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The population structure of a stand of saltbush (Atriplex vesicaria Hew. ex Benth.) was studied within one paddock by sampling the shruLq3opulationon a grid radiating from the only watering point. The pattern of both contemporary and cumulative grazing influence was found to be focussed on the watering point but it was not a simple symmetrical one. The existence and distribution of preferred grazing areas could not be explained by the data collected. There was a preferential grazing pressure of the female shrubs. The cumulative effects of this were reflected in a five-fold change in the sex ratio (males/females) of the shrub population.

Bladder saltbush (Ahiplex vesicaria Heward ex Benth) is a valuable perennial chenopod shrub of the northem Riverine Plain of south-eastem Australia. From 1977 to 1983, dieback affected stands of this shrub over a wide area, reducing the drought reserves on many pastoral holdings. By early 1983 reports of new outbreaks of dieback had ceased, and by late 1983 regeneration, both vegetatively and from seedlings, was evident in most areas. This study reviews what is known of this dieback event. The extent of healthy bladder saltbush stands, pre-dieback and towards the end of the dieback period was mapped. It was found that the area of leafy bush had declined by 53 per cent, from 1.1 to 0.5 million hectares, by the end of 1983. There was considerable variation in timing, pattern and progress of dieback. The cause was not established.

Six shrub species were studied to determine their microhabitat relationships as well as their effect on the immediate environment. Analysis of site characteristics and mineral composition of soils in open areas adjacent to shrubs and beneath shrubs allowed for comparison of the different habitats following shrub establishment. Soil pH differs beneath the various shrubs and all six species tended to create more alkaline soils beneath their canopy. All species showed increased soil salinity beneath their canopy. However, the concentration of total soluble salts in the soil surface beneath the shrubs varied with the species and was highest beneath fourwing saltbush. Significant increases in the concentration of magnesium and potassium ions beneath shrubs were observed. Nitrogen and phosphorus were also found in greater concentration beneath the shrub canopy. Soil depth differed beneath the shrub species, with sagebrush and fourwing saltbush growing on the deeper more highly developed types. There was a positive relationship between the presence of shrubs and the depth of the soil profile. It has long been known that shrubs influence the soil characteristics beneath their canopy (Fireman and Hayward 1952). Studies done in the last decade show that shrubs influence both the horizontal and vertical patterning of soil chemicals (Charley and West 1975). Sharma and Tongway (1973) studied the effects of two species of saltbush (Atriplex nummularia and Atriplex vesicaria) on soil salinity and related properties. They recognized an accumulation zone beneath the shrubs, a zone of compensation where leaching of minerals replaced those absorbed, and ‘a depletion zone from which mineral absorption exceeded the rate of replacement. Salt accumulation under shrubs, therefore, represents a redistribution of salts from peripheral regions of root activity (Charley and West 1975). Plants employ several “strategies” for the removal of mineral wastes. Leaching of minerals from leaves is accomplished when the solution of the leaf surface connects with that of the intercellular spaces of the mesophyll and ions are lost by diffusion. Salts are also excreted with the aid of salt glands, as is the case with many Atriplex species. Salts are also concentrated in the extracellular spaces of leaves during the process of transpiration, thus accumulating minerals in leaves. Leaf fall subsequently serves as a mechanism for the elimination of mineral wastes (Epstein 1972). Charley and West (1975) used the distributional patterns of carbon and nitrogen under and between shrubs as a measure of

