High species richness of sheep-grazed sand pastures is driven by
disturbance tolerant and weedy short-lived species
Abstract
We selected 15 sheep-grazed sand pastures along increasing grazing
intensity to study fine scale biomass patterns of main fractions (green
biomass, litter) and that of plant species and functional groups (life
forms and social behaviour types). We classified them into five grazing
intensity levels based on stocking rate, proximity to drinking and
resting places, and the number of droppings and other tracks of grazing
animals. We formulated three study questions: i) How does increasing
intensity of sheep grazing affect the amount of green biomass, species
richness and their relationship in sand pastures? ii) How does
increasing intensity of sheep grazing affect the biomass of perennial
and short-lived graminoids and forbs? iii) How does disturbance value
(expressed in the biomass ratio of disturbance tolerant and ruderal
species) change along the gradient of grazing intensity? A unimodal
relationship between green biomass and species richness was detected.
Along the grazing intensity gradient, we found an increasing trend for
species richness; significant differences for green biomass (decreasing
trend) and litter (decreasing trend), moreover for graminoids
(decreasing trend), and short-lived forbs (increasing trend). We found
an increasing amount of disturbance tolerant and ruderal species with
increasing grazing intensity. We concluded that stocking rate and
proximity to drinking and resting places jointly affected vegetation and
created an uneven pattern for composition and amount of biomass in all
grazing intensity levels. Our findings might be instructive for pastures
in densely populated regions which are prone to the encroachment of
disturbance-tolerant and ruderal species.