58 BULLETIN 791, IT. S. DEPARTMENT OF AGEICULTURE. 



from the time of the waning of the earl3'-weed stage to the passing of 

 the late- weed stage ; therefore, on the higher ecological tj^pes, an in- 

 crease in the abundance of larkspur ma^^ be declared a reliable 

 indicator of overgrazing. 



Generally low larkspur is most conspicuous early in the develop- 

 ment of the second-weed stage. Accordingly, on cattle range the 

 heaviest losses from poisoning by low larkspur are apt to occur where 

 the lands have been depleted so seriously that the vegetation is in the 

 second-weed stage or in the first and second mixed-weed stage. 



BED GROUNDS. 



Although some variation is found in the vegetation of different 

 bed grounds and adjacent lands of the region, depending chiefly on 

 the character of the soil and the topographic features, the predomi- 

 nating species are generally the same where the extent of the deple- 

 tion of the soil is the same. 



On long-used bed grounds, where the adjacent cover is more or 

 less intact, various distinct vegetative stages may commonly be dis- 

 tinguished, radiating from the bed ground proper. This is exempli- 

 fied in the bed ground shown in figure 24.^ 



The main part of the bed ground (zone 1) is practically circular 

 and covers 22 acres. Owing to the heavy use made of the bed ground 

 each year, not a vestige of the original wheat-grass vegetation re- 

 mains; indeed, even the most aggressive annual plants are for the 

 most part lacking. 



Adjacent to the bed gi'ound proper is an irregular zone of about 85 

 acres. Here the colonization is composed solely of plants of the first 

 or early weed stage. The plants are widely scattered (the density be- 

 ing estimated at 0.05 on a basis of ten-tenths representing full cover) 

 and are distinctlj^ lacking in luxuriance of growth. The species pre- 

 dominating in 1917, named in the order of abundance, were Douglas 

 knotweed, Tolmie's orthocarpus, tansy mustard, tarweed, goosefoot, 

 and androsace. Much less conspicuous were the following species: 

 knotweed {Polygonum aviculare)^ monolepis, peppergrass, and 

 slender-leaved collomia.^ As already indicated, this type of cover 

 afforded practically no grazing for any class of stock. 



Zone 3 comprises approximately 215 acres, and consists of a weed 

 cover of the early and late stages, with the early-stage species dis- 

 tinctly predominating. An occasional grass specimen is also seen. 

 Here the density of the cover is estimated at 0.15, or three times that 

 of the pure early- weed stage adjacent to the bed ground. The pre- 



^ The bed gi'ound here represented has been used annually for several successiTe years 

 by a band of about 1,400 ewes and their lambs. As a rule, the forage cropped in con- 

 junction with the use of this camp has been grazed during the main growing season. 



- Slender-leaved collomia is often among the first to colonize abandoned bed grounds and 

 sometimes is a predominating species. 



