Effects Of Grazing Treatments Research Articles

The impact of sheep grazing on shrub communities at the Afrikaner and Hereford grazing trials at Grootfontein in the Eastern Upper Karoo

In the Nama-Karoo, grazing by livestock is an important driver of Karoo shrub composition. Many different breeds of livestock are farmed in the Nama-Karoo, and the stocking rate varies greatly over the region. In this study we examine how grazing by dorper and merino sheep applied at three stocking rates affected two Karoo shrublands on a long-term grazing trial at Grootfontein in the eastern Karoo. The effects of grazing treatment on shrub communities at two sites of the Afrikaner-Hereford grazing trial differed greatly and were measurable after ten years of rest. At the sandier, grassier Afrikaner site, heavy grazing by dorper sheep had a significant effect on shrub composition, density and cover, whereas the effect of grazing treatment was less pronounced at the Hereford site. Lenient grazing by merino sheep resulted in a vastly different community compared to all other grazing treatments. Individual Karoo shrub species responded differently to grazing treatment. Overall shrub recruitment has faltered for all but three species, and populations were dominated by intermediate-sized and large individuals. Results indicate that grazing management, animal type and stocking rate are important determinants of Nama-Karoo rangeland composition and structure with evidence of a legacy effect longer than ten years.

Effect of Grazing Treatments on Phenotypic and Reproductive Plasticity of Kobresia humilis in Alpine Meadows of the Qinghai-Tibet Plateau

Plant phenotypic and reproductive plasticity is strongly influenced by long-term grazing activities. It is important to understand the life history of dominant plant species, such as Kobresia humilis of alpine meadow, for the stability and sustainable grazing administration meadow on the Qinghai-Tibetan Plateau (QTP). We compared the effects of different grazing treatments (grazing yak, Y; grazing Tibetan sheep, S; and grazing Tibetan sheep and yak, S+Y) on the reproductive and phenotypic plasticity of K. humilis in an alpine meadows on the northeastern margin of the Qilian Mountains in China. The results showed that different grazing treatments had significantly effects on the K. humilis phenotype and reproductive plasticity. The Y treatment significantly reduced the plant height, crown width and K. humilis biomass, but increased the density, which was 1.27 and 1.53 times higher than that in the S+Y and S treatments, respectively. Further, the S+Y treatment significantly increased the crown width, biomass, and future life expectancy of K. humilis. Whereas the S treatment increased the height of K. humilis significantly, which was 1.57 and 1.10 times higher than that in the Y and S+Y treatments, respectively. Both Y and S treatments significantly increased the sexual reproduction efficacy of K. humilis but reduced the storage efficacy. The storage efficacy at S+Y treatment was highest among these treatments. Further, grazing treatments did not change the resource allocation strategy of K. humilis, while the sexual reproductive efficacy was significantly higher than the vegetative reproduction efficacy. The storage efficacy was significantly higher than the growth efficacy among the different grazing treatments. The increase of Cyperaceae indicates the degradation of Cyperaceae—Poaceae meadows. This study showed that grazing Tibetan sheep is a more sustainable grazing method in cold season pastures of alpine meadows on the QTP.

The cascading impacts of livestock grazing in upland ecosystems: a 10‐year experiment

Livestock grazing is a major driver of land‐use change, causing significant biodiversity loss globally. Although the short‐term effects of livestock grazing on individual species are well studied, a mechanistic understanding of the long‐term, cascading impacts is lacking. We manipulated livestock densities using a unique, replicated upland experiment over a 10‐year period and found significant effects of grazing treatment on plant and arthropod biomass; the number of Anthus pratensis breeding bird territories; the amplitude of Microtus agrestis population cycles and the activity of a top predator, Vulpes vulpes. Lower plant biomass as a result of higher stocking densities led to cascades across trophic levels, with fewer arthropods and small mammals, the latter affecting predator activity. Breeding bird territories were a function of arthropod abundance and vegetation structure heterogeneity. Our results provide a novel food‐web analysis in a grazing experiment to provide a mechanistic understanding of how food‐webs in upland ecosystems respond to long‐term livestock grazing pressure, with consequences for management.

Variable effects of dipteran parasitoids and management treatment on grasshopper fecundity in a tallgrass prairie

Grasshoppers host a number of parasitoids, but little is known about their impact on grasshopper life history attributes or how those impacts may vary with land use. Here, we report on a three-year survey of nine grasshopper species in a tallgrass prairie managed with fire and bison grazing treatments. We measured parasitoid prevalence and the impact of parasitoid infection on grasshopper fecundity to determine if grasshopper-parasitoid interactions varied with management treatment. Adult female grasshoppers were collected every three weeks from eight watersheds managed with different prescribed burning and grazing treatments. Grasshopper fecundity with and without parasitoids was estimated through dissections of reproductive tracts. Dipteran parasitoids from two families (Nemestrinidae and Tachinidae) were observed infecting grasshoppers. We found significant effects of grazing treatment, but not burn interval, on grasshopper-parasitoid interactions. Parasitoids were three times more abundant in watersheds with bison grazing than in ungrazed watersheds, and the relative abundance of nemestrinid and tachinid flies varied with grazing treatment. Parasitoid prevalence varied among grasshopper species from <0.01% infected (Mermiria bivittata) to 17% infected (Hypochlora alba). Parasitoid infection reduced individual grasshopper fecundity, with stronger effects on current reproduction than on past reproduction. Furthermore, current fecundity in parasitized grasshoppers was lower in grazed watersheds compared to ungrazed watersheds. Nemestrinid parasitoids generally had stronger impacts on grasshopper fecundity than tachinid parasitoids, the effects of which were more variable.

