Influence of Environmental Factors and Sheep Grazing on an Andean Grassland
Journal of Range Management
Society for Range Management
Chronic overgrazing in the central Andes alters vegetation
and may cause erosion and loss of productivity, but quantitative
studies are lacking. We measured the relative influence of
environmental factors and sheep grazing on local plant species
composition, diversity, and soil organic matter in a remote site
in northwestern Argentina. Using redundancy analysis, we
found that environmental variables explained 22% of variation
in species composition between sites, while grazing-related
variables explained 24% of variation. The complete model,
incorporating all significant variables, explained 33% of variation.
Aspect, season of grazing (wet vs. dry) combined with
total vegetative cover, and soil type formed the basis for the
first 3 ordination axes. Unpalatable or toxic species and very
low-growing species were significantly more abundant on
heavily grazed sites compared to relatively protected sites.
Stocking rate in wet season pastures was negatively correlated
with total cover, forage volume, soil organic matter, and
species richness. Season of grazing had a more dramatic effect
on total cover, forage volume, species diversity and soil organic
matter, which were all significantly lower in wet season pastures
compared to dry season pastures. Season of grazing and
aspect interacted strongly: wet season pastures on north
aspects appear more susceptible to degradation and changes
in species composition than south-facing sites. Our results suggest
that protecting pastures during the summer rainy season
may be an important complement to traditional management
efforts to reduce stocking rates.
Adler, P.B. and J.M. Morales. 1999. Influence of environmental factors and sheep grazing on an Andean grassland. Journal of Range Management 52: 471-481.