PALEIC INDICATORS. 99 



Kinds. — The basic practices concerned in a system of indicators are agri- 

 culture, grazing, and forestry. The primary consideration, however, is which 

 of these is possible or most desirable in a particular area or region. Since 

 successful agriculture brings the largest returns per unit area, the first question 

 is whether the land is agricultural. If not, the next question deals with its 

 value for forestry or grazing, or for a combination of the two. The methods 

 employed in reaching a decision as to the most desirable of the three practices 

 constitute land classification, which in a new region at least is to be regarded 

 as a practice prerequisite to the others. It is preeminently dependent upon 

 plant indicators, as is shown by the first serious endeavor to classify the lands 

 of the western United States upon anything approaching a scientific basis 

 (Shantz and Aldous, 1917). It is obvious that similar methods, refined by 

 quantitative methods and increasing experience, must sooner or later be used 

 in all the new regions of the world where maximum economic returns are 

 desired. 



In addition to distinguishing areas as primarily agricultural, grazing, or 

 forest land, practice indicators serve also to indicate particular types of 

 agriculture, grazing, or forestry, as well as to suggest the crop of the greatest 

 promise. Thus, in the case of agriculture, indicators may be used to denote 

 the greater feasibility of humid, dry, or irrigation farming, or the importance 

 of combining grazing with dry-farming. Where grazing is concerned, the type 

 of vegetation not only determines whether cattle, sheep, or goats are prefer- 

 able, or a combination of two or three possible, but it also indicates whether 

 the introduction of other dominants is possible or desirable. In similar 

 fashion, indicators may be employed to determine the possibility of afforesta- 

 tion or reforestation, as well as the most promising dominants for any particu- 

 lar region. Finally, practice indicators have more or less value for reclama- 

 tion projects and other engineering operations, especially road-building, and 

 they are of the first importance for indicating the course and intensity of 

 climatic cycles and the modifications of current practice which they demand. 



Because of their direct economic importance, a chapter is devoted to the 

 indicators of each of the great basic practices, agriculture, grazing, and 

 forestry, respectively. Land classification is considered in the following 

 chapter in connection with agriculture, and the relation of climatic cycles to 

 optimum production is discussed in connection with each type of practice. 



PALEIC INDICATORS. 



Paleo-ecology. — The significance of paleic indicators rests upon the con- 

 viction that ecologic processes were essentially the same during the geological 

 past as they are to-day (Clements, 1916 : 279; 1918 : 369). It is assumed 

 that the vegetation of the globe was differentiated into climax formations 

 corresponding to the primary climates. Such formations possessed a develop- 

 ment and structure strictly comparable with that of present-day climaxes. 

 They were divisible into associations, consociations, and societies, and they 

 exhibited primary and secondary seres wherever bare areas occurred. The 

 control of the direct factors, water, light, temperature, etc., must have been 

 just as to-day, and this is equally true of their modification by physiographic 

 processes and climatic changes, as well as by the competition and reaction of 

 plant communities. Then, as now, the latter furnished food and shelter to the 



