Weeds of Australian rangelands

Despite recognition that non-native plant species represent a substantial risk to natural systems, there is currently no compilation of weeds that impact on the biodiversity of the rangelands within Australia. Using published and expert knowledge, this paper presents a list of 622 non-native naturalised species known to occur within the rangelands. Of these, 160 species (26%) are considered a current threat to rangeland biodiversity. Most of these plant species have been deliberately introduced for forage or other commercial use (e.g. nursery trade). Among growth forms, shrubs and perennial grasses comprise over 50% of species that pose the greatest risk to rangeland biodiversity. We identify regions within the rangelands containing both high biodiversity values and a high proportion of weeds and recommend these areas as priorities for weed management. Finally, we examine the resources available for weed detection and identification since detecting weeds in the early stages of invasion is the most cost effective method of reducing further impact.

Validating economic and environmental sustainability of a short-term summer forage legume in dryland wheat cropping systems in south-west Queensland.

The present study set out to test the hypothesis through field and simulation studies that the incorporation of short-term summer legumes, particularly annual legume lablab (Lablab purpureus cv. Highworth), in a fallow-wheat cropping system will improve the overall economic and environmental benefits in south-west Queensland. Replicated, large plot experiments were established at five commercial properties by using their machineries, and two smaller plot experiments were established at two intensively researched sites (Roma and St George). A detailed study on various other biennial and perennial summer forage legumes in rotation with wheat and influenced by phosphorus (P) supply (10 and 40 kg P/ha) was also carried out at the two research sites. The other legumes were lucerne (Medicago sativa), butterfly pea (Clitoria ternatea) and burgundy bean (Macroptilium bracteatum). After legumes, spring wheat (Triticum aestivum) was sown into the legume stubble. The annual lablab produced the highest forage yield, whereas germination, establishment and production of other biennial and perennial legumes were poor, particularly in the red soil at St George. At the commercial sites, only lablab-wheat rotations were experimented, with an increased supply of P in subsurface soil (20 kg P/ha). The lablab grown at the commercial sites yielded between 3 and 6 t/ha forage yield over 2-3 month periods, whereas the following wheat crop with no applied fertiliser yielded between 0.5 to 2.5 t/ha. The wheat following lablab yielded 30% less, on average, than the wheat in a fallow plot, and the profitability of wheat following lablab was slightly higher than that of the wheat following fallow because of greater costs associated with fallow management. The profitability of the lablab-wheat phase was determined after accounting for the input costs and additional costs associated with the management of fallow and in-crop herbicide applications for a fallow-wheat system. The economic and environmental benefits of forage lablab and wheat cropping were also assessed through simulations over a long-term climatic pattern by using economic (PreCAPS) and biophysical (Agricultural Production Systems Simulation, APSIM) decision support models. Analysis of the long-term rainfall pattern (70% in summer and 30% in winter) and simulation studies indicated that ~50% time a wheat crop would not be planted or would fail to produce a profitable crop (grain yield less than 1 t/ha) because of less and unreliable rainfall in winter. Whereas forage lablab in summer would produce a profitable crop, with a forage yield of more than 3 t/ha, ~90% times. Only 14 wheat crops (of 26 growing seasons, i.e. 54%) were profitable, compared with 22 forage lablab (of 25 seasons, i.e. 90%). An opportunistic double-cropping of lablab in summer and wheat in winter is also viable and profitable in 50% of the years. Simulation studies also indicated that an opportunistic lablab-wheat cropping can reduce the potential runoff+drainage by more than 40% in the Roma region, leading to improved economic and environmental benefits.

Poor adoption of ley-pastures in south-west Queensland: biophysical, economic and social constraints.

