services in Patagonia. In this context, more humid areas possibly deserve special attention, because they provide scenarios where more drastic changes can occur compared to arid areas. In the future, more intensive interventions than the regulation of stocking rates will probably be needed to stop degradation and to restore degraded areas. Strategies like surface soil manipulation, nutrient and seed addition, or planting of target species in seasons or years with favorable precipitation and under grazing exclusion should be identified, and experiments conducted as a basis to develop future sustainable management tools.