Monachather Paradoxa Research Articles

Death model for tussock perennial grasses: a rainfall threshold for survival and evidence for landscape control of death in drought

We investigated relationships between rainfall (and landscape, zonation and nearby grazing disturbance) and the death rates of four perennial grass species in a highly functional semi-arid wooded grassland in eastern Australia. Two grasses were palatable C3 species (Monachather paradoxa Steud. and Thyridolepis mitchelliana (Nees) S. T. Blake) and two were unpalatable C4 species (Aristida jerichoensis (Domin) Henr. var. subspinulifera Henr. and Eragrostis eriopoda Benth.). During the 10-year study the grasses were protected from large herbivore grazing within paddocks continuously grazed by sheep. Death occurred only during droughts and rates of death were species-dependent. When plotted against several water availability indices, rainfall and rainfall/evaporation during the preceding 3 months provided best predictions of death. Longer preceding periods gave inferior predictions. A 3-month rainfall total of 75 mm and a 3-month rainfall/evaporation ratio of 0.15 were survival critical thresholds below which deaths began. The 3-month rainfall totals, rainfall/evaporation and estimated water status of plants were equally reasonable predictors of deaths, but were inconsistent in their effectiveness. Rainfall was adopted for the grass death model; death begins when 3-month rainfall total declines below a threshold of 75 mm and the death rate rises with lower rainfall. Position of plants in the gently undulating landscapes influenced water status and, hence, death rates. Water status of grasses on the two water-shedding zones and the ‘flat’ zone were similar at each assessment, but higher on ‘ridge run-on’ and ‘toe-of-slope’ zones. Foliage height and diameter also influenced death rate but were species dependent. Basal diameter did not influence death rate. Survivorship of several perennial grass species at widely spaced sites in south-eastern Australia provided equivocal support for generality of the grass death model.

Herbage Production Following Rainfall Redistribution in a Semi-Arid Mulga (Acacia Aneura) Woodland in Western New South Wales.

The effects of stocking rate (nominally ranging from 0.3 up to 0.8 dry sheep equivalents per ha) on rainfall redistribution, soil-water storage and herbage production were studied in three contiguous geomorphic zones (run-off, interception and run-on zones) in a semi-arid mulga (Acacia aneura) woodland in western New South Wales. The amount of rainfall redistribution increased directly with rainfall but there was no significant effect of stocking rate on the amount of soil-water stored in various zones. while soil-water storage differed little between zones following a minor rainfall event (11.9 mm), it was significantly higher (P < 0.001) in the run-on zone following a major rainfall event (42.7 mm). The interception zone was by far the most productive herbage zone contributing a significantly (P < 0.01) disproportionate amount of forage (c. 90% of total paddock production at low stocking rates) despite this zone only occupying a relatively small proportion (c. 12%) of landscape catenae. Herbage in the interception zone principally comprised palatable C3 perennial grasses such as Thyridolepis mitchelliana (mulga grass) and Monachather paradoxa (bandicoot grass). Experimental manipulation confirmed the fundamental importance of rainfall redistribution as a landscape process mediating herbage production in these semi-arid plant communities. Dry matter production by Eragrostis eriopoda (woollybutt) was significantly enhanced (P < 0.05) in the run-off zone when incident rainfall was retained in situ by metal barriers. Conversely, production by Thyridolepis mitchelliana in the lower interception zone was significantly depressed (P < 0.01) where similar barriers prevented access by overland flow. The results are discussed in the context of developing conservative management strategies designed to maintain effective landscape processes in these extensive ecosystems.

The Influence of Recent Grazing Pressure and Landscape Position on Grass Recruitment in a Semi-Arid Woodland of Eastern Australia.

