PLANT MORPHOGENESIS FOR SCIENTIFIC MANAGEMENT OF RANGE RESOURCES 65 



(a) 50 ~ (b) 



— ^-^^^ At pa 



Alrh 



O O- Cr<iu 



— A A- Kopy 



40 



730- 



0) 

 U 



o.20i 



-C 



a 



-10 



19 



40- 



""*" **«*. 



30- 



20" 



10 



1953 



54' 55' 56' 57' 58' 59' 60' 



1953 





54' 55' 56 1 57 1 " 



58' 59' 



bO 



Figure 4. — Changes in species occurrence with (a) exclosure, and (b) open grazing in a halophytic community in 

 Western Australia. Atpa — Atriplex paludosa R.Br. ; Atrh — Atriplex rhagodiodes F.Muell. ; Crsu — Cratystylis 

 subspinescens (F.Muell & Tate) S.Moore; and Kopy — Eochia pyramidata Benth. 



pastures grazed at 0.4 and 0.5 sheep per hectare. 

 However, this trend was reversed with increased 

 rainfall as the heavily grazed plants produced 

 more leaf and the number of plants per hectare 

 increased. The enhanced production from the 

 heavily grazed plots was considered to be due to 

 an acceleration of the fertility cycle. Animals 

 were important as circulators of nutrients which 

 stimulated growth of mature plants and the de- 

 velopment of young seedlings. They concluded 

 that the productivity of shrub pastures may be 

 considered as a function of grazing intensity and 

 effective seasonal rainfall. However, Rixon (26) 

 found that the rate of decomposition of residues 

 on the soil surface in an Atriplex community in 

 New South Wales was slow, and that the returns 

 from animal residues, were extremely small. The 

 return of nutrients was of local significance where 

 grazing pressure was high or where animals 

 tended to congregate. Rixon suggested that the 

 pattern of behavior of grazing animals was im- 

 portant in any consideration of nutrient recycling. 

 He found a localized intensity of nutrient cycling 

 beneath individual elements of the shrub cover. 



Elimination of this plant cover could be ex- 

 pected to cause a significant reduction in the rate 

 of nutrient cycling in the pasture, and a conse- 

 quent reduction of potential productivity. 



A series of investigations on halophytic shrub- 

 grassland pastures in southwestern New South 

 Wales has questioned the value of the shrub 

 component in providing a source of basic diet 

 or even of supplementary feed during periods 

 of moisture stress. 



Wilson and Leigh (32) compared the produc- 

 tivity of sheep grazing mixed A. vesicaria-grsiss 

 pastures with that of sheep grazing Danthonia- 

 Stipa, and mixed Danthonio-Stipa-iovh pastures. 

 At a stocking rate of 1.2 sheep per hectare, sheep 

 grazing the shrub-grass pastures were superior 

 in the first year only, and subsequently declined 

 in condition due to death of the shrubs. On the 

 grassy pastures the sheep were maintained indefi- 

 nitely. At 2.4 sheep per hectare, both pastures 

 failed. In a similar investigation, Leigh and 

 others (15) studied the performance of merino 

 sheep grazing a Kochia aphylla ~R.'F>Y.-Stipa-Dan- 

 thonia community at 1.6 sheep and at 0.9 sheep 



