Andrew Ash

Rotational Grazing on Rangelands: Reconciliation of Perception and Experimental Evidence

Abstract In spite of overwhelming experimental evidence to the contrary, rotational grazing continues to be promoted and implemented as the only viable grazing strategy. The goals of this synthesis are to 1) reevaluate the complexity, underlying assumptions, and ecological processes of grazed ecosystems, 2) summarize plant and animal production responses to rotational and continuous grazing, 3) characterize the prevailing perceptions influencing the assessment of rotational and continuous grazing, and 4) attempt to direct the profession toward a reconciliation of perceptions advocating support for rotational grazing systems with that of the experimental evidence. The ecological relationships of grazing systems have been reasonably well resolved, at the scales investigated, and a continuation of costly grazing experiments adhering to conventional research protocols will yield little additional information. Plant production was equal or greater in continuous compared to rotational grazing in 87% (20 of 23) of the experiments. Similarly, animal production per head and per area were equal or greater in continuous compared to rotational grazing in 92% (35 of 38) and 84% (27 of 32) of the experiments, respectively. These experimental data demonstrate that a set of potentially effective grazing strategies exist, none of which have unique properties that set one apart from the other in terms of ecological effectiveness. The performance of rangeland grazing strategies are similarly constrained by several ecological variables establishing that differences among them are dependent on the effectiveness of management models, rather than the occurrence of unique ecological phenomena. Continued advocacy for rotational grazing as a superior strategy of grazing on rangelands is founded on perception and anecdotal interpretations, rather than an objective assessment of the vast experimental evidence. We recommend that these evidence-based conclusions be explicitly incorporated into management and policy decisions addressing this predominant land use on rangelands.

Constraints and opportunities in applying seasonal climate forecasts in agriculture

Climate variability has an enormous impact on agricultural productivity, rural livelihoods, and economics at farm, regional, and national scales. An every-day challenge facing farmers is to make management decisions in the face of this climate variability. Being able to minimise losses in droughts and take advantage of favourable seasons is the promise of seasonal climate forecasts. The criteria for their adoption depends on what variables are forecast, their accuracy, the likely economic and/or natural resource benefits and how well they are communicated. In reviewing how current seasonal climate forecasts meet these criteria, it is clear that they offer considerable potential to buffer the effects of climate variability in agriculture, particularly in regions that have high levels of inter-annual rainfall variability and are strongly influenced by El Nino and La Nina events. However, the current skill, lead time, relevance to agricultural decisions, and communication techniques are not well enough advanced and/or integrated to lead to widespread confidence and adoption by farmers. The current challenges are to continue to improve forecast reliability and to better communicate the probabilistic outputs of seasonal climate forecasts to decision makers.

Simulation of Grazing Strategies for Beef Production in North-East Queensland

A simulation study was conducted to compare diverse grazing strategies for steers grazing open woodlands in northeast Queensland. Simulations included a wide range of possible stocking rates and pasture utilisation levels using 108 years (1889–1996) of daily climate data for Charters Towers. Five strategies were compared in terms of steer liveweight gain per ha, risk of weight loss, pasture availability, frequency of burning and soil loss. The strategies included constant stocking, stocking in response to available feed, and stocking in response to predicted future feed availability based on a climate forecast. For strategies achieving an average annual liveweight gain per head of about 100 kg, the simulation studies indicated that a responsive stocking rate strategy in June using a forecast of the next year’s pasture growth would increase liveweight gain per ha by about 10%, reduce the risk of liveweight loss by 57%, reduce risk of low pasture yield, but would slightly increase the risk of soil loss (4%). Maximum LWG/ha was achieved at high utilisation rates (> 35%). However, at such high levels of utilisation burning was achieved in less than 10% of years and soil loss was 30–40% more than at levels of utilisation regarded as safe (≈20%). The simulations highlighted the potential value of achieving in June, the skill from seasonal forecasting that is now available in November using average SOI in the Aug-Oct period as the indicator of season type. Assumptions in the model development are outlined and future work required is discussed. Despite the complexity of the simulation analysis, it is concluded that there is a trade-off between production and environmental damage, and that improved forecasting may improve production and/or reduce damage.

Factors affecting the management of cattle grazing distribution in northern Australia: preliminary observations on the effect of paddock size and water points

Achieving more uniform grazing at landscape and paddock scales is seen as an important management objective by pastoralists in northern Australia, but it is difficult to attain in practice. This paper presents a brief review of some key factors to be considered in attempts to modify grazing distribution in extensive rangelands by drawing on the preliminary results of a project that is investigating several options for achieving more uniform grazing. Subdividing the landscape into smaller paddocks and, to a lesser extent, installing additional water points in large paddocks are effective in distributing grazing more widely across the landscape. However, these approaches are less effective in achieving uniform grazing within paddocks, and areas of concentrated use still occur even in small paddocks. To achieve spatial grazing objectives, it is necessary to use management tools that operate at the appropriate scale. Attaining more even use within paddocks should therefore be viewed as a separate management objective, requiring different techniques, to obtaining more effective use of the landscape as a whole. Integrating the use of several spatial management tools that act at different scales is likely to be most effective in improving grazing distribution. Our findings also highlight the importance of understanding paddocks in terms of the spatial arrangement of forage resources and their acceptability and quality in relation to water points and other landscape features. Differences between individual cattle in the way they use the landscape are important in producing more uniform use in larger paddocks and may also offer other opportunities for improving the use of landscape resources overall. Finally, the implications of more uniform use for livestock production and other land use values should be considered, with the protection of biodiversity values potentially requiring special management arrangements where more even use is achieved.

