ELECTRICAL INJURIES TO TREES. 



GEORGE E. STONE. 



Introduction. 



lu 1903 there was issued from Ibis station a bulletin dealing with 

 some new pbases of tbe subject of electrioal injury to trees.^ This 

 bulletin has been out of print for some time, and as manj- new observa- 

 tions — the result of years of careful study of the influence of elec- 

 tricity on plants — have been made, it has been thought wise to issue 

 another edition. Many people are quite unfamiliar with certain types 

 of injury from electricity occasionally to be found, and even those 

 directly responsible often do not realize how serious the harm done is 

 likely to prove. 



The increase in electric railroads, electric lighting systems and tele- 

 phone lines, whose Avires are usually located near the tree belts of our 

 cities and towns, has made necessary a lamentable amount of disfig- 

 uring pruning. When stning too close to trees, wires also often cause 

 serious injury by burning, and sometimes mechanical injury is done; 

 and even lightning discharges will cause harm when gi^y wires are 

 attached to trees. (See Fig. 1, Plate I.) 



Both the alternating and direct currents are used. Thej^ produce 

 different physiological effects on plant life, the alternating current 

 apparently being less injurious than the direct; and when either is used 

 at a certain amperage it acts as a stimulus to the plant, and growth and 

 development are accelerated. 



There are minimum, optimum and maximum currents affecting plants. 

 The minimum represents that strength of current which just percepti- 

 bly acts as a stimulus, and is a. very insignificant current. The optimum 

 is that producing the greatest stimulus — about .2 milliamperes — and 

 the maximum, that causing death. ( See Fig. 3. ) Between the optimum 

 and the maximum there is a strength of current that causes retarda- 

 tion in the jDlant activities, this being rej^resented between R and MX 

 in Fig. 3. The maximum current necessai-y to cause death is very 

 variable. The direct current has a less stimulating effect than the 

 alternating, and on account of its electrolyzing eft'eet is capable of 

 causing more injury to vegetable life than tbe alternating current. 



Most of the injury to trees from trolley or electric light currents is 

 local; i.e., 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 



1 G. E. Stone, "Injuries to Shade Trees from Electricity," Bui. No. 91, Mass. (Hatch) Agr. 

 Exp. Station, 1902. 



