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MISCELLANEOUS PUBLICATION 1271, U.S. DEPARTMENT OF AGRICULTURE 



a significant winter component in southern and 

 central Queensland. The soils are everywhere 

 fine-textured cracking clays, and relief ranges 

 from flat to very gently undulating. The land- 

 scapes are essentially stable, with little risk of 

 either water or wind erosion. The vegetation is 

 dominated by one or several of the Mitchell 

 grasses (Astrebla spp.), which are all rather 

 coarse bunch grasses (figure 2). Following rains, 

 a cover of mainly palatable annual grasses and 

 forbs is produced in the interspaces between the 

 bunch grasses. Livestock concentrate on these 

 palatable annuals. Normally, by late winter the 

 annuals have been consumed, and the stock then 

 graze the less palatable and less nutritious bunch 

 grasses, which nevertheless provide a reserve of 

 low quality standing hay to maintain stock until 

 the next summer. In the event of failure of sum- 

 mer rains, there is little forage to carry stock 

 through another winter. 



Mitchell grasses respond to small falls of rain 

 by sprouting from axillary buds on the lower 

 12 to 20 cm. of the dry culms. Larger falls of 

 rain also ' produce new tillers from basal buds 

 and rhizomes (14-) • 



In these communities, where the desirable pe- 

 rennial Mitchell grasses are naturally deferred 

 by stock, yearlong grazing appears to be a satis- 

 factory system, provided that intensity of stock- 



ing is so adjusted that the Mitchell grasses are 

 not grazed shorter than 15-20 cm., so that they 

 retain their capacity to respond to small falls 

 of rain. If summer rains fail, the only forage 

 available to stock is Mitchell grass stubble re- 

 maining from the previous year. In this event, 

 stock should be removed, not only to retain the 

 capacity of Mitchell grass to respond to small 

 rains, but because there is evidence of heavy 

 mortalities in plants grazed below 3 to 5 cm. 



A century of grazing by livestock has caused 

 very little erosion in Mitchell grass country and 

 little apparent change in the vegetation of most 

 areas. However, there are some exceptions to this 

 general picture. On large areas of the Barkly 

 Tableland in the Northern Territory, Mitchell 

 grass has decreased dramatically over the last 

 2 decades; in fact, in some areas it has been vir- 

 tually eliminated, and the community trans- 

 formed to an annual grassland. With the low 

 erosion hazard, the landscape remains stable, but 

 the late winter/early summer forage reserve no 

 longer exists, and thus the community has lost 

 its stable j T earlong stock carrying capacity. The 

 cause of the degeneration is almost certainly 

 heavy grazing of the Mitchell grass plants, prob- 

 ably during attempts to carry stock on the stub- 

 ble remaining during a year following failure of 

 summer rainfall. Rest periods following summer 



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Fiouee 2. — Mitchell grass grassland near Charleville in central Queensland. 



