16 BULLETIN 14 9 7, XT. S. DEPARTMENT OE AGRICULTURE 
completely destroyed, the others remain to provide a timber crop on 
the area. 
Theoretically it is desirable to plant a rapidly growing species with 
one of slower growth which will thrive in spite of the shade and com- 
petition of its associate. However, in plantations at Ottawa, On- 
tario, in which the slow-growing sugar maple was planted with 
European larch and Norway spruce, the maples were almost entirely 
eliminated before the conifers were 38 years old. Here the theory 
did not work out; and the outcome emphasizes the need for experi- 
ment. 
Different kinds of trees have different capacities for obtaining from 
the soil the water and other materials that they need. For example, 
the roots of trees of two or more kinds planted in mixture make 
different demands upon different layers of the soil, and each is able 
to fill its needs more completely than if its neighbors were of its own 
kind, making similar demands upon the same layer of the soil. 
As evidence of the more complete use of the soil and site by two 
kinds in mixture as compared with one, and as a practical reason 
for mixed plantings, European experience may be cited. This has 
shown that mixed stands of pine and spruce, pine and beech, and 
oak and beech produce higher yields, sometimes as much as one-third 
higher, than either kind by itself. 
The hardwoods are desirable in mixtures because their presence 
decreases the risk of loss by fire, particularly by fires which might 
otherwise burn and spread through the crowns of the trees. The 
green foliage in summer and the bare branches in winter will not 
carry a fire. Actually, however, the application of this principle in 
the northern Lake States is limited; the dry sandy soils where the 
fire hazard is greatest are not suitable for the planting of hardwoods, 
and on the heavier soils a certain number of hardwoods are usually 
growing naturally, so that there is little need for planting. 
Another reason for mixed plantings is that different kinds of 
trees are not equally beneficial in their effect in building up the fer- 
tility of the soil. As soil builders the hardwoods, such as oak, maple, 
and ash, are more effective than the pines and spruces. Some species 
may even be detrimental; in Germany, for instance, pure Norway 
spruce plantations have created soil conditions so unfavorable that 
the growth of the trees has been grea ( tly reduced. This condition is 
avoided if other species, such as beech, are planted in mixture with 
the spruce. 
Northern white pine occurs naturally in mixture with hardwoods 
on the heavier soils and undoubtedly produces the highest quality 
of timber under those conditions {18). The presence and mainte- 
nance of natural hardwoods in a plantation of white or Norway pine 
or white spruce is desirable as long as the hardwoods do not seri- 
ously interfere with the development of the planting conifers. If 
hardwoods are not present naturally, they may be planted in mix- 
ture with the pine or spruce. 
With experience in mixed plantings lacking, however, there is 
little basis for recommendations or for predictions of success. In 
this, as in the selection of species for pure plantings, the best guide 
is probably the trees which grow naturally in mixed forests in the 