The present review identifies various constraints relating to poor adoption of ley-pastures in south-west Queensland, and suggests changes in research, development and extension efforts for improved adoption. The constraints include biophysical, economic and social constraints. In terms of biophysical constraints, first, shallower soil profiles with subsoil constraints (salt and sodicity), unpredictable rainfall, drier conditions with higher soil temperature and evaporative demand in summer, and frost and subzero temperature in winter, frequently result in a failure of established, or establishing, pastures. Second, there are limited options for legumes in a ley-pasture, with the legumes currently being mostly winter-active legumes such as lucerne and medics. Winter-active legumes are ineffective in improving soil conditions in a region with summer-dominant rainfall. Third, most grain growers are reluctant to include grasses in their ley-pasture mix, which can be uneconomical for various reasons, including nitrogen immobilisation, carryover of cereal diseases and depressed yields of the following cereal crops. Fourth, a severe depletion of soil water following perennial ley-pastures (grass + legumes or lucerne) can reduce the yields of subsequent crops for several seasons, and the practice of longer fallows to increase soil water storage may be uneconomical and damaging to the environment. Economic assessments of integrating medium- to long-term ley-pastures into cropping regions are generally less attractive because of reduced capital flow, increased capital investment, economic loss associated with establishment and termination phases of ley-pastures, and lost opportunities for cropping in a favourable season. Income from livestock on ley-pastures and soil productivity gains to subsequent crops in rotation may not be comparable to cropping when grain prices are high. However, the economic benefits of ley-pastures may be underestimated, because of unaccounted environmental benefits such as enhanced water use, and reduced soil erosion from summer-dominant rainfall, and therefore, this requires further investigation. In terms of social constraints, the risk of poor and unreliable establishment and persistence, uncertainties in economic and environmental benefits, the complicated process of changing from crop to ley-pastures and vice versa, and the additional labour and management requirements of livestock, present growers socially unattractive and complex decision-making processes for considering adoption of an existing medium- to long-term ley-pasture technology. It is essential that research, development and extension efforts should consider that new ley-pasture options, such as incorporation of a short-term summer forage legume, need to be less risky in establishment, productive in a region with prevailing biophysical constraints, economically viable, less complex and highly flexible in the change-over processes, and socially attractive to growers for adoption in south-west Queensland.

The performance of irrigated mixtures of tall fescue, ryegrass and white clover in subtropical Australia. 1. The effects of sowing mixture combinations, nitrogen and oversowing on establishment, productivity, botanical composition and persistence.

In the subtropics of Australia, the ryegrass component of irrigated perennial ryegrass (Lolium perenne) - white clover (Trifolium repens) pastures declines by approximately 40% in the summer following establishment, being replaced by summer-active C4 grasses. Tall fescue (Festuca arundinacea) is more persistent than perennial ryegrass and might resist this invasion, although tall fescue does not compete vigorously as a seedling. This series of experiments investigated the influence of ryegrass and tall fescue genotype, sowing time and sowing mixture as a means of improving tall fescue establishment and the productivity and persistence of tall fescue, ryegrass and white clover-based mixtures in a subtropical environment. Tall fescue frequency at the end of the establishment year decreased as the number of companion species sown in the mixture increased. Neither sowing mixture combinations nor sowing rates influenced overall pasture yield (of around 14 t/ha) in the establishment year but had a significant effect on botanical composition and component yields. Perennial ryegrass was less competitive than short-rotation ryegrass, increasing first-year yields of tall fescue by 40% in one experiment and by 10% in another but total yield was unaffected. The higher establishment-year yield (3.5 t/ha) allowed Dovey tall fescue to compete more successfully with the remaining pasture components than Vulcan (1.4 t/ha). Sowing 2 ryegrass cultivars in the mixture reduced tall fescue yields by 30% compared with a single ryegrass (1.6 t/ha), although tall fescue alone achieved higher yields (7.1 t/ha). Component sowing rate had little influence on composition or yield. Oversowing the ryegrass component into a 6-week-old sward of tall fescue and white clover improved tall fescue, white clover and overall yields in the establishment year by 83, 17 and 11%, respectively, but reduced ryegrass yields by 40%. The inclusion of red (T. pratense) and Persian (T. resupinatum) clovers and chicory (Cichorium intybus) increased first-year yields by 25% but suppressed perennial grass and clover components. Yields were generally maintained at around 12 t/ha/yr in the second and third years, with tall fescue becoming dominant in all 3 experiments. The lower tall fescue seeding rate used in the first experiment resulted in tall fescue dominance in the second year following establishment, whereas in Experiments 2 and 3 dominance occurred by the end of the first year. Invasion by the C4 grasses was relatively minor (<10%) even in the third year. As ryegrass plants died, tall fescue and, to a lesser extent, white clover increased as a proportion of the total sward. Treatment effects continued into the second, but rarely the third, year and mostly affected the yield of one of the components rather than total cumulative yield. Once tall fescue became dominant, it was difficult to re-introduce other pasture components, even following removal of foliage and moderate renovation. Severe renovation (reducing the tall fescue population by at least 30%) seems a possible option for redressing this situation.

