APPEKDIX. 
ASPEN AS A RAW MATERIAL FOR PAPER PULP. 
DISTRIBUTION AND CHARACTERISTICS OF THE TREE.* 
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 pulp wood, 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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