PLANT MORPHOGENESIS FOR SCIENTIFIC MANAGEMENT OF RANGE RESOURCES 



169 



Water Balance 



Effects of stock on the water balance compo- 

 nent are examined in terms of the water balance 

 equation in which 



P = R+AD + AM + AU + /Edt (1) 



where P is rainfall; R is net surface runoff; ±D 

 is the change in surface water storage provided 

 by dead and living plant material, and by sur- 

 face hollows; ^M is the change in soil water 

 storage in the plant rooting zone; ^U is the 

 change in storage below the plant rooting zone 

 and /Edt is the total evaporation over the time, 

 t, under consideration. 



Reduction In Vegetation Cover 



By reducing vegetation cover, trampling and 

 grazing expose more of the soil surface to direct 

 raindrop action. In shrub steppe communities, the 

 shrubs may occupy over 33 percent of the ground 

 area and, consequently, their removal adds sub- 

 stantially to the area of soil surface exposed. 

 Further, the ground between perennial shrubs or 

 tussock grasses is seasonally occupied by ephem- 

 erals which, when present, form a major com- 

 ponent in the diet of sheep (36, 37, 52, 68). The 

 duration of the ephemeral vegetation cover is 

 consequently reduced. The additional area and 

 duration of bare ground exposed to raindrop 



TRAMPLING 



7J7- 



i Vegetation 

 i reduced 

 .Soil 

 i compacted 



RADIATION 

 MICROCLIMATE 



WATER 

 BALANCE 



i (over reduced i 

 i Dominant i 

 i sptao i 

 i changed i 



GRAZING 



i VfO'n cover i 

 i reduced, i 

 i especially i 

 I p/rtnnial spp.i 



i Soil awrf^ates i 

 i destroyed i 

 i Surface soil i 

 i disturbed i 





Increased l 

 i runoff and i 

 i ujater I 



i rrwlon i 

 i j 



^ 



SOIL 

 STABILITY 



i Reduction of I 

 i major re- i 



iCjcUngcpcacd 



i 



i 



i Soil loss by i 



iwiod and r* 

 i water i 



'erosion i 

 u I 



ALTERED CONDITIONS FOR 

 COMMUNITY REGENERATION 



EXCRETION 



Mwralisaicor? 

 nfe itattitd | 

 (oflccnfratian 

 'of mitrienij ', 



NUTRIENT 

 BALANCE 



Figxjbe 2. — Stock-mieroenvironment interactions. The direction of the interaction lines is from top to bottom for the 

 stock-mieroenvironment interactions and from left to right for interactions between microenvironmental com- 

 ponents. 