This study examined the effects of previous grazing pressure, position in the landscape and apparent seed trapping capability of soil surface micro-sites on recruitment of the perennial grass Monachather paradoxa (mulga oats) in a semi-arid woodland. Seedling emergence was counted on small plots which had been kept moist for one month. The plots were on bare ground, or at grass tussocks, or at log mounds, sited in the run-off, interception and run-on zones of paddocks that had been grazed for six years at 0.3 and 0.8 sheep equivalent/ha. Few naturally occurring perennial grass seedlings emerged on any of the sites. The level of previous grazing pressure influenced the recruitment of grasses from natural sources as well as from seed of M. paradoxa broadcast on the soil surface; significantly more grass seedlings recruited in paddocks stocked at 0.3 than at 0.8 sheep/ha. Emergence of the sown grass did not differ significantly between the three zones in the landscape, but trends in the data suggest the interception zone may have been the most favourable. Recruitment from in situ grass seed was highest in the mulga grove (run-on) zone. Most seedlings of the sown grass emerged around the bases of existing perennial grass tussocks, but recruitment of volunteer perennial and annual grasses was more evenly distributed between the mulga log-mounds and perennial grass tussocks. It is concluded that very low levels of readily germinable seed of perennial grasses remained in the soil at the end of the drought and that areas with a history of high grazing pressure have less probability of grass recruitment when suitable rain occurs.

Effects of Temperature and Age on the Germination of Naked Caryopses of Indigenous Grasses of Western New South Wales.

The effects of temperature and age on the germination of naked caryopses of nine native grasses from western New South Wales were studied in the laboratory. Maximum germination percentages varied from >90% for Astrebla lappacea to <<1% for Eragrostis setifolia. Optimum temperatures for germination of A. lappacea, Bothriochloa macra, Dichanthium sericeum, Enneapogon avenaceus, Monachather paradoxa, Paspalidium constrictum and Thyridolepis mitchelliana were 20-30�C. Highest germination of Danthonia caespitosa was at 15�C. At temperatures close to their respective optima, most seeds germinated within seven days of imbibition, although rates of germination varied with temperature. In three species (A. lappacea, D, caespitosa, P. constrictum), germination percentages were similar or higher for two-year-old seed compared with 6-month-old seed. At its optimum temperature, two-year-old seed of T. mitchelliana had > 10% germination. In the other five species, germination was <10% for seed stored for more than 12 months. These results have implications for the agronomic use of these species.

Photographic Utilisation Standards for Three Perennial Grasses.

Height-weight profiles were established for Monachather paradoxa, Thyridolepis rnitchelliana and Eragrostis eriopoda based on field populations from semi-arid mulga woodlands in north-western New South Wales. These profiles were subsequently used to develop photographic standards of percentage canopy remaining by weight as a guide to field assessment of the severity of grazing. Examples of the standards are presented.

Does grazing reduce survival of indigenous perennial grasses of the semi‐arid woodlands of western New South Wales?

Abstract Exclosures were used to examine the impact of grazing upon the mortality patterns of populations of six indigenous grass species. The experiment compared unfenced areas with areas from which either sheep only or sheep, rabbits and kangaroos were excluded. There were large interspecific differences in mortality patterns, with Stipa nitida and Aristida browniana having relatively high mortality rates and Eragrostis eriopoda having relatively low mortality rates. Grazing‐induced mortality was observed in treatment areas that were grazed by sheep, rabbits and kangaroos and in areas grazed only by rabbits and kangaroos. The short‐lived S. nitida appears less likely to suffer grazing‐induced mortality than species of intermediate longevity such as Monachather paradoxa. These observations help explain the decline in endemic perennial grasses that has taken place in the vegetation of western New South Wales since European settlement. Management of these rangelands to encourage these grasses must consider total grazing pressure and not simply the impact of livestock.

Forage utilization by sheep and kangaroos in a semi-arid woodland

The utilization of forage species by sheep and western grey kangaroos, and their contribution to the diets of those animals, were determined in a mulga (Acacia aneura) woodland in western New South Wales. Utilization was determined from measurements of forage yield, on pastures that were grazed by either sheep, sheep and kangaroos together or kangaroos, at a range of stocking rates. The sheep and kangaroos had similar preferences for the major grasses, with high utilization of species such as Monachather paradoxa and low utilization of the more fibrous species such as Eragrostis eriopoda. At times of forage abundance, annual and perennial forbs were a major component of sheep diet but a relatively minor component of kangaroo diet. Differences in species preference thus arose mainly in species that were uncommon or of seasonal occurrence. The overall diets of sheep and kangaroos were similar, with a year-round predominance of the same group of perennial grasses such as Thyridolepis mitchelliana. In the treatment where sheep and kangaroos grazed together, kangaroos had access to areas exclosed from sheep and their use of these areas increased with increase in stocking rate. Thus the exclosures received a similar grazing pressure by kangaroos alone, to that of the surrounding paddocks grazed by a mixture of sheep and kangaroos. It is concluded that there is direct competition between sheep and kangaroos for the main forage species. There are also long-term effects of high kangaroo populations on sheep production because the movement of kangaroos to rested paddocks negates any pasture management practice that requires periodic resting of pastures from grazing.

