Effect of Forest Pires on Trees. 201 



The healing of a scar which takes four or five years, can rarely 

 be accomplished before decay starts. During the period following 

 a fire two opposing forces are acting ; one, growth, trying to repair 

 the damage and close the wound ; the other, insects and fungi 

 together, trying to destroy the remaining tissue. Healing must 

 take place from the outside, each growth ring closing over more 

 of the injured area, till at last the layers meet from the opposite 

 sides. Sometimes they unite and the cambium ring again be- 

 comes complete. More often they merely remain in contact. 

 Before the wound has closed the wood has usually commenced to 

 decay at the surface. If this is not too rapid and healing is fast 

 enough the growth rings meet across the opening and a closed 

 cavity is formed. Otherwise the forward growing edges are 

 rolled further and further inward in a vain attempt to coat the in- 

 side of the cavity which always remains open. If the decay be in 

 the inside in the heartwood, the surface scar may heal, but in time 

 a rotten butted tree results. 



While decay at the point of attack is going on, it is also creep- 

 ing up the heartwood and down into the larger roots. The tree 

 has no means of repairing this damage. Its ability to resist decay 

 is the sole consideration. A species with a decay-resistant wood 

 remains sound above the point of injury for long periods. It is 

 often a consideration what fungus attacks a tree. Some are more 

 virulent than others. 



///. BFFBCT OF RECURRING FIRBS. 



If but one fire ever burned a stand, the effects of fire would not 

 be nearly as great as they are. Many tracts are subject to recur- 

 ring fires at frequent intervals, often annually. Although fires in 

 a repeated burned stand are never as intense as in one previously 

 unburned, the culminative effects are much greater. There are 

 two causes for this : ( i ) Indirect effect of fires by changing the 

 site conditions, (2) Direct effect of the fires on the trees. The 

 resistance which trees put forth against recurring fires and the 

 agencies associated with them we may call continued resistance. 



Indirect Effects of Recurring Fires : The loss of the forest floor, 

 destruction of reproduction, drying out of soil, perhaps followed 

 by erosion, are among the indirect effects of recurring fires. 



