REFORESTATION ON THE NATIONAL FORESTS. 
55 
spring and continues later in the fall, thus subjecting the plants to 
greater danger from either early or late frosts. 
The relation of altitude to the suitability of a planting site is 
found in its influence upon precipitation, humidity, evaporation, soil 
moisture, accessibility, and length of the growing season. With in- 
crease in altitude, there is normally an increase in and a better dis- 
tribution of the precipitation, the relative humidity is greater and 
evaporation less, the soil moisture is greater, the region is usually 
less accessible, and the length of the growing season is shorter. The 
intermediate altitudes within the natural limits of any particular 
species of tree offer the most favorable climatic conditions for its 
successful planting. High altitudes are usually difficult of access; 
and unless the stock for planting is grown at a similar elevation it- 
will not be in a condition for setting out at the time when the opera- 
tion should be conducted. Stock grown in nurseries at a lower alti- 
tude will start growth in the spring before planting can be carried 
on at higher altitudes, and it will not be hardened sufficiently for fall 
planting by the .time it is needed. 
The immense total acreage on the National Forests in need of 
planting, the cost of the operation, and the necessity of securing satis- 
factory results make it highly desirable to plant the better 'sites first. 
Planting at best, under the conditions encountered and with the em- 
ployment of unskilled and usually uninterested laborers, is always of 
doubtful success. The selection of the better sites, however, will 
mean that a larger proportion of the planted trees will live ; they will 
make better growth after becoming established and form a better 
stand at maturity; and much experience in regard to methods of 
planting and the most desirable classes of stock will be gained. The 
poorer sites can be planted later when cheaper stock, cheaper labor, 
and better methods make it more feasible. 
Although results do not yet permit a final judgment in regard to 
the comparative suitability of different sites on the National Forests 
of the West for planting or sowing or of the best class of stock to 
be used, an attempt is here made to classify them in the order of their 
favorableness. It must be remembered that in this classification of 
sites the altitudes given are not exact; that they change with 
latitude; and that the best planting and sowing sites are almost 
without exception found at elevations somewhere between the 
extremes. 
Experience will undoubtedly lead to a change in the order in 
which these sites are listed and may prove some of them unfitted for 
planting or sowing. There are other sites which because of their 
unfitness or for other reasons are not considered for reforestation. 
