matic records for the studies — nearly 60 years 

 by now. Vegetation has been surveyed peri- 

 odically ever since 1912. Surface runoff and 

 the resulting sediment have been measured 

 since 1915, and summer storm intensities have 

 been recorded since 1919. Continuous records 

 of temperature and precipitation have been 

 maintained on the Watersheds, at headquar- 

 ters, and elsewhere on the Experimental Range. 

 These long-term detailed records of climatic 

 factors, of growth of vegetation, and of results 

 of treatments applied to these two Watersheds 

 constitute a tremendous mass of data. Inter- 

 pretation of these data has had far-reaching 

 significance, as will appear later. 



The treatments of Watersheds A and B in- 

 cluded manipulations of vegetative cover. 

 When the studies began in 1912, vegetation 

 on Watershed A had already been depleted to 

 a 16-percent cover, whereas Watershed B had 



about 40-percent cover. This condition was 

 maintained by carefully controlled grazing 

 through eight growing seasons, i.e., through 

 the summer of 1919, so as to determine the 

 amount of surface runoff and sediment pro- 

 duction from a severely depleted watershed as 

 compared to runoff and erosion from a water- 

 shed having fair plant cover. During that 

 8-year period Watershed A produced six times 

 as much runoff and five times as much sedi- 

 ment as Watershed B, which was maintained 

 with a 40-percent cover of vegetation. Prelimi- 

 nary results of the study were published by 

 Sampson and Weyl (1918). 



In 1920, cover on Watershed A was al- 

 lowed to recover naturally by excluding graz- 

 ing; within 5 years the vegetation built up to 

 about the same 40-percent cover that Water- 

 shed B had in the beginning (fig. 7). During 

 this period, Watershed A produced about 



Figure 7. — Eastern boundary of Watershed A, 1970. Foreground shows small area of virtually bare ground, 

 but most of the watershed is covered by grass, forbs, and shrubs. 



10 



