An analysis of the annual costs of weeds in seven winter crops across Australia demonstrated that the most important 15 weed species cause substantial annual costs in both financial and economic terms. Using survey data captured over the 1998-1999 growing season, the financial cost of these weeds in seven crops was estimated to be AU$1,182 million. The main components of this cost were herbicides (AU$571 million), the competitive effects of residual weeds (AU$380 million), and tillage (AU$206 million) while weed contamination of grain was a minor cost (AU$25 million). Across all regions, the most economically important weeds were annual ryegrass, wild oats, and wild radish, although there were regional differences in importance. An economic surplus analysis determined the annual economic cost of weeds in annual winter crops to be AU$1,279 million. This surplus loss represented 17% of the gross value of Australian grain and oilseed production in 1998-1999. Australian grain producers incurred a major loss, with a reduction in producer surplus of AU$1,047 million. Australian grain consumers had a large consumer surplus loss (AU$229 million), while international consumers suffered a small loss and international grain producers gained a small producer surplus from the higher grain prices.JEL classification: D60, Q11, Q16

The introduction of domesticated animals into new environments can lead to considerable ecological disruption, and it can be difficult to predict their impact on the new ecosystem. In this study, we use faecal metabarcoding to characterize the diets of three ruminant taxa in the rangelands of south-western New South Wales, Australia. Our study organisms included goats (Capra aegagrus hircus) and two breeds of sheep (Ovis aries): Merinos, which have been present in Australia for over two hundred years, and Dorpers, which were introduced in the 1990s. We used High-Throughput Sequencing methods to sequence the rbcL and ITS2 genes of plants in the faecal samples, and identified the samples using the GenBank and BOLD online databases, as well as a reference collection of sequences from plants collected in the study area. We found that the diets of all three taxa were dominated by the family Malvaceae, and that the Dorper diet was more diverse than the Merino diet at both the family and the species level. We conclude that Dorpers, like Merinos, are potentially a threat to some vulnerable species in the rangelands of New South Wales.

Abstract. The growing popularity of the Dorper breed of sheep potentially may have implications for the ecological sustainability of the semiarid and arid rangelands of southern Australia. The implications are heightened by forecasts of a warming and drying climate in these rangelands, which may in itself place native vegetation under increasing stress. While the Dorper breed of sheep offers important production advantages, little is known from research under Australian conditions about their grazing ecology and management requirements from a natural resource perspective. Key factors identified from this review of literature from other countries include a high fertility and fecundity, a generalist feeding strategy, a high growth rate and a capacity to survive and reproduce under low-rainfall conditions. The wider range of plant species selected by the Dorper compared with the traditional Merino breed of sheep potentially creates both opportunities and risks for rangeland condition. Less selective grazing may reduce pressure on some species but the capacity to harvest sufficient nutrients over a smaller area could concentrate grazing and promote resource degradation. High reproductive efficiency under a wide range of seasonal conditions may lead to more rapid onset of overgrazing and will require close attention to both natural resources and animal marketing if resource degradation is to be avoided.

Thickening of native shrubs is a major problem in many ‘semi-arid woodlands’ as significant increase in shrub density is often negatively correlated with herbaceous vegetation and leads to reduced pasture production and soil erosion. This project aimed to test the hypothesis that temporary cropping (up to three crops in 15 years) consistently increases the density of native perennial grasses following the removal of shrubs. A total of 30 paddocks that had been cropped during the last 20 years were randomly selected using a satellite-based database that documented annual clearing and cropping history from 1987 to 2003. Paddocks were classified into four types based on clearing and cropping history and grazing management – not cleared (shrubs), regrowth (re-invaded by shrubs), set stocked (cropped and grazed), light/rotationally grazed (cropped and grazed). The responses of vegetation and soil (chemical and physical) properties to clearing and cropping were evaluated. Results indicated that ground cover, native perennial grass cover and standing dry matter were highest under light/rotationally grazed conditions. The shrub state represents a stable state within the Cobar pediplain brought about due to land-use change in the form of overgrazing and/or the removal of fire from the system. An alternative stable state was achieved as a result of disturbance in the form of clearing, cropping and grazing management thereby directly altering the shrub population. The resilience of this state is largely dependent on the grazing management system used and on the prevention of shrub from re-establishing while failure to control shrubs could lead to the re-emergence of the Shrub State. We conclude that native grasslands do regenerate following cropping after removal of shrubs. The importance of grazing management for restoring perennial ground cover following removal of shrubs and temporary cropping has been clearly demonstrated by the study.

Chicory is a highly productive and nutritious forage that is sensitive to grazing. A challenge for grazing management is to prevent pasture decline associated with the replacement of productive species by undesirable weedy species. The competitive ability, persistence and productivity of chicory were investigated under a gradient of grazing management practices ranging from continuous to short grazing–long rest treatments by merino wethers. Chicory density and percentage composition declined after the first year of continuous grazing. The density of chicory in all rotationally grazed treatments initially increased and then declined significantly after the third year, except in the short grazing–long rest treatment. The percentage composition of chicory in the pasture was influenced mainly by the frequency of grazing and to a lesser extent by stand age and was inversely related to the combined percentage composition of annual grasses and broadleaf species. The percentage composition of legumes was dependent more on seasonal conditions than on treatment. The interactions between chicory, grasses and broadleaf weeds are most probably driven by their competition for nitrogen.

