326 THE STUDY OF PLANT COMMUNITIES • Chapter XII 



The establishment of general principles is being followed by 

 more and more intensive studies of local variations in communities 

 and environments. The productivity of most range lands has been 

 reduced by man's domestic animals coupled with seasons of un- 

 favorable climate, and to rebuild ranges to a higher level of pro- 

 ductivity will require an understanding of the special conditions 

 of local areas as well as the broad principles for the region. Our 

 public lands in the West, most of which are grazed, have been di- 

 vided, for research and administration, in a fashion that suggests 

 a natural application of the above. Several grazing regions are 

 designated, which correspond to the major differences in the 

 grassland and scrub formations. These in turn are divided into 

 several districts, which represent local variations in dominants and 

 environment. Application of the general principles is possible for 

 regional administration and management, but local application 

 must be modified in terms of detailed local studies. 



AGRICULTURE 



If a crop is planted and grown successfully, it follows that the 

 methods applied, within the general region, to the particular field 

 and for that season, were ecologically correct since cultivated 

 crops are as subject to ecological laws as are plants growing nat- 

 urally. Study of the ecology of cultivated plants has progressed 

 rapidly in recent years. It includes crop ecology, which is applied 

 ecology in the ordinary sense, and ecological crop geography, 

 which considers the effects of both physiological and economic 

 factors on production and distribution of crop plants. 143 With 

 this addition of "social" factors to the physical and physiological 

 ones, the already complex environment becomes still more so, and 

 the crop ecologist must integrate his observations and conclusions 

 with additional fields. This phase of ecology is, as a whole, beyond 

 our consideration here, but it is appropriate to emphasize that 

 ecological principles are becoming a part of our way of thinking. 

 They should undoubtedly be given even greater attention in these 

 days of a planned economy, which affects us all. 



Crop Ecology.— The cultivated plant is as subject to ecological 

 law as a native one, and, consequently, there is as much ecology 

 to be studied in a corn, tobacco, or cotton field as there is in a 



