ELECTRICAL INJURIES TO TREES. 



Effects of Alterxatiis-g Currents. 



The alternating current systems emiiloyed for lighting purposes vary 

 greatly in their potential. Cases of burning from alternating currents 

 are more numerous than those from direct currents because trees are 

 brought into more frequent contact with the wires, and owing to the 

 higher potential more leakage is likely to occur. The high and low 

 voltage lines may vary from 100 to 100,000 volts. The high-tension 

 systems are invariably constructed across country, and are naturally 

 not brought into very close proximity to shade trees. No injury to 

 trees whatever occurs from the low voltage (110-volt) lines, but the 

 lines of higher potential found on streets constitute a source of danger 

 to trees. The higher the electrical potential the more dangerous the 

 wires become to trees, for owing to the lessened effectiveness of the 

 ordinary insulation, more leakage occurs and consequently greater 

 opportunity for burning. 



The effects of alternating currents on trees are local, producing in- 

 jury only near the point of contact with the wire. Such contact results 

 in death of that part of the tree, and if it is a leader or a large limb 

 it usually has to be sacrificed. In no case, to our knowledge, has an 

 alternating current caused the death of a tree, although it may burn 

 or disfigure the tree so badly that it amounts to practically the same 

 thing. It is doubtful whether the current from a fairly high potential 

 wire would kill a large tree under any circumstances. It is different 

 in the case of small plants, as has been frequently demonstrated in the 

 laboratory, although the current must produce heat enough to kill the 

 protoplasm. Owing to the close relationship between the maximum 

 temperature required to kill a plant and that induced by electrical cur- 

 rent, the collapse of the plant tissue in such eases is therefore due to 

 the heat rather than to any sjDecific electrical shock, as it is possible 

 to pass the same current through larger plants where heat is not gen- 

 erated without causing any collapse of the tissue. The ordinary house 

 circuit wires are perfectly harmless to trees, and it seems strange that 

 a judge could render a verdict to the effect that an ordinary insulated 

 110-volt house circuit was responsible for the death of a tree whose 

 terminal branches were located within 3 feet of it. This is the only 

 court record of which we know where such a judgment has been given. 



Very high-tension line wires are not provided with insulation and 

 are known to affect the atmosphere suiTounding them to a considerable 

 extent. Any increase in the electrical potential of the atmosphere if 

 not too high would favorably affect vegetation in general.^ 



"• There is evidently much difference in plants in this respect. A crop of radishes showed a 

 gain of 57 per cent, when subjected to an average atmospheric potential of 167 volts, whereas an 

 electrical potential equal to 500 or 1,000 volts is beyond the stimulation zone for some plants 

 (16th Ann. Rept. Mass. Agr. Exp. Station (Hatch), 1904, p. 31). 