Efficacy of herbicides on weedy Sporobolus grasses in the glasshouse in Australia

Twenty three herbicides including the current registered herbicides were screened for activity on pre-emergent, juvenile and mature plants of the weedy Sporobolus grass species Sporobolus pyramidalis P.Beauv. and Sporobolus fertilis (Steud.) Clayton. No new herbicides trialled effectively controlled mature plants. Propaquizafop, fluazifop-P-hutyI, flupropanate, haloxyfop-R-methyl ester, glyphosate-ipa and clethodim + haloxyfop-R-methyl ester mix showed good activity on juvenile plants while atrazine, flupropanate, dithiopyr and imazapyr where effective as pre-emergent herbicides. Further work needs to be done to define the recommended application rates for juvenile and pre-emergent plant stages and to determine the selectivity of these herbicides on native and exotic pasture grasses.

Amenity grasses for salt-affected parks in coastal Australia

In February 2004, Redland Shire Council with help from a Horticulture Australia research project was able to establish a stable grass cover of seashore paspalum (Paspalum vaginatum) on a Birkdale park where the soil had previously proved too salty to grow anything else. Following on from their success with this small 0.2 ha demonstration area, Redland Shire has since invested hundreds of thousands of dollars in successfully turfing other similarly “impossible” park areas with seashore paspalum. Urban salinity can arise for different reasons in different places. In inland areas such as southern NSW and the WA wheatbelt, the usual cause is rising groundwater bringing salt to the surface. In coastal sites, salt spray or periodic tidal inundation can result in problems. In Redland Shire’s case, the issue was compacted marine sediments (mainly mud) dug up and dumped to create foreshore parkland in the course of artificial canal developments. At Birkdale, this had created a site that was both strongly acid and too salty for most plants. Bare saline scalds were interspersed by areas of unthrifty grass. Finding a salt tolerant grass is no “silver bullet” or easy solution to salinity problems. Rather, it buys time to implement sustainable long-term establishment and maintenance practices, which are even more critical than with conventional turfgrasses. These practices include annual slicing or coring in conjunction with gypsum/dolomite amendment and light topdressing with sandy loam soil (to about 1 cm depth), adequate maintenance fertiliser, weed control measures, regular leaching irrigation was applied to flush salts below the root zone, and irrigation scheduling to maximise infiltration and minimise run off. Three other halophytic turfgrass species were also identified, each of them adapted to different environments, management regimes and uses. These have been shortlisted for larger-scale plantings in future work.

Adaptation and management of Australian buffalograss cultivars for shade and water conservation

Soft-leaf buffalo grass is increasing in popularity as an amenity turfgrass in Australia. This project was instigated to assess the adaptation of and establish management guidelines for its use in Australias vast array of growing environments. There is an extensive selection of soft-leaf buffalo grass cultivars throughout Australia and with the countrys changing climates from temperate in the south to tropical in the north not all cultivars are going to be adapted to all regions. The project evaluated 19 buffalo grass