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MISCELLANEOUS PUBLICATION 1271, U.S. DEPARTMENT OF AGRICULTURE 



ments of problems and views which I hope will 

 stimulate discussion. These statements will be 

 based largely on the morphogenetic information 

 available from perennial pasture species of the 

 moist temperate regions of the world. 



I propose to discuss the different morphological 

 stages in the life cycle of perennial grasses using 

 information which is available for grasses in 

 general. The stages selected for discussion are: 

 germination and establishment; quantity and 

 quality of vegetative growth; perennation; flower- 

 ing and seed production. In dealing with each of 

 these, I will first outline the process and then 

 discuss, where available, the results of research on 

 Australian rangeland species. Where appropriate, 

 this will be followed by speculation on the im- 

 plications for adaptation and management. 



Perennial Grasses In The Australian 

 Rangelands 



Two grassland communities (subformations) 

 are recognized in the rangelands of Australia (9, 

 11), and these are each dominated by perennial 

 grass species. 



Arid Hummock Grassland 



The dominant plants in the community belong 

 to the genra Triodia and Plectrachne. It competes 

 with Acacia shrubland as the most extensive com- 

 munity of arid Australia (22.6 percent) (9) and 

 it occurs in both the winter and summer rainfall 

 zones. 



The dominant grasses form characteristic hum- 

 mocks; some (for example, Triodia Jongiceps J. 

 M. Black) extend to 6 m. in diameter and 1.8 m. 

 high (11). Frequently the centers of these hum- 

 mocks die out, leaving expanding rings of dense 

 tillers. The leaves are generally harsh with pun- 

 gent tips, and they are highly xeromorphic (1). 

 Arid hummock grassland supports few stock (11) 

 probably because of the extreme leaf xeromorph- 

 ism and dense, pincushion growth form. 



Arid Tussock Grassland 



This grassland is much more restricted in its 

 distribution, lying to the north and northeast of 

 the arid zone and well within the summer rain- 

 fall areas. In it each plant forms a discrete tus- 



sock some 20 cm. in diameter and 50 to 100 cm. 

 tall. Often the ground between the tussocks is bare. 

 There are several species of tussock grasses but 

 nearly all belong to the genus Astrebla (mitchell 

 grass) and in most areas few other species occur. 



Unlike hummock grassland, the tussock grass- 

 land is very productive and has been estimated 

 to support one half the livestock of arid Aus- 

 tralia (11), despite the fact that it constitutes less 

 than 10 percent of the rangeland area. Growth of 

 these grasses is rapid following rain, and the 

 grasses can be utilized for several months during 

 the winter as standing hay. Some research on the 

 growth and development of the mitchell grasses 

 has recently been published (7) and has demon- 

 strated the value of morphogenetic research as 

 a basis from which sound management policies 

 can be developed. 



There are numerous perennial grasses which 

 grow in the shrub and woodland communities of 

 the Australian arid zone. Some of these provide 

 fodder for grazing animals (9, 11). For example, 

 in the northern, summer rainfall woodlands — 

 which are dominated by Eucalyptus spp. — the 

 genera of both the hummock and tussock grass- 

 lands are found in addition to species of Hetero- 

 pogon, Chrysopogon. Aristida, Sorghum, Them- 

 eda, and Sehima. In the southern woodlands, 

 characterized by erratic winter rainfall and dom- 

 inated by eucalypts, CaUitris, and Casuarina, the 

 most important perennial grass genera are Aris- 

 tida, Stipa. C Moris. Neurachne, Eragrostis, and 

 Enneapogon with species of Danthonia and Poa 

 growing where the annual rainfall rises to be- 

 tween 25 and 50 cm. (9). 



In the saltbush shrub steppes, which achieve 

 their maximum development in the southern, 

 winter rainfall areas, Danthonia, Stipa, Eragros- 

 tis, and Aristida provide a winter and spring 

 ground cover between the shrubs, provided the 

 winter rains have been adequate. Where overgraz- 

 ing and past cultivation have removed or greatly 

 weakened the shrub cover, the land may become 

 completely dominated by Stipa. 



Eucalypt shrublands of the north are closely 

 related to the summer rainfall woodlands de- 

 scribed earlier, and the perennial grass genera 

 found there are much the same. The Acacia shrub- 

 lands form a different community and are wide- 

 spread in the arid and semiarid zones occupying 



