SHADE TREES. 153 



located. This may possibly be explained by the fact that whatever 

 moisture reaches the soil under these paved streets is to a certain extent 

 conserved, the surface evaporation being less than where no pavements 

 are found. The severity of the conditions to which trees are subjected 

 when surrounded by pavements varies considerably, and when more or 

 less water is allowed to leach through them the soil moisture conditions 

 cannot be unfavorable. The more thoroughly' a roadbed is sealed the 

 more soil aeration must be affected. How largely this factor enters into 

 the problem is unknown, but while trees do survive under extremely severe 

 conditions, their length of life must be limited. 



Excavations, Curbings and Sidewalks. 



Remodeling and regrading streets are a frequent cause of injury to 

 trees. In placing curbstones large roots are often cut, and in regrading 

 streets so much soil is frequently removed that the base of the tree is 

 left high in the air and the exposed root surfaces become injured by traffic, 

 l^esides these mechanical injuries, the exposed roots are likely to be injured 

 from other causes such as winterkilling, sun scald, road oil, etc. If the 

 roots are cut to any extent the tree deteriorates in value, and if grown 

 under other unfavorable conditions it usually succumbs to a lingering 

 death. Again, root mutilation too often takes place when sidewalks are 

 being laid, and it is quite difficult to prevent it when the trees are large 

 and have extensive root systems. The cement sidewalk with its deep 

 foundation constitutes more of a menace to roots than a tar or brick 

 walk, but if care is used in excavating, much root cutting may be pre- 

 vented. The roots of trees located under a modern roadbed have little 

 chance of remaining uninjured, with the sewers, water pipes, gas lines, 

 telephone systems, electric wire and other conduits that are constantly 

 being installed. Electric railways may also cause injury to trees in various 

 ways. It is more injurious, of course, to the tree to cut the large roots 

 close to the trunk than the small ones some distance from it. In widening 

 a certain road a few years ago 4 or 5 feet of the banking adjoining a row 

 of ash trees were removed, destroying a large number of the smaller roots 

 on the west side of the trees, but this cutting had little or no noticeable 

 effect upon the trees. They were j^oung and vigorous, and on the east 

 side the roots extended into cultivated ground, apparently soon making 

 up for the loss on the roadside. Since the cutting of these roots, every 

 other tree has been removed, and measurements of the rings of the stumps 

 show that not the slightest retardation in growth had taken place follow- 

 ing the operation. One fact should be remembered: mutilation of the 

 root system is not so serious as that of the stems and branches, the former 

 responding more quickly to the stimulus caused bj'- mutilation. In 

 transplanting young trees 80 to 95 per cent, of the essential part of the 

 root system is usually destroyed, and even with a slight pruning of the 

 top the tree usually survives when the work is properly done. Indeed, 

 the cutting of the roots has been known to be beneficial, as, for instance. 



