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The objective of this 3-year study was to investigate the relationships between soil salinity and ecophysiological responses of C3 and C4 native plant species around Lake Altham and Lake Coyrecup (both are salt lakes in Western Australia), and to evaluate their potential for use in the remediation of salt-affected soils. Three shrubs (Atriplex vesicaria, Tecticornia lepidosperma and T. indica) that grew in highly saline soil of average Na concentration greater than 300 mM had higher leaf δ13C and δ15N ratios. These species also had higher Na-to-K and Na-to-Ca ratios in both their leaves and stem xylem sap, indicating that these species accumulate high amounts of sodium in their tissues. In contrast, tree species Eucalyptus loxophleba, Casuarina obesa and Acacia acuminata grew in soil of average Na concentration of less than 100 mM and had lower values of δ15N, δ13C, Na content, and Na-to-K ratio in their leaves. These species also had lower xylem Na-to-K and Na-to-Ca ratios. Seasonal effects were observed in leaf total N content, leaf Na, xylem sap Na-to-K ratio and xylem sap Na-to-Ca ratio. Strong and significant positive correlations (r > 0.75; P

The native budworm, Helicoverpa punctigera (Wallengren), is an important economic insect pest of cotton and other crops. It is widely distributed in Australia and has been recorded on a range of host plants including native, non-crop hosts in inland regions. To date, there are few records of its occurrence on plants with the C4 photosynthetic pathway. Here, we assessed the oviposition preferences of H. punctigera for naturally occurring C3 and C4 plants under glasshouse conditions, to establish their potential as hosts. We conducted bioassays on two C4 plants, saltbushes Atriplex nummularia Lindl. and Atriplex vesicaria Heward ex Benth.; and two C3 plants, legumes Medicago polymorpha L. (burr medic) and Cullen cinereum (Lindl.) J.W.Grimes (annual verbine). The two C4 plants attract egg laying in the field; however, C3 plants are the preferred hosts. Ovipositing females showed a preference for the C3 over the C4 plants but oviposition occurred on both. Of the C4 plants, females preferred to oviposit on A. nummularia (77%) over A. vesicaria (24%) in both a multi- and two-choice test. In addition, ovipositing females preferred the upper leaf surface of A. nummularia (68%) and the under leaf surface of A. vesicaria (64%) as their oviposition site. Our findings suggest that under field conditions, when C4 plants such as saltbushes grow near C3 plants, as occurs in inland regions, the C4 plants could receive eggs along with the C3 plants, enabling the initial stages of larval recruitment to occur in C3 plants.

Ephemeral gilgai wetlands of the stony-plains of arid Australia have a relatively high diversity of native plant species and are extensively utilised for livestock grazing. We sampled the standing vegetation (SV) and germinable soil seed bank (SSB) of 40 gilgais, comparing gilgais near and far from watering points, and continually stocked versus rarely stocked. Despite historically heavy stock grazing, we found no significant differences in native species richness between treatments, indicating the general resilience of gilgai vegetation. One contributing factor is the abundance of Atriplex nummularia ssp. omissa. Cover of this long-lived shrub did not differ significantly between treatments and was positively correlated with “highly palatable” species’ cover, suggesting that it may act as a nurse species. In contrast, two other long-lived species, Atriplex vesicaria and Astrebla pectinata, had significantly reduced cover or were absent near to watering points. These and other long-lived species had a poorly developed SSB and thus limited ability to regenerate from seed if killed by sustained heavy grazing. The absence of fifteen locally rare species (including 12 short-lived species) from water-near gilgais indicates the need for more intensive survey to determine whether the proliferation of watering points poses a threat to such species.

Atriplex vesicaria Heward ex Benth. (Chenopodiaceae) is a widespread perennial shrub in southern Australia's chenopod rangelands but is sensitive to grazing. A detailed investigation of the demography and population dynamics of A. vesicaria under sheep grazing was conducted over 6.5 years at a range of sites across a typical paddock to assess the long-term effects of grazing on the species and elucidate the mechanisms of population change under grazing. The effects of rainfall on recruitment and mortality were also examined. Six-monthly censuses of all A. vesicaria individuals were conducted in permanent grazed and ungrazed plots at sites located across an 1100-ha paddock. Grazing increased adult shrub mortality close to water and reduced recruitment over a broader area of the paddock, but seedling survival did not appear to be affected by grazing. As a result of these changes, the population declined on grazed plots up to 2200 m from water during the study, but the decline was greatest closer to water. The population was most dynamic at the sites furthest from the water point where it was unaffected by grazing because of the greater recruitment and mortality of young plants, but because these processes balanced out over time, population density was effectively unchanged by the end of the study. Although statistical models indicated that six-monthly rainfall did not explain temporal variation in recruitment or mortality, rainfall nevertheless has a central role in both processes. In particular, longer periods of favourable rainfall and drought appear to have an important influence on recruitment and mortality, respectively, with heavy grazing during a drought period increasing mortality. Occasional shortages of seed or rains occurring during the warmer months when seed germination is limited possibly explain poor recruitment at sites unaffected by grazing following good rainfall.