Root depth of native and sown perennial grass-based pastures, North-West Slopes, New South Wales. 1. Estimates from cores and effects of grazing treatments

Studies were undertaken on native and sown perennial grass-based pastures as part of the Sustainable Grazing Systems National Experiment to estimate root depth and describe root distribution in these pastures. Samples from soil cores (0–210 cm maximum sampling depth) taken in 1997 (before grazing treatments were imposed) and 4 years later in spring 2001 were used to examine the effects of different grazing regimes on root length density (cm/cm3), root mass density (mg/cm3), root volume density (cm3/cm3), and diameter (mm) at each of 3 sites. In spring 1997, mean maximum root depth was 107 cm for a native perennial grass pasture near Barraba and 74 cm for a pasture sown with phalaris (Phalaris aquatica) and subterranean clover (Trifolium subterraneum) near Nundle, with values being lower for a native pasture near Manilla (65 cm for a Brown Vertosol and 97 cm for a Red Chromosol). For all pasture types, &gt;20% of root mass density, root length density or root volume density was in the 0–5 cm soil layer and &gt;60% was at a depth of 0–30 cm. At all sites, mean total root mass was around 1000 kg DM/ha. After 4 years of grazing (spring 2001) there were relatively few significant effects of grazing treatment on root length density, root mass density, root volume density, or root diameter. Effects that were significant mostly occurred at 0–5 cm for the native pastures and 0–50 cm for the sown pasture. For the Barraba native pasture, root length, volume and mass densities (0–5 cm) were higher (P&lt;0.05) in the continuously grazed, low stocking rate treatment compared with all other treatments. Similarly, for the Manilla native pasture, root length density was higher (P&lt;0.05) in this treatment at soil depths of 0–5 and &gt;5–10 cm compared with all other treatments. In contrast, for the Nundle sown pasture, root length density (0–5 cm) was lowest (P&lt;0.05) in 2 continuously grazed treatments compared with those that were strategically grazed in autumn and spring.

Effects of simulated grazing on different genotypes of Bouteloua gracilis : how important is morphology?

Populations of grasses exposed to grazing by vertebrates often exhibit reduced stature, increased tillering, reduced flowering, and other morphological differences which distinguish them from ungrazed populations. These differences frequently are interpreted as an adaptive response that reduces grazing damage; however, there are few experimental tests of this hypothesis. This paper describes a field experiment designed to determine whether morphological variation among genotypes of the grass Bouteloua gracilis is related to variation in their responses to grazing. Eleven genotypes differing in morphological and reproductive characters were transplanted into a shortgrass steppe community near Fort Collins, Colorado. Replicates of each genotype were subjected to clipping treatments intended to realistically simulate three grazing intensities. After two growing seasons, different genotypes still maintained significant differences in a wide range of morphological and demographic characters. However, there were few significant effects of grazing treatment, and no significant genotype×treatment interactions. These results suggest that for B. gracilis clipped in simulation of natural grazing, defoliation has few short-term effects on fitness components, and intrapopulation morphological variation has few consequences for defoliation resistance.

Complex effects of grazing treatment on an annual in a species‐poor grassland community

Abstract. The effects of grazing upon the establishment, survival, growth and reproduction of a grassland annual Geranium dissectum growing in a sward dominated by grasses were examined in a replicated grazing experiment with sheep. Seeds were sown in both summer and autumn, and grazing was controlled to produce two levels of grazing in winter, two levels in spring, and two in summer, combined in a 2 x 2 x 2 factorial experimental design. Higher intensities of grazing in the period immediately before emergence benefitted plant establishment, but subsequent survival showed many interactions between factors, demonstrating that under certain conditions and at certain times grazing was detrimental. It is suggested that the frequency of G. dissectum in the grassland was low because the heavy grazing conditions that foster seedling emergence also jeopardize subsequent survival. This may also be why productive grassland communities in general contain few palatable dicots.

The effects of grazing on local colonisation and extinction during early succession

AbstractEstimates of colonisation of plant species were made at three spatial scales in an old‐field on limestone subject to five experimental sheep grazing regimes. Local extinctions within grazing treatments were estimated in 1‐m2 permanent quadrats. These data were used to assess the effects of grazing treatment and spatial scale on the process of species change over a period of six years. Colonisation of the lOha field was virtually a random draw of plant species from adj acent vegetation, irrespective of plant life‐history traits including dispersal strategy. The effects of grazing on colonisation increased at smaller spatial scales. Colonisation rates changed little during the study on the 10 ha scale, but declined steeply with time at smaller scales. Colonisation rates of short‐lived species declined more than those of perennials, and short‐lived species were subject to erratic episodes of extinction which did not affect perennials.Short periods of grazing enhanced colonisation rates of all species, but extinction rates were the same as in ungrazed controls. Grazing for longer periods further enhanced colonisation rates, but also increased extinction rates. This produced diversity patterns consistent with a ‘hump‐backed model’, except that no grazing treatment was heavy enough to decrease diversity. Ungrazed controls had low species diversity, but areas grazed for longer periods were no more diverse after six years than those grazed for short periods.