THE NORTHERN HARDWOOD FOREST. 7 



growth stands. They are light-foliaged trees, intolerant of shade, 

 which shelter beneath their crowns the reproduction of maple, 

 beech, hemlock, and other shade-tolerant and heavy-foliaged species. 

 One generation of the intolerant trees is all that is possible under 

 these conditions, for their seedlings can not live in the dense shade of 

 the other undergrowth already started. Survivors of the original 

 temporary stands, however, are often found in the hardwood forest, 

 as well as isolated individuals which have sprung up among old 

 timber where there are accidental openings in the crown cover. 

 Most of the conifers, notably white pine and red spruce, also grow 

 in well-marked types of their own, often in pure stands. Basswood 

 and elm, on the other hand, rarely grow otherwise than as scattered 

 individuals, except in Michigan and Wisconsin, where they some- 

 times form fully a third of the total stand. 



About 15 species of hardwoods are common to the northern and 

 southern forests, and 8 (birches, aspens, fire cherry, and black ash) 

 are found only in the northern. Grouped according to geographical 

 range, north and south, the trees of the northern hardwood forest, 

 excluding a 'few of the less important, are as follows : 



Range northern. Range northern and southern. 



Hardwoods : Hardwoods : 



Yellow birch. Sugar (and black) maple. 



Paper birch. Red maple. 



Gray birch. Silver maple. 



Aspen. Black birch. 



Large tooth aspen. Beech. 



Balm of Gilead. Basswood. 



Black ash. White elm. 



Fire cherry. Slippery elm. 



Conifers: Cork elm; 



Red spruce. Ironwood. 



White spruce. White ash. 



Black spruce. Black cherry. 



Balsam fir. Red oak. 



Hemlock. 



White pine. 



Norway pine. 



Jack pine. 



Tamarack. 



Arborvitse. 



The northern forest with about 21 hardwoods is much simpler in 

 composition than the southern, which contains fully 95 of local or 

 general commercial value. It has been still further simplified by 

 selective lumbering. Not only the white pine, spruce, and hemlock, 

 but in many places the better hardwoods also, have been heavily 

 cut, thus increasing the proportion of the less valuable kinds in the 

 culled forests. 



