54 BULLETIN" 475, U. S. DEPARTMENT OP AGRICULTURE. 



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 Avhose 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 only suited to reforesting with very drought-resistant species 

 and that even then success will be uncertain. 



Locally, the amount of precipitation over various sites will differ 

 very little at the same altitude, but regionally and at different alti- 

 tudes it will vary considerably both in amount 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 

 likely 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, gravelly, 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 will be in danger of drought or winter killing during 

 that period. Moreover, on these slopes growth starts earlier in the 



