PLAISTT SUCCESSIOlSr AND RANGE MANAGEMENT. 5 



give character to the landscape, and the interlacing roots and rhi- 

 zomes bind the soil somewhat firmly, though at this point of develop- 

 ment the grasses are not sufficiently abundant to form a sod. 



By the time the second-weed stage has had its gi'owth and has 

 thus prepared the way for the next set of plants the soil is sufficiently 

 decomposed and contains sufficient organic matter and soil moisture 

 to make possible the establishment of the climax or the subclimax 

 grass cover/ 



In the utilization of lands as grazing areas, the invasion by the 

 higher type of vegetation is often prevented, especially where the 

 species high in the development are grazed with greater relish than 

 those lower in the succession. Thus the plants well up in the de- 

 velopment of the type may disappear gradually or suddenly, accord- 

 ing to the degree of disturbance caused b}^ the adverse factor, until 

 the plant stages lower in the development predominate. If the 

 factor adverse to the progressive development of the vegetation con- 

 tinues to have its play for an indefinite period the vegetation will 

 continue to revert until the first-weed stage reappears, or, indeed, 

 until practically all the soil is carried away and the pioneer stage 

 returns. Such a succession of the plant cover down the scale from 

 the more complex to the primitive type will be referred to in this 

 bulletin as retrogression,- retrogressive succession, or degeneration. 



The destruction of the entire soil formation and the exposure of 

 consolidated rock occurs only in the worst possible cases. More com- 

 monly the productivity of the soil is decreased to a point where it 



1 Areas well within the woodland type are often occupied by a temporary cover in 

 which grasses constitute tlie herbaceous climax. Within a woodland formation, however, 

 grasses seldom if ever hold their own permanently against the invasion of timber species 

 as they do on prairie and plain. 



2 The writer's concept and use of the term " succession " differs from that of some ecolo- 

 gists Ce. g., Clements, F. E., " Plant Succession, an Analysis of the Development of Vege- 

 tation," Carnegie Inst. Wash. Pub. No. 242 : 161-167, 1916) in that both progressives and 

 retrogressive succession are recognized. Coming as it does from the Latin verb " succedo," 

 meaning literally " I go under," the word " succeed " originally had nothing to do with 

 the superiority of one crop over another. Thus, succession is here considered in the sense 

 to " follow," " take the place of," etc., and is applied in a vegetative izivasional sense. 

 Accordingly, if the developmental trend of an association or other plant unit is ascending 

 toward the climax, it may be referred to as a positive or progressive succession ; if de- 

 scending from the climax it may be termed a negative or retrogressive succession. Re- 

 gardless of whether retrogressive succession occurs in the same specific descending series 

 as it has been recorded to occur in the ascending development toward the climax, the use 

 of the term " retrogression " or " retrogressive succession " is a convenient and self- 

 explanatory term, and its use in no way involves a fundamental principle. 



For a further discussion of the subject of progressive succession the reader is re- 

 ferred to : 



Cowles, Henry C, The Physiographic Ecology of Chicago and Vicinity. Botanical Gaz., 

 vol. 31, No. 2 : 7.3-108, Feb., 1901. 



Moss, C. E., The Fundamental Units of Vegetation. The New Phytologist, vol. 9, Nos. 

 1 and 2 : 36-37, Feb., 1910. 



Hole, R. S., On Some Indian Forest Grasses and Their Ecology. Indian Forest Memoirs, 

 vol. 1, No. 1 : 13-16, 1911. 



Sampson, Arthur W., Succession as a Factor in Range Management. Journal of For- 

 estry, vol. 15, No. 5 : 593-96, May, 1917. 