How season of grazing and herbivore selectivity influence monsoon tall‐grass communities of northern Australia

. The hypothesis that season of defoliation and herbivore selectivity may be as important as level of use in determining plant community response to grazing was tested in a monsoon grassland in northern Australia. Plots, dominated by the tussock grasses Themeda triandra and Chrysopogon fallax, were grazed by cattle at low, medium and high rates of utilization in either the early wet, late wet or dry seasons. Effects of grazing on species composition were greatest in the early wet season when high rates of utilization significantly reduced the proportion and occurrence of Themeda and increased the proportion of forbs. Grazing in the dry season had no significant effect on composition. At medium and high levels of utilization in the early wet season, the pasture responded negatively to defoliation, only partially compensating for plant tissue lost to herbivory. The negative response to defoliation carried over to the next wet season when these same medium and high-grazing treatments produced only 80 % and 60 % growth, respectively, of that in treatments grazed at low levels of utilization or those grazed during the dry season. The frequency of Themeda was still lower, and that of annual grasses and non-leguminous forbs higher, in plots that had been grazed at a high rate of utilization for just eight weeks in the early wet season two years previously. Species richness and diversity were also significantly affected by this grazing disturbance. If species composition is to be maintained in these grasslands then stocking rates must be set at low levels to cope with the combined effect of undercompensation in response to defoliation in the wet season and strong dietary preferences for grazing sensitive species.

How land condition alters plant-animal relationships in Australia's tropical rangelands

Abstract Changes in vegetation composition and land condition that occur in response to grazing in natural grassland systems may alter plant and animal production, but the relationships are poorly understood. This study examined the effect of a change in land condition on herbage and animal production in two tropical tallgrass regions of northern Australia. The contrasting land condition classes, selected along fence-lines separating paddocks with different grazing histories, were defined as: State I. Dominated by palatable tussock perennial grasses; State II. Less palatable tussock perennial grasses, annual grasses and forbs as the major species. State II produced considerably less herbage than State I. Cattle grazed the two land condition classes to achieve comparable utilisation rates over the range 5–60% utilisation in a number of 8 week seasonal grazing periods over 2 years. At both Charters Towers and Katherine, steer growth was greater in State II than in State I, most rapid in the early wet season and least in the late dry season, and greatest at low utilisation rates. Differences in liveweight gain due to land condition class were greatest at the lightest levels of utilisation. Owing to the differences in pasture productivity between land condition classes, comparable levels of utilisation were achieved by imposing contrasting stocking rates. Steer growth was higher from State II land at low stocking rates while at high stocking rates State I produced better liveweight gains. The greater liveweight gain by steers grazing State II at low stocking rates can be explained by better diet quality which was reflected in higher levels of faecal nitrogen. The proportion of C3 species (forbs, native legumes, shrubs, eucalypt leaves) in the diet of animals grazing State II vegetation was about twice that of steers in State I. These C3 species were considerably higher in nitrogen than the C4 grasses at the end of the wet season. At high stocking rates, animals in the State II treatment had less available feed on offer, resulting in lower liveweight gains compared with State I. The likelihood of further deleterious changes to land condition and productivity occurring should management attempt to maximise production from State II land are high.

From Oceans to Farms: The Value of a Novel Statistical Climate Forecast for Agricultural Management

The economic value of seasonal climate forecasting is assessed using a whole-of-chain analysis. The entire system, from sea surface temperature (SST) through pasture growth and animal production to economic and resource outcomes, is examined. A novel statistical forecast method is developed using the partial least squares spatial correlation technique with near-global SST. This method permits forecasts to be tailored for particular regions and industries. The method is used to forecast plant growth days rather than rainfall. Forecast skill is measured by performing a series of retrospective forecasts (hindcasts) over the previous century. The hindcasts are cross-validated to guard against the possibility of artificial skill, so there is no skill at predicting random time series. The hindcast skill is shown to be a good estimator of the true forecast skill obtained when only data from previous years are used in developing the forecast. Forecasts of plant growth, reduced to three categories, are used in several agricultural examples in Australia. For the northeast Queensland grazing industry, the economic value of this forecast is shown to be greater than that of a Southern Oscillation index (SOI) based forecast and to match or exceed the value of a “perfect” category rainfall forecast. Reasons for the latter surprising result are given. Resource degradation, in this case measured by soil loss, is shown to remain insignificant despite increasing production from the land. Two further examples in Queensland, one for the cotton industry and one for wheat, are illustrated in less depth. The value of a forecast is again shown to match or exceed that obtained using the SOI, although further investigation of the decision-making responses to forecasts is needed to extract the maximum benefit for these industries.