Abstract. The recent trend to farming or re-domestication of feral goats poses serious questions for the ecological sustainability of the semiarid and arid rangelands of southern Australia. This paper reviews aspects of the biology and grazing habits of goats, and aspects of the Australian goat industry, relevant to their sustainable management in livestock enterprises. Key factors identified include high fertility and fecundity even under low seasonal rainfall conditions and a generalist feeding strategy. Adverse consequences for rangeland condition can be expected if seasonal or market conditions result in an imbalance between population growth and turnoff, resulting in high grazing pressures. Given the limited control of the reproductive process at the current stage of the development of goat farming, strategies aimed at ensuring continuity of sale of goats (e.g. on-property feed lots or supply chain and market development) will be important in ensuring that imbalances are avoided. Conservative stocking rates and use of seasonal risk management tools are also particularly relevant. The major research and development needs identified by this review, from a resource management perspective, concern the appropriate dry sheep equivalent rating for goat classes based on age, sex and reproductive status, the extent and consequences of heterogeneity of grazing in space, time, and across forage species, and development of means of establishing sustainable stocking rates based on the use of all available forage sources, including browse.

The potential carbon sequestration in rangelands is largely due to the extensive areas they occupy, even though levels of soil organic carbon (SOC) are low. There is considerable uncertainty in achieving this potential due to the inherent patchy spatial and temporal distribution of rangeland vegetation and resources. At a paddock scale, determining appropriate sampling scales is a critical first step in the accurate estimation of size and spatial distribution of stocks of SOC. This issue was addressed by examining the spatial distribution of SOC and determining the association of SOC with other site characteristics such as ground cover and vegetation. This was done in a pilot study conducted in a 136-ha paddock located on the Cobar Pediplain Bioregion in western New South Wales, Australia. Each of 104 sites was sampled using a 0.25-m2 quadrat to assess biomass and ground cover category (percentage of perennial plants, bare ground, cryptogams, annual plants and litter) of a soil core taken from the centre of each quadrat, and proximity to trees and shrubs. The soil core was used to determine total organic C (TOC), total N (TN) and the C : N ratio at four depths (0–5; 5–10; 10–20; 20–30 cm). From the quadrat and ground cover categories of the soil cores, six microsite categories were identified using cluster analysis: cryptogams; litter (≥25% litter); bare (≥60% bare ground); annual (≥40% annual plants); litter-P (≥15% litter and ≥10% perennial plants) and perennial (≥30% perennial plants). Microsite, depth in soil profile and the presence of trees and shrubs all had a significant (P < 0.001) effect on TOC concentration. The predicted means (s.e. of mean) of TOC at the soil surface (0–5 cm) were perennial 1.26 (0.04) %; litter-P 1.20 (0.05) %; annual 1.18 (0.06) %; litter 1.12 (0.05) %; bare 1.03 (0.05) % and cryptogams 0.88 (0.06) %. Higher concentrations of TOC were associated with the presence of trees and were almost 30% higher in close proximity (<1 m) to a tree. There was a consistent finding that higher concentrations of TOC, TN and the high values of C : N ratio were each associated with higher ground cover of perennial plants. The autocorrelation range for soil C stocks was ~30 m and for categories of ground cover which varied from 10 m to over 200 m. The spatial predictions for ground cover of perennial plants closely mirrored those for C stocks, which were 22.9 Mg C ha–1 in the top 30 cm of soil in this environment. As both tree proximity and ground cover had a significant effect on TOC, quantifying the levels of soil organic C at a paddock scale will require an understanding of the spatial patterns of vegetation (woody and ground cover), which provides a basis for within-paddock stratification before soil sampling.

This study compared the effects of grazing management on soil organic carbon (OC) stocks in the semi-arid rangelands of New South Wales, Australia. A field survey was conducted at three locations (Brewarrina, Cobar–North and Cobar–South), with paired sites of long-term (>8 years) rotational grazing management and continuously grazed pastures (either set stocked or no stocking). At each location, soil OC, carbon (C) fractions, soil nitrogen (N) and microsite and site factors (including ground cover and woody vegetation) were measured. The control of total grazing pressure (TGP) through rotational grazing and exclusion fencing did not increase soil C stocks compared with continuous grazing for the majority of comparisons. However, in some parts of the landscape, higher soil C stock was found with TGP control, for example on the ridges (21.6 vs 13.3 t C ha–1 to 0.3 m). C stocks increased with litter and perennial ground cover and with close proximity to trees. At Brewarrina, C stocks were positively affected by perennial plant cover (P < 0.001) and litter (P < 0.05), whereas at Cobar–North and Cobar–South C stocks were positively affected by the presence of trees (P < 0.001), with higher C stocks in close proximity to trees, and with increasing litter cover (P < 0.01). The present study demonstrates that natural resource benefits, such as increased perennial cover, can be achieved through controlling TGP in the rangelands but increases in soil C may be limited in certain parts of the landscape. These findings also highlight that interactions between managed and unmanaged TGP and microsite factors, such as ground cover and proximity to woody vegetation, need to be considered when evaluating the role of changed grazing management on soil C.