cultivars along with other warm-season grasses including green couch, kikuyu and sweet smother grass. The soft-leaf buffalo grasses were evaluated for their growth and adaptation in a number of regions throughout Australia including Western Australia, Victoria, ACT, NSW and Queensland. The growth habit of the individual cultivars was examined along with their level of shade tolerance, water use, herbicide tolerance, resistance to wear, response to nitrogen applications and growth potential in highly alkaline (pH) soils. The growth habit of the various cultivars currently commercially available in Australia differs considerably from the more robust type that spreads quicker and is thicker in appearance (Sir Walter, Kings Pride, Ned Kelly and Jabiru) to the dwarf types that are shorter and thinner in appearance (AusTine and AusDwarf). Soft-leaf buffalo grass types tested do not differ in water use when compared to old-style common buffalo grass. Thus, soft-leaf buffalo grasses, like other warm-season turfgrass species, are efficient in water use. These grasses also recover after periods of low water availability. Individual cultivar differences were not discernible. In high pH soils (i.e. on alkaline-side) some elements essential for plant growth (e.g. iron and manganese) may be deficient causing turfgrass to appear pale green, and visually unacceptable. When 14 soft-leaf buffalo grass genotypes were grown on a highly alkaline soil (pH 7.5-7.9), cultivars differed in leaf iron, but not in leaf manganese, concentrations. Nitrogen is critical to the production of quality turf. The methods for applying this essential element can be manipulated to minimise the maintenance inputs (mowing) during the peak growing period (summer). By applying the greatest proportion of the turfs total nitrogen requirements in early spring, peak summer growth can be reduced resulting in a corresponding reduction in mowing requirements. Soft-leaf buffalo grass cultivars are more shade and wear tolerant than other warm-season turfgrasses being used by homeowners. There are differences between the individual buffalo grass varieties however. The majority of types currently available would be classified as having moderate levels of shade tolerance and wear reasonably well with good recovery rates. The impact of wear in a shaded environment was not tested and there is a need to investigate this as this is a typical growing environment for many homeowners. The use of herbicides is required to maintain quality soft-leaf buffalo grass turf. The development of softer herbicides for other turfgrasses has seen an increase in their popularity. The buffalo grass cultivars currently available have shown varying levels of susceptibility to the chemicals tested. The majority of the cultivars evaluated have demonstrated low levels of phytotoxicity to the herbicides chlorsulfuron (Glean) and fluroxypyr (Starane and Comet). In general, soft leaf buffalo grasses are varied in their makeup and have demonstrated varying levels of tolerance/susceptibility/adaptation to the conditions they are grown under. Consequently, there is a need to choose the cultivar most suited to the environment it is expected to perform in and the management style it will be exposed to. Future work is required to assess how the structure of the different cultivars impacts on their capacity to tolerate wear, varying shade levels, water use and herbicide tolerance. The development of a growth model may provide the solution.

