Understanding the responses of vegetation to grazing exclusion along a salinity gradient is useful for the management of grasslands. We studied the responses of vegetation to grazing removal (ungrazed areas) in three semiarid regions with different soil salinity levels: non-saline, moderately saline and hyper-saline. The results showed that Bray-Curtis dissimilarity between grazed and ungrazed areas were highest in the non-saline region. In the hyper-saline region, the grazing removal had no significant effect on any of the diversity indices, while in the non-saline regions, vegetation changes were occurred by grazing exclusion at the highest magnitude. Generally, the magnitude of vegetation changes by livestock grazing exclusion was decreased along the soil salinity gradient. This research could help to understand how disturbances and stresses interactively influence grasslands dynamics in semiarid regions and to understand the effects of grazing on grassland dynamics and sustainability in deserts in the context of salinization.

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.

Global warming, elevated atmospheric CO 2 concentrations, and increased likeliness of extreme drought and wildfires in many regions will likely favour C4 grass species. We explored the effect of the encroachment of an invasive perennial C4 grass, Sporobolus cryptandrus on the composition of soil seed banks in dry sand grasslands in Central Europe. In five mass-locality sites of the species we assessed the composition and vertical segmentation of the soil seed bank in twelve 1-m 2 plots along an increasing cover of the invasive species. We found that the seed bank diversity and density decrease with the increasing sampling depth; the decrease of density is affected by the increasing Sporobolus cover. Neither the diversity nor the seed bank density of other species were affected by increasing Sporobolus cover but, affected by the sampling site. Most of the studied seed bank characteristics were affected by the sampling depth, but none of them were affected by the increasing cover of Sporobolus. Increasing cover of Sporobolus in the vegetation was associated with an increasing proportion of Sporobolus seeds in the seed bank, and we found viable seeds of the species in the soil even in plots with no Sporobolus cover. Given that a decrease in the precipitation of the summer months and an increase in the frequency of droughts is projected in this region, we expect that the accumulated massive seed bank of Sporobolus will facilitate the further rapid spread of the species.