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MISCELLANEOUS PUBLICATION 1271, U.S. DEPARTMENT OF AGRICULTURE 



per hectare. Even at the higher stocking rate, 

 K. aphylla did not contribute more than 7 per- 

 cent of the total forage taken. The major con- 

 stituents of the diet were two compositae in win- 

 ter, and Danthonia with an herbaceous chenopod 

 in summer. It is significant that Medicago poly- 

 morpha L. was recorded as a principal constituent 

 in autumn, a species found rarely in more arid 

 environments and never in large quantities. 



In a further study Wilson et al. (33) meas- 

 ured the performance of sheep grazing an A. 

 resicaria-K. aphylla community at 2.5, 1.2 and 

 0.6 sheep per hectare. In summer, sheep preferred 

 the perennial grasses, annual grasses and forbs 

 to the more abundant shrubs, but were inclined 

 to take more shrub during autumn prior to the 

 advent of winter rains. At the lowest stocking 

 rate, animal production was maintained and there 

 was no decline in shrub population, but at the 

 higher levels of stocking the shrubs were almost 

 completely, if not totally, removed. The authors 

 noted the adverse effect of heavy or complete de- 

 foliation on A. vesicaria as it failed to recover 

 during subsequent years. In a later paper, Leigh 

 and Mulham (in press) suggest that this inability 

 of A. vesicaria to persist after this type of use is 

 due to the removal by grazing of potential growth 

 sites which apparently occur only along the young 

 stems. In contrast, Leigh and Wilson (16) report 

 the A. nummularia is capable of producing new 

 leaves along the main stems and branches follow- 

 ing complete defoliation. These differences in 

 morphology are obviously important in planning 

 management strategies for pastures containing 

 these shrub species. 



Wilson (31) reviewed the role of browse in 

 the nutrition of grazing animals and suggested 

 that evaluations of browse should be made com- 

 parative to the alternative vegetation (table 1). 

 There is an obvious need to define the pasture 

 plants required for specific locations. In some 

 places an ability to survive long periods of mois- 

 ture stress may be an advantage, whereas in 

 others high annual productivity may be more 

 desirable. 



Jones and others (13) reported a capacity in 

 A. nummularia to produce 2.33 kg. dry wt. of 

 material from a basal area of one square meter 



in 500 days from establishment. They conclude 

 from this, and from a further study with A. vesi- 

 caria, that the rangeland species of Atriplex are 

 capable of high production and efficient growth 

 in a favorable environment. This investigation, 

 under plantation conditions, was not extended 

 to the field situation where survival, durability, 

 and resistance to water stress are important con- 

 siderations in the arid zone. 



Malcolm (18) worked with Kochia brevifolia 

 R.Br, and a number of Atriplex species in a 

 750 mm. winter rainfall dominant region in West- 

 ern Australia. He applied five handstripping re- 

 gimes to the species and found that K. brevifolia 

 produced most with heavy and moderate simu- 

 lated stocking, while Atriplex responded better 

 to light and moderate use. In a grazing situation, 

 K. brevifolia declined under conditions of light 

 use in autumn though it .fluctuated less than 

 Atriplex with variation in rainfall. Together the 

 species produced about 600 kg. per hectare when 

 the rainfall was about 380 mm. per annum. Yields 

 were correlated in both species with rainfall 

 which fell up to two years prior to grazing. 



Hellmuth (10) reported an eco-physiological 

 study on Rhagodia baccata (Labill.) Moq. in 

 Western Australia in a 200 mm. annual rainfall 

 area. He concluded that a sensitive hydroactive 

 reaction by stomata once a "critical water deficit" 

 was reached appeared to confer considerable 

 drought resistance on this species. The species 

 has a high heat resistance and capacity for posi- 

 tive continuous net assimilation. These charac- 

 teristics, together with its ability to withstand 

 water stress, make it particularly suited to the 

 environment for grazing during moisture stress. 



Considerations such as these are involved in the 

 selection of plants worthy of promotion in an 

 arid environment. While Leopold's (17) view 

 that senescence or the ability to become deciduous 

 in part has positive survival value for a species, 

 this morphological feature is of negative value 

 in the arid range situation. Jessup (11) referred 

 to thorniness and unpalatability as aids to species 

 survival in his description of halophytic commu- 

 nities in northwest South Australia, but these 

 morphological characteristics have similarly no 

 range value. 