While the abundance of some plant species decreases under high grazing intensity, others become more abundant. Release from competition by decreaser species contributes to this pattern in mesic systems, but this may not be the case in xeric systems where competition may be less intense. Here we examine three mechanisms that may be involved: (i) increased recruitment and growth because of soil changes produced by grazing, for example, increased soil nutrient availability through dung accumulation; (ii) increased recruitment favoured by the breaking up of the lichen crust; and (iii) reduced competition because of the decline of decreaser species. We used field and glasshouse experiments to determine the possible contribution of these mechanisms to the increase of the chenopod Maireana pyramidata around a watering point in a chenopod shrubland of South Australia. There was no evidence of nutrient accumulation close to the watering point, and while seedlings of M. pyramidata responded to nutrient addition, their growth was the same in soil collected from areas with different grazing intensity. While a broken lichen crust increased the emergence of both M. pyramidata and the decreaser Atriplex vesicaria, the effect was larger for the former. We found no competition between seedlings of the two species or between juveniles of A. vesicaria and seedlings of M. pyramidata in glasshouse experiments. Adult plants of both A. vesicaria and M. pyramidata produced similar growth reduction in seedlings of M. pyramidata. Furthermore, a field removal experiment failed to detect any competitive effect of A. vesicaria on M. pyramidata. Our data indicate that the disintegration of the soil crust by grazer activities can be a major factor controlling floristic changes in overgrazed rangelands. These results imply that factors that control establishment may be more important than competition in shaping shrub population dynamics in these systems. Ground surface itself can affect establishment opportunities, and this should be taken into account in management and restoration efforts in arid lands.

Five new species and a new genus of gall midge are described from flower galls on native chenopod plants in Eyre Peninsula, SouthAustralia. Asphondylia vesicaria sp. n. induces galls on Atriplex vesicaria; A. mcneilli sp. n. on Sclerolaena diacantha; and A. tonsura sp. n. on Enchylaena tomentosa. Infested flowers develop into galls and produce no seeds. DNA analysis of part of the cytochrome-c oxidase subunit I mitochondrial gene supported the morphological and biological differences between each of the new species and the previously described A. floriformis (Veenstra-Quah & Kolesik) and A. sarco- corniae (Veenstra-Quah & Kolesik) that induce galls on leaves and branches, respectively, of Sarco- cornia quinqueflora (Chenopodiaceae) in Australian salt marshes. A new genus, Dactylasioptera gen. n. and two new species of Lasiopterini, D. adentata sp. n. and D. dentata sp. n. are described - both were reared from galls of A. mcneilli and A. tonsura.

Repeated visits to 1082 Atriplex vesicaria shrubs over a 3.5 year period detected sexual lability in this species, with 536 changes in gender expression recorded. The majority of switches (77%) occurred between the bisexual and male phenotypes. However, bisexual to male changes were more common than male to bisexual changes. Switches between the male and female phenotypes occurred in 12% of cases. The genetic, hormonal and environmental aspects of sex change are well known for other species in the genus but unknown for A. vesicaria.

In October 2000, the flow of the River Murray entering South Australia was increased from 32 000 to 42 050 ML day−1 by release of water from an offstream reservoir, and a downstream weir was raised by 500 mm to impound the flood and enhance local floodplain inundation. The flood was maintained for about two weeks, although the duration of inundation was longer at low elevations on the floodplain. Vegetation at three sites was surveyed before and after the flood to examine the impact of inundation on the growth and germination of flood-tolerant, flood-dependent and flood-intolerant species. Among 32 recorded species, Atriplex vesicaria (bladder saltbush, Chenopodiaceae), Sporobolus mitchellii (rats tail couch, Graminae) and Sarcocornia quinqueflora (samphire, Chenopodiaceae) accounted for nearly 82% of the total cover/abundance. Flood-tolerant and flood-dependent species (e.g. S. mitchellii) grew and germinated and flood-intolerant species (e.g. A. vesicaria) senesced. No aquatic plants germinated or established, despite favourable conditions, suggesting an impoverished seed bank or grazing. Based on the growth but lack of germination of flood-tolerant and flood-dependent species, the value of small, occasional interventions in environmental flow management may be to maintain existing communities rather than restore degraded ones. Copyright © 2004 John Wiley & Sons, Ltd.

Cover and survivorship of perennial chenopods, Atriplex vesicaria and Maireana astrotricha, declined markedly during a prolonged dry period at Roxby Downs in arid South Australia. Despite their resilience to browsing in favourable seasons, only 2% of the A. vesicaria shrubs browsed heavily by cattle survived the drought. M. astrotricha exhibited greater drought survivorship, although the post-drought cover retention in browsed shrubs was only half that of unbrowsed controls. Survivorship was highest for unbrowsed chenopods growing in moisture-enhanced run-on or dune-base environments. Maintenance of these patchy areas with reduced water-stress is hence important for the persistence of browsed chenopod shrublands. Light browsing by either European Rabbits ( Oryctolagus cuniculus ) or Greater Stick-nest Rats ( Leporillus conditor ) had no measurable impact upon chenopod survivorship.

Summary Eight Greater Stick-nest Rats (Leporillus conditor S.) were re-introduced into a 8 ha release pen within the Arid Recovery Reserve, South Australia, in September 1998. Their weight, reproductive condition, activity, habitat use and grazing impacts were investigated during the 8 month experimental trial. Greater Stick-nest Rats increased in weight and bred successfully after the end of summer (April 1999). They consumed native vegetation including Bladder Saltbush (Atriplex vesicaria), Ruby Saltbush (Enchylaena tomentosa) and Sturt's Pigface (Gunniopsis quadrifida) but Sturt's Pigface was most heavily browsed and no monitored plants died from over-browsing during the trial. Rats preferred dune habitat and the two largest female rats maintained discrete activity areas and shelter sites. Nocturnal activity of adult male rats was centred around adult females with both sexes generally staying within 150 m of daytime shelter sites. Shelter sites were commonly within dead Umbrella Wattle (Acacia ligulata) or Narrow-leafed Hopbush (Dodonaea viscosa) shrubs covered in low vegetation, and rats also adapted burrows of other species to use as below-ground components. Although supplementary water was provided and may have ensured survival over the hot summer months, the trial release was considered a success and a full-scale re-introduction of the Greater Stick-nest Rat was conducted in 1999.

