10 BULLETIN 1301, U. S. DEPARTMENT OF AGRICULTURE 
SHELTER-BELT COMBINATION TESTS 
A series of 22 shelter-belt combinations has been planted, in which 
a number of tree species are arranged in different combinations and 
spacings. The object of these tests is to determine, in a general way, 
the ability of a given species to grow in direct competition with trees 
of the same or different species in adjacent rows. 
Table 6 gives the details of the spacing, arrangement of species, 
and year of planting these shelter-belt combinations. 
Trees in these shelter-belt combinations have not reached a size 
large enough to show any marked effect of the different spacing dis- 
tances. In general, however, the wider spacings seem to produce the 
better growth. 
Green ash growing in alternate rows with box elder does not do 
as well as where it is in competition with other species, the box elder 
showing a marked ability to outgrow the ash in both height and lateral 
spread of branches. | 
Several of the species, notably Norway poplar, Carolina poplar, 
laurel willow, Russian golden willow, and killdeer birch, have not 
proved hardy or drought resistant and have largely died out in most 
of the combinations. 
TESTS OF PRUNING, SPACING, AND METHODS OF CULTIVATION 
Shelter-belt combinations of both hardwood and evergreen trees 
have been planted in series where the kind and arrangement of the 
trees are identical, but the spacing and care are varied. 
The details of the different units of the hardwoods in this experi- 
ment are shown in Figure 2. Each block consists of 10 rows of trees 
spaced and treated as indicated in the illustration. Beginning with 
the east row of each block, the arrangement of species is as follows: 
Buffalo berry, sharpleaf willow, box elder, green ash, box elder, 
northwest poplar, green ash, boxelder, red laurel-leaf willow, and 
Tatarian maple. 
At the end of the fifth year of growth the trees are hardly large 
enough to show the effects of spacing except in the series planted 4 
by 4 feet, where the trees have grown completely together and begin 
to show the effects of crowding. | 
Moderate pruning seems to have no detrimental effect as com- 
pared with no pruning, but decided damage is done by severe pruning. 
The mulched blocks still compare favorably with the clean-culti- 
vated ones, but the neglected blocks are rapidly dying out in certain © 
places. 
TEN-ROW BLOCKS IN PURE STAND 
Four species, boxelder, green ash, northwest poplar, and sharp- 
leaf willow, have been planted in pure stands in 10-row blocks. 
Each species occupies two blocks, one spaced 4 by 4 feet and one 4 
by 8 feet. At the end of the fifth growing season the trees in the 
blocks spaced 4 by 4 feet begin to show the effects of crowding. 
CONIFER COMBINATIONS AND SPACING TESTS 
Two combinations of conifers have been planted, with three differ- 
ent spacings each. ‘The arrangement of the species and the spacing 
in this experiment are shown in Table 7. The trees are not yet large 
enough to show any effects of close spacing. 
