Ecological, biophysical and animal production responses to strategic-rest grazing in Australia and worldwide

Abstract

Livestock grazing can facilitate the maintenance of biodiversity in landscapes or cause landscape degradation and biodiversity loss. With a global population expected to surpass 9 billion people by 2050, there will be increasing pressure on the world's grazing lands to produce protein while minimising impacts on landscapes. This thesis explores the potential for grazing that incorporates extended and planned rest (Strategic-rest grazing, hereafter SRG) to enable continuing livestock production while also maintaining biodiversity and biophysical functions. In Chapter 2, I conducted a global meta-analysis comparing impacts of SRG to continuously grazed or ungrazed areas. I found that total groundcover and animal production per hectare were significantly greater with SRG compared to continuous grazing, while biomass, plant richness, plant diversity and animal weight gain did not differ between grazing treatments. Where the length of rest, relative to graze time increased with SRG, there were significant increases in biomass and further increases in groundcover and animal production per hectare in comparison to continuous grazing. These findings highlight the importance of incorporating the length of rest relative to graze duration into analyses comparing grazing systems. I found that the main focus of research around SRG differed between major geographic regions and climate zones. North American, Australian and New Zealand research mostly focused on short-term animal productivity, as did research in temperate areas. In contrast, research from Europe predominantly focused on biodiversity conservation. Research in more arid areas has focused largely on general sustainability for continuing animal production. Where richness and diversity of flora and fauna were compared between SRG and continuously grazed areas, responses were mostly favourable in SDG areas, or there was no difference. There were few examples of negative outcomes in SRG areas. Where richness and diversity in SRG areas were compared to ungrazed areas there was often no difference between SRG and ungrazed. Despite the often-favourable responses for production and ecological outcomes with SRG, a very small number of studies have considered the potential to achieve animal production and biodiversity conservation simultaneously with SRG approaches. This suggests we have limited understanding of trade-offs and synergies between these two goals. Ground-layer biodiversity and landscape function outcomes were assessed in naturalised pastures on six properties managed with short-duration grazing (hereafter SDG, a form of SRG) and compared with outcomes on properties managed in ways more typical of the region (largely continuous and with unplanned rest; hereafter RP). With SDG management there was approximately 19% greater perennial herbaceous cover and a corresponding 14% lower cover of undesirable introduced annual plants. Significant improvement in attributes relating to landscape functioning were also seen with SDG management, with environmental factors less important in influencing these attributes. Pasture composition also differed between management approaches with increased cover of favourable forage species and reduced cover of species that increase under heavy grazing pressure with SDG management. There was minimal difference in the richness and Shannon-Wiener diversity in the ground-layer of pastures managed in contrasting ways. Insects are an important component of overall landscape biodiversity and are sensitive to changes in land-use and agricultural intensification. Insect richness and abundance were assessed on RP and SDG properties and found to be significantly higher on SDG sites. These increases were likely largely due to the greater cover of tall perennial plants and litter cover and increased structural heterogeneity of the pasture sward with SDG management. These increases suggest there is potential for altered grazing practices to improve the capacity of grazed landscapes to provide ecosystem services from insects such as natural pest control and pollination, as well as provide food resources for wildlife. This thesis has highlighted the potential to balance animal production, biophysical and biodiversity outcomes with grazing incorporating extended rest and that research to-date has largely been on animal production outcomes rather than biodiversity responses. Importantly, it highlights that minimal research has considered trade-offs and synergies between animal production and biodiversity conservation outcomes, and the potential to achieve both simultaneously. If we are to meet the growing demand for protein from the world's grazing lands, while also preventing landscape degradation and sustaining biodiversity, it is essential to fill this knowledge gap.