| Sumario: | In the Monte Biogeographic Province, located
in the arid region of Argentina, the presence
of Prosopis flexuosa DC. produces spatial
heterogeneity through edaphic modifications and
microclimate changes. This results in vegetation
patches differing in species composition and
abundance. However, this interaction can be
modified by the occurrence of gradients of biotic
stress or disturbance intensity. In particular,
grazing has been observed to enhance or reduce
vegetation heterogeneity. Such complex of
interactions could determine forage availability for
cattle in one of the driest areas of the Monte Desert.
We assessed the effect of Prosopis on understory
species and analyzed whether the outcomes of this
interaction differed with distance to watering points,
as a proxy of grazing intensity, in the Northeast of
Mendoza Province, Argentina. We used a two-way
factorial design including the following factors:
1) microsite (under the cover of P. flexuosa trees
and in intercanopy microsites) and 2) distance
to watering points ("near the watering point",
500-700 m away, and "far from the watering
point", 3-4 km away). Cover of each species,
total cover, bare soil, and litter were recorded,
and plant diversity, richness, and evenness were
estimated with the modified Point Quadrat method.
Results showed that P. flexuosa cover, distance
from watering points, and the interaction between
them determined species composition, abundance
and spatial distribution of understory species, and
were, consequently, a determining factor for forage
availability. The presence of P. flexuosa enhances
carrying capacity by supporting higher abundance
of grasses under its canopy. Near watering
points, high grazing intensity appears to disrupt
the patches formed under P. flexuosa canopies,
reducing the differences between microsites.
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