APPENDIX. 



ASPEN AS A RAW MATERIAL FOR PAPER PULP. 



DISTRIBUTION AND CHARACTERISTICS OF THE TREE.i 



Aspen (Populus tremuloides Michx.), or quaking aspen, as it is sometimes called, is 

 one of the most widely distributed and best-known American trees. Together with 

 the closely related European species, Populus tremula Linn., from which paper pulp 

 of excellent quality is also prepared, it encircles almost the entire globe. In America 

 aspen extends from Labrador to Alaska and southward to Tennessee and Arizona. 

 Yet it occurs scatteringly, and pure stands of any extent are comparatively rare. For 

 this reason it is not possible to give even approximately the present total stand. In the 

 western forests, notably those of Utah and western Colorado, there are vast quantities 

 which will doubtless be an important source of future supply. In the past New Eng- 

 land furnished most of the aspen pulpwood, and although the supply there is badly 

 depleted, considerable quantities yet remain in certain regions, notably in northern 

 Maine. 2 



Aspen is a very rapid grower and quickly covers burned or logged-over lands. How- 

 ever, it is comparatively short-lived, and the larger trees suffer severely from fire, 

 windshake, insects, and fungi. In fact, aspen is defective from decay to a greater 

 extent than any other commonly used pulpwood, except perhaps balsam fir. The 

 trees ordinarily used for pulpwood are from 5 to 14 inches in diameter. If grown in 

 close stands, the trunks are fairly free from knots and limbs. Logging is compara- 

 tively easy. 



Aspen wood after cutting is also susceptible to fungous attack unless kept very dry. 

 It is particularly perishable in contact with the soil. The ability of the wood to season 

 rapidly, especially after being barked, is of much advantage. Nevertheless, mills 

 which store a year's supply or more in open yards undoubtedly have a large proportion 

 of their older wood affected. The general opinion is that "old wood " produces infe- 

 rior pulp and lower yields. 



PROPERTIES AND STRUCTURE OF THE WOOD. 



The wood of aspen is soft, light in weight, not strong, and close grained, but with 

 numerous minute, open ducts. The medullary rays are very thin and hardly distin- 

 guishable with the naked eye. The color is light brown, the sapwood almost white and 

 very thick, often representing 25 to 30 layers of annual growth. In the green or freshly 

 seasoned material, however, the difference between heartwood and sapwood is in most 

 cases scarcely appreciable. A cubic foot of air-dried wood usually weighs from 25 to 

 30 pounds. 



i A more complete discussion of the silvical characteristics of aspen is given in Forest Service Bulletin 

 93, The Aspens; Their Growth and Management, by W. G. Weigle and E. H. Frothingham, 1911. 

 2 Forest Service Bulletin 93, pp. 13 and 17, 1911. 



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