A comparison was made between the productivity of sheep and cattle grazing on a semiarid saltbush (Atriplex vesicaria Heward) community (median annual rainfall 303 mm) over a 4 year period. Hereford cattle were grazed at 11.7 and 17.5 ha/cow and Merino sheep were grazed at 1.7 and 2.5 ha/ewe. The cows and ewes were joined annually so that they calved and lambed in the May- June period. Calves were weaned at 7-8 months, and the lambs were weaned at c. 4 months. Both calves and lambs were then retained on separate plots for a further 12 months. The saltbush community consisted of a low shrub layer containing 250-750 kg A. vesicaria forage per ha and a herbage layer containing 25-650 kg of forage per ha. Despite the higher digestibility and nitrogen content of the sheep diets, the sheep and cattle had similar productivity. The production of body weight to weaning was a mean of 10.6 and 15.1 kg/ha/year (low and high stocking rates) for the cattle and a mean of 9.4 and 13.2 kg/ha/year for the sheep. After correction for metabolic mass (kg0.9/ha), the body weight production of sheep was raised to 12.4 and 17.3 kg/ha/year. At 12 months after weaning, the equivalent values were 12.9 and 19.4 kg/ha for cattle, and 13.4 and 20.1 kg/ha (corrected) for sheep. Thus differences are small and arise from the stocking rate chosen rather than from biological differences in productivity. There was no relative change between sheep and cattle in body weight growth between good and moderately poor seasons. The livestock numbers for equivalence of grazing pressure were calculated as 9.2 sheep to 1 cattle. The cattle drank an average of 46,300 litres of water each in a year, while sheep drank only 3300 litres per year. On this basis the water supply for cattle grazing would need to be 50% greater than for sheep grazing on the same saltbush land. In addition to body growth, the sheep produced 1.4-2.0 kg clean wool per ha, which provides a substantial economic advantage for sheep in these lands.

The application of multiple pattern analysis (multiscale ordination) to a phase-differentiated sample of perennial saltbush (Atriplex vesicaria) rangeland, along with assessments of the vegetative and reproductive states of individual plants, served to indicate the importance of sheep in determining some scales of distributional pattern in the shrub population. By comparison with conventional pattern analysis, it is shown that multiple pattern analysis can be used to provide an economic description of 'total' pattern in temporally related phases of a monospecific plant population. It is demonstrated that the pattern-determining interaction between sheep and saltbush individuals is dependent on plant size, sex and location with respect of other shrub individuals, in particular due to the trampling of seedling and pioneer phases and the selective grazing of sexually mature shrubs by sheep.

The majority of pattern analyses of total density data collected from geographically separated populations of Atriplex vesicaria, both in the western Riverine Plain of New South Wales and in areas of north-western New South Wales, provided evidence of bi- or trimodal contagion. More detailed analyses of pattern in age-related phases of these populations exhibited most intense patterning in 'seedling' phases, with a progressive reduction of pattern intensity in subsequent ('pioneer', 'building' and 'mature') phases of the entire population. It has been found that the pattern of young individuals may be correlated with patterned variation in microtopography, as well as with water and nutrient availability, and that the indirect effects of grazing animals may be responsible for the intermediate scales of the mosaic pattern in populations of sexually mature individuals. The performance of A. vesicaria plants was assessed experimentally in relation to a range of natural soils, with associated watering and defoliation treatments, and in controlled nutrient solution culture. The results suggest that performance (as estimated by dry weight yield) is affected significantly by soil type, water stress and defoliation. In an experimental context the prime effect of soil variation on yield appeared to be mediated by variation in soil cation balance, a patterned balance that may have been historically induced in the field situation.

Factors contributing to changes in the condition of saltbush communities (Atriplex vesicaria) in the Riverine Plain and Barrier Range regions of New South Wales were measured under a variety of seasonal situations. Groups of eight plots, representing a range of past grazing intensity, were established at each location and measurements were made of species biomass, canopy cover and frequency, forage availability and soil fertility. In both regions, high grazing intensity was characterized by the elimination of the saltbush (A. vesicaria) and an increase in other species, such as Astrebla (mitchell grass), Sclerolaena spp. (copperburrs), annual Atriplex spp. and a wide range of ephemeral species. These changes were best characterized by canopy cover measurements which gave a quantitative assessment of the vegetation changes (in contrast to frequency) and gave values that were less seasonally variable than biomass. Up to 83 species were recorded, but these were aggregated into approximately 9 groups to simplify the collection and analysis of data, without loss of information. On the Barrier Range site, the A. vesicaria was replaced by palatable species, so that there was little loss of overall forage production. Similarly, there was little evidence of loss of soil fertility, as measured by various measures of soil nitrogen, available phosphorus and organic carbon. There was no erosion on these sites, although this may occur on other saltbush communities that grow on texture contrast soils. On the basis of these results, four separate indices of condition are proposed for saltbush communities. These are based on the measurement in the growing season of the canopy cover of major perennial and biennial species or species groups. They are (i) the relative cover of A. vesicaria (the major observable change in these communities), (ii) the relative total cover of desirable forage species (an index of forage productivity), (iii) percentage similarity (an index of community change for conservation purposes), and (iv) the relative area of eroded soil surface.

