The effects of sheep grazing on seedling establishment and survival in grassland

Abstract

This paper examines the effects of sheep and insect grazing on the generation of natural gaps in turf and the establishment of seedlings therein. The site is on an old field on limestone. There were five sheep grazing treatments: ungrazed, and grazed briefly in spring, briefly in autumn, in autumn or in summer and autumn. The first three of these treatments also contained plots in which insecticide was applied regularly during the growing season. Pins of increasing size (1.6 m m -12.8 mm diameter) were lowered at grid intersections in permanent quadrats to record gap type and the occurrence of seedlings on seven dates over 15 months.Heavily-grazed plots had more bare ground in spring and more herb seedlings established in them. Seedlings of annual species of Bromus were able to establish in gaps (bare ground and litter) of smaller size than was required by herb seedlings (which had much smaller seeds). The use of an insecticide increased seedling establishment in October in ungrazed and in spring-grazed paddocks but decreased it in autumn-grazed paddocks. This may indicate the greater importance of insect herbivory in making gaps in the matted sward of autumngrazed plots. Seedlings which established in October 1986 and March 1987 were more likely to die than those establishing earlier in 1986. This may be because of winter-kill and especially vigorous spring vegetation growth respectively. Seedling mortality was not affected by gap size or grazing treatment (unless such effects operated before we detected the seedlings).

Herbivory and competition slow down invasion of a tall grass along a productivity gradient

“…We think this lag period in establishment can largely be explained by strong interspecific competition from the short vegetation which prevents invasion. First, seedlings need gaps in the vegetation and the dense cover of vegetation may prevent seedlings from establishing (Gross and Werner 1982;Goldberg and Werner 1983;Watt and Gibson 1988). Second, strong competition from neighbouring plants prevents a rapid expansion after establishment as shown in the present study.…”

Effect of Grazing and Climatic Changes on Alpine Vegetation of Tungnath, Garhwal Himalaya, India

“…However, the intensity of grazing affects the balance between survival and vegetative spread of plants and establishment of its seedlings (Bullock et al, 1994). As grazing intensity increases, the growth of the dominant grasses or forbs is suppressed and gaps are open in the sward (Watt and Gibson, 1988). On moist meadows in alpine region of Garhwal, we found that on these gaps invasion of new species takes place, which increases the diversity.…”

Sheep grazing vs. cutting: regeneration and soil nutrient exploitation of the grassland weed Rumex obtusifolius

“…This may be due to the fact that sheep are reported to show a selective feeding behaviour (Arnold, 1987;Watt and Gibson, 1988) and usually avoid this weed or only consume it in very early stages. However, the sheep variety, East-Prussian Skudden, used in the current study are known to be very frugal regarding their diet and non-selectively feed plant grassland plant species including mature individuals of R. obtusifolius.…”

“…G. Winter, while only a few studies examined ruminant grazing for R. obtusifolius control (see Zaller, 2004b). The exclusion of ruminants -and here especially sheep -in R. obtusifolius control may be due to general reports that sheep show a selective feeding behaviour (Arnold, 1987;Watt and Gibson, 1988) and that R. obtusifolius is mainly refused or consumed only in very young stages by cattle, sheep and horses (Cavers and Harper, 1964). Despite this, it can be observed that certain sheep (Ovis aries L.) breeds indeed consume even up to 1.5-m tall individuals of R. obtusifolius and R. crispus (J. Zaller, personal observation).…”