76 Plant Protection Quarterly Vol.13(2) 1998 benefit would be captured by wool and Campbell, M.H. (1977). Assessing the area Outline. Unpublished mimeograph, lamb producers who operate in that part and distribution of serrated tussock CSIRO Division of Plant Industry, Can- of the Australian wool and lamb indus- (Nassella trichotoma), St. John’s wort berra. tries represented by the study area. (Hypericum perforatum var. angusti- Prograze (1995). NSW Agriculture. It must be emphasized that these re- folium) and sifton bush (Cassinia Vere, D.T., Sinden, J.A. and Campbell, sults are preliminary because both the arcuata) in New South Wales. Depart- M.H. (1980). Social benefits of serrated RPM and econometric modelling compo- ment of Agriculture New South Wales tussock control in New South Wales. nents require further refinement. In rela- Technical Bulletin No. 18. Review of Marketing and Agricultural Eco- tion to the RPM, further work is required Campbell, M.H. (1987). Area and distribu- nomics 48, 123-38. on refining the soils and rainfall digitized tion of serrated tussock (Nassella Vere, D.T., Auld, B.A., Auld, J.A. and data and to incorporate elevations into the trichotoma (Nees) Arech.) in New South Campbell, M.H. (1993). ‘Economic as- GIS model so as to be able to determine Wales, 1975 to 1985. Plant Protection sessments of serrated tussock (Nassella arable and non-arable country. Also, the Quarterly 2, 161-4. trichotoma) as a pasture weed. Weed livestock feed energy requirements in the Cousens, R. (1985). A simple model relat- Technology 7, 776-82. model are preliminary values as the study ing yield loss to weed density. Annals of Vere, D.T., Griffith, G.R. and Bootle, B.W. is awaiting the inclusion in the model of Applied Biology 107. (1994). The development and applica- energy requirements calculated by the Crean, J. (1996). New South Wales wool tion of a quarterly econometric model GRAZFEED model. Further work is nec- and sheepmeat budgets. In ‘Farm of the Australian prime lamb industry. essary in refining the econometric model’s Budget Handbook’. (NSW Agricul- NSW Agriculture, Economics Services wool industry specification and in the in- ture). Unit, Agricultural Economics Bulletin tegration of this component into the other Denne, T. (1988). Economics of nassella No. 11. livestock industry models. tussock (Nassella trichotoma) control in Vere, D.T., Jones, R.E. and Griffith, G.R. Despite the recognized deficiencies in New Zealand. Agriculture, Ecosystems (1997a). An integrated economic meth- the analysis, the study represents a signifi- and Environment 20, 259-78. odology for evaluating the impacts of cant economic contribution to the study of Edwards, G.W. and Freebairn, J.W. (1982). weeds in agricultural production sys- serrated tussock. The 1997 survey repre- The social benefits from an increase in tems and the farm and industry ben- sents the most accurate collection of data productivity in a part of an industry. efits of improved weed control. Techni- on the extent and distribution of serrated Review of Marketing and Agricultural Eco- cal Series No. 2, CRC for Weed Man- tussock in New South Wales. Having nomics 50, 193-210. agement Systems. these data incorporated into a GIS model Labys, W.C. (1984). ‘Commodity Models Vere, D.T., Jones, R.E. and Griffith, G.R. has made this information far more ame- for Forecasting and Policy Analysis’. (1997b). Evaluating the farm and indus- nable to modelling, particularly for incor- (Croom Helm, London). try impacts of weeds and the benefits of poration into an economic analysis. McDonald, W. (1996). Matching pasture improved weed control in agricultural production to livestock enterprises in production systems. Plant Protection References the Northern Tablelands and North Quarterly 12, 145-50. Alston, J.M. (1991). Research benefits in a West Slopes and Upper Hunter. Agnote multimarket setting: a review. Review of DPI/130, NSW Agriculture. Marketing and Agricultural Economics 59, Moore, A.D., Donnelly, J.R. and Freer, M. 23-52. (1990). The GRAZPLAN Model: An plants that invade native vegetation usu- The biology of Nassella and Achnatherum species ally adversely affecting the survival of the indigenous flora. A potential impact of en- naturalized in Australia and the implications for vironmental weeds is a loss of biodiversity and a decrease in aesthetic value. management on conservation lands Stipoid grasses (in particular, N. neesiana and N. trichotoma) have proven to M.R. GardenerA and B.M. SindelB be difficult to control and have continued Division of BotanyA and Division of Agronomy and Soil ScienceB, School of to spread in conservation lands. They are Rural Science and Natural Resources and CRC for Weed Management successful because they have many bio- Systems, University of New England, Armidale, NSW 2351, Australia. logical traits which allow them to out- compete native vegetation. Stipoid grasses Summary Introduction generally invade plant communities Several species of Nassella and Several species of Nassella (Barkworth which are already highly degraded and Achnatherum