

210 FAUNAL DIVISIONS OF EASTERN NORTH AMERICA. 



is controlled by three factors— heat, atmospheric precipitation {including winds) , 

 and soil, and of these "climatic humidity" or precipitation is the most potent 

 influence in producing the broad types of vegetation. He recognizes three 

 such types or "formations": Woodland, Grassland, and Desert, the development 

 and spread of each being related mainly to the abundance of the ground-water 

 in the superficial or the deeper levels of the soil 

 according to Schimper, has " w™ 



sub-soil, damp and calm 



A good woodland climate, 

 warm vegetative season, a continuously moist 



especially 



winter." Grassland depends on 



frequent, even if weak, atmospheric precipitation during the vegetative season, 

 so that the superficial soil is kept in a moist condition, and further a moderate 

 degree of heat during the same period." Strong deviations from these two cli- 

 matic types produce a desert. 1 > t 



I have not attempted in this paper to do more than indicate the general 

 relations existing between faunas and certain broad areas of vegetation and I 

 have confined my observations mainly to the eastern portion of the North Ameri- 



is a region of exceedingly 



can continent 



The western half of the continent 



Its mountain 



complex topography as compared with the eastern section, 

 ranges, and the belt of arid country to the east, have formed a barrier to the 

 spread of numerous eastern species of animals, although on the other hand, 

 certain species quite characteristic of the east have undoubtedly come originally 



I do not believe that we can regard an Austral 



from this western plateau region 



The few 



Zone as extending entirely across the continent from ocean to ocean, 

 typically eastern forms that have spread west are mainly of northerly distri- 

 bution and related to the coniferous forest which reaches far into the northwest, 

 while the species which are of undoubted plateau origin, when they have pene- 

 trated eastward, have not ranged north beyond the deciduous forest to any great 



extent. 



The following outline is a synopsis of the faunal divisions of North America 

 based on the distribution of vegetation. Although this discussion is confined 

 to the east, as stated above, I have included the western aspect of the fauna, 

 in a wholly provisional and inadequate way, merely to complete the genera 



scheme. 



Synopsis of the Faunal Divisions of North America. 



I. THE SUB-ARCTIC FAUNA. 



(a) The Barren Ground Type 

 (6) The Tree-limit Type. 



II. THE ATLANTIC FOREST FAUNA. 



(a) The Coniferous Forest Type. 

 (6) The Deciduous Forest Type. 



III. THE COASTAL PLAIN FAUNA. 



(a) The Alluvial Forest Type. 



(b) The Marshland Type. 



(c) The Pine Barren Type. 



1 Schimper, Plant Geography, English translation, Oxford, Clarendon Press 



1903 



