USES OF COMMEKCIAL WOODS. 19 



j^,5,./,. — o.'Sl per oeut of weijrht of dry wood (Sarj^eiit). 



Fuel value. — 88 i)er ceut that of white oak (Sargent). 



Breaking strength (modnlus of rupture). — IT.fKHJ i.ounds per square inch, or 

 138 per cent that of white oak (Sargent). 



Faetor of stiffness (modulus of elasticity).— 2.47s.(HX> pounds per square inch, 

 or 188 per cent that of white oak (Sargent). 



Heavy, very hard and strong, con pact, satiny. suscei)tible of a beautiful 

 polish, medullary rays numerous, obscure; color light-brown, tinged with red. 

 the sapwood nearly white. 



Height, GO to SO feet: diameter. U to 3 feet. 



SUPPLY. 



The range of yellow ])ircli extends from eastern Maine to northern 

 Minnesota and southward to Tennessee and North Carolina alono- the 

 Appalachian ranges. It is a northern tree and reaches its best devel- 

 opment near the Canadian border. It is known also as gi'ay. silver. 

 and swamp birch. Its names are all descriptive, but swamp birch 

 may mislead, as it does not grow well in deep, cold swamps, thougii it 

 is often found around their margins. The young tree is silver white, 

 but as it increases in size the bark takes on a yellow tinge. The wood 

 is not yellow, but the sapwood is white and the heartwood brown. 

 or often reddish. 



Within its range the species is fairly abundant, and in the past it 

 has easily met all demands made upon it. It is not probable, however, 

 that it will continue abundant, for it is being rapidly cut. and the 

 changing forest conditions in logged regions are not conducive to 

 new growth of this species. It is. besides, a very slow-growing tree, 

 and a century is required to produce a trunk large enough for small 

 saw timber. It is an abundant seeder, and it disperses its seeds well ; 

 but their natural germinating bed is the ground of an old forest Avith 

 plent}^ of shade and moss. Old moss-covered logs and rocks buried in 

 moss are favorite sprouting jolaces for the seeds of yellow birch. The 

 roots grow into the ground, and when the log decays the tree is left 

 standing high on its proplike roots. Occasionally a tree stands above 

 a bare rock, with roots doAvn the sides to the ground, presenting the 

 appearance of having grown from a seed which germinated on a 

 naked rock. Forest-grown yellow birches develop tall, clean trunks 

 with small crowns, splendid sticks for lumbering. When grown in the 

 open, however, they are limby. They push vigorously into vacant 

 ground that has been opened by windfalls or fire and also into 

 abandoned fields, and in such situations are often able to hold their 

 place. Few yellow-birch forests of considerable extent, however, are 

 coming on. and the species can not contribute much to the lumber 

 supply after the present stand is cut. 



EARLY ITSE.S. 



Early records showing the use of yellow I)iii'h are comparatively 

 few. It was not a wood to attract mncli attention when forests were 