Vegetation and soil patterning in semi‐arid mulga lands of Eastern Australia

Abstract Vegetation and soil patterns across a 200 ha semi‐arid site 40 km north‐west of Louth, NSW, are described using plant cover data from line transects and soils data from points, sampled systematically (50 m intervals) across the site. A patterned sequence of alternating groves and intergroves with three vegetation types was identified: an Eragrostis eriopoda savanna occurring on runoff slopes (<0.5%) from low ridges, with a Monachather paradoxa savanna occurring at the toe of these runoff slopes (intergroves), followed by an Acacia anuera woodland occurring on runon areas (groves, either as discrete islands or more continuous along drainage lines). Data on landform, micro‐topography, and hydrological features indicate that the grove‐intergrove pattern is maintained by differential erosion–deposition processes similar to the dynamic erosion–transfer–sink geomorphic systems described for Central Australia. This vegetation grove–intergrove patterning in Eastern Australia is similar to, but differs in detail from, such patterns reported for arid and semi‐arid Western and Central Australia. Groves or ‘bands’ of A. anuera in the Centre and the West tend to occur on the downslope side of ‘risers’ or on ‘convex slope‐breaks’ where in the East such groves occur in distinct 'steps’ or ‘flats’ in the landscape; there is a drop into the grove and a sharp ‘erosion‐scarp’ below the grove. A prominent ‘grass band’, identified by cluster analysis as the M. paradoxa community type, occurs immediately upslope of A. anuera groves in the East. The A. anuera groves in the East are also fertile’ patches as soils data demonstrate that groves have much higher levels of organic and exchangeable nutrients (and plant cover) than soils in the intergroves. This paper demonstrates that patterning in mulga lands is more extensive geographically, and has a wider climatic range, than previously reported.

The effects of burning, fertilizing and clipping on populations of Aristida armata, Thyridolepis mitchelliana and Monachather paradoxa in a mulga woodland pasture.

The effects of burning, clipping, applying nitrogenous fertilizer, and protection from grazing on populations of three perennial grasses were monitored over four years in permanent quadrats in a mulga (Acacia aneura) woodland pasture near Charleville. Queensland. The grasses were the weedy invader Aristida armata (wiregrass), and two desirable species, Thyridolepis mitchelliana (mulga grass) and Monachather paradoxa (mulga oats). They comprised 70%, 16%, and 12%. respectively, of the pasture at the start of the experiment. Rainfall had a greater effect on plant numbers. especially of A. armata, than any treatment other than repeated clipping. The greatest mortality amongst A. armata plants occurred during a protracted dry period between March 1982 and April 1983 but the losses were more than compensated by mass germination during April 1983. The other two species responded similarly but less markedly. Repeated clipping caused attrition of all three species but failed to improve pasture composition. Pasture recovery after burning was slow and accompanied by a minor deterioration in pasture composition as measured by the proportion of A. armata plants. Burning caused greater mortality in A. armata plants than in the other two species but this was offset by greater A. armata seedling regeneration. Both initial survival and subsequent seedling recruitment were reduced by slashing a week prior to burning. When left ungrazed. T mitchelliana and M. paradoxa were more drought tolerant than A. armata and their relative numbers in the ungrazed plots increased over the four years of the experiment. Thus, protection from grazing offers the best prospect of improving pasture condition as none of the other treatments reduced A. armata numbers without adversely affecting those of T. mitchelliana and M. paradoxa.

