THE SPRUCE REGION 211 



As the slopes are ascended the timber naturally becomes 

 smaller, due both to the absolute elevation and because the soil 

 and moisture decrease with increasing height. Finally, on a 

 few of the higher mountains, timber line is reached, above which 

 no tree growth is found. This line is between 4500 and 5000 feet 

 above sea level. 



On the upper slopes, from 3500 feet in elevation up to timber 

 line, the slope type does not contain trees of merchantable size. 

 They are scrubby and twisted and often only a few feet high. 

 Balsam usually predominates in these stands at high elevations, 

 and may form the entire growth. Black spruce also occurs at 

 these high elevations. These unmerchantable stands perform 

 a most important function as protection forests where such 

 forests are badly needed. 



Excellent reproduction takes place in the spruce slope type. 

 Even in the virgin stands plenty of seedlings and young growth 

 ordinarily are found. Balsam seedlings are apt to exceed the 

 spruce in such stands, though the latter is well represented. 



5. Birch and Poplar. — This is one of the temporary types 

 occurring on no particular kind of soil or site. It is confined, 

 however, to lands of differing qualities of soil which have been 

 burned over. 



On such land the leaf litter and moss have been destroyed and 

 the mineral soil is left bare and exposed. Such a seed bed is 

 preferred by yellow and paper birch and poplar. The light seeds 

 of these species are blown in by the wind, often for several 

 thousand feet, and germinate on the bare soil of the burned lands, 

 creating the type. 



Yellow and paper birch and poplar {Populus tremuloides and 

 grandide?itata and a little halsamea) are the chief species. Other 

 light-seeded species, such as red maple and mountain maple, are 

 often abundant. One fairly heavy-seeded species may be pres- 

 ent in considerable quantities. This is the bird cherry, the seeds 

 of which are brought in by birds and scattered over the burned 

 areas. 



This composition is but temporary, as under the light shade 