Summary 1 Plants that grow beneath trees in arid systems may frequently experience both water and light limitation, although protection from high radiation loads during drought may compensate for a loss of productivity due to reduced light availability when water is plentiful. 2 We examined the effects of shading, during an imposed water deficit, on the carbon gain, stomatal conductance (gs) and shoot water potential (Ψs) of seedlings of three shrubs: Atriplex vesicaria (Heward ex Benth.), a C4 species, and Enchylaena tomentosa (R. Br.) and Rhagodia spinescens (R. Br.), which are restricted to shaded sites beneath trees. 3 Under conditions of limiting water, photosynthetic rates measured at saturating light (Amax) were negative in high-light grown Enchylaena plants but remained positive in shade-grown plants. When water was not limiting, Amax was reduced in shade-grown Atriplex but shade did not affect carbon gain in the other two species. 4 AtriplexΨs was higher in shaded than in unshaded plants, but in unshaded plants positive carbon gain was maintained at Ψs below −10 MPa. Stomatal conductance and Amax decreased more slowly with increasing water deficit in shaded conditions in all species. 5 Atriplex was tolerant of a broader range of light and soil moisture conditions than Enchylaena, with Rhagodia intermediate between these two species. The interactive effect between drought and shade and the ecophysiological tolerances of these three species have consequences for their field distributions.

The invasive stem succulent Orbea variegata (L) Haw. (Asclepiadaceae) tends to be more abundant underneath shrubs than in open areas in chenopod shrublands near Whyalla, South Australia. To assess the role of facilitation in the life cycle of O. variegata, we investigated the effect of chenopod shrubs on different life stages of the species by experimentally manipulating temperature, light, soil moisture and nutrient levels. Experimental results suggest that the reduction in light and temperature under shrubs, but not increased nutrient levels, are the main facilitative mechanisms for O. variegata. Temperatures above 30°C, which are more likely to occur on the soil surface of open areas than under shrubs, inhibited seed germination. Seedling survival at low watering frequency and the growth of established ramets were increased by 75-80% shade cloth. Ramets growing in full light contained a high concentration of anthocyanin pigments. One of the functions of these pigments is to absorb excess radiation, suggesting that O. variegata experiences radiation stress in full light. In the field O. variegata performed considerably better under Atriplex vesicaria Heward ex Benth. (Chenopodiaceae) or under 75-80% shade cloth than in full light. Monthly irrigation of 20 mm did not reduce this positive effect of the A. vesicaria canopy on O. variegata, suggesting that O. variegata is inhibited by high light intensities or temperatures, independent of water availability. In conclusion, whereas shrub canopies do not seem to be required for the establishment or survival of O. variegata, shrubs improve adult growth and can improve establishment. The possibility of exotic plants being facilitated by other plants has to be taken into account when assessing the probability and rate of invasion.

The presence of shrubs in arid lands creates spatial heterogeneity that affects the distribution and performance of annual plants; several possible mechanisms have been implicated. A preliminary survey in a chenopod shrubland in South Australia showed differences in the distribution of annual plants under canopies of Atriplex vesicaria and Maireana sedifolia (the two dominant shrub species) and open spaces. A series of experiments were conducted to test the potential contribution to these patterns of nutrient enrichment under shrubs, differential seed accumulation, stress reduction by the canopy, competition by shrub roots, and protection against grazing. The germinable soil seed-bank under A. vesicaria and M. sedifolia was different from that in open spaces, but these differences can only explain a fraction of the differences observed in the growing annual plant community in different microsites. The soil under A. vesicaria had higher total nitrogen content than soil in open spaces, whereas soil under M. sedifolia had lower available phosphorus than open spaces. Although annual plant densities under A. vesicaria were higher than in open spaces, experimental removal of shrubs increased their density, suggesting that shrub canopies inhibit annual plants in this system. Surprisingly, trenching of open areas close to shrubs (severing lateral shrub roots) decreased annual plant density. We suggest that water moves laterally through shrub roots, in a process akin to a hydraulic lift, increasing water availability for the annual plants. Exclusion of vertebrate grazers had a stronger effect on annual plant biomass in open spaces than under M. sedifolia, suggesting that this shrub provides shelter against herbivory. Overall our results show that shrubs can have simultaneously facilitative and inhibitory effects on the annual plant community through different mechanisms, but more importantly that different shrub species have different effects. This is a potential mechanism allowing for species coexistence of annual plants.

Uromyces vankyorum (Basidiomycota, Uredinales) growing on Atriplex lampa in the cool Patagonian dwarf shrub semi-desert is described as a new species and a new member of the Argentinean rust mycota. The fungus is morphologically similar to Uromyces atriplicis on Atriplex vesicaria from halophytic shrublands of South Australia. U. atriplicis seems to be derived from U. vankyorum as indicated by its shortened life cycle lacking the urediniospore stage. The species are interpreted as trans-pacific vicariants and represent one of the rare examples for the austral South American-Australasian element among rust fungi. The disjunct distribution of rust fungi between austral South America, Australia and New Zealand is reviewed and discussed. Available data suggest migration of rust fungi along Gondwanan land bridges rather than long-distance dispersal of spores by air currents.