Management Guidelines for New Warm-Season Grasses in Australia

After more than 30 years in which ‘Tifgreen’ and ‘Tifdwarf’ were the only greens-quality varieties available, the choice for golf courses and bowls clubs in northern Australia has been expanded to include six new Cynodon hybrids [Cynodon dactylon (L.) Pers x Cynodon transvaalensis Burtt-Davy]. Five of these – ‘Champion Dwarf’ (Texas), ‘MS-Supreme’ (Mississippi), FloraDwarf™ (Florida), ‘TifEagle’ (Georgia), MiniVerde™ (Arizona) - are from US breeding programs, while the sixth, ‘TL2’ (marketed as Novotek™) was selected in north Queensland. The finer, denser and lower growing habit of the “ultradwarf” cultivars allows very low mowing heights (e.g. 2.5 mm) to be imposed, resulting in denser and smoother putting and bowls surfaces. In addition to the Cynodon hybrids, four new greens quality seashore paspalum (Paspalum vaginatum O. Swartz) cultivars including ‘Sea Isle 2000’, Sea Isle Supreme™, Velvetene™ and Sea Dwarf™ (where tolerance of salty water is required) expands the range of choices for greens in difficult environments. The project was developed to determine (a) the appropriate choice of cultivar for different environments and budgets, and (b) best management practices for the new cultivars which differ from the Cynodon hybrid industry standards ‘Tifgreen’ and ‘Tifdwarf’. Management practices, particularly fertilising, mowing heights and frequency, and thatch control were investigated to determine optimum management inputs and provide high quality playing surfaces with the new grasses. To enable effective trialling of these new and old cultivars it was essential to have a number of regional sites participating in the study. Drought and financial hardship of many clubs presented an initial setback with numerous clubs wanting to be involved in the study but were unable to commit due to their financial position at the time. The study was fortunate to have seven regional sites from Queensland, New South Wales, Victoria and South Australia volunteer to be involved in the study which would add to the results being collected at the centralised test facility being constructed at DEEDI’s Redlands Research Station. The major research findings acquired from the eight trial sites included: • All of the new second generation “ultradwarf” couchgrasses tend to produce a large amount of thatch with MiniVerde™ being the greatest thatch producer, particularly compared to ‘Tifdwarf’ and ‘Tifgreen’. The maintenance of the new Cynodon hybrids will require a program of regular dethatching/grooming as well as regular light dustings of sand. Thatch prevention should begin 3 to 4 weeks after planting a new “ultradwarf” couchgrass green, with an emphasis on prevention rather than control. • The “ultradwarfs” produced faster green speeds than the current industry standards ‘Tifgreen’ and ‘Tifdwarf’. However, all Cynodon hybrids were considerably faster than the seashore paspalums (e.g. comparable to the speed diference of Bentgrass and couchgrass) under trial conditions. Green speed was fastest being cut at 3.5 mm and rolled (compared to 3.5 mm cut, no roll and 2.7 mm cut, no roll). • All trial sites reported the occurrence of disease in the Cynodon hybrids with the main incidence of disease occurring during the dormancy period (autumn and winter). The main disease issue reported was “patch diseases” which includes both Gaumannomyces and Rhizoctonia species. There was differences in the severity of the disease between cultivars, however, the severity of the disease was not consistent between cultivars and is largely attributed to an environment (location) effect. In terms of managing the occurrence of disease, the incidence of disease is less severe where there is a higher fertility rate (about 3 kgN/100m2/year) or a preventitatve fungicide program is adopted. • Cynodon hybrid and seashore paspalum cultivars maintained an acceptable to ideal surface being cut between 2.7 mm and 5.0 mm. “Ultradwarf” cultivars can tolerate mowing heights as low as 2.5 mm for short periods but places the plant under high levels of stress. Greens being maintained at a continually lower cutting height (e.g. 2.7 mm) of both species is achievable, but would need to be cut daily for best results. Seashore paspalums performed best when cut at a height of between 2.7 mm and 3.0 mm. If a lower cutting height is adopted, regular and repeated mowings are required to reduce scalping and produce a smooth surface. • At this point in time the optimum rate of nitrogen (N) for the Cynodon hybrids is 3 kg/100m2/year and while the seashore paspalums is 2 to 3 kg/100m2/year. • Dormancy occurred for all Cynodon and seashore paspalum culitvars from north in Brisbane (QLD) to south in Mornington Peninsula (VIC) and west to Novar Gardens (SA). Cynodon and Paspalum growth in both Victoria and South Australia was less favourable as a result of the cooler climates. • After combining the data collected from all eight sites, the results indicated that there can be variation (e.g. turfgrass quality, colour, disease resistance, performace) depending on the site and climatic conditions. Such evidence highlights the need to undertake genotype by environment (G x E) studies on new and old cultivars prior to conversion or establishment. • For a club looking to select either a Cynodon hybrid or seashore paspalum cultivar for use at their club they need to: - Review the research data. - Look at trial plots. - Inspect greens in play that have the new grasses. - Select 2 to 3 cultivars that are considered to be the better types. - Establish them in large (large enough to putt on) plots/nursery/practice putter. Ideally the area should be subjected to wear. - Maintain them exactly as they would be on the golf course/lawn bowls green. This is a critical aspect. Regular mowing, fertilising etc. is essential. - Assess them over at least 2 to 3 years. - Make a selection and establish it in a playing green so that it is subjected to typical wear.

Establishment and management of salt-tolerant amenity grasses to reduce urban salinity effect

