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MISCELLANEOUS PUBLICATION 1271, U.S. DEPARTMENT OF AGRICULTURE 



They observed that intermittent but heavy use 

 promoted the vigor of shrubs between the outer- 

 most and inner zones due to the effects of pruning 

 and trampling which suppressed the weaker 

 bushes. 



Barker and Lange (1) point out that grazing 

 pressure or dietary preference is not, per se, the 

 only agency affecting drifts in vegetation struc- 

 ture in a halophytic community. They include 

 resistance to use and brittleness as factors which 

 should be considered in any application of the 

 effects of morphological characteristics upon 

 community structure. Lange's (14) piosphere 

 concept, which he defines as a fundamental eco- 

 logical condition imposed by grazing animals 

 upon the natural pattern, was used by these au- 

 thors in an analysis of change of vegetation 

 around watering points. Annual species of Atri- 

 plex were found to reflect rapidly a changing 

 environment, whereas changes in population of 

 the perennial A. vesicaria were considered to be 

 the product of long term effects of grazing and 



not immediately indicative of any vegetation 

 change. 



Figure 4 (Wilcox unpublished) shows the 

 order of changes which occurred in degraded 

 saltbush communities after exclosure and under 

 yearlong use. In a period of generally low rain- 

 fall from 1953 to 1960 when effective rain fell 

 only on two occasions, a number of species re- 

 mained relatively static, or even disappeared 

 under grazing pressure. However, A. paludosa 

 R.Br, is shown to be particularly labile and could 

 be used as an indicator of range condition and 

 as a detector of drifts in structure. 



A number of workers have studied the effects 

 of grazing on halophytic communities. Trumble 

 (27) and Woodroffe (35) investigated the graz- 

 ing of a K. sedifolia pasture in South Australia. 

 In a pasture containing about 900 bushes per 

 hectare, the green weight of bluebush fluctuated 

 from 517 to 1,600 kg. per hectare, dependent upon 

 rainfall. In a period of six years of low rainfall 

 there was a downward trend in production in 



Table 1. — Changes in relative contribution to pasture with time and season in exclosed and freely 



grazed saltbush association 1 



[production in kg./ha., fresh wt.] 



Date 



Species : 



Atpa 



Atrh 



Crsu 



FRAN 



Kopy 



Ground 



Total 



Annual 



railfall 



mm. 



October 1953 



347 

 111 



156 

 135 



237 

 119 



4 



54 

 8 



N/A 3 



N/A 



798 

 373 



494 



April 1954 



208 

 Ilk 



78 

 102 



86 



ks 



3 



36 



6.8 

 0.35 



417.8 

 259.35 



137 



April 1956 



125 



72 



24 

 35 



27 



17 



— 



5 



0.26 

 Nil 



154.26 

 Ilk 



217 



April 1957 



154 

 121 



18 

 5k 



17 

 11 



— 



3 



0.02 

 Nil 



192.02 



1 86 



152 



April 1958 



35 

 S 



8 

 k 



6 



— 



4 



Nil 

 Nil 



53 



75 



322 



April 1959 



85 

 k6 



24 



22 



14 



7 



— 



4 



Nil 

 Nil 



127 

 75 



196 



May 1960 



151 



79 



94 



2k5 



4 

 IS 



22 



67 



N/A' 

 N/A* 



316 

 359 



231 



'Roman figures indicate exclosed: italicized figures indicate freely grazed. 



"Species are indicated as follows: Atpa — Atriplex paludosa, Atrh — Atriplex rhagodioides, Crsu — Crati/stylis 

 subsplnescens, FRAN — Frankenia sp., Kopy — Kochia pyramidata, and Ground — annual grasses and forbs. 

 8 N/A indicates data not available. 