Poor recruitment in Atriplex vesicaria Hewd exBenth (bladder saltbush) under sheep grazing in the chenopodshrublands of southern Australia contributes to a decline in the shrub'spopulation growth rate. This may lead to local extinction of the species overlarge areas around watering points. This study investigated whether low seedavailability may contribute to poor recruitment. It examined the incidence offlowering and seed bank size at sites distributed across a large grazedpaddock,and examined the longevity of seed in the soil. Grazing by sheep reduced theincidence of flowering and input to the seed bank. The proportion of shrubswithflowers increased with distance from water, showing the characteristicpiosphereresponse. Shrubs on grazed sites closer to water experienced extended periodswhen they failed to flower or flowered poorly. The seed bank was negligible atthree of the sites within 1650 m of water for all three years ofsampling. In contrast, the seed bank at the most distant site sampled (2800m from water) was small in 1990 (37 ± 5.1seeds/m2) but in 1991 and 1992 seed numberswere substantial (626 ± 315.2 seeds/m2and 318 ± 169.0, respectively). Soil seed was short-lived inthis study, with only 34% and 17% of the original seed remainingas viable ungerminated seed after 12 months for the under-canopy andexposed treatments respectively. Whilst recruitment may also be limited byaltered soil conditions due to grazing and trampling and the availability ofsafe sites, the results of this study suggest that low seed availability may bean important factor contributing to poor recruitment and may limit the abilityof the population to recover from the loss of established plants. Management ofgrazing must take into account the need for A. vesicariapopulations to flower and set seed on a regular basis.

Summary 1 Population modelling and field measurements of births, growth and deaths were used to investigate the long-term change in abundance of Atriplex vesicaria (Chenopodiaceae), a long-lived, palatable, perennial shrub, under sheep grazing. Of particular interest was whether A. vesicaria is at risk of being eliminated throughout grazed paddocks when the recommended practice of continuous grazing at conservative stocking rates is employed. 2 Time-invariant matrix population models indicated that the A. vesicaria population was in decline over much of the study paddock, but the rate of decline was greatest nearer to the water point (population growth rate λ ≈ 0·8). Time-varying stochastic matrix models projected that the A. vesicaria population would become locally extinct at most sites up to approximately 2200 m from water, occurring first closer to water (within 12–29 years). The population was stable (i.e. λ ≥ 1) at sites greater than 2200 m from water over the projection period of 100 years. 3 Decreases in adult survival and recruitment made the largest contributions to reductions in the population growth rate. However, there were spatial patterns centred on the water point in the degree to which particular demographic processes contributed to these reductions, because of a grazing gradient and the differential sensitivity of demographic processes to grazing. Thus decreases in recruitment contributed to reductions in the population growth rate at greater distances. Such responses, together with the sensitivity of the population growth rate to these processes, determined the spatial pattern in population growth. 4 The results suggest that piospheres (i.e. the zone of impact) continue to expand over many years under set-stocking so that the area around the water point that is devoid of A. vesicaria becomes larger. The process of expansion appears to first involve the inhibition of recruitment, followed by eventual mortality of established shrubs. 5 The large contribution of adult survival to the population growth rate in A. vesicaria suggests that minimizing the mortality of established adults should be a priority for management. This is likely to involve resting from grazing at critical times such as during extended dry periods. This may also permit increased levels of recruitment during subsequent moister periods.

This paper reports on a laboratory study of the effects of water drop impacts on litter and sand splash beneath desert shrubs. Individual drops of 5.7 mm diameter were released from heights of 0.5, 1.0, and 1.5 m (selected to encompass the height range of typical desert shrubs) onto targets of bare or partially litter-covered, saturated fine sand. The natural litter, largely derived from the saltbush Atriplex vesicaria , was collected from desert shrubland sites in western New South Wales (NSW). The drop impacts caused both sand and litter particles to undergo splash displacement. The mass of sand splashed was found to increase with drop fall height, while mass of litter particles splashed did not vary significantly with fall height. Weights of sand moved by airsplash were significantly diminished by surface litter applied at the rate of 200 g/m 2 . These findings indicate that gravity drops released from desert shrubs may provide both an erosive force beneath these plants, and a means for dispersing litter from the plant base into the surrounding landscape, where litter may continue to affect hydrologic and erosional processes. By restricting splash of mineral particles, litter acts to limit soil splash from beneath shrubs, and in this way may contribute to the persistence of plant mound microtopography that is common in desert shrublands. Under open-field conditions, large raindrops delivered in convective showers must cause similar airsplash transport of litter particles, thus playing a role in the distribution of litter within the landscape.

The canopy interception storage capacity of three plants in an arid, banded (runoff-runon) landscape was determined in the field from weight gain under artificial rain. The plants, two shrubs and a grass, were the bladder saltbush Atriplex vesicaria (Heward ex Benth.), the pearl bluebush Maireana sedifolia (F. Muell.) P. G. Wilson, and perennial Mitchell grass Astrebla lappacea (Lindl.) Domin. For saltbush and Mitchell grass, canopy water storage capacity (1.3 mm) correlated strongly with projected canopy area, while for the dense canopy of the bluebush (2.0 mm capacity), plant weight was a better predictor. In view of canopy cover amounts in each plant community, and the mean rain day rainfall of 5.7 mm, estimated annual water losses amount to 32% for Mitchell grass communities, 5% for saltbush communities, and

This study measured the impact of an introduced plant species, Orbea variegata (African carrion flower), upon the dominant shrub Atriplex vesicaria (bladder saltbush) and the annual plant community in chenopod shrublands of South Australia. Shrubs with Orbea growing underneath were likely to be less healthy than shrubs without Orbea . Pre-dawn water potential and growth of saltbush decreased in the presence of Orbea . Orbea appears to limit water availability to saltbush either by direct competition, a decrease in rainfall penetration through the soil, or a combination of both. Orbea also reduced both the germinable soil seed bank and the biomass of annual plants. Our data suggest that Orbea has a severe detrimental effect on the native vegetation. We speculate that Orbea has the potential to spread further into the chenopod shrublands during years of particularly high summer rainfall.

