44 



juries from many sources. Seldom is a 

 sewer, drainage, or utility line put in 

 on a tree-lined street but that some 

 damage is done to the roots. Because 

 the health of a tree is in direct propor- 

 tion to the extent and effectiveness of 

 its feeder roots, great care should be 

 exercised that a minimum of damage 

 be done to the tree roots during con- 

 struction. This damage might not kill 

 the tree, but it might so debilitate it 

 that it would become easy prey to 

 insects and disease. 



The power and telephone companies 

 used to expect their line-clearing crews 

 to hack off the tops and sides of trees 

 for line clearance. The branches ex- 

 posed to the sun by the sudden re- 

 moval of the protecting canopy were 

 vulnerable to sunscald, which cracked 

 the tender bark and permitted the in- 

 roads of disease and insect pests. For- 

 tunately such butchering is on the 

 wane, and few cities permit it today. 

 More and more underground conduits 

 are used; they eliminate unsightly poles 

 and wires and do away with the neces- 

 sity for any type of drastic tree pruning. 

 Many trees are killed annually by il- 

 luminating gas from underground gas 

 lines. One should be suspicious of 

 chlorosis or yellowing of leaves and of 

 any other signs of the unexplained de- 

 clining health of a tree when it is lo- 

 cated near an underground gas line. 



Additional hazards of city trees are 

 the bumps and splintering from ve- 

 hicular accidents, the thoughtlessness 

 of the boy who breaks off branches and 

 gouges with his new knife or ax, and 

 girdling by squirrels in a small park. 



A mower in the hands of a careless 

 maintenance man can severely damage 

 the bark and cambium layer at the base 

 of trees ; those cuts and bruises can be- 

 come immediate focal points for in- 

 fectious diseases like verticillium wilt 

 and canker stain of our sycamores. In- 

 deed, there are several instances on 

 record where injuries by lawn mowers 

 were responsible for the spread of can- 

 ker stain and the subsequent loss of 

 rows of fine old sycamores. 



Another disadvantage under which 



Yearbook^ of Agriculture 1949 



city trees live is the lack of humus 

 build-up provided by the decay of 

 fallen leaves. Humus or duff, formed 

 by decayed leaves, is nature's food for 

 the tree and her protection for its feed- 

 ing roots from the sun and drying 

 wind. When we remove this humus 

 or do not permit its manufacture, we 

 are disturbing one of nature's proc- 

 esses for tree growth and vigor. 



In large city parks like Fairmount 

 Park in Philadelphia and Rock Creek 

 Park in the District of Columbia, much 

 of the total area is left naturalized and 

 the fallen leaves are allowed to remain, 

 decay, and form the humus that pro- 

 vides much of the tree's natural food 

 and its mulch for moisture retention. 

 Public opinion demands, however, that 

 the small park square, the quadrangle, 

 and parking space along the street be 

 kept free of fallen leaves and other 

 debris. As a practical matter, it would 

 be almost impossible, even if desired, 

 to allow a build-up of fallen and de- 

 caying leaves. Clogged gutters and 

 drain pipes, fire hazard, dangerously 

 slippery streets, to name only a few, 

 make necessary their prompt removal 

 along streets and in most parks. 



In their natural habitat trees usually 

 grow in soils and moisture conditions 

 that are best suited to them. Thus (in 

 New England, Middle Atlantic, and 

 Midwestern States to which this dis- 

 cussion pertains) we find elms, pin 

 oaks, and sweetgums in low-lying land 

 along the streams and even in swamps. 

 Tuliptrees seem to like the mountain 

 valleys from which they spread to the 

 low-lying ridges. Red and white oaks 

 and sourgums, on the other hand, may 

 be found on higher mountains where 

 their roots have to go deep for water. 



Too often in city planting, particu- 

 larly along the streets, we put in elms, 

 oaks, and honeylocusts, with but little 

 regard to their preference of soil and 

 moisture conditions. Trees that in their 

 native environment search deeply for 

 water are planted alongside those with 

 shallow roots. It is a tribute to nature's 

 adaptability that elms can thrive along- 

 side the deep-rooted white or red oaks. 