Vegetation Dynamics in a Grazed Mulga Shrubland Community. II. The Ground Storey

Population dynamics of annual forbs and of the grasses Eragrostis xerophila and Monachather paradoxa were studied in relation to a gradient in range condition within a mulga shrubland community in the arid winter rainfall zone of Western Australia. Frequency of annual forbs appeared to be influenced more by local environmental factors than by grazing. Species which showed definite trends in relation to the range condition gradient were either relatively insensitive to condition changes or occurred at low frequencies and would thus be susceptible to sampling error. The perennial grass E. xerophila decreased under heavy grazing but also appeared insensitive to relatively small variations in grazing pressure. Regeneration of this species following drought appears to be a protracted process and may be inhibited by ephemeral growth in the immediate post-drought period. Under severely degraded conditions the semiperennial M. paradoxa displayed a marked reduction in vigour, as reflected in plant size (density/cover ratio), but neither foliar cover nor dry matter production were much affected. The stability of its production under degraded conditions, however, is likely to be reduced relative to sites subjected to more conservative management.

Seedling growth on Mulga soils and the ameliorating effects of lime, phosphate fertilizer and surface soil from beneath poplar box trees.

Phosphate fertilizer, lime (CaCO3), and soil from beneath poplar box trees (Eucalyptus populnea) were incorporated into the surface of an acid sandy red earth (mulga soil) in pots. The effect of these treatments was studied on the growth rate and yield of seedlings of 7 exotic pasture species, Cenchrus ciliaris cv. Biloela, C. ciliaris Q10087, C. ciliaris Q10077. Schmidtia pappophoroides, Eragrostis curvula CPI 30379, Anthephora pubescens and Stylosanthes fruticosa, plus 3 native species Monachather paradoxa, Digitaria ammophila and Aristida armata. Phosphate fertilizer significantly increased growth rates and yields on all soils of all species except E. curvula, S. fruticosa, M. paradoxa and A. armata. Lime, sufficient to raise the pH from 4.8 to 7.7, only slightly improved plant growth overall, although the effect was significant on the three C. ciliaris lines in the absence of added phosphorus. Box surface soil significantly increased growth rate and size of C. ciliaris, especially the cultivar Biloela, and to a lesser extent that of A. pubescens, M. paradoxa and .T. pappophoroides. This improvement in seedling growth on soil from beneath box trees could be at least matched by the addition of phosphorus to mulga soil. Yet the shoots of seedlings growing in box surface soil appeared deficient in phosphorus, indicating a lower availability to plants of such phosphorus than chemical tests would indicate. Evidence in research literature indicates that the results obtained point to aluminium toxicity as being a major factor limiting seedling growth of C. ciliaris on mulga soils.

Importance of phosphorus and nitrogen in the nutrition of grass seedlings growing in mulga soil

A pot experiment was conducted to compare the Importance of nitrogen and phosphorus fertilizers to seedling growth of four grasses on mulga soil. Two native species, Monachather paradoxa (mulga oats) and Digitaria ammophila (silky umbrella grass), and two exotic ones, Anthephora pubescens (wool grass) and Cenchrus ciliaris cv. Biloela (buffel grass), were tested. Digitaria and the two exotic grasses reacted similarly to applied phosphorus while Cenchrus utilized soil nitrogen more readily than the others. Phosphorus produced marked growth responses, increased the nitrogen and phosphorus contents of the plants, reduced the time between emergence and tillering and reduced root/shoot ratios. Nitrogen fertilizer produced no significant responses and actually retarded very early seedling growth. There were no nitrogen x phosphorus interactions.

Emergence, seedling development and survival of native and exotic grasses on a sandy red earth in South-Western Queensland.

The growth and development of eight perennial grasses, from sowing until flowering, was studied in the field on a sandy red earth near Charleville, south-western Queensland. They included four species native to this soil, Thyridolepis mitchelliuna, Aristida armata, Digitaria ammophila and Monachather paradoxa, and four exotic species Cenchrus ciliuris cv. Biloela, Anthephora pubescens, Eragrostis curvula and Schmidtia bulbosa. Cenchrus ciliaris, A. pubescens and S. bulbosa emerged much more promptly than the other species and much less viable seed was left in the soil after the fist germination event. The native species tillered and flowered earlier than the exotic grasses and survived better under adverse growing conditions. Average survival at the end of the first growing season, during which good seasonal conditions pre- vailed, was 30% of the emergent seedlings. Schmidtia bulbosa performed best within the exotic group and this was associated with early tillering and earlier flowering. The exotic species needed at least a four month growing season before they flowered under field conditions compared with two months or less for the native grasses. However this disadvantage was offset somewhat by their greater dry matter yield at this stage of development.