This project built upon the successful outcomes of a previous project (TU02005) by adding to the database of salt tolerance among warm season turfgrass cultivars, through further hydroponic screening trials. Hydroponic screening trials focussed on new cultivars or cultivars that were not possible to cover in the time available under TU02005, including: 11 new cultivars of Paspalum vaginatum; 13 cultivars of Cynodon dactylon; six cultivars of Stenotaphrum secundatum; one accession of Cynodon transvaalensis; 12 Cynodon dactylon x transvaalensis hybrids; two cultivars of Sporobolus virginicus; five cultivars of Zoysia japonica; one cultivar of Z. macrantha, one common form of Z. tenuifolia and one Z. japonica x tenuifolia hybrid. The relative salinity tolerance of different turfgrasses is quantified in terms of their growth response to increasing levels of salinity, often defined by the salt level that equates to a 50% reduction in shoot yield, or alternatively the threshold salinity. The most salt tolerant species in these trials were Sporobolus virginicus and Paspalum vaginatum, consistent with the findings from TU02005 (Loch, Poulter et al. 2006). Cynodon dactylon showed the largest range in threshold values with some cultivars highly sensitive to salt, while others were tolerant to levels approaching that of the more halophytic grasses. Coupled with the observational and anecdotal evidence of high drought tolerance, this species and other intermediately tolerant species provide options for site specific situations in which soil salinity is coupled with additional challenges such as shade and high traffic conditions. By recognising the fact that a salt tolerant grass is not the complete solution to salinity problems, this project has been able to further investigate sustainable long-term establishment and management practices that maximise the ability of the selected grass to survive and grow under a particular set of salinity and usage parameters. Salt-tolerant turf grasses with potential for special use situations were trialled under field conditions at three sites within the Gold Coast City Council, while three sites, established under TU02005 within the Redland City Council boundaries were monitored for continued grass survival. Several randomised block experiments within Gold Coast City were established to compare the health and longevity of seashore paspalum (Paspalum vaginatum), Manila grass (Zoysia matrella), as well as the more tolerant cultivars of other species like buffalo grass (Stenotaphrum secundatum) and green couch (Cynodon dactylon). Whilst scientific results were difficult to achieve in the field situation, where conditions cannot be controlled, these trials provided valuable observational evidence of the likely survival of these species. Alternatives to laying full sod such as sprigging were investigated, and were found to be more appropriate for areas of low traffic as the establishment time is greater. Trials under controlled and protected conditions successfully achieved a full cover of Paspalum vaginatum from sprigs in a 10 week time frame. Salt affected sites are often associated with poor soil structure. Part of the research investigated techniques for the alleviation of soil compaction frequently found on saline sites. Various methods of soil de-compaction were investigated on highly compacted heavy clay soil in Redlands City. It was found that the heavy duplex soil of marine clay sediments required the most aggressive of treatments in order to achieve limited short-term effects. Interestingly, a well constructed sports field showed a far greater and longer term response to de-compaction operations, highlighting the importance of appropriate construction in the successful establishment and management of turfgrasses on salt affected sites. Fertiliser trials in this project determined plant demand for nitrogen (N) to species level. This work produced data that can be used as a guide when fertilising, in order to produce optimal growth and quality in the major turf grass species used in public parkland. An experiment commenced during TU02005 and monitored further in this project, investigated six representative warm-season turfgrasses to determine the optimum maintenance requirements for fertiliser N in south-east Queensland. In doing so, we recognised that optimum level is also related to use and intensity of use, with high profile well-used parks requiring higher maintenance N than low profile parks where maintaining botanical composition at a lower level of turf quality might be acceptable. Kikuyu (Pennisetum clandestinum) seemed to require the greatest N input (300-400 kg N/ha/year), followed by the green couch (Cynodon dactylon) cultivars ‘Wintergreen’ and ‘FLoraTeX’ requiring approximately 300 kg N/ha/year for optimal condition and growth. ‘Sir Walter’ (Stenotaphrum secundatum) and ‘Sea Isle 1’ (Paspalum vaginatum) had a moderate requirement of approximately 200 kg/ha/year. ‘Aussiblue’ (Digitaria didactyla)maintained optimal growth and quality at 100-200 kg N/ha/year. A set of guidelines has been prepared to provide various options from the construction and establishment of new grounds, through to the remediation of existing parklands by supporting the growth of endemic grasses. They describe a best management process through which salt affected sites should be assessed, remediated and managed. These guidelines, or Best Management Practices, will be readily available to councils. Previously, some high salinity sites have been turfed several times over a number of years (and Council budgets) for a 100% failure record. By eliminating this budgetary waste through targeted workable solutions, local authorities will be more amenable to investing appropriate amounts into these areas. In some cases, this will lead to cost savings as well as resulting in better quality turf. In all cases, however, improved turf quality will be of benefit to ratepayers, directly through increased local use of open space in parks and sportsfields and indirectly by attracting tourists and other visitors to the region bringing associated economic benefits. At the same time, environmental degradation and erosion of soil in bare areas will be greatly reduced.

Salt-tolerant amenity grasses to reduce salt effect

Assess establishment and management of salt tolerant turf grasses on salt affected parklands.

Management guidelines for warm-season greens grasses

Golf green, turf.

Enhancing pasture stability and profitability for producers in Poplar Box and Silver-leaved Ironbark woodlands.

