30 



A PRIMER OF FORESTRY. 



Fig. 27.— Light crown of 

 an intolerant tree, the 

 "Western Larch. The 

 tree with heavy foli- 

 age and horizontal 

 branches in the back- 

 ground to the left is a 

 Western White Pine, 

 a tolerant species. 

 Xorthern Idaho. 



tbe rolliug laud between. (See PI. 

 XV.) A mound uot more thau a 

 foot above the level of a swamp is 

 often covered with trees entirely 

 different from those of the wetter 

 lower laud about it. 



Such matters as these have far 

 more to do with the places in which 

 different trees grow than the chemi 

 cal composition of the soil. But its 

 mechanical nature — that is, whether 

 it is stiff or loose, fine or coarse in 

 grain, deep or shallow — is very im- 

 portant, because it is directly con- 

 nected with heat and moisture and 

 the life of the roots in the soil. 



REQUIREMENTS OF TREES FOR 

 LIGHT. 



The relations of trees to heat and 

 moisture are thus largely responsible 

 for their distribution upon the great 

 divisions of the earth's surface, such 

 as continents and mountain ranges, 

 as well as over the smaller rises and 

 depressions of every region where 

 trees grow. But while heat and mois- 

 ture decide where the different kinds 

 of trees can grow, their influence has 

 comparatively little to do with the 

 struggles of individuals or species 

 against each other for the actual pos- 

 session of the ground. The outcome of 

 these struggles depends less on heat 



