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MISCELLANEOUS PUBLICATION 1271, U.S. DEPARTMENT OF AGRICULTURE 



Figube 1. — Vegetation change as a result of variation in sheep stocking rate at "Emmet Vale", 49 km. N.N.W. of 

 Deniliquin, N.S.W. The bladder saltbush (Atriplex vesicaria) on the right of the fence originally covered the 

 entire area but was eliminated from the plot on the left of the fence after grazing for 5 years in 7 at a stock- 

 ing rate of 1.2 sheep/ha. The plot on the right of the fence remained substantially unaltered after the same pe- 

 riod of stocking at 0.6 sheep/ha. Details of the grazing experiment are given by Wilson and others (78). The 

 condition of the vegetation is that under which the water-use results in figure 7 were obtained. 



nudation (9, 16, 29, 1$). Many of the more strik- 

 ing changes resulted from past failure to recog- 

 nize inherent differences in susceptibility of the 

 range added to which were the effects of drought, 

 competition from rabbits, conditions of tenure, 

 and financial pressures (1, 1$). 



Stock influence microenvironments as a result 

 of their three basic activities : grazing, trampling, 

 and excretion which here refers to both defeca- 

 tion and urination. Spatial variation in these 

 activities, due to differences in stocking rate and 

 to animal behavior, lead to effects on at least 

 two scales : the former on a regional scale and the 

 latter on a smaller, within paddock scale. Varia- 

 tion on a regional scale is evident at the State 

 level from maps of stock numbers (18) while 

 within paddock variation can arise from aggre- 

 gation behavior concentrating effects around wa- 

 tering points (35, Jf5, 58), camping areas (26), 

 and the tendency for some animals to graze into 

 the wind. 



Stock-Microenvironment Interactions 



The ways in which grazing, trampling, and ex- 

 cretion influence the microenvironment can be 

 considered in relation to the four microenviron- 

 mental components: water balance, nutrient bal- 

 ance, soil stability, and radiation microclimate. 



Interactions between the three stock factors and 

 these components are shown in figure 2. Of the 

 twelve possible interactions only eight are ob- 

 vious and reasonably direct. The interactions af- 

 fect the components of the microenvironment in 

 different ways but resolve themselves into three 

 basic effects: reduction and changes in vegeta- 

 tion; modification of surface soil structure and 

 modification in the availability of nutrients. The 

 implications of these three effects of stock for 

 water balance, nutrient balance, soil stability, and 

 radiation microclimate are examined in the fol- 

 lowing sections. 



