Data from: Effects of grazing intensity on plant richness and diversity: a meta-analysis

Most of our knowledge of the effect of grazing on grassland structure is
based on grazed-ungrazed contrasts. The effects of grazing in the most
common scenario, where grazing intensity varies from low to high grazing
intensity, are less known. The objectives of this paper were to (1)
quantify the effect of stocking rates on species richness and diversity of
grasslands world-wide, and (2) evaluate the response under different
environmental and experimental conditions. We conducted a meta-analysis of
experiments with at least two levels of controlled stocking rates and
evaluated their effect on species richness and diversity. The results
showed that the response of richness and diversity to either reducing or
increasing stocking rate from a moderate level mostly fell within the
range ± 25% or ± 5 species. Mean response of species richness and
diversity to increasing stocking rate from moderate to high levels was
negative. Mean response to lowering stocking rate from moderate levels was
not different from 0. However, overall, species richness significantly
decreased as stocking rate increased. The response of richness and
diversity to stocking rate was not related to mean precipitation,
productivity or aridity. However, the most negative responses of richness
to stocking rate were larger in arid, low productivity systems than in
subhumid and humid systems. The effects of grazing on richness and
diversity found in this review were smaller than the effects on species
composition shown by the literature. Thus, grazing drastically changes
species composition, but the net change of species and diversity is much
smaller.