AMERICAN FORRSTRY 



are being- formed, which are tender and 

 naturally sensitive to abnormal condi- 

 tions. This is very well shown by the 

 damage of late spring fires. Thus, a 

 surface fire in May or June may entirely 

 kill hardwood trees which in the early 

 fall would successfully resist a fire of 

 equal severity. 



Living tissue is killed when it is 

 heated to fifty-four degrees Centigrade 

 ( 1 20,. 2 degrees Fahrenheit)/ 1 Very 

 often the forester wishes to determine 

 after a fire the extent of the injury. 

 If the inner bark is brown or black, 

 in contrast to the normal green color, 

 this is an indication that the cambium 

 is dead. 



Injury to Trees 



Many surface fires do not kill trees 

 outright, but seriously injure them by 

 killing a portion of the roots or trunks. 

 It is very common to find, after a fire, 

 that nearly all the trees is the forest 

 have been killed on one side. (PI. Ill, 

 fig. I.) This is usually the leeward side, 

 because here the flames have an oppor- 

 tunity to burn in immediate contact with 

 the tree long enough to injure it. If 

 a fire is burning up a slope, even when 

 there is no wind, the upper side of a 

 tree is usually more damaged than the 

 lower side, both because of the accumu- 

 lation of leaves and other litter above 

 the tree and because fires are carried 

 upward by the currents of hot air, just 

 as a fire on level ground is swept along 

 by the wind. 



In the case of a well-established tree, 

 the killing of one side may not result 

 in its death for a long period ; and if the 

 wound is not large it may heal over. 

 Very commonly, however, the killing of 

 one side of the tree induces the attack 

 of some fungous disease, which ulti- 

 mately results in the tree's death. (PI. 

 II, fig\ I.) Trees injured and weakened 

 by fire are subject to the attack of in- 

 sects. In many cases the death of trees 

 after a burn is the result of insects' 

 work and not of the killing of the tis- 

 sues by the fire. Damage by fire often 

 follows damage by insects. Thus, in 



*Der Waldhau, by Heinrich Mayr, p. 12. 



certain conifers insects injure the 

 trunks, causing a local accumulation of 

 pitch. A surface fire later burns the 

 tree at this point and kills one side. The 

 defect called "cat-face" is often caused 

 in this way. Insect attacks_, moreover, 

 by increasing the number of 'dead trees 

 in the forest, increase the fire danger. 



In the case of large trees, which are 

 very resistant to fire, a first fire may kill 

 the tissues on one side, and subsequent 

 fires may then burn into the dead wood 

 until the trunk is nearly hollow. This 

 result is very commonly seen in large 

 white pines, that have a large propor- 

 tion of the butt gouged out by repeated 

 fires and are still alive. Many of the 

 larger trees on the Pacific coast, like 

 red fir. yellow pine, sugar pine, and big- 

 tree, stand for many years after injury 

 of this character. 



The damage to a tree by killing a 

 part of the trunk or a part of the roots 

 depends on its resisting power and a 

 variety of other circumstances. In 

 some cases the tree is so weakened by 

 the burning that it is afterward broken 

 off at the butt. This is very common 

 in longleaf pine forests, where old tur- 

 pentine "boxes" burn out and weaken 

 the tree. (PI. Ill, fig. 2.) 



The injury to the tree usually results 

 in a reduced rate of growth. It is ob- 

 vious that if a portion of the tree is 

 killed the whole tree cannot perform its 

 functions so effectively as before. The 

 killing of a part of the crown, stem, or 

 root system necessarily reduces the 

 amount of nourishment which the tree 

 can take in and furnish the growing 

 parts. 



It is not only in shortening life and in 

 reducing growth that fires injure trees; 

 the quality of the product is also af- 

 fected. Even where there is no infec- 

 tion by insects or fungous disease, a fire 

 that has killed one side of a tree usually 

 leaves its scar. In time the wound may 

 entirely heal over, but there is nearly 

 always a point of weakness which may 

 ultimately cause a seam or wind shake 

 and unfit the butt log for lumber. If 

 rot sets in. it may spread throughout the 

 trunk and make 'the tree worthless, even 

 if it does not kill it. 



