Historical evidence indicates that substantial changes have occurred in the botanical composition of native pastures in temperate southeast Australia as a result of grazing by sheep and cattle. However, the resulting pastures now appear to be relatively stable and there has been limited success in changing composition experimentally. This paper reports the results of experiments conducted at four locations in south-east Australia designed to increase the proportion of desirable species in native pastures by grazing management

Dowling, P M

Friend, D A

Garden, D L

Lodge, G M

English

University of Kentucky

Session 21 - Temperate and Tropical Native Grasslands 21-11ABSTRACTHistorical evidence indicates that substantial changes have occurredin the botanical composition of native pastures in temperate south-east Australia as a result of grazing by sheep and cattle. However,the resulting pastures now appear to be relatively stable and therehas been limited success in changing composition experimentally.This paper reports the results of experiments conducted at fourlocations in south-east Australia designed to increase the proportionof desirable species in native pastures by grazing management.KEYWORDSNative, pastures, grazing, botanical, composition, herbage, mass,sheepINTRODUCTIONSince European settlement in 1788, the native pastures of south-eastAustralia have been grazed by sheep and cattle. This, together withapplication of fertiliser, sowing of legumes and, frequently,replacement of pastures with sown species has caused large changesin botanical composition (Whalley and Lodge 1987). In temperateareas, grazing alone has resulted in many of the taller caespitoseperennial grasses (eg Poa, Themeda, Stipa) being replaced by shorteror rhizomatous species (eg Danthonia, Microlaena) (Whalley et al1978). As well, cool-season annual grasses, legumes and weeds haveinvaded the pastures. In general, such pastures are regarded as havingsuperior production and quality and give higher animal performancethan the original pastures (Whalley and Lodge 1987).While there is historical evidence that these changes have taken place,there has been limited success in duplicating these changes inexperimental studies (Whalley and Lodge 1987).  One such study(Lodge and Whalley 1985) used grazing and resting periods relatedto grass phenology to reduce the presence of the undesirable speciesAristida ramosa and increase Danthonia linkii var. linkii. However,there is little information available on the use of grazing managementto change the composition of native pastures with other species mixes.The studies reported here were part of the Temperate PasturesSustainability Key Program conducted throughout the high rainfallzone (600-900mm) of temperate south-east Australia. This programwas commenced to determine methods of changing the compositionof a number of pasture types in temperate south-east Australia. Withinthe project there were four sites where grazing management effectson native or naturalised pastures were investigated (Table 1).METHODSA communally grazed design was used for the trials, with eighttreatments common to all sites and a small number of local treatments.Two replications were used. Grazing treatments were imposed byopening and closing fenced plots (10x20m) located within a paddockwhich was continuously grazed by dry sheep. Control plots wereleft open throughout. A range of measurements were made on thepastures, including botanical composition, pasture mass and growth,basal area and frequency and seed banks and seedling recruitment.However, only the botanical composition measurements are reportedhere. Experiments commenced in September 1993 and pastures weresampled at 6-7 week intervals thereafter until April 1996. At eachsampling, the Botanal technique (Tothill et al 1992) was used toassess herbage mass and botanical composition in 10 fixed quadratsalong a transect in each plot.RESULTS AND DISCUSSIONMuch of south-east Australia was affected by drought during theperiod of the study, and results at most sites were influenced by this.Stocking rates were reduced at most sites during the drought but, ingeneral, the native pasture sites required less stocking rate adjustmentthan sites based on introduced species. This demonstrates the stabilityof native pastures under dry conditions (Noy-Meir and Walker 1986)and reinforces the perception held by farmers that native pasturescan be relied upon during drought (Dalglish 1993). The dry conditionsalso produced less change in perennial grass composition in the nativepastures than that found in pastures based on introduced species -total perennial grass content generally remained constant at the nativesites (Table 2) whereas it declined at many of the introduced pasturesites.Treatment effects on botanical composition were also small. At thenorthern NSW site there was a general change from