The restoration of severely degraded vegetation communities is often said to require mechanical intervention. However, the degree of intervention required, and its capacity to successfully restore areas of bare (scalded) soil and high weed cover into functioning chenopod shrubland, is unknown. Ten years on from mechanical intervention and direct seeding using a Contour Seeder and Camel Pitter, the abundance and cover of species was compared across disturbed and undisturbed microtopographic zones using one-way repeated-measures ANOVA and pairwise t-tests. Along Contour Seeder rip lines, recruitment of perennial species was greatest in the furrow (e.g. direct seeded: F2,78 = 27.15, P

A dune-swale-dune transect in north-eastern South Australia with a regular covering of saltbush (Atriplex vesicaria and Atriplex stipitata) was studied. The transect topography was surveyed, as were the Δ (discrimination against 13C in CO2) of the saltbush plants, and the electrical conductivity and chloride profiles of the soil. Increasing soil salinity, surveyed as electromagnetic (EM) soil conductivity, correlated with a decrease in A composition in the leaves of the C4 Atriplex species. No such correlation occurred with the whole plant. Further, the Δ of foliage was more variable than the Δ of whole plants. The Δ of foliage was higher than that of corresponding stems. We suggest that soil conductivity measured in this way is a meaningful assessment of plant growth conditions, and that further study will demonstrate its scope for incorporation into field studies of native plants at a quantitative level.

The recruitment and survival of small and large shrubs of Atriplex vesicaria were examined for 21 periods from 1977 to 1987. Recruitment occurred in all seasons, including summer, and survival was independent of the size of the recruitment event. Recruitment was not related to the density of the large shrubs, suggesting that the available seed pool at this site was not limiting. Survival of both shrub components was only weakly correlated with rainfall (measured at a location between 6 and 30 km from the study transects) and with a ratio of rainfall and evaporation. Survival of small shrubs was constant over all cohorts, with half-lives of only 7–8 months. Turnover of the population was substantial — an average of 60% of the individuals present at any one time were less than 24 months old.

This study examined the variability in palatability of populations of Atriplex vesicaria and the influence of past grazing history on mean palatability to sheep. Twenty saltbush plants (10 male, 10 female) were collected from each of six locations across chenopod shrubland of South Australia; three populations came from areas with long records of intensive sheep pastoralism and three from areas with negligible stock grazing in the past. The plants were transplanted into an experimental paddock at Middleback Station, near Whyalla, South Australia and the paddock was grazed by three sheep for nine days. Relative palatability of the populations was assessed by their rates of decline in bush biomass, as indexed by loss of tagged terminal shoots. Overall accumulated tag loss after 9 days was significantly different between populations. These differences were enhanced when dung drop in paddock subdivisions, flowering status of bushes, and leaf sodium and potassium concentrations were included as covariates in tag loss models. Although there was no clear separation of grazed versus ungrazed populations by tag loss alone, the covariate models demonstrated a significant difference between grazing history types, with grazed populations being less palatable. Examination of model residuals showed heterogeneity of palatability to be higher in the grazed populations. This study indicates that the piosphere is a gradient of variability in palatability as well as a gradient of floristic composition.

A grazing experiment in mixed chenopod shrubland near Whyalla, South Australia, is reported, in which the survivorship probabilities of saltbush shoots were measured, contrasting isolated (small seedling) shoots with equivalent shoots in outermost adult plant foliage. Throughout the experiment, measurements showed that seedlings were spared relative to shoots of adult plants. This is in agreement with visual assessments from numerous earlier experiments. When the experiment was terminated, adult root survivorship was 0.035 whereas seedling survivorship was 0.49. This outcome is discussed.

This paper reports the results of the first intensive grazing trials to study palatability variation between the sex phenotypes of bladder saltbush (Atriplex vesicaria Hew. ex Benth.). The results show that Merino sheep preferentially graze female shrubs over male and bisexual shrubs in South Australia, which supports earlier paddock-scale observations made in New South Wales. Male shrubs with higher densities of flower spikes were consumed less than those with lower densities. However, when male flowers were small and/or sparse, the removal of male flowers by clipping did not significantly increase the consumption of male shrubs. Female shrubs with very low or very high densities of fruit tended to be consumed significantly more than those with moderate fruit densities. Other physical aspects such as plant growth habit and foliage density did not have a consistent influence on grazing behaviour. Chemical differences between the sex phenotypes are implicated. The presence of palatability variation between the sex phenotypes suggests that there is potential to refine the existing use of bladder saltbush as an indicator species in southern Australia.

This paper reports the results of three cafeteria trials used to study palatability variation between the sex phenotypes of bladder saltbush (Atriplex vesicaria Heward ex Benth.). The results of the first trial show that Merino sheep preferentially grazed female samples compared to male ones, which supported earlier paddock-scale grazing trials and observations. In the second trial, the removal of male flower spikes led to increased consumption of male samples, suggesting that male flower spikes contain a grazing deterrent. The third trial showed that sheep were able to detect male material with or without spikes even when it was completely hidden within female plant material. In combination with observations made during the trials, these results suggest that there is a grazing deterrent present in male plants and that sheep use the male flower spike primarily as a visual cue when making grazing decisions.

The TGB Osborn Vegetation Reserve at Koonamore, South Australia, is a 390-ha exclosure in semi-arid chenopod shrubland. The area was heavily overgrazed in 1925 when it was fenced to exclude sheep. Permanent quadrats and photopoints have been maintained to the present. Feral rabbits were sometimes numerous until the mid-1970s but have since been controlled. The records represent 50 years without sheep grazing, followed by 26 years without either sheep or rabbits. Dramatic seedling establishment events have occurred since 1978 for the following species: Acacia aneura Benth., Myoporum platycarpum R.Br., Senna artemesioides subsp. coriacea Randell, S. artemesioides subsp. petiolaris Randell, Acacia burkittii Benth., Dodonaea attenuata A.Cunn., Eremophila longifolia (R.Br.) F.Muell., E. sturtii R.Br. and Maireana pyramidata (Benth.) Paul G.Wilson. However, the chenopod shrubs Atriplex vesicaria Benth. and A. stipitata Benth. increased earlier and did not respond in the same way to episodic rainfall events or rabbit control. Numbers of Alectryon oleifolius (Desf.) S.T.Reynolds and Casuarina pauper F.Muell. ex L.A.S.Johnson have remained almost unchanged, whereas Maireana sedifolia (F.Muell.) Paul G.Wilson and M. astrotricha (L.Johnson) Paul G.Wilson have shown a very gradual increase over time. The data show evidence for both episodic and gradual change among different species.

