Were it not for this amazing adapta- 

 bility, the selection of trees for urban 

 use would be even more complex. It is 

 true, though, that the nearer we can 

 duplicate natural conditions of the soil 

 and the water table, the better we can 

 expect our tree to thrive. 



The runoff of rainfall is high in 

 cities almost 100 percent from paved 

 areas. The ground has no chance to 

 absorb and store up the moisture for 

 future needs; most of the rainfall, 

 rather, is immediately carried off into 

 gutters and drains. Trees in sizable 

 city parks seldom suffer from lack of 

 moisture in periods of normal rainfall, 

 but the street tree in a narrow parking 

 never gets a fair share of water and 

 cannot absorb the little it receives. An 

 oak tree gives off some 120 tons of 

 water in only one season through its 

 leaves water that must be replenished 

 from the soil and it seems almost 

 miraculous that our street trees sur- 

 vive at all. An interesting observation 

 is that in times of drought, street trees, 

 which are conditioned to a constant 

 substandard amount of moisture, fare 

 better than those accustomed to ade- 

 quate rainfall. 



How can these adverse conditions be 

 improved? 



First, we must see that the tree we 

 select for planting has a sufficiently 

 large tree pit filled with good soil to 

 accommodate potential roots for some 

 years to come. The hole must have 

 natural or artificial drainage to insure 

 against wet feet and root suffocation. 

 The variety selected should be environ- 

 mentally suited to the designated site 

 from the standpoint of exposure, eleva- 

 tion, and purity of air. It should be 

 planted where physical hazards are 

 few. If natural moisture is lacking, 

 particularly during periods of drought, 

 it must be watered. If it shows signs 

 of starvation, it must be fed with in- 

 organic fertilizer or organics like ma- 

 nure, tobacco stems, sludge, or tankage. 



Use determines whether a tree is 

 desirable or undesirable for city plant- 

 ing. A broad-spreading, low-hanging 

 Chinese magnolia may be ideal as a 



City Trees 45 



specimen in a small city park or on 

 home grounds but impossible as a 

 street tree. A fastigiate English oak 

 may be perfect for a narrow street 

 but of limited use in the large park. 

 Individual peculiarities may make cer- 

 tain trees undesirable for any urban 

 use the female ginkgo, whose fruit 

 has a bad odor, for example, or the 

 silver maple, which breaks easily in 

 wind and snow, or the boxelder, which 

 has rapid but unsightly growth. Lom- 

 bardy and Carolina poplars are out of 

 favor because their roots fill sewer lines. 



For street use, species or varieties 

 should be avoided that are subject to 

 disease and insect pests. Just as a con- 

 tagious disease will tend to spread 

 rapidly through a family whose mem- 

 bers are in close contact with one 

 another, so the Dutch elm disease, for 

 instance, will spread rapidly through a 

 concentrated group of city elms unless 

 strong preventive measures are taken. 



Dutch elm disease and phloem ne- 

 crosis of elm and the canker stain of 

 sycamores make unwise their wide- 

 spread planting, particularly for cities. 



The Dutch elm disease, dissemi- 

 nated principally by the elm bark 

 beetle, has spread quite rapidly and is 

 difficult to control. The control of the 

 carrier by spraying and a rigorous 

 sanitation program, involving the im- 

 mediate removal and destruction of all 

 dead and dying wood, are at present 

 the only effective means of dealing 

 with this serious threat to our elms. 

 This control is difficult because of the 

 inaccessibility to spray machines of 

 scattered infected trees. Canker stain of 

 sycamores seems to be carried largely 

 by man's own activities. Bruises made 

 by lawn mowers and particularly prun- 

 ing operations seem to be the chief 

 means by which this canker stain is 

 spread. For districts where canker stain 

 is established, there are several primary 

 control measures to be taken : Remove 

 all diseased sycamores or diseased por- 

 tions of them, and avoid all unneces- 

 sary mutilation. In zone 4 (New York 

 and Philadelphia) prune the sycamore 

 only between December 1 and Febru- 



