. Canadian forest industries January-June 1923. Lumbering; Forests and forestry; Forest products; Wood-pulp industry; Wood-using industries. Fig. 2—Douglas fir with different rates of growth. Fig. 1—Cross-section of balsam fir log er diameter and have thicker walls. The wood formed in summer being composed of thick-walled fibres with comparatively small cavities, is denser and harder than the wood formed at the beginn- ing of the growth period. As during the winter the tree is dormant and no additional growth takes place the successive annual layers are sharply defined by the contrast in textu
. Canadian forest industries January-June 1923. Lumbering; Forests and forestry; Forest products; Wood-pulp industry; Wood-using industries. Fig. 2—Douglas fir with different rates of growth. Fig. 1—Cross-section of balsam fir log er diameter and have thicker walls. The wood formed in summer being composed of thick-walled fibres with comparatively small cavities, is denser and harder than the wood formed at the beginn- ing of the growth period. As during the winter the tree is dormant and no additional growth takes place the successive annual layers are sharply defined by the contrast in texture and color of hard summerwood of a previous ring which abuts the softer springwood of the subsequent year's growth. Rate of Growth Shown By Width of Annual Rings Only softwoods will be discussed in this paper. Softwoods form the bulk of Canadian forests and include all the needle-leafed trees, usually spoken of as "evergreens" or conifers. Their structure is simpler than that of hardwoods and for this reason they are best dis- cussed separately. The annual rings of this group are often more strikingly divided into springwood and summerwood than is the case with hardwoods and, therefore, the softwoods offer more favor- able material for studies in growth-rate. It is obvious that a tree, which continually forms wide annual rings, will increase its volume more rapidly than one which adds only narrow layers. Wood with wide rings is therefore spoken of as fast-growth material and that with narrow rings is said to be slow growing. Fig. 2 shows samples taken from Douglas fir timbers having different rates of growth. The end section of the 1% inch board, which was taken from the centre of a tree, shows fast growth while the section of a 3 inch by 3 inch tie shows narrower annual rings denoting much slower growth. The summerwood shows clear- ly in both as dark bands defining each annual layer. The scale, which reads in inches, gives some idea of the actual proportions. I
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectforests, bookyear1923
