NATIVE WOODY PLANTS OF THE UNITED STATES 
5 
cover plants should be unobjectionable from the agricultural stand- 
point. The striking similarity of Leopold's criteria for game-cover 
plants and the characters valuable in erosion control is at once 
apparent. 
It has been pointed out that the restoration of cover, important alike 
for soils and for wildlife, is the objective sought in soil conservation 
as well as in wildlife conservation. The correlation of erosion control 
with wildlife planting, therefore, is obviously an easy one to make. 
Furthermore, the utilization for wildlife production of submarginal 
lands upon which man-made erosion is unusually severe is a sound 
economic practice. 
PLANTING FOR SOIL AND WILDLIFE CONSERVATION 
It is obvious to those who have had experience in landscaping or 
forestry that the old maxim about putting all of the eggs in one 
basket applies very well to the planting of woody species. The most 
important rule to follow, whether planting for timber, pulpwood, ero- 
sion control, wildlife, or any combination of these, is that the species 
used must be varied — that the planting must be a mixture, not a pure 
stand. This is true for several reasons (^8^), namely: 
1. Solid stands of plants favor the rapid spread of disease and 
insect pests. Fungi, as well as insects, mid it easy to travel from 
one plant to another of the same kind. In mixed plantings spread is 
slower and control is consequently easier. Isolation of individuals 
and gToups from others of their own kind is the natural safeguard 
against infection. 
2. Solid plantations of one species have for some time been known 
to result in depletion of the soil. Further, pure stands do not repre- 
sent the maximum productive capacity of the soil. 
3. Maximum interspersion of species ensures that all ecological 
niches will be filled. This results in a greater utilization of space 
and better erosion control. Competition between individuals, and 
therefore waste of energy, is at its highest in pure stands. 
4. In planting for wildlife, variety is essential. What one species 
of plant may lack, another may possess. The effort should be mad© 
to attain a well-balanced habitat, approaching as nearly as possible 
the "orderly confusion of nature." Insectivorous birds are generally 
discouraged by pure stands, but encouraged by mixtures. The en- 
couragement of such birds leads to gTeater control of injurious insects. 
In several European countries it has been found an economically 
justifiable practice to put up bird houses in forest plantations to 
attract insectivorous birds and thereby to ensure some control of 
insects. The idea is extending even to this country, but proper mix- 
ing of species in planting should make such a practice unnecessary. 
It is very essential that careful planning precede actual field opera- 
tions. Press of work and the need that considerable planting be 
done in a short time are often advanced as excuses for improper 
spacing, poor selection of site and species, and faulty organization 
of the work. Actually such excuses are never valid, for the planting 
seasons are preceded by periods sufficiently long to permit of careful 
planning. Because of the impossibility of obtaining sufficient plant- 
ing stock of the kind desired, it may often be necessary to substitute 
