350 THE STUDY OF PLANT COMMUNITIES * Chapter XII 



has been the only concern, after effects on drainage and erosion 

 have frequently created serious problems. Not only has natural 

 beauty been destroyed unnecessarily at times, but extensive ex- 

 panses of bare soil, in fills and cuts, have been left for nature to 

 recover and stabilize. The re-establishment of natural vegetation is 

 often impossible before erosion and slumping cause disruption of 

 drainage, road blocks, and similar difficulties. Consequently, stabil- 

 ization must be provided for through artificial means and by seed- 

 ing and planting. The problem is intensified by the infertility of 

 the subsoil, upon which few things will grow. Although the first 

 concern should be stabilization, there should be consideration of 

 succession and the possibility of harmonizing the developing vege- 

 tation with that of the surrounding terrain. 



In addition to large cuts and fills along mountain highways, 

 there are problems of maintaining road shoulders, ditches, and 

 spillways. Certainly not all is known about the best species for 

 such purposes under all conditions. Also the natural beauty de- 

 stroyed by a new right-of-way need not be permanently lost. 

 With a minimum of management it would seem that native species 

 could be encouraged to provide cover and beauty, especially along 

 the new express highways, which are increasing in number. It 

 does not seem impossible that ecological knowledge applied in 

 advance could prevent some erosion and drainage problems and 

 save some of the destruction of natural vegetation. Certainly road- 

 side ecology is worth considering both practically and aesthetic- 

 ally. 



PLANT INDICATORS 



Elsewhere we have emphasized that plant communities give a 

 better indication of the nature of environment than we can obtain 

 by measurements of individual factors. The character and make- 

 up of vegetation is an expression of the integrated effects of all 

 factors operating in a habitat. When the relationships involved are 

 well known, the vegetation becomes an indicator that can be in- 

 terpreted or, in some instances, read like an instrument. 



The practical use of plants as indicators is nothing new, for 

 Pliny 135 wrote of selecting soil for wheatland by the natural vege- 

 tation it supported. More recently, in the settling of North Amer- 

 ica the pioneers used the principle widely in selecting their lands 



