Paper No. 16 



EFFECTS OF STOCK ON MICROENVIRONMENTS IN AUSTRALIAN 



RANGELANDS 



By J. K. Marshall x 



Abstract 



The paucity of investigations inquiring spe- 

 cifically into the question of the effects of stock 

 on microenvironments is noted. There is, however, 

 a fair coverage of related investigations. From 

 these and the inclusion of new information the 

 interactions of stock grazing, trampling and ex- 

 cretion are considered in relation to four micro- 

 environmental components: water balance, nutri- 

 ent balance, soil stability, and radiation micro- 

 climate. 



Of the possible total of 12 stock-microenviron- 

 ment interactions (3x4), eight are identified and 

 discussed, four associated with grazing, three 

 with trampling, and one with excretion. In addi- 

 tion, two interactions between microenvironmen- 

 tal components, namely, between water balance 

 and soil stability and between soil stability and 

 nutrient balance are discussed. 



The relative simplicity of these interactions is 

 contrasted with the complexity of interrelation- 

 ships between them in a discussion of scald for- 

 mation and of microenvironmental diversity. Fi- 

 nally, the capacity of microenvironments to re- 

 cover and the importance of prediction of sus- 

 ceptible (or relatively unstable) and nonsuscepti- 

 ble (or relatively stable) ecosystems in relation to 

 stock use is discussed. 



Additional key words: Grazing, trampling, ex- 

 cretion, water balance, nutrient balance, soil sta- 

 bility, radiation microclimate, scalds, microen- 

 vironmental diversity, ecosystem stability 



Introduction 



Little research has been reported in Australia 

 on the effects of stock on microenvironment. How- 



ever, many studies exist from Australia and else- 

 where from which the effects of stock may be 

 inferred. These include reports on changes in 

 vegetation and soils and on the end-products of 

 stock-landscape interaction. This account at- 

 tempts to draw together both published and new 

 information to provide an outline of stock-micro- 

 environment interaction of particular relevance to 

 Australian rangelands. 



Much of this account implies that stock gen- 

 erally affect the microenvironment adversely. 

 This is not necessarily so. Adverse effects only 

 show themselves in circumstances of mismanage- 

 ment of domestic or wild stock in relation to 

 the ecosystem used, particularly in the failure 

 to realize that ecosystems vary considerably in 

 their susceptibility to stock. An example of this 

 is provided by one of the commonest observa- 

 tions on stock effects, that of change in vegeta- 

 tion composition. Thus, disclimax Danthonia 

 caespitosa Gaudich. — Stipa variabilis Hughes - 

 grasslands (44) on heavy Riverine clay have 

 shown little change under grazing by sheep dur- 

 ing 19 years of observation (71, 72). By contrast, 

 shrub steppe dominated by Atriplex vesicaria 

 Heward ex Benth. (bladder saltbush) growing on 

 similar soils is moderately susceptible to variation 

 in stocking rate of sheep, the most noticeable 

 effect being elimination of the saltbush at stock- 

 ing rates of 1.2 and 2.5 sheep per hectare (73) 

 (figure 1). Finally, many shrub steppe communi- 

 ties variously dominated by Atriplex vesicaria, 

 Kochia astrotricha Johnson (low bluebush), K. 

 pyramidata Benth. (black bluebush), and K. 

 sed? 'folia F.v.M. (pearl bluebush) growing on 

 desert sandy loams or texture contrast soils have 

 been seriously depleted by effects of both rabbits 

 and sheep, sometimes resulting in complete de- 



1 Senior Research Scientist, C.S.I.R.O.., Division of 

 Plant Industry, Deniliquin, N.S.W. 2710, Australia. 



Most plant names follow Black (13) and Eichler (19). 



167 