Plant population data for the pass white-top (Danthonia caespitosa) and for bladder saltbush (Atriplex vesicaria) were collected for four years from a pasture continuously grazed by either cattle or sheep (at equivalent stocking rates) at a site near Booligal, New South Wales. During the four years of the experiment the cattle and sheep had different Impacts on the grass and scrub components of the pasture Sheep tended to deplete the numbers of pass plants far more than did cattle, whereas saltbush shrub numbers here little affected by either type of stock. The rainfall pattern experienced throughout the experiment had a far greater influence on the survival of both grass and shrub than did grazing.

Merino sheep grazing a semi-arid natural grassland were given water containing 0.0, 1.2, 1.6 or 2.0 per cent (w/v) soluble salts and similar sheep grazing on saltbush (Atriplex vesicaria) were given water containing 0.0, 0.8, 1.2 or 1.6 per cent soluble salts. The saline water was made up from sodium chloride and magnesium sulphate to give an ionic concentration similar to that occurring in natural underground waters. On grassland, 1.2 per cent saline water was without effect on the sheep, 1.6 per cent water reduced weight and wool growth in the first year and 2.0 per cent water reduced both wool growth and body weight by a significant amount. The effects were confined to the summer period of November to March. On saltbush, the results for four years were essentially similar to those for sheep on the grassland, although the effects of 1.2 per cent and 1.6 per cent saline waters were more pronounced. However, in the fifth year when drought conditions prevailed, the effects of both these treatments were more severe Water intakes were up to 1 lday-1 higher on the saline water treatments than on the fresh water, except when water intakes of the sheep on saltbush were high (7-11 lday-1) and then water salinity reduced water intakes. It was concluded that water salinities up to 1.2 per cent on grassland and 0.8 per cent on saltbush will not affect sheep productivity. Higher concentration (up to 1.6 per cent on grassland and 1.2 per cent on saltbush) can be used for adult sheep when forage conditions are good.

Longevity, recruitment, survivorship and change in population size of three dominant shrubs were investigated at Koonamore, South Australia. Particular attention was paid to the effects of grazing by sheep and rabbits. Atriplex vesicaria Heward ex Benth. has negative exponential survivorship with a half-life of ca 11 yr. Its populations decline under heavy grazing but increase at the expense of Maireana sedifolia (F. Muell.) P. G. Wilson under intermittent grazing. They also increase after release from grazing. M. sedifolia has negative exponential survivorship with a half-life of ?150 yr. Its populations decline under grazing, and even after 50 yr release from grazing continue to decline. Acacia aneura F. Muell. ex Benth. lives to ca 250 yr. Grazing prevents recruitment, causing its populations to decline. Recruitment resumes after release from grazing, but requires exceptional climatic sequences. These trends if continued will cause drastic change in the dominance of the important low (chenopod) shrubland and low woodland communities of inland Australia.

During late summer, Border Leicester wethers running with Merinos on a pure Atriplex nummularia stand turned over 10.6 to 17.5 litres (mean 13.7 litres) of water daily, and diluted the sodium and potassium ingested to less than 1000 m-osmoles/litre in the urine. Leicesters used 46% more water than Merinos as litres/24 hr, and 71% more as ml/kg0.82/24 hr. The two breeds produced similar urine concentrations. The sheep showed a wide variation in response, and their individual water turnovers while feeding on Atriplex vesicaria and A. nummularia ranged from 120 to 833 ml/kg0.82/24 hr. This suggests differences in functional types of adjustment to saltbush associations. On a Danthonia community Leicesters again turned over more water than Merinos but only about half as much water was required as on saltbush. Merinos grazing on A. vesicaria (with some grasses available) over 2 years maintained good condition with half the water intake of Merinos on A. nummularia, although the two species of saltbush had similar sodium and potassium contents. Total body water tended to increase with water turnover rate on saltbush. Plasma sodium concentration was inversely related to water turnover, extracellular volume, and total body water on saltbush pastures. The content of extracellular sodium was, however, greatest in the sheep with the least sodium in the food taken.

Reflection and transmission spectra were measured for the leaves of a number of species of South Australian arid zone vegetation, over the wavelength range 350- 1350 nm. Spectra were also obtained for several non-arid species for comparison. Coefficients of reflection, transmission, and absorption of solar radiation were calculated from these spectra, and also obtained from direct measurements made with a specially constructed reflecting hemisphere. The coefficients of reflection for the arid zone species covered a wide range of values, and the group as a whole could not be clearly separated from the comparison group on the basis of reflection or absorption coeficients. Of the species in the group, Atriplex vesicaria had the highest coefficient of reflection, and also the lowest coefficient of absorption.

