Canadian Forestrti Journal, October, 1917 



1341 



Do Electric Wires Damage Trees? 



A Point of Much Concern to Tree 

 Owners Discussed By Authorities. 



Can any deleterious effect be traced 

 to electric wires strung through 

 branches of shade trees? What are 

 the possibilities of injury from this 

 cause? 



These cjuestions have been asked 

 of the Forestry Journal not only by 

 those owning shade trees on town 

 streets but by a reader identified 

 with an electrical transmission enter- 

 prise in Ontario. 



By the kindness of Prof. G. H. 

 Collingwood, of Cornell University, 

 who made a search for some authentic 

 information on the subject, the Journ- 

 al reproduces part of a bulletin issued 

 by the Massachusetts Experiment 

 Station. "It is rather interesting to 

 note," writes Prof. Collingwood to 

 the Journal, "that this bulletin states 

 that alternating currents are appar- 

 ently less injurious than direct cur- 

 rents although tills may be because 

 alternating currents are usually car- 

 ried on high powered transmission 

 lines across country and are therefore 

 less often in contact with shade trees. 



"Most of the injury to trees from 

 trolley or electric light currents is 

 local," reports the Massachusetts 

 Station. "The injury takes place at 

 or near the point of contact of the 

 wire with the tree. This injury is 

 done in wet weather when the tree 

 is covered with a film of water, which 

 provides favorable conditions for 

 leakage, the current traversing the 

 film of water on the tree to the 

 ground." The writer of this bulletin 

 never found leakage in dry weather. 

 Resistance of Trees 



"Th3 electrical resistance of trees 

 is so high that it is doubtful whether 

 injury ever occurs to them from con- 

 tact with low or even high tension 

 wires, except that produced by 

 grounding when the bark is moist. 

 Any escaping current from trans- 

 mission lines that can be transmitted 

 even through the least resistant tissue 

 is likely to be insignificant. 



"It might be possible for direct 

 currents to affect trees without caus- 

 ing any perceptible burning. If, for 

 example, a tree were subjected to a 

 sufficient strength of current, thete 

 might occur a disintegration of the 

 cell contents, causing the tissues to 

 become abnormal and finally to die, 

 but the electrical resistance of trees 

 is so great that a quite high potential 

 would be necessary. 



Other Causes at Work 



"On the whole, the cases 6f;^death 

 to trees from electricity are by no 

 means so numerous as is generally 

 believed. Because a large number of 

 trees near electric roads, etc., often 

 look sickly it must not be concluded 

 that electricity is always the_ cause. 

 In cities and towns, where most of 

 these unhealthy specimens are found, 

 there are innumerable destructive 

 factors for trees to contend with. 

 It is cjuite essential in diagnosis work, 

 therefore, that all these factors be 

 taken into consideration before a 

 definite opinion in regard to the 

 cause of any abnormal condition is 

 formed." 



Readers will also be interested in 

 what Dr. Fernow states in his book 

 on "The Care of Trees: 



Watch the Wire Stringer 



"Every tree owner should look out 

 for the wire stringer, who not only 

 disfigures the tree by chopping off 

 branches, regardless of consequences, 

 but introduces the danger of electro- 

 cution. Trees and branches, beat- 

 ing against electric wires in winter 

 storms, wear off the insulation and 

 thus establish short circuits, which 

 under certain weather conditions as, 

 for example, in a thunderstorm, may 

 bring about the total destruction of 

 a long-cherished tree. 



"According to the latest investiga- 

 tions there is a difference in the 

 effects of direct currents which are 

 used chiefly in operating electric 



