Paper No. 10 



MORPHOGENESIS AND MANAGEMENT OF ANNUAL PLANTS IN 



AUSTRALIA 



By R. Milton Moore 1 



Abstract 



The distribution and characteristics of annuals 

 in pastures and grazing lands of Australia are 

 outlined. The growth and shoot apex develop- 

 ment of the most widely occurring sown and nat- 

 uralized species are described and Australian 

 studies of effects of defoliation are reviewed. 

 Management of annual communities is discussed 

 in relation to the morphology and reaction to 

 grazing of their principal species. 



Additio?ial hey words: shoot apex, naturalized 

 species, defoliation, grazing. 



Annual Species Of Australian Pastures And 

 Grazing Lands 



All of the annual species sown in Australia 

 are introduced. Many of the most widely sown 

 are locally occurring biotypes of species accident- 

 ally brought into the country and now natural- 

 ized in communities grazed by domestic livestock 

 or otherwise subjected to disturbance. Others are 

 not sown but are volunteer in sown pastures and 

 in grazing lands of native species; some of these 

 species are useful, but others are weeds and harm- 

 ful to animal production. 



In some arid and semiarid communities, native 

 annual grasses and forbs germinate rapidly after 

 drought-breaking rains. Although they do not 

 last long, they reduce the grazing pressure on 

 perennials during the early part of a new period 

 of growth. 



Figure 1 shows areas where annual pasture 



1 Senior Research Fellow in Woodland Ecology, Com- 

 monwealth Scientific and Industrial Research Organisa- 

 tion, Cunningham Laboratory, St. Lucia, Queensland, 

 Australia. 



species are of actual or potential significance 

 for animal production in Australia. 



There are about 157 million ha. suitable for 

 existing cultivars and varieties of annual pasture 

 species and of these 85 million are in southern 

 or temperate Australia and about 72 million in 

 northern or tropical Australia. 



In southern and western Australia, the inland 

 limit of naturalized annual pasture species is ap- 

 proximately the 254 mm. annual isohyet. North 

 of 30 °S. latitude in eastern Australia, the propor- 

 tion of rain falling in the winter months of the 

 year declines and the limits of temperate pasture 

 species are at increasingly higher annual rainfalls 

 until at the northern end of their range the in- 

 land boundary is at approximately the 508 mm. 

 annual isohyet (25, 26). 



On acid soils in temperate Australia pastures 

 of cool season annual species have evolved under 

 sedentary grazing in a system in which nitrogen, 

 and frequently phosphorus and sulphur as well, 

 are increasing. Nitrogen has been added to the 

 system by introduced legumes and sulphur and 

 phosphorus by applications of superphosphate. 

 (26). 



On neutral and alkaline soils Trifolium species 

 are replaced in Mediterranean annual pastures 

 by annual species of Medicago (26). In sown pas- 

 tures the common species are barrel medic (M. 

 truncatvla Gaertn.) and strand medic (M. litto- 

 ralis Rhode), and in volunteer communities the 

 burr medics (M. minima (L.) Bartol, M. poly- 

 morpha L., and M. laciniata (L.) Mill.). 



Wimmera ryegrass (Lolium rigidum Gaud.) is 

 the only grass sown in Mediterranean annual pas- 

 tures, but barley grass (Hordeum leporinv/m 

 Link.) volunteers and is almost invariably the 

 dominant grass on both neutral and alkaline soils. 

 Barley grass also replaces L. mgidum in old pas- 

 tures on acid soils in eastern Australia. 



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