Atriplex vesicaria, a xerophytic perennial pasture species of inland Australia, was found to have an extraordinary high tolerance to saline water'cultures; seed, lings were successfully established in solutions up to 1M NaCl.

The factors controlling the relative distribution of Atriplex vesicaria and Kochia sedifolia were obscure, and explanations in the literature unsatisfactory. This paper describes the results of an experimental approach to an understanding of these factors. A survey of the soils on which A. vesicaria and K. sedifolia are found in the arid zone of South Australia revealed that the distribution of the two species is usually correlated with the depth to which the soil is wetted by the normal rainfall. K. sedifolia, a deep-rooted species, is frequently found on soils which can be wetted to a depth of 2 ft or more. A. vesicaria, a shallow-rooted species, is found on soils in which a heavy clay subsoil or hardpan impedes penetration of water beyond 12 in. From experimental evidence it appears that: (1) either species can grow successfully in pots of the surface soil associated with the other species; (2) each community utilizes water at the same rate; (3) there is no difference between the two species in the rate of defoliation in response to drought conditions, when held at night either in a dry atmosphere or in one with a relative humidity exceeding 85 %; (4) A. vesicaria can reduce the percentage moisture in the soil to a significantly lower level than can K. sedifolia when subjected to drought. These observations are discussed in relation to field conditions, and hypotheses are proposed to explain why these two species are usually found in distinct communities. More detailed work is necessary to test these hypotheses. I.

These two species are shown to have a closely similar leaf anatomy, and this is fully described with relevant notes on all the minor points of difference. In discussion, the origin and development of the lamina are compared with other plant groups. The autecological significance of the vesicular hairs is also briefly considered from an anatomical point of view. Brief comments are made on the water-storage properties of the hypodermal layer. The widespread occurrence of the 'Kranz' type of assimilatory tissue (concentric to the xylem of the leaf veins) in the Australian species of Atriplex is noted. The need for further investigations on the thick-walled phloem elements and bundle sheath cells is stressed. A taxonomic significance is suggested for the peculiar ventral development of the midrib in both species.

Soil moisture, soil salinity, and phenological measurements were made over two years on adjacent pastures with and without bladder saltbush (Atriplex vesicaria) in the Riverina district of New South Wales. Soil moisture percentages beneath pastures with and without saltbush were similar in the first year. In the second year moisture percentages were slightly higher under pastures without saltbush. The soil profile was at matric tensions higher than 15 atmospheres for 48 per cent of the first year and 64 per cent of the second. Phenological observations related soil moisture levels to vegetative and reproductive response of the pastures. The maximum depth of soil wetting was 30 inches in the exceptionally wet autumn-winter of and 10 inches in the slightly drier than average winter of 1964. Salt was leached during the first winter of sampling, the chloride level at four inches falling from 0.107 per cent in the previous summer to 0.008 per cent. The level was partly restored during the following summer (0.055 per cent) and this was maintained during the drier second winter.

The diet selected by Merino sheep grazing a bladder saltbush (Atriplex vesicaria Hew. ex Benth.)- cottonbush (Kochia aphylla R.Br.) community was determined by analysing extrusa from wethers fitted with oesophageal fistulas. Visual assessments were combined with hand clipped samples to determine the amount of forage available. The results showed that the dominant constituent of the pasture, bladder saltbush, was sparingly grazed, whereas many of the associated species, which often constituted only a minor portion of the total available forage, were heavily grazed.

