TREE PROTECTION 7 



Other Girdling. Wire guards, fences, and supports in contact with trees may 

 girdle the trunks and cause permanent scars, injury, or death. 



Injury by Animals. In former days the gnawing of the bark of street trees 

 by horses was often cited as a source of injury and possibly wounds caused in 

 this way may again become common. At present, however, damage by horses 

 is not a serious problem although limited injury to tiees may be caused directly 

 or indirectly by some other animals. 



Frost Cracks. A sudden drop in temperature may result in the withdrawal of 

 water from the cells of the wood in a tree trunk and its fixation as ice crystals. 

 The resulting cell shrinkage lacks uniformity and creates a tension within the 

 woody tissue. With the development of sufficient stress, rending occurs along 

 the grain of the wood. An accompanying loud report may be the first warning 

 of this type of injury. The sharp lengthwise clefts commonly seen on the south 

 and southwest exposures of trees are the ultimate wounds of this sequence. Frost 

 ridges in which splitting of the wood results without rupturing the bark differ 

 only in the degree to which the shrinkage of woody tissue takes place or sufficient 

 tension develops. Many frost cracks close and heal readily (Fig. 5, A) when the 

 shrunken tissues thaw and absorb a sufficient amount of water. Sometimes, 

 however, a frost crack may become a permanent weak spot (Fig. 6) which will 

 reopen each winter and may be effectively closed only by mechanical aid, such 

 as screw rods inserted through the tree trunk at right angles to the fissure. 



Slime-flux. Wet yellowish streaks e.xtending down the limbs and trunks of 

 trees are frequently observed to originate at an injured crotch (Fig. 6), the cut 

 at which a branch has been severed, or in some other wound. A slimy ooze in 

 which fermentation organisms become active may continue to flow down the 

 surface of the bark for a considerable period of time and in persistent cases where 

 the bark and growing tissue are continually wet, extensive injury may result. 



Lost Protection. Some trees requ're protection from drying winds or excessive 

 heat or cold. Since the hurricane of 1938 in which such protection was sometimes 

 lost, resultant injury has been particularly conspicuous. Tree owners reasoned 

 that sheltered trees survived the hurricane, but failed to evaluate critically the 

 post hurricane exposure of these trees resulting from lost protection. 



Branch Wounds. Friction resulting from the rubbing of branches or the con- 

 tact of public utility wires with branches often causes wounds which may later 

 directly or indirectly result in the death of certain parts of trees. Utility compan- 

 ies have long since learned that where wires are in direct contact with trees there 

 is not only the immediate prospect of interrupted service from burning as a result 

 of contact of the energized wire and grounded tree, but also the later penalty of 

 the killed branch crashing through the wires. 



Trunk Woimds. It is not uncommon to find the trunks of trees debarked by 

 automobiles, snowplows, or lawnmowers. Such injuries may be the beginning 

 of serious trouble, serving as points of entrance for decay organisms and the 

 ultimate weakening and collapse of trees. 



Unusual instances of trunk wounding, as those associated with the Connecticut 

 Valley flood of 1936, are sometimes difificult to explain after the conditions caus- 

 ing them no longer prevail. For example, trees situated In locations which now 

 appear to be at a safe distance from flooding waters show bark injury known to 

 have been caused bv ice floes. 



