Forest Distribution. 463 



8. The interior valleys of the Sierra, comprising 

 about 30,000 square miles, which, under irrigation, 

 have become the garden spots of the Pacific. 



To these topographic subdivisions correspond in 

 part the climatic and the forest conditions, although 

 variation of soil, and of northern and southern cli- 

 mate produce further differentiation in types, and in 

 distribution of field and forest. 



The first three sections were originally densely 

 wooded the great Atlantic forest region but farms 

 now occupy most of the arable portions; the fourth 

 and seventh are forestless, if not treeless, while the 

 fifth and sixth were more or less forested the Pacific 

 Coast region. 



Floristically also, these topographic conditions are 

 reflected, namely in the wide, north and south dis- 

 tribution of species, unimpeded by intervening 

 mountain ranges, and in the change in composition 

 from east to west. The two grand floristic divisions 

 of the Atlantic and the Pacific forest, having but few 

 species in common, are separated by the plains and 

 prairies. The Atlantic forest is in the main composed 

 of broadleaf trees with conifers intermixed, which 

 latter only under the influence of soil conditions form 

 pure stands, as in the extensive pineries of the South 

 and North, and in the northern swamps and on 

 southern mountain tops. The central region west of 

 the Alleghanies exhibits little conifer growth in its 

 composition, and is most widely turned to farm use. 

 White Pine, hemlock and spruce are the important 

 coniferous staples of the northern section, and a num- 

 ber of Yellow Pine species, with Bald Cypress and 



