26 BULLETIN 1113, U. S. DEPARTMENT OF AGRICULTURE. 
1918. In five of the blocks the trees are spaced 4 by 4 feet and in 
the others 4 by 8 feet. One block of each rate of planting is not 
pruned, one block is moderately pruned, one block is severely pruned, 
one block is mulched, and one is neglected (given no cultivation). 
The first three blocks are given clean cultivation; the last two are 
not pruned. 
An unpruned shelter belt in its third summer of growth in Valley 
County, Mont., is shown in Figure 14. A severely pruned shelter 
belt of the same age in Grant County, N. Dak., is shown in Figure 15. 
Both the effectiveness of the shelter belt and its ability to protect 
itself is destroyed by pruning. 
Two other blocks were planted in which 4 by 12 and 8 by 8 feet 
spacing distances, respectively, were used. These blocks were not 
pruned and were given clean cultivation and with the other unpruned 
Fig. 15. — A severely pruned shelter belt in the third summer of growth. Planting in 
Grant County, N. Dak. 
blocks form a series of spacing tests. It is yet too early to present 
results from this series of experiments. 
Species combinations. — A number of plantings were made in 1915 
in which different tree species were arranged in varying combina- 
tions. This experiment was designed to determine the ability of the 
different species to compete with each other in adjacent rows. 
SUMMARY AND CONCLUSIONS. 
During the 5-year period from 1916 to 1920, inclusive, 1,234 co- 
operative demonstration shelter belts were planted in the Great 
Plains area of Montana, North Dakota, South Dakota, and Wyoming. 
Of this number, 716 were still growing at the close of the summer 
of 1920. A total of 1.488.658 trees were used in making these plant- 
ings. 
