16 BULLETIN 1113, U. S. DEPARTMENT OF AGRICULTURE. 
fore competition with the adjacent trees for the soil moisture begins. 
There is a generally accepted belief that close spacing is desirable 
in order that the trees may quickly grow together and shade the 
ground, thus keeping out the grasff and weeds. Careful cultivation 
must be practiced until this result is attained. Wider spacing of 
trees naturally lengthens the period during which cultivation is 
necessary. The guiding principle for spacing, therefore, is to plant 
the trees as .close together as possible without forcing them to com- 
pete with each other for moisture at too early an age. It seems 
probable that 6 by 8, 8 by 8, or 6 by 10 feet apart are preferable 
to closer distances in this section. 
Figure 6 shows clean cultivation in the first year of a planting 
spaced 6 by 6 feet at Archer, Mont. The light-colored row is north- 
west poplar. 
Fig. 10. — A planting made in 1917 at Dupree, S. Dak. The trees have had clean culti- 
vation and made good growth. Photographed in 1921. 
Figure 7. shows a planting of box elder, green ash. and white elm 
in Ziebach County, S. Dak. The rows in this planting were 8 feet 
apart. The photograph, taken in the fifth year of growth, shows 
that the trees have met and fill the spaces between the rows. 
The selection of species and their arrangement are made with the 
view of establishing a dense shade that will exclude the sunlight both 
from above and on the sides. Outside rows are planted to low-grow- 
ing species, such as caragana, Russian olive, chokecherry. and buffalo 
berry. The interior of the belt is planted to alternating rows of box 
elder and green ash, green ash and white elm. box elder and poplar, 
or a combination of all these species. 
The ideal tree for shelter is the conifer, or evergreen. It is found, 
however, that in this region it is necessary to provide some kind of 
shelter for them when they are first planted. A plan has been 
