Grazing pressure and tree competition affect cattle performance and native pastures in Eucalypt woodlands of Queensland, north-eastern Australia

Context Well managed grazing pressure will optimise animal and pasture production, and preserve the soil to maintain a viable beef business on native pastures in eucalypt woodlands. Aims A cattle grazing experiment was established to measure animal and pasture performance under management practices used in the Aristida/Bothriochloa native pastures in central Queensland. Methods Performance of Brahman-cross steers and pastures were measured in an experiment with three grazing pressures by two tree densities in a Eucalyptus populnea woodland in north-eastern Australia over 8 years in paddocks of 4–18 ha. Key results At low grazing pressure with trees killed by herbicide (‘cleared’), stocking rate increased 35% as pasture composition and biomass improved over 8 years. At low grazing pressure where treed, stocking rate remained constant, however, at high grazing pressure where treed, it was reduced after 4 years. The annual liveweight gain increased from 0.37 to 0.45 to 0.51 kg/head.day as grazing pressure was reduced from high to medium to low grazing pressure respectively, and across grazing pressures it decreased from 0.49 where cleared to 0.39 kg/head.day where treed. Liveweight gain per hectare increased under low grazing pressure and declined at medium and high pressures. Body condition scores responded positively to lower grazing pressure and a lack of tree competition to pastures. This treatment combination also produced higher animal sale values. Pasture biomass, basal area and ground cover were all affected negatively by increasing grazing pressure. Conclusions Grazing 25% of autumn pasture improved dry matter production, species composition and land condition, and increased steer growth rates, body condition and their market value. This grazing pressure produced an increasing trend in stocking rates relative to the decline at higher grazing pressures. Higher liveweight gain/ha was produced initially at high grazing pressure (75% utilisation), however, after 4 years animal condition and pastures deteriorated, requiring a reduction in stocking rate to maintain the condition of both the remaining animals and the pastures. Managing tree competition to pastures is necessary to maintain the higher animal production potential. Implications This objective information demonstrates the benefits for cattle, pastures and long-term economic outcomes of managing for conservative grazing pressure and controlling tree competition to pasture in this woodland. Applying these findings can improve beef business outcomes and provide management groups with objective educational resources.

Grazing Altered the Pattern of Woody Plants and Shrub Encroachment in a Temperate Savanna Ecosystem

Ulmus pumila-dominated temperate savanna is an important tree-grass complex ecosystem in the Otindag sand land, northern China. To date, few investigations have been undertaken on the spatial patterns and structure of this ecosystem and its driving factors under different grazing pressures. The objective of our study therefore is to explore whether grazing has affected the population structure/pattern of woody plants and shrub encroachment in a temperate savanna ecosystem. Results indicate that species richness and seedlings decreased with increasing grazing pressure. An increase in grazing pressure did not significantly affect adult-tree density, but it hindered the normal regeneration of U. pumila seedlings, further inducing population decline. U. pumila seedlings had a more significant aggregated distribution than juvenile or adult trees. The adult and juvenile trees had an aggregated distribution at the small scale and a random distribution at the large scale. Shrubs also showed a significant aggregated distribution. No clear effect on the spatial patterns of adult trees was observed; however, there was a noticeable effect for juveniles and seedlings under different grazing pressures. U. pumila seedlings had a positive association with their juveniles and Spiraea aquilegifolia, but a negative association with Caragana microphylla. Shrub encroachment occurred with decreasing grazing pressures. In conclusion, overgrazing led to the decline of U. pumila population, but the decrease in grazing pressure increased shrub encroachment in the temperate savanna ecosystem. Moderate grazing management may be a better way to enhance the stability of U. pumila population and reduce shrub encroachment.

Grazing and tree ‘clearing’ alter grass-associated invertebrate assemblages in an Australian tropical grassy woodland

To evaluate the response of invertebrates to ‘clearing’ and grazing pressure impacts, a previously grazed but uncleared grassy woodland in central Queensland was manipulated to provide four grazing pressures (destocked, low, moderate and high) and two tree treatments (with trees, i.e. untreated, and ‘cleared’, i.e. trees and saplings poisoned with herbicides), with two replicates of each, making 16 plots in total. Monitoring was carried out in 1998, approximately four years post-establishment of the treatments. Two types of samples were taken: pitfall for ground-active fauna and suction for grass-associated fauna. Overall, 23 orders of invertebrates were sampled by pitfalls and 22 by suction. Significant effects of grazing on invertebrate assemblages were detected by both methods, but no effects were detected from ‘clearing’. There was a gradation in the invertebrate assemblages from low to high grazing pressure, the invertebrate assemblages in the paddocks with the highest grazing differing most from those in the destocked and low-grazing-pressure paddocks. Notwithstanding the lack of effect of ‘clearing’ at the assemblage level, ground-active invertebrates and some grass-associated invertebrates increased in abundance following ‘clearing’, possibly reflecting an increase in the quality of the resource base. However, ground-active invertebrates and grass-associated invertebrates showed contrasting responses to grazing pressure, the former increasing, possibly reflecting changes in trapability due to the more open vegetation structure at higher grazing pressures. The abundance of grass-associated invertebrates declined by 50–80% with increased grazing – although with complex changes in assemblage structure. Despite those declines, the basic trophic pyramid remained, and, along with that, the potential for recovery of invertebrate assemblages and associated ecosystem services with reduction in grazing intensity. With 80% of Queensland grazed, the reduction in invertebrate abundance has implications for the viability of insectivores, particularly mobile fauna such as birds, at a landscape scale. It is recommended that the utility of using suction samples as a basis for assessing ecosystem functional health be investigated and that grazing pressure be reduced to increase invertebrate assemblages of rangeland pastures and to improve sustainability.

Factors determining shrub abundance on uncultivable hill country

Development of mānuka (Leptospermum scoparium) and gorse (Ulex europaeus) is a widespread problem on pastoral hill country and is associated with reduced fertiliser inputs and grazing pressures. Using mānuka as a source for specialty products offers a potentially new, profitable enterprise alongside livestock and forestry. However, there is a lack of quantitative information on the optimum soil nutrient status and associated fertiliser programme to encourage presence and growth of this species. In a survey across 324 grazed sites, mānuka had greatest presence on steep slopes (>25o) and soils with Olsen P

Impact of Livestock Grazing on the Floristic Composition: A Case Study of the Mount of Tessala, Western Algeria

The present work focuses on evaluating the impact of livestock grazing on the floristic composition in the mount of Tessala (Western Algeria). Phytoecological surveys were carried out at seven stations around north and south slopes of the mount. The obtained results through Principal Components Analysis (PCA) indicated the impact of man and herd on the floristic composition of sampling stations. Indeed, stations where grazing is low, have greater species richness marked by the strong presence of palatable species, unlike stations under permanent grazing, characterized in particular by the appearance of non-palatable species. Moreover, we note the dominance of therophytes at all stations not only due to grazing pressures but also to drought in the study area. DOI: http://dx.doi.org/10.3126/ije.v3i3.11078 International Journal of Environment Vol.3(3) 2014: 186-200