54 
BULLETIN 475, U. S. DEPARTMENT OF AGKICUlTUEE. 
the growing season, the soil moisture, and the depth and character 
of the soil. 
The suitability of an area is very strongly indicated by the natural 
growth present. This is a pretty fair criterion of the quality of the 
site, and it points out the species which are most likely to succeed — 
either those which naturally occupy the area or others whose demands 
upon soil and climate are quite similar. A heavy growth of trees 
on similar adjacent sites will indicate that the area is quite prob- 
ably suitable for sowing or planting; while a sparse growth of a 
drought-resistant species of tree on such sites will indicate that the 
area is onh^ suited to reforesting Avith very drought-resistant species 
and that even then success will be uncertain. 
Locally, the amount of precipitation over various sites will dilfer 
very little at the same altitude, but regionally and at different alti- 
tudes it will vary considerably both in amoimt and distribution, and 
thus be of considerable influence in determining the suitability of 
a site. Precipitation in conjunction with the soil depth and char- 
acter will largely determine its moisture content. This, in turn, is 
most influential in determining the success of properly conducted 
reforestation operations, provided the stock used is otherwise cli- 
matically adapted to the site. The total precipitation is not alone 
important. A total of from 12 to 15 inches will support a tree 
growth if it is distributed rather evenly throughout the growing sea- 
son ; but if it comes mostly during winter, for instance, and the other 
seasons are characterized by extreme drought, planted stock is not 
likel}^ to succeed. Drought of moderate duration can be withstood 
by plants after they have become firmly established, but for two or 
three years following planting they are less able to withstand any 
protracted dry period. 
The depth and character of the soil are important in conjunction 
with precipitation. Deep, fine, retentive soils, by virtue of their 
water-holding capacity, or even looser surface soils with retentive 
subsoils at a depth of from 2 to 3 feet, offer better conditions for 
planting than loose, sandy, gravelh\ or rocky soils which drain 
rapidly and soon become dry, or even soils of finer texture which are 
very shallow and soon dry out for that reason. 
Exposure is of influence chiefly in its relation to soil moisture. 
South and west slopes become much hotter than north and east 
slopes; and, other conditions being equal, evaporation is much greater 
from the former and drought condition more prevalent. Further, 
on south and west slopes the snow may melt during the winter and 
planted stock Avill be in danger of drought or winter killing during 
that period. Moreover, on these slopes growth starts earlier in the 