Over 7 years, this project collected data about the pasture, tree and soil surface dynamics of two major Aristida/Bothriochloa pasture types within the eucalypt woodlands of central Queensland. Six different grazing management scenarios were compared ecologically and economically, along with the effects of spring burns and tree killing. Heavy stocking (3-4 ha per adult equivalent) produced the greatest short-term financial return from healthy pastures but was not a sustainable practice and long-term cash returns were no better than those from moderate stocking. The environmental benefits of moderate grazing over heavy grazing were very clear. Light stocking produced better environmental outcomes compared to moderate stocking but was clearly inferior with respect to economic returns. Killing silver-leaved ironbark trees near Rubyvale produced no measurable improvement in pasture growth or quality for at least 6 years whereas at Injune the same treatment of poplar box trees resulted in an immediate and large enhancement in pasture production and carrying capacity. The gritty red duplex soil at Rubyvale was much more erodible than the grey solodic at Injune although the latter becomes very erodible if the stable surface soil is breached. Good seasonal rainfall produced faster changes in pasture composition than extremes of grazing management. The perennial grasses were easier to recruit than to eliminate by grazing management changes.

Soil carbon stock in the tropical rangelands of Australia: Effects of soil type and grazing pressure, and determination of sampling requirement.

On-going, high-profile public debate about climate change has focussed attention on how to monitor the soil organic carbon stock (C(s)) of rangelands (savannas). Unfortunately, optimal sampling of the rangelands for baseline C(s) - the critical first step towards efficient monitoring - has received relatively little attention to date. Moreover, in the rangelands of tropical Australia relatively little is known about how C(s) is influenced by the practice of cattle grazing. To address these issues we used linear mixed models to: (i) unravel how grazing pressure (over a 12-year period) and soil type have affected C(s) and the stable carbon isotope ratio of soil organic carbon (delta(13)C) (a measure of the relative contributions of C(3) and C(4) vegetation to C(s)); (ii) examine the spatial covariation of C(s) and delta(13)C; and, (iii) explore the amount of soil sampling required to adequately determine baseline C(s). Modelling was done in the context of the material coordinate system for the soil profile, therefore the depths reported, while conventional, are only nominal. Linear mixed models revealed that soil type and grazing pressure interacted to influence C(s) to a depth of 0.3 m in the profile. At a depth of 0.5 m there was no effect of grazing on C(s), but the soil type effect on C(s) was significant. Soil type influenced delta(13)C to a soil depth of 0.5 m but there was no effect of grazing at any depth examined. The linear mixed model also revealed the strong negative correlation of C(s) with delta(13)C, particularly to a depth of 0.1 m in the soil profile. This suggested that increased C(s) at the study site was associated with increased input of C from C(3) trees and shrubs relative to the C(4) perennial grasses; as the latter form the bulk of the cattle diet, we contend that C sequestration may be negatively correlated with forage production. Our baseline C(s) sampling recommendation for cattle-grazing properties of the tropical rangelands of Australia is to: (i) divide the property into units of apparently uniform soil type and grazing management; (ii) use stratified simple random sampling to spread at least 25 soil sampling locations about each unit, with at least two samples collected per stratum. This will be adequate to accurately estimate baseline mean C(s) to within 20% of the true mean, to a nominal depth of 0.3 m in the profile.

Are high-impact species predictable? An analysis of naturalised grasses in northern Australia

Predicting which species are likely to cause serious impacts in the future is crucial for targeting management efforts, but the characteristics of such species remain largely unconfirmed. We use data and expert opinion on tropical and subtropical grasses naturalised in Australia since European settlement to identify naturalised and high-impact species and subsequently to test whether high-impact species are predictable. High-impact species for the three main affected sectors (environment, pastoral and agriculture) were determined by assessing evidence against pre-defined criteria. Twenty-one of the 155 naturalised species (14%) were classified as high-impact, including four that affected more than one sector. High-impact species were more likely to have faster spread rates (regions invaded per decade) and to be semi-aquatic. Spread rate was best explained by whether species had been actively spread (as pasture), and time since naturalisation, but may not be explanatory as it was tightly correlated with range size and incidence rate. Giving more weight to minimising the chance of overlooking high-impact species, a priority for biosecurity, meant a wider range of predictors was required to identify high-impact species, and the predictive power of the models was reduced. By-sector analysis of predictors of high impact species was limited by their relative rarity, but showed sector differences, including to the universal predictors (spread rate and habitat) and life history. Furthermore, species causing high impact to agriculture have changed in the past 10 years with changes in farming practice, highlighting the importance of context in determining impact. A rationale for invasion ecology is to improve the prediction and response to future threats. Although our study identifies some universal predictors, it suggests improved prediction will require a far greater emphasis on impact rather than invasiveness, and will need to account for the individual circumstances of affected sectors and the relative rarity of high-impact species.