Aristida toBothriochloa, mainly caused by recovery from the drought. Atreatment previously designed to reduce Aristida (Lodge and Whalley1985) was not effective during the drought conditions. TheDanthonia/Microlaena pastures in Central and Southern NSW weregenerally stable. There was a suggestion that cell grazing at Orangemay have increased Microlaena, but a similar treatment at Canberrahad no effect. Danthonia appeared to be decreased at Canberra byresting the pasture from grazing in spring or autumn. However, thismay have been a secondary effect as these treatments alsosignificantly increased the amount of Holcus lanatus in the pasture.The Themeda dominant pasture in Tasmania was also relativelystable. A year-long rest followed by burning appeared to decreasethe amount of Themeda. This was unexpected, as light grazing isnormally regarded as beneficial to Themeda (Robinson and Dowling1976) and Themeda is known to be well adapted to burning. However,this result may have been an artefact of the treatment as, followingburning and opening up to grazing, sheep maintained the pasture ina shorter condition than on the control plots which had beencontinuously grazed.These results demonstrate the stability of native pastures undergrazing, even during drought conditions. Treatments to alter botanicalcomposition may need to be more extreme, and be applied for alonger periods, than those used in these experiments. Studies of plantphenology and population dynamics of the species comprising thepastures may be required to effectively design treatments to causerapid change.ACKNOWLEDGMENTFunding for this work was provided by the Australian Meat ResearchCorporation through the Temperate Pastures Sustainability KeyProgram.ID NO. 411MANIPULATION OF BOTANICAL COMPOSITION OF NATIVE PASTURES BYGRAZING IN TEMPERATE SOUTH-EAST AUSTRALIAD.L. GardenA, D.A. FriendB, P.M. DowlingC and G.M. LodgeDANSW Agriculture, PO Box 1600, Canberra, ACT 2601, AustraliaBDepartment of Primary Industries and Fisheries, Kings Meadows, Tas 7249, AustraliaCNSW Agriculture, Agricultural Research and Veterinary Centre, Forest Rd, Orange, NSW  2800, AustraliaDNSW Agriculture, Centre for Crop Improvement, RMB 944, Tamworth 2340, NSW, AustraliaSession 21 - Temperate and Tropical Native Grasslands 21-12REFERENCESDalglish, J. 1993. Native grass pastures - A grazier’s perspective.Proc. 8th Ann. Conf. Grassld. Soc. NSW, pp. 46-49.Lodge, G.M. and R.D.B. Whalley. 1985. The manipulation ofspecies composition of natural pastures by grazing management onthe northern slopes of New South Wales. Aust. Rangel. J. 7: 6-16.Noy-Meir, I. and B.H. Walker. 1986. Stability and resilience inrangelands. Pages 21-25 in P.J. Joss, P.W. Lynch and O.B. Williams,eds. Rangelands: a resource under siege (Proc. 2nd Int. Rangel.Cong.). Cambridge University Press, Cambridge.Robinson, G.G. and P.M. Dowling. 1976. Management of naturalpastures on the Northern Tablelands of New South Wales - A survey.Aust. Rangel. J. 1: 70-74.Tothill, J.C., J.N.G. Hargreaves, R.M. Jones. and C.K. McDonald.1992. BOTANAL - A comprehensive sampling and computingprocedure for estimating pasture yield and composition. 1. FieldSampling. CSIRO Aust. Div. Trop. Crops and Past., Trop. Agron.Tech. Mem. No. 78.Whalley, R.D.B. and G.M. Lodge. 1987. Use of native and naturalpastures. Pages 533-550 in J.L. Wheeler, C.J. Pearson and G.E.Robards, eds. Temperate pastures: their production, use andmanagement. Aust. Wool Corp./CSIRO, Australia.Whalley, R.D.B., G.G. Robinson and J.A. Taylor. 1978. Generaleffects of management and grazing by domestic livestock on therangelands of the Northern Tablelands of New South Wales. Aust.Rangel. J. 1: 174-190.Table 1Details of native pasture sites used in grazing management studiesLocation Annual Rainfall Previous fertiliser Pasture type Major generaTamworth, Northern 650mm Limited Unsown Aristida,New South Wales BothriochloaOrange, Central 700mm Moderate Previously sown Microlaena,New South Wales to introduced species DanthoniaCanberra, Southern 700mm Limited Unsown Danthonia,New South Wales MicrolaenaNile, Northern 530mm Nil Unsown Themeda,Tasmania DanthoniaTable 2Changes in major perennial grass components as a percentage of total herbage mass in  continuously grazedpastures, Autumn 1994-Autumn 1996Aristida Bothriochloa Microlaena Danthonia ThemedaTamworth, Northern Decrease IncreaseNew South Wales 40%-20% 40%-80%Orange, Central Increase IncreaseNew South Wales 35%-45%3 5%-40%Canberra, Southern Constant ConstantNew South Wales 25% 60%Nile, Northern Constant IncreaseTasmania 20% 55%-60%

Manipulation of Botanical Composition of Native Pastures by Grazing in Temperate South-East Australia

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Manipulation of Botanical Composition of Native Pastures by Grazing in Temperate South-East Australia

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