Revista Chilena de Historia Natural 75 (3): 613-623, 2002
RESEARCH ARTICLE
Grazing effects on the floristic and structural diversity in mountain grasslands from central
Argentina
The effects of grazing and 10 years of cattle exclusion on floristic composition and
diversity and on structural diversity were studied in natural mountain grasslands at Sierras de Córdoba (2,200 m of elevation),
Argentine. We consider structural diversity as the arrangement complexity of biomass in space, both horizontal and vertical. The
abundance of all plant species and their vertical and horizontal arrangement were recorded by means of 50 randomly assorted pins,
each of them subdivided into 20 cm height intervals. Sampling was performed inside five replicates, each of them consisted of two
adjacent 20 x 20 m plots separated by a fence, one grazed and another excluded from grazing. Floristic and vertical structure diversity
were estimated by means of Shannon index. The variance in floristic and vertical structure diversity indexes were compared among
treatments to study possible variations in the horizontal distribution of both floristic diversity and vertical structure, respectively. Species
richness and floristic diversity were higher in grazed grasslands. Over 85 % of total plant species occurred at grazed grasslands, in
contrast to 65 % in sites excluded from grazing. Only three exotic plant species were found, one of them exclusive to grazed sites.
Cattle grazing produced a significant decrease in vertical structure diversity and in the variance in horizontal space of floristic diversity,
but did not produce significant changes in the variance in horizontal space of vertical structure diversity. Although cattle grazing
promotes lawns of high floristic diversity, it produces an over simplification of the community structure, both vertical and horizontal,
probably affecting other trophic levels of the ecosystem. We consider that the mixture in space of both types of patches studied in the
present work would allow a better balance between cattle grazing and conserving floristic and structural diversity.
Key words:
diversity, grazing,
grazing exclusion, horizontal structure, vertical structure