Dietary preferences of the greater stick-nest rat (Leporillus conditor) and the European rabbit (Oryctolagus cuniculus) were compared using cafeteria trials and direct observations. Despite overlap, these species exhibited differences in dietary preference. L. conditor showed a strong preference for chenopod shrub species and other plant species with a high water content including Gunniopsis quadrifida and Calandrinia remota. L. conditor also preferred female bladder saltbush (Atriplex vesicaria) foliage to male. O. cuniculus ate a greater selection of plant species in most trials with their most preferred species including mulga (Acacia aneura), Salsola kali and Calandrinia remota. Both O. cuniculus and L. conditor preferred seedlings of perennial species to adult cuttings. L. conditor has recently been re-introduced to a 14 km� O. cuniculus, cat (Felis catus) and red fox (Vulpes vulpes) proof exclosure in the arid zone of South Australia. The re-introduction of this herbivore and the removal of exotic herbivores may change the vegetation structure and composition within the exclosure by restricting growth of some succulent chenopod species but allowing the regeneration of tall shrub species such as Acacia aneura which are usually limited by O. cuniculus grazing.

The initial effect of two pulses of heavy cattle grazing on chenopod shrubland plants and invertebrates in northern South Australia was assessed in a two year trial. Both plant and invertebrate communities were structured by subhabitats which were defined by edaphic and water-distribution features. The cover of grasses and the dominant shrubs, Atriplex vesicaria and Maireana astrotricha, declined significantly following grazing but only total vegetation cover was significantly lower than controls one year after grazing. Plant species richness was not affected by the grazing pulses. Abundance of ants increased, but the responses of other invertebrates were inconsistent following grazing. Rainfall had a marked effect upon both plant cover and invertebrate abundance. Key words: chenopod shrublands, pulsed cattle grazing, Atriplex vesicaria, invertebrates, bioindicators

(1) Survival was recorded at intervals in five cohorts of Atriplex vesicaria seedlings germinating between February 1979 and August 1985. This paper considers survivorship in relation to microtopography, soil surface conditions and proximity to mature shrubs. (2) For various cohorts and times, survival of seedlings varied with soil surface, microtopography and proximity to large shrubs. There was no consistency, however, between cohorts as to which microsites supported greatest survival.

Over the 8-year period 1980-87, moderate grazing did not affect the population dynamics of A. vesicaria, M. astrotricha and M. pyramidata. Density of A. v. declined on both grazed and ungrazed transects, but that of Maireana spp. remained almost constant. Turnover rates of A.v. were quite high for both grazed and ungrazed populations, but were extremely low for Maireana spp. Shrub size was the only population parameter significantly affected by grazing. Heights and diameters for both grazed and ungrazed populations declined during dry periods, but this decline was greater for grazed shrubs (...)

This thesis deals with some aspects of the population ecology of arid zone perennial chenopod shrubs. It examined the effects of grazing on the population dynamics of Atriplex vesicaria, Maireana astrotricha and Maireana pyramidata, the influence of weather on recruitment and survival of Atriplex vesicaria and the effects of various microtopographical features on seedling survival of Atriplex vesicaria.

A study was made of grazing and watering behaviour of free-ranging Merino sheep in a hot dry area of the pastoral zone in south-western New South Wales. The study site was a level, reeless paddock 1 400 ha in area. Saline drinking water (0.5% total soluble salts) was available at two sites about 1.5 km apart. The vegetation was a relatively homogeneous stand of bladder saltbush ( Atriplex vesicaria ) with a herb layer of predominantly annual forbs and grasses. The temporal patterns of activity, grazing behaviour and distribution patterns of a flock of 1 000 Merino ewes were recorded on 3 consecutive days in each of 4 months in summer when the mean daily maximum temperature was in the range of 32–38°C. Observations were made from a tower (10 m high) located near the centre of the paddock. Behaviour at each sampling was consistent between days. The activity pattern had a bimodal frequency distribution with long periods devoted to idling. The sheep travelled an average of 8 km (5 miles) per day. Travel to and from water occupied about 7% of the daylight hours. About half the paddock was used on a regular basis while the remainder was used occasionally or not at all. The areas of maximum utilization within the paddock were those in which the perennial grass Danthonia caespitosa was the dominant species in the herb layer, and which lay within a range of 0.8 km from a watering point.

Nitraria billardieri occurs in all mainland states of Australia and on several adjacent islands south of the Tropic of Capricorn between Lat. 25° and 38°S and Long. 113° and 147°E. Other species of Nitraria are found in North Africa, the Middle East and Eurasia. The probability that Nitraria is a very old genus, having its origins in central Asia, is discussed. The wide disjunction between N. billardieri in Australia and the closely related N. schoberi in eastern Europe and Asia is difficult to explain. Observations on various populations grown under nursery conditions at Deniliquin, combined with those undertaken during field traverses across Australia, clearly indicate that considerable inter-population variability occurs. Whether these different forms are ecotypes in which particular characters have become genetically fixed in specific habitats, is uncertain; but the form growing along the Indian Ocean coast of Western Australia shows marked contrasts to the other forms and may ultimately be described as a distinct species. Possible uses for N. billardieri in arid and semi-arid zones of Australia are discussed. Particular reference is made to the abundance of N. billardieri in low shrubland communities which were dominated by chenopods prior to the introduction of domestic livestock. The marked increase in N. billardieri on overgrazed saltbush (Atriplex vesicaria) communities of the Riverine Plain suggests that it may serve as an indicator species in range condition assessment of these communities.

