Effect of Forest Fires on Trees. 207 



sprouts produced a few must attain supremacy before rapid de- 

 velopment of any is possible. 



F/. EFFECT OF AGE ON FIRE RESISTANCE. 



As age increases so does size and thickness of bark. More 

 heartwood is formed. The roots go deeper. All this gives the 

 tree added powers of resistance ; initial, subsequent, and to a 

 degree, continued. It might be argued that the life energy of a 

 tree past middle life is falling off, consequently its resisting 

 powers would likewise decrease, but the increased size, thickness 

 of bark, etc., far outweighs this. 



It is true, however, that old trees do not recover from injury as 

 rapidly as younger, more vigorous ones. We may say that 

 while resistance increases with age, recovery power varies with 

 life energy. 



Old trees are more or less unable to withstand changes in the 

 character of their site. They are thus more susceptible to the 

 indirect effect of fires, more especially continued fires, and so lose 

 some of the power of continued resistance. 



SUMMARY. 



The fire problem in southern New England has many phases 

 peculiar to itself. It is here discussed only in reference to the 

 effect of fire on the trees themselves and on reproduction. 



Trees exhibit three kinds of resistance to fire ; ( i ) Initial 

 Resistance, the resistance which sound trees put forth at the time 

 they are first burned. It depends upon several factors, chiefly 

 thickness of bark, (2) Subsequent Resistance, that which trees 

 once killed by fire, exhibit to insects, fungi and wind following the 

 fire, (3) Continued Resistance, that which trees oppose to re- 

 curring fires. It depends upon the character of the wood, and the 

 tree's ability to withstand adverse conditions. It is the final test of 

 a resistant species. 



Hardwoods frequently sprout after a fire. This is an advan- 

 tage when they are killed to the ground, but not when they are 

 merely injured. 



Fire generally kills all reproduction and may delay it indefini- 

 tely; when not holding back its development by making seedling 

 sprouts of the seedlings escaping. 



Fire resistance in general increases with age, but Recovery 

 Power varies with life energy. Continued Resistance declines 

 after a tree passes its prime. 