are weeds of both conser- 1990) and Achnatherum (Barkworth 1993) have a history of disturbance (G. Carr per- vation and pasture lands. These species have become naturalized in Australia. sonal communication), and lands with have proven to be difficult to control and They include Nassella charruana (Arech.) higher fertility soil often previously used have continued to spread since their in- Barkworth, N. hyalina (Nees) Barkworth, for grazing or farming. These communi- troduction to Australia. The impact of N. leucotricha (Trin. & Rupr.) Pohl, N. ties may originally have been grasslands these species on conservation lands in- megapotamia (Spreng. ex Trin.) Barkworth, or grassy woodlands. Some conservation cludes a perceived drop in biodiversity N. neesiana (Trin. & Rupr.) Barkworth, N. areas in Victoria with significant inva- and a decrease in aesthetic value. Rea- trichotoma (Nees) Hackel ex Arech., sions of stipoid grasses include the Derri- sons for the ability of these species to Achnatherum caudatum (Trin.) S.W.L. mut Grasslands Reserve, Organ Pipes Na- out-compete native vegetation include Jacobs & J.Everett and Achnatherum tional Park and Southern Plenty Gorge. effective dispersal mechanisms, the pro- brachychaetum (Godr.) Barkworth. These Anecdotal evidence suggests that there duction of large amounts of aerial and species are referred to as stipoid grasses. is a drop in biodiversity in stipoid grass- clandestine seeds and large long-lived They are considered both environmental dominated grasslands because litter from seedbanks. Management strategies must and pasture weeds. Carr et al. (1992) de- the tall tussocks accumulates in the inter- take these factors into account. fines environmental weeds as exotic tussock spaces and excludes shade Plant Protection Quarterly Vol.13(2) 1998 77 intolerant species. However, thick stands to be achieved. Do we try to eradicate flowers (self-fertilized) which are ex- of undisturbed Themeda triandra Forssk. stipoid grasses or accept them as a perma- tremely variable and morphologically dif- have a similar inhibitory effect on other nent part of that community and try to ferent from those borne in the panicles. species (Stuwe and Parsons 1977). The di- manipulate the system to favour the na- Seeds from these flowers, known as versity of cryptogams (e.g. mosses, li- tive components? The aim of this paper is cleistogenes, originate from nodes on the chens, bryophytes) is thought to decline in to discuss some of the biological attributes flowering stem and are concealed under stipoid grass-dominated grasslands be- of Nassella and Achnatherum species which the leaf sheaths. In N. neesiana there is a cause the mosaic of substrates such as have resulted in their proliferation on con- progressive reduction in inflorescence rocks and bare soil becomes covered with servation lands. length and number of spikelets and floral litter (V. Stajsic personal communication). parts from panicle spikelets to spikelets at Quantitative studies are needed to com- Dispersal the base of the tillers (Connor et al. 1993). pare diversity of stipoid grass-dominated Long distance dispersal of the stipoid Five of the eight stipoid grasses in this grasslands and adjacent native remnants. grasses is by adhering to the coats of ani- study have axillary cleistogenes and four If there is reduced diversity, does it result mals, clothing or machinery via a sharp produce basal cleistogenes on the lowest from general degradation or is it specific callus at the end of the seed (Table 1). node of the flowering tiller (Table 1). to stipoid grass-dominated grasslands? Sheep can carry seed of N. neesiana in their Nassella neesiana and N. trichotoma have Likewise, what effect do stipoid grasses wool for at least 166 days (Gardener un- the potential to produce huge numbers of have on the diversity of vertebrate and in- published data). Thus there would be am- viable panicle seeds. In a dense, ungrazed vertebrate species? The striped legless liz- ple opportunity for dispersal over large infestation, seed production of N. neesiana ard (Delma impar) appears to prefer dense distances. Seeds probably also adhere to ranged from 1584 to 22 203 seeds m-2 intact swards of native tussock grasses other animals such as kangaroos and rab- (Gardener et al. 1996). These differences such as T. triandra and Austrostipa ssp., but bits. were correlated with the amount of spring can also use exotic species such as Phalaris Nassella trichotoma has tumbling inflo- rainfall, the former being in a drought spp. (Osbourne et al. 1993). How well do rescences which detach at the base, and year and the latter being in an above aver- they exist in degraded stipoid grass- can be windblown for up to 10 km dis- age year. Fluctuation in seed production dominated grasslands? persing seeds as they go (Campbell 1982). can be attributed mainly to the change in Management of weeds in natural sys- Jarava plumosa (Spreng.) S.W.L.Jacobs and number of flowering tillers produced per tems is often more difficult than in pas- J.Everett can also be blown by wind but unit area.