No. 468.] AMERICAN FOREST CENTERS. 885 
In the southern Appalachians the ratio also rises above 110 per- 
cent and coincides with the occurrence of the southern exten- 
sion of the northeastern forests. No data are available for the 
mountainous parts of Pennsylvania, so that this apparently iso- 
lated area may be climatically connected northward along the 

ER, 
= 80% 
: N 
um M 




Fic. 6.— Map showing ratio of rainfall to'evaporation expressed in. percentages. (Compare 
with Sargent's map of the “ Forests of North America," roth Census Report.) 
higher mountain crests. The Northeastern Conifer forest center 
is marked by ratios above 100 percent and centering in the St. 
Lawrence basin. It is probable that the northern limits of this 
formation will not be indicated by the rainfall-evaporation ratios, 
for the factors commonly accepted (Schimper, : 03, p. 168) as 
determining the northern limits of forests are very different from 
those causing the boundaries of other formations. It should 