Grazing Management in Tropical Savannas: Utilization and Rest Strategies to Manipulate Rangeland Condition

Abstract Grazing management is important for sustaining the productivity and health of rangelands. However, the effects of grazing management on herbage growth and species composition in the tropical savannas of northern Australia are not well known. In this eight-year study the influences of utilization rate and resting pastures from grazing on vegetation dynamics were measured at three sites in northeast Queensland, Australia. The sites had high, medium, and low soil fertility, and there were two land condition classes (States I and II) at each site. Severe drought occurred during the first four years, but above-average rainfall was received in the second half of the study. High utilization rates reduced biomass, perennial grass basal area, and ground cover. The reduction in biomass was due to both higher consumption and decreased primary production. State I condition plots at the high and medium soil fertility sites were initially dominated by decreaser perennial grasses, but these declined at all utilization levels, particularly the high rate. They were largely replaced by exotic perennial grasses. At the low fertility site there were no exotic grasses, and the decreaser grasses increased in all treatments, with the increases greatest in plots with low utilization or medium utilization plus resting. In the State II condition plots at the high and medium fertility sites, low or moderate utilization, led to an increase in both decreaser and exotic perennial grasses; with high utilization the decreaser perennial grasses declined and were replaced largely by exotic perennial grasses. This study clearly demonstrated that either conservative stocking with year-round grazing or a grazing system that includes some wet-season resting will help maintain land in a desirable state or help facilitate the transition from a less desirable ecological state to one more desirable for pastoral production and rangeland condition.

An economic assessment of the impact of grazing land condition on livestock performance in tropical woodlands

Beef cattle grazing is the dominant economic use of the tropical woodlands of northern Australia. Land condition has declined over a large part of the region as a result of over-utilisation of pastures through poor management of grazing, fire and vegetation. While often assumed to be the case, there is little empirical evidence to support a link between deteriorating land condition and reduced economic outcomes for livestock production. A model of a representative livestock enterprise near Charters Towers in northern Queensland is used in conjunction with a simulation of 100 trials that is consistent with long-term rainfall in the region to examine the relationship between stocking rates, animal production and economic outcomes. The present study supports a view that ecological and economic outcomes of grazing management do have some general linkages. However, the linkages are less direct than suggested by common definitions of resource degradation and simple stocking rate models. Key economic parameters include the reproductive performance of breeding herds, the level and duration of supplementary feeding required to meet seasonal feed shortages under different land condition and stocking rate regimes, and additional capital invested in larger herds when stocking rates are increased. An overgrazing spiral is hypothesised whereby there is a short-term economic incentive to exploit the natural capital of land in good condition by grazing at relatively high stocking rates. Should land condition deteriorate, a much lower stocking rate is warranted. In an extreme case of a shift to very poor land condition, there is limited scope for profitable production. The 100 year mean values of many production variables for good and moderate condition land for the range of stocking rates trialled are similar. The inherent variation in climatic conditions in the woodlands region and the ability and skills of managers may lead to the actual differences in these measures passing un-noticed before major land resource problems become apparent.

The role of trees in enhancing soil nutrient availability for native perennial grasses in open eucalypt woodlands of north-east Queensland

To investigate the effects of eucalypt trees on pasture in open eucalypt woodlands of north-eastern Queensland, 2 common native pasture species, Chrysopogon fallaxand Heteropogon contortus, were grown in soil collected from under tree canopies and inter-canopy areas. These soils were collected from 2 localities that differed in soil fertility. The objective was to determine whether trees enhanced soil nutrient levels beneath their canopies and whether such changes affected pasture productivity and quality. It was hypothesised that tree effects would be greater when overall soil fertility was low. Shade and water stress treatments, which aimed to simulate field conditions, were also imposed to investigate their independent and interactive effects on plant growth. Chemical analyses showed that nutrient levels were higher in under-canopy soils, and plants grown in under-canopy soil produced 42% more biomass than plants in outside-canopy soil. This increase in biomass was significantly greater when the soil was from the low fertility site than from the high fertility site. Leaf quality, in terms of N and P concentration and dry matter digestibility (DMD), was generally higher in plants in under-canopy soil. Shading reduced plant root biomass but had no effects on above ground biomass or leaf quality. Water stress reduced above and below ground biomass and increased leaf quality. Shading and water stress effects were greater in plants in the more fertile soil types. Simulated ‘under-canopy’ plants (shaded, water-stressed plants in under-canopy soil) produced more biomass and had higher leaf N concentration and DMD than simulated ‘outside-canopy’ plants (unshaded, well-watered plants in outside-canopy soil). In a pastoral context, trees in tropical woodlands are generally considered in terms of their competitive effect on pasture productivity. This study has demonstrated that soil nutrient availability is enhanced under eucalypt canopies. The biomass results indicate that this effect is greater when overall soil fertility conditions are low. These enhanced soil nutrient conditions influence forage productivity and quality. Such positive benefits should be considered when management decisions are taken to remove or kill trees in eucalypt woodlands.