ILLINOIS AUDUBON BULLETIN 5 
area. Pathogens, including both 
insects and diseases, are selective 
in the species they infect. Examples 
are: Dutch elm disease, oak wilt, 
fire blight, anthracnose, heart rot- 
ting fungi, bores, mites, galls, and 
thrips. 
Fortunately, the species selectiv- 
ity of pathogens is an asset to the 
urban forester. He can_ identify 
each type of tree and examine the 
pathogens that could infect it. 
Once identified, control measures 
may be taken to combat the spe- 
cific problem. 
Physiological problems in city 
trees usually stem from lack of 
sensitivity to a tree’s biological 
needs. An example would be a city 
that is over-exuberant in its love for 
trees, and plants elms with only a 
ten-foot space between trees. The 
trees appear healthy at first, but 
problems arise after several years. 
The trees compete for the same 
light, air, space, water, and soil 
nutrients. The result is an over- 
crowded condition in which trees 
are stunted and develop extensive 
dead wood. This leads to infection 
from secondary biological patho- 
gens which would not infect a 
healthy tree. No consideration was 
given to the species’ maximum 
size. 
Planting trees such as sugar 
maples or lindens — which need a 
rich loam soil — in leaching sand 
will cause problems in years to 
come. Planting evergreens next to 
expressways where winter salt 
damage will result is an example of 
insensitivity to biological toler- 
ances. Establishing trees that are 
susceptible to sun scald or winter 
burn in open sunny areas is an- 
other. 
Public Problems 
The majority of the urban for- 
ester’s headaches develop from 
public problems with trees. 
Years ago many of our boule- 
vards and parks were devoid of 
trees. People wanted fast-growing, 
large trees to shade the multi-story 
homes which exemplified the ar- 
chitecture of the time. The most 
popular choices were elms, soft 
maples, and cottonwoods. These 
fast-growing giants were _ ideal; 
they grew in almost any soil and 
under many adverse city condi- 
tions. At that time, boulevards were 
large, and sidewalks were virtually 
non-existent. The trees thrived and 
now comprise the majority of our 
green corridors. 
Our nation’s love affair with the 
automobile ‘‘paved’’ the way for 
wider streets, curbs, gutters, and 
sidewalks. The walks had to be 
placed on the inside of our grassy 
boulevards to accommodate snow 
removal. These innovations and 
others have been detrimental to 
our large boulevard trees. 
Boulevards, which once mea- 
sured 25 feet wide, now have been 
reduced to eight or six feet. Today 
it is not uncommon to find a ma- 
ture elm, five feet across at the 
base, growing on a six-foot boule- 
vard. Its roots are pushing up the 
sidewalk and forcing out the curb 
