8 MISC. PUBLICATION 303, U. 8. DEPT. OF AGRICULTURE 
the most appropriate plant materials to be used, and such an analytical process 
should develop selective appreciation of natural plantings upon the highways. 
The ecological or natural landscape approach to the highway planting pro- 
gram aims to avoid the typical static, or garden-estate type of plantation design 
in favor of fitness with the more dynamic requirements of highway travel. 
Nature is to be followed as closely as possible with fullest utilization of native 
materials or harmonizing types if the landscape development of highways is to 
proceed * * *, It is imperative, therefore, that the landscape technician adopt 
the broadest ecological viewpoint concerning the planting phases of the land- 
scape development of highways. 
The use of shrubs bearing beautiful fruits automatically provides 
food for wildhfe. As Howard (293, p. 103) has mentioned, if road- 
side improvement designed primarily to improve the scenery is made 
with “due regard * *“ * to ecological associations and as much 
diversity as is consistent with natural groupings * * *” in the 
plantings, it will in all probability contribute materially to the increase 
of bird life in the immediate vicinity. 
Plantings of species effective in erosion control provide excellent 
cover for wildlife. The danger of luring birds and mammals to high- 
ways where wildlife mortality is undoubtedly great can be obviated 
by placing plantings made for the production of wildlife food well 
back from the roadway. This is ordinarily done since on highway 
rights-of-way, plantings made too close to the road may easily become 
a hazard for motorists. 
Highway plantings are generally given more than ordinary care. 
Fertilizers are often used to ensure that the plants start; and water- 
ing, pruning, and cultivating are commonly employed to assist them 
in growing and producing flowers or seed. Under such conditions the 
remarks on plant competition and succession in the section treating of 
the selection of species for planting may apply only partially or not 
at all. 
The utilization of vegetation in highway planting is comparatively 
new, but is rapidly increasing in importance. A recent report for one 
State (7) mentions, for instance, that 700 miles of planting on main 
highway rights-of-way have nearly been completed. Future work 
may well be directed along the lines so clearly drawn by Simonson. 
PLANTS OF OBJECTIONABLE CHARACTERISTICS 
Certain species of plants possess characters that may partially or 
entirely preclude their use in many kinds of planting. A list of these 
would include plants that are: 
_ 1. Poisonous to man, either when taken internally or through skin 
irritations. 
2. Poisonous to livestock, usually internally. 
3. Secondary hosts to economically injurious fungi or insects. 
4. Susceptible to the ravages of insects the control of which is 
difficult. 
5. So exceedingly vigorous and aggressive as to crowd out more 
valuable or useful species. 
It is rare to find a situation in which plants possessing one or several 
of the above characteristics cannot be used. However, it may often 
be advantageous to substitute forms less objectionable, a procedure 
which is usually easy since the site is very unusual upon which at 
least two species of good character cannot be grown. 
