Io8 RECOGNIZING AND CORRECTING DECLINING FORAGE 



(3) second or late weed stage (the foxglove-yarrow-sweet sage 

 cover); (4) first or early weed stage (the annual weed cover). 

 Although the species concerned in this investigation are not 

 the same everywhere/ the character of growth and the habitat 

 requirements of the plants of the different stages are the same 

 on native pasture lands generally. 



CLIMAX HERBACEOUS STAGE 



The wheatgrasses (Agropyron) in the Wasatch Mountains, 

 and generally over their natural range, constitute the climax 

 or highest herbaceous cover. Both the " bunch " wheatgrasses 

 and the turf-forming kinds are characteristic, but generally the 

 bunchgrass forms distinctly predominate (Fig. 29). Usually 

 between the tufts grows a considerable admixture of vegetation. 

 The turf-forming wheatgrasses, on the other hand, usually make 

 so dense a stand in their unhampered development as practically 

 to exclude other plants. 



Destruction of the Wheatgrass Cover. — The opening up, by 

 destructive grazing or otherwise, of a well-estabHshed stand of 

 wheatgrass immediately stimulates the invasion and establish- 

 ment of both deep-rooted and shallow-rooted plants. Where 

 the fertility of the soil is not appreciably impaired as a result of 

 the depletion of the wheatgrass cover, yellowbrush {Chryso- 

 thamnus lanceolatus) and small porcupinegrass {Slipa minor) 

 are among the first to gain a foothold. Where the tufted or 

 " carpet " form of wheatgrass is permitted to revegetate, this 

 cover again completely reoccupies the area, thus entirely re- 

 placing the yellowbrush and porcupinegrass. As shown in 

 Figure 30, this destruction of the more temporary invaders is 

 due to the network of superficial wheatgrass roots. So com- 

 pletely do these roots occupy the soil that practically all of the 

 available soil water is absorbed, and the soil below, with the 

 deeper roots of the invading plants, like yellowbrush, is left in a 

 state of dryness. Thus any vegetation whose main moisture- 

 absorbing roots extend well below those of the turf- forming 



^ Clements, F. E., "Plant Indicators." Carnegie Institution of Washington, 

 Publication 290, pp. 270-335, 1920. 