Two species of Atriplex were grown under low temperature (8 C day/6 C night) and high temperature (28 C day/20 C night) regimes. The photosynthetic capacity of these plants was studied as a function of temperature in a leaf gas exchange cuvette. Both species showed substantial photosynthetic capacity between 4 and 10 C and this was not enhanced by growth at low temperatures but rather, was somewhat greater in plants grown at higher temperature. Photosynthetic capacity of low temperature-grown plants at high temperature was greater in Atriplex confertifolia (Torr. and Frem.) S. Watts., a native of cool deserts, than in Atriplex vesicaria (Hew. ex. Benth.) from warmer desert areas. Leaves of both species were also subjected to (14)CO(2) pulse-chase and steady-state feeding experiments under controlled temperature conditions. These experiments revealed that the kinetics of carbon assimilation through the intermediates of the C(4) pathway is not substantially disrupted at low temperature in either species. There was, however, a substantial interchange of label between aspartate and malate at low temperature which was not evident at high temperature. There was also an increase in the pool sizes of the C(4) acids involved in photosynthesis of A. confertifolia. Speculation as to the explanation of these changes and their possible significance in promoting low temperature C(4) photosynthesis in these plants is presented.

The initial development of a piosphere created by stocking a new watering trough with ca. 200 sheep at a near-pristine site in arid chenopod shrubland near Whyalla, South Australia, was studied. The following variables were monitored for up to 8 years using fenced plots as controls:shrub mortality; forage biomass and defoliation of the dominant shrubs and short-lived grasses; linear dimensions of Rhagodia ulicina; the density of short-lived species; and the invasion of exotics. Patterns in these variables were looked for which reflected the attenuation of stocking pressure with distance from water; that is, ‘piosphere patterns’. Piosphere patterns were detected for many variables. Those with values increasing towards the trough were mortality of the main forage shrub Atriplex vesicaria. the density of three short-lived taxa, viz. the bassias (Sclerolaena obliquicuspis, S. patenticuspis. Maireana sclerolaenoides), Tetragonia tetragonoides, and annual Zygophyllum spp. (Z. crenatum. Z. ovatum), and growth of short-lived grass species when sheep stocking pressure was low. Variables with values decreasing towards the trough were grass biomass, percentage of A. vesicaria individuals in flower, the percentage foliation of A. vesicaria and of the forage shrub Maireana sedifolia, and shrub forage biomass of A. vesicaria and M. sedifolia. The rate at which these patterns were registered varied. After only 3 months, a piosphere pattern was evident for grass biomass. Marrubium vulgare, an introduced weed, invaded the trough site within the first 6 months. Almost no A. vesicaria shrubs had died after 2 years, but after 8 years there was a marked piosphere pattern in their mortality. The piosphere patterns in forage biomass and defoliation of A. vesicaria and M. sedifolia became more pronounced with time. Some variables did not exhibit a piosphere pattern, such as the dimensions of the shrub R. ulicina and the densities of successive cohorts of the forb Erodium spp., even though there was an overall effect of grazing in reducing their values. There was no mortality of two dominant shrubs, M. sedifolia and R. ulicina, during the first 8 years.

Detailed investigations were undertaken to determine the requirements for optimal germination and establishment of Nitraria billardieri. Germination of N. billardieri on the Riverine Plain is aided considerably by prior ingestion of the fruit by the emu (Dromaius novaehollandiae). Experiments suggested that the increase in germination of emu-ingested seed is largely a response to the removal of the saline outer pericarp during digestion. In one experiment, 62% of emu-ingested seed germinated after 24 days compared with 6% of the hand-picked seed. Studies of field populations of N. billardieri seedlings indicated that they are susceptible to competition from cool season annual species. A competition experiment in sand boxes between seedlings of N. billardieri and Atriplex vesicaria showed N. billardieri to have a slower growth rate and to be susceptible to competition by the seedlings of the perennial A. vesicaria. Studies of the root extension of N. billardieri and Atriplex nummularia in root observation boxes demonstrated the poor performance by the Nitraria roots which grew only 53 cm in 7 weeks whereas the Atriplex roots grew 160 cm in 4 weeks. These data suggest that N. billardieri establishes and successfully competes in the field only with severely weakened saltbush stands. Other important factors are the availability of 'safe sites’ and the degree of competition from annual species. Glasshouse experiments using sand culture indicated that both Nitraria and Atriplex vesicaria could survive in salinities of 0.9 M NaCl and both responded in terms of dry matter production to low salt inputs (e.g. 0.3M NaCl) although growth of Nitraria decreased more rapidly as salinity increased.

Soil water regimes and water extraction patterns estimated over a period of two years are described for two plantation communities of semi-arid shrubs, Atriplex vesicaria Hew. ex Benth. and A. nummularia Lindl., growing on the same soil type under identical climatological conditions near Deniliquin, New South Wales. In spite of poor water flow properties of the soil, surface run-off was negligible.About 90% of the extractable water was stored in the top (45 cm) soil layer. Both species withstood exceedingly low water potentials, although A, vesicaria reduced soil water to a much lower water potential than did A. nummularia. Water potentials at depths below 60 cm were always – 15 bars and remained constant. Water extracted beyond –15 bars amounted to 41% more than the water available within conventionally accepted water potential limits (between –0.3 to – 15 bars). During Slimmer, the plant water potential of A. vesicaria fell to much lower values than that of A. nummularia. Relationships between relative leaf water content and plant water potential differed between the two species, and the suggestion is made that at low plant water potential, leaf targidity of A. vesicaria would be higher, and thus this species would have a higher tolerance to desiccation. On a yearly, half-yearly and even a quarterly basis, evapotranspiration (FT) of the two communities did not differ. Fortnightly FT rates were similar during winter but during early summer, the initial ET rate of A. vesicaria was higher than that of A. nummularia; A, nummularia can therefore conserve water for later use. These differences in water extraction patterns and evapotranspiration were associated with differential rooting characteristics and probably differential stomatal functioning. The relationships between fortnightly ET/FO (ratio of actual evapotranspiration to that from a Class A pan) and profile water content, for both communities, were linear but different.

