PLANT SUCCESSION 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 growth 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. 1 
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 by 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, 2 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 the 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. 
y 2 The writer's concept and use of the term " succession " differs from that of some ecolo- 
gists (e. 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 invasional 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 : 73-108, 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. 
