352 THE STUDY OF PLANT COMMUNITIES * Chapter XII 



a group of species or a whole community is more reliable as an 

 indicator than a single species and that dominants, especially of 

 the climax, 57 or at least characteristic species 34 are more useful in- 

 dicators than lesser species. Above all, application of the method 

 cannot be successful without judgment, good sense, and interpre- 

 tation in terms of each situation. 



Agricultural Indicators.— That crop centers and types of agri- 

 culture are correlated with climate and climax vegetation is obvi- 

 ous. The agricultural areas of North America follow a pattern 

 very similar to that of a map of natural vegetation. 229 The north- 

 eastern conifer region suggests general agriculture at the lower 

 altitudes and latitudes where the land is level and soil is deep. In 

 the transition from boreal to deciduous forest, white pine-red 

 pine-jack pine forests are on sandy soils, which are, in general, 

 undesirable for agriculture, while the northern hardwoods-hem- 

 lock forest indicates the best soils for cultivation. The range of the 

 deciduous forest formation marks the best agricultural region of 

 the east with the greatest diversity of crops. Away from the south- 

 ern Appalachian and Ohio Valley center, as the associations be- 

 come less complex and oak and hickory become relatively more 

 important, so also does agriculture become more specialized. 



On the prairie, both tall and mixed grasses indicate fertile and 

 productive land for cereals, hay, and fodder. Likewise, the natural 

 grass cover provides valuable grazing facilities. The short grass 

 area indicates productive soil whose cultivated crops are limited 

 by moisture. The most favorable sections can be dry-farmed, but 

 otherwise irrigation is necessary for cultivation. As a result, the 

 land is most widely used for grazing. 



Vegetation indicating general land use has been given more at- 

 tention in the western United States than elsewhere. 230 Subalpine 

 vegetation indicates a growing season too short for cultivated 

 crops, steep slopes, and poor agricultural soil. The montane zone 

 also has a short season with cool weather but permits some culti- 

 vation if the land is not too rough. Pinon-juniper in the woodland 

 zone indicates productive soil if irrigation is possible, but chap- 

 arral indicates inferior agricultural land under almost any circum- 

 stances. 



Plant indicators of land use in the arid regions of the West are 