A study was made of Merino sheep grazing a bladder saltbush (Atriplex vesicaria Hew. ex Benth.)–cotton-bush (Kochia aphylla R.Br.) community set stocked at three stocking rates (2.5, 1 .2, and 0.6 sheep/hectare) over a 3-year period. In spring the sheep preferred the perennial grass Danthonia caespitosa Gaudich. and the annuals Medicago polymorpha L. and Vulpia myuros (L.) K. C. Gmel. to the more abundant A. vesicaria. From summer to early winter the diet consisted mainly of A. vesicaria with the proportion of dead matter and Medicago burr increasing as the availability of A. vesicaria decreased. Seasonal fluctuations in wool growth were evident at all three stocking rates. Maximum wool growth rates occurred in spring when the nitrogen content (2.3%) and in vitro digestibility (65%) of the forage eaten was high. During autumn and early winter values for nitrogen (1.4%) and digestibility (50%) were lower and wool growth was at a minimum. At 0.6 sheep/ha animal productivity was maintained and there was little decline in the A. vesicaria population during the 3 years. Grazing eliminated all the A. vesicaria from the pasture stocked at 2.5 sheep/ha, and 98% at 1.2 sheep/ha. At these higher stocking rates the pasture proved incapable of maintaining the sheep for the 3-year period. The inability of A. vesicaria to recover after heavy or complete defoliation by grazing demonstrates the necessity of adopting a low stocking rate if the bush is to be retained.

The productivity of Merino sheep grazing on the semi-arid natural shrub (Atriplex vesicaria) and grassland (Danthonia caespitosa-Stipa variabilis, D. caespitosa, S. variabilis) pastures of the Riverine Plain was measured over three years. At 0.5 sheep to an acre, the sheep on A. vesicaria (bladder saltbush) community at first grew more wool than those on the grasslands, but wool growth rate declined in autumn to the same degree as on the grassland. In the second year most of the A. vesicaria bushes did not recover from grazing and wool growth-rate fell to half that on the grasslands. The sheep on A. vesicaria had to be removed in the second year, but on the grasslands there was no evidence that sheep could not be maintained indefinitely at that stocking rate. At 1.0 sheep to an acre, both the A. vesicaria and the D. caespitosa-S. variabilis grassland were incapable of maintaining the sheep for the duration of the experiment. Wool growth of the sheep on the grasslands showed an annual rhythm, with high growth-rate in spring (14 g per day) followed by a gradual decline in rate to 6-8 g per day in late summer and autumn. However, the extent of this decline was dependent on summer rainfall, as in one summer when rainfall was high, wool growth-rate was maintained at near the spring rate. The mean annual rate of wool growth was found to be correlated (r = + 0.92, P

To determine the response of the perennial shrub Atriplex vesicaria Hew. ex Benth. (bladder saltbush) to grazing, bushes were grazed by Merino sheep to two levels of defoliation, severe and complete. Ungrazed bushes were used as controls. Separate groups of plots were defoliated in October and February and two levels of soil moisture were imposed. Results showed that the more heavily the bushes were grazed the less likely they were to regenerate. Completely defoliated bushes did not regrow, irrespective of soil moisture status or season. It is hypothesized that the inability of A, vesicaria to persist after complete or severe grazing is due to the removal, by grazing, of potential growth sites which apparently occur only along the young stems.

The diet selected by sheep grazing a pasture community dominated by bladder saltbush (Atriplex vesicaria Hew, ex Benth.) and pig-face (Disphyma australe (Sol.) N.E. Br.) was determined by botanically analysing the extrusa from Merino wethers fitted with oesophageal fistulas. Quality of the pasture and of the forage consumed was assessed from the nitrogen analysis of samples of material hand-plucked in the field, and of extrusa from the fistulated sheep. Results showed that in spring almost half of the forage consumed consisted of minor species which represented only 4 per cent of the pasture. In summer, when very little other material was available, Atriplex vesicaria made up 90 per cent of the diet. Disphyma australe contributed little to the diet at any time. At no time did the level of crude protein in the diet fall below that necessary for maintenance of sheep although the sodium content of the plants available in summer was high.

The distribution pattern of Atriplex vesicaria (perennial saltbush) was examined in a number of locations extending from Hay in western New South Wales to Koonamore Station in South Australia. The populations sampled were from a range of locations exhibiting a variety of topographical, edaphic, and effective rainfall conditions. The scales and intensities of pattern varied considerably between sites, but in all sites there was evidence of contagion on at least two scales (both larger than could be attributed to the morphology of the individual plants) and in no instance was there evidence of uniform (underdispersed) distribution. The two major scales of pattern were attributable to the development of gregariousness and either the patchiness of nodulated limestone (or gypsum) in the soils or the development of gilgai relief. It was demonstrated for one site that drought stress had brought about an apparent decrease in the stocking density of A. vesicaria; this reduction of density was associated with a decline in pattern intensity, although the scales of pattern present in the original vegetation were maintained in the residual population.