56 BULLETIlSr 791, U. S. DEPARTMENT OF AGEICULTUEE. 



they have been used. Not uncommonly they represent the most 

 serious destruction of the plant cover that can occur on the range. 



In order to determine what plant species characteristically colo- 

 nize heavily on long-used driveways and bed grounds, taking into 

 account the rate at which such areas may revegetate under different 

 methods of management, a number of small sample plots were care- 

 fully selected for special study. Some of the selected plots have been 

 protected from live stock by fencing; others received no protection 

 and were subject to normal seasonal grazing. 



STOCK DRIVEWAYS. 



A generalized sketch of the vegetation and other features on a 

 portion of the driveway selected for special study is shown in 

 figure 22.^ 



While a few grasses have gained a foothold on this driveway, the 

 ground cover is quite open and composed chiefly of a mixed stand 

 of Aveeds, characteristic of the first and the second weed stage. Listed 

 in the order of their abundance, it will be noted that Douglas knot- 

 weed, slender-leaved collomia, and tansy mustard constitute the domi- 

 nant early-Aveed species on this portion of the driveway, as indeed 

 they do on the driveway as a whole; tongue-leaved violet, dan- 

 delion, and low larkspur constitute the predominating late-weed- 

 stage plants. Other typical species of the late-weed stage are chick- 

 weed, evening primrose, low pea vine, meadow rue, and plantain. 

 The more persistent species, blue foxglove and sweet sage, have 

 gained a foothold, but apparently conditions do not yet favor rapid 

 colonization of these plants. In 1917 the vegetative blocks represent- 

 ing the unprotected driveway had a density of stand of about 0.15.- 

 The protected area when fenced in 1915 was identical as to species 

 and density with that of the outside range, but in 1917 supported a 

 cover of approximately 0.2. This slight increment in the stand over 

 that on the adjacent unprotected range is composed of annual and 

 perennial weed species in equal proportions. 



Much the same vegetative development occurs on another pro- 

 tected plot, a bisect detail of which is shown in Figure 23.^ Of the 



1 The area here sketched had been so severely overgrazed at the time the lands v?ere 

 included within the National Forest in 1905 that practically every vestige of the herba- 

 ceous perennial vegetation had been destroyed. During the past 12 years the area has 

 been grazed in moderation, during the main growing season, by cattle, sheep, and horses. 

 In listing the plants it was the aim to record the species that occurred in each vegeta- 

 tional unit but not every individual. The relative density of the respective blocks, how- 

 ever, is shown. 



2 Density measurement is on the basis of ten-tenths for full cover. 



8 It Is noteworthy that of the eight species that occur in the bisect all are typical 

 either of the first or of the second weed stage, a fact which strongly substantiates the con- 

 clusion that their increase in abundance on a range in a higher stage of development 

 would announce the waning of the higher type. 



