GENERAL RELATIONS. 113 



triangle of a few yards was discovered. Even areas which were mowed but 

 unpastured were very rare and of small extent. If it were not for the unin- 

 tentional protection afforded by fencing railroad right-of-ways, it would often 

 be impossible to determine the original vegetation of many regions. The 

 appreciation of this fact has led to the development of a method which has 

 been of the utmost value during the last five years in reconstructing the 

 primitive vegetation of regions where it has been greatly modified or almost 

 entirely displaced. This method has yielded surprising results throughout 

 grassland, sagebrush, and desert scrub, but its most striking success has been 

 in the great interior valleys of California, where ruderal grasses have almost 

 undisputed sway. The constant examination of fenced right-of-ways and 

 other chance protected areas the past three years has confirmed the theoretical 

 assumption that this was formerly a vast Stipa association. This determina- 

 tion of the original climax might well seem to be without practical importance, 

 but it is actually of the greatest value in indicating the proper method and 

 the objectives in restoring overgrazed areas to their normal productiveness, 

 as is shown in detail in Chapter VI. 



The relation of the subsere to the climax is so definite and organic that, 

 once established for a single locality, it can be extended to all others where 

 the subsere occurs. Obviously the reverse is true also, namely, that a particu- 

 lar climax will exhibit the same subsere wherever similar or identical dis- 

 turbances occur. This same organic correlation applies likewise to the prisere. 

 The succession in water, on rock, or in sandhills is essentially the same through- 

 out the vast area of the grassland formation, for example. The relation 

 between climax and prisere once established, it is possible to predict the 

 climax from the prisere or the prisere from the climax wherever either is 

 absent. There is also a close correlation between subsere and prisere, espe- 

 cially in the later stages, and it is further possible to anticipate the effect of 

 disturbance in a region where the prisere is present, or to prophesy the course 

 of the slowly moving prisere from that of the subsere. When it is clearly 

 recognized that practically all human activities in nature result in disturbed 

 areas, the correlations between climax, subsere, and prisere will be seen to be 

 of the greatest practical importance. 



Summary of the climax formations. — In presenting a sketch of the climax 

 formations as a background against which indicator values may stand out 

 more clearly, the treament is purposely limited to the western half of the 

 country. This is chiefly for the reason that indicator values are greatest in 

 newer regions, but partly also because the climax relations are simpler and 

 hence more certain. For this reason the prairie is the most eastern associa- 

 tion considered, though this necessarily involves occasional reference to the 

 deciduous climax. It is also recognized that some of the western climaxes 

 are not confined to the United States, but occur also in Canada and Mexico. 

 Our knowledge of vegetation and especially of succession in these countries 

 is so scanty that only occasional reference to them is warranted. 



The following outline will serve to show the climax formations and their 

 associations, and will also serve as a guide to the discussion of each in its 

 proper sequence. The treatment of each formation and association is neces- 

 sarily brief, as the primary object is not a detailed account of the vegetation, 

 but only such as will serve the general purposes of indicator studies. This 



