SILVICULTURE. 187 



Young crops, during the seedling and brush- 

 wood stage, are readily killed, while older timber 

 may stand scorching without much or any damage. 

 Different species behave differently in this re- 

 spect. The giant trees, or Sequoias, covered with 

 a dense bark more than a foot thick, and their 

 wood hardly inflammable, the Douglas fir, with a 

 similar protection, are less liable to be damaged 

 than the thin-skinned firs or spruces, beech or 

 white birch and aspen. The green, succulent 

 foliage and wood of broad-leaved trees is more 

 resistant than the dry resinous foliage and wood 

 of conifers. Drouthy conditions and dry soils are 

 more likely to induce danger from fire damage 

 than the opposite conditions. Finally, the presence 

 or absence of an undergrowth, or debris, of dead 

 and dry branches of trees, and the character of 

 the forest floor, must make a difference in the ease 

 with which a fire may start and run, the amount 

 of heat it develops, and the consequent damage. 



The damage may consist in the total loss of the 

 crop, which is usual until the pole-wood stage is 

 reached. In pole wood and young or old timber the 

 trunks may be only blackened, but more often the 

 cambium layer below the bark is partially or en- 

 tirely killed, causing either the death of the tree, 

 especially when recurring fires accumulate the 

 damage, or secondary damage results through rot 

 or insects which develop, especially in the weakest 

 trees. 



