ognomy; the other controls the local aspect. One determines 

 the coniferous forest; the other controls the formation of the 

 alpestrine meadow and the Alpine-Tundra. 



The question now most naturally presents itself: why in one 

 place do we have the forest and in another its entire absence? 

 Why is the coniferous forest dominant here, and the deciduous 

 there? The present condition of these various plant societies 

 is evidently the resultant of the inter-action of a complex of 

 natural agencies operating- upon them. Hence an interpretation 

 of these conditions will largely depend upon an understanding 

 of these determining factors. For convenience of discussion 

 they may be treated under four heads, climatic, edaphic, biotic, 

 and historical. 



A. CLIMATIC FACTORS. 



The factors to be treated under this head are composite and 

 inclusive in nature. Of these temperature and moisture are, 

 perhaps, the most important. A general survey of our entire 

 country shows us a central prairie region bordered east and west 

 by forest formations. The Atlantic and Middle States present 

 a forest because the resultant of these factors produces a condi- 

 tion congenial to forest development. For similar reasons the 

 Pacific coast is dominated by a vast coniferous belt. The 

 absence of these favorable forest developmental conditions in the 

 middle west, results in a climatic prairie formation. 



Within this great Eastern forest we find a varied physiog- 

 nomy. The Central states are dominated by a deciduous forest, 

 while the extreme Northern states are coniferous in aspect. 

 These differences are likewise climatically determined, being due 

 to a different adjustment of the determining forces which vary 

 in different latitudes. Such homogeneous plant groupings are 

 known as climatic formations. 



The Ktaadn region lies within the Northern Pine Belt of 

 Sargent, 1 the boreal of Merriam, 2 the black spruce-fir balsam 



1. Sargent, C. S. Tenth Census Rpt. 9 : 494. 1880. 



2. Merriam, C. H. The geographic distribution of life in North America. 

 Rpt. Smith. Inst. 18pl : 365-415. 



combination being the climatic mesophytic type. The entire 

 absence of temperature and rainfall readings in this region makes 

 a discussion of the climatology impossible, but a general consid- 



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