Sheep faeces enclosed in terylene mesh bags were placed in two contrasting microenvironments within a semi-arid rangeland dominated by Atriplex vesicaria Hew ex Benth., and one within an irrigated pasture. Groups of bags were retrieved and their contents analysed at 3-monthly intervals over a total of 20 months. Sheep faeces from semi-arid rangeland and irrigated pastures were used at each site. Irrespective of source, microenvironment, and season, the amount of faecal material remaining on the semi-arid rangeland sites decreased consistently by approximately 2% month−1. The rate of disappearance for faeces placed under irrigated pastures was 2.5% month−1. The retention of N in the faeces was proportionately greater than the retention of faecal material. The presence of faecal pellets increased the mineral and total N of the soil beneath bags in the betweenbush microenvironment, but not the mineral-N content beneath bags placed under bushes of A. vesicaria in semi-arid rangeland. After 20 months, the proportion of total and inorganic P remaining in the faecal material placed under bushes was 50 and 40% respectively, and in faecal material placed between bushes the corresponding figures were 30 and 20% More Truog “available” P accumulated in soil under bags placed between bushes than under bags placed below bushes. The amount of total and inorganic P remaining after 20 months in the faecal pellets on the irrigated pastures was 20 and 10% respectively. The small loss of organic P from the faecal material indicated an absence of mineralization.

Several Eucalyptus species were grown in plantations at three locations ranging in average annual rainfall from 420 to 850 mm. The main objective was to find for each site the species with the highest transpiration. At the latest sampling which was in summer about two years after germination, E. globulus showed the highest rate per tree (37 l d −1 ) immediately above a seepage area at the 850-mm site. At the 500-mm site E. cladocalyx var. nana had the highest rate (30 l d −1 ), and at the 420-mm site E. wandoo (26 l d −1 ) ranked first. Transpiration varied greatly between species. For those species common to all locations, transpiration declined with rainfall. Transpiration per unit leaf area also varied between species. At the 420-mm site an increase in the average transpiration per unit leaf area, over all species, from 340 mg cm −2 d −1 in early summer to 1110 mg cm −2 d −1 in late summer suggested that the roots had reached a zone of higher water content.

Arid shrublands of southern Australia are of interest to the soil zoologist as an example of a plant association whose stability seems to depend on the cycling of plant nutrients at a rate that appears to be surprisingly rapid for a severe, arid environment (Charley and Cowling, 1968). It is possible that the soil fauna plays a significant part in this system through its effects on decomposition of organic matter. General accounts of arid shrublands in Australia are given by Perry (1970) and Specht (1972). Their principal use is for sheep grazing. All work described here is concerned with the salt bush (Atriplex vesicaria Chenopodiaceae) association of the low shrubland formation (Specht, 1972), and is being carried out in South Australia at Koonamore, 340 km north-northeast of Adelaide, rainfall 190 mm per annum. The climate, soils and vegetation are described by Carrodus, Specht and Jackson (1965) .

Following a build-up in population of the saltbush scale Pulvinaria maskelli, the resulting damace caused to the saltbush Atriplex vesicaria was estimated to be a mean of 17% branches killed per bush. The attendant ant Iridomyrmex sp. affords a measure of protection to the scale against predators and climatic extremes, and so contributes to its damage potential.

SODIUM has been recorded as an essential nutrient element only for the blue-green alga Anabaena cylindrica Lemm.1. It has, however, been shown that increase in dry weight occurs following application of sodium salts to various higher plants growing in low-potassium culture solution and also to members of the Chenopodiaceae growing in solutions containing adequate potassium; views have been expressed that sodium may partially replace the function of potassium or may prevent toxic accumulations of other elements2. The object of this communication is to record sodium as an essential micro-nutrient element for the bladder saltbush (Atriplex vesicaria, Heward), to describe the visual deficiency symptoms when plants were grown in solutions carefully freed from sodium and the recovery of such deficient plants on addition of sodium salts.

Distance walked per day, time and frequency of drinking, volume of water consumed and grazing distribution of Merino sheep flocks on a saltbush (Atriplex vesicaria) and a grassland (Danthonia caespitosalStipa variabilis) community were assessed during summer. Both sites were located within the same region and observed simultaneously for three consecutive days in each of the four months December, January, February and March. The sheep on the saltbush site (1 3 10 ha) grazed as a single flock or as several large subflocks ( >300 sheep) and spent much of their time grazing on a relatively small proportion of the paddock. Drinking frequency was once daily in early summer and twice daily in late summer. The volume of water consumed varied from 2.3 l/day in December to 9.3 l/day in March. Average daily distance walked reflected the change in frequency of drinking and ranged from 8 km/day in December (once daily drinking) to 14 km/day in March (twice daily drinking). Subgrouping occurred on the grassland site (910 ha) where as few as two or three sheep would graze at distances of 10-200 m from other subgroups. Drinking frequency was once daily and volume of water consumed varied from 0.6 l/day in early summer (December) to 3.1 l/day in late summer (March). Average daily distance walked was 4.7 km/day with a peak of 6.2 km/day in late summer when forage on offer had fallen to low levels.