Softwoods growth

Figure 9. Light micrograph of the earlywood-to-latewood transition within softwood growth increments as viewed in cross section. Key A, abrupt transition in eastern larch, with thick-walled latewood fibers (D = resin duct) and B, gradual transition in eastern white pine, with relatively thin-walled latewood fibers.

Other distinct classes of wood in a tree include the portion formed in the first 10—12 years of a tree s growth, ie, juvenile wood, and the reaction wood formed when a tree s growth is distorted by external forces. Juvenile fibers from softwoods are slightly shorter and the cell walls thinner than mature wood fibers. Reaction wood is of two types because the two classes of trees react differentiy to externally applied stresses. Tension wood forms in hardwoods and compression wood forms in softwoods. Compression wood forms on the side of the tree subjected to compression, eg, the underside of a leaning tmnk or branch. Tension wood forms on the upper or tension side. Whereas in compression wood, the tracheid cell wall is thickened until the lumen essentially disappears, in tension wood, tme fiber lumens are filled with a gel layer of hemiceUulose. 

Candida utilis is grown on sulfite waste Hquor in Western Europe and North America, on sugar cane molasses in Cuba and Taiwan and on ceUulose acid hydrolysates in Eastern Europe and the former Soviet Union. C. ///i/if utilizes hexoses, pentoses, and many organic acids. Sulfite Hquor from hardwoods contains 2—3% fermentable sugars of which 20% are hexoses and 80% pentoses in softwood Hquors the proportions are reversed. The SO2 must be stripped out to allow yeast growth, which is carried out in large, highly-aerated fermentors. Eor continuous fermentations, carried out at pH 4 and 30°C, the dilution rate is 0.27—0.30 (34). 

Fast grown softwood from plantation sources is generally characterized by a high proportion of juvenile wood and often poorly developed heartwood. A fast rate of growth results in wide growth rings, producing low-density timber that exhibits inferior mechanical... 

In 1976 the Pacific Coast supplied 50 percent of the nations softwood products while the South provided 36 percent. These figures are expected to reverse by 2030 after old growth timber on the Pacific coast has been cut (Anonymous 1982). However, the total forestry land base over this period is expected to remain fairly constant. A major increase in forest management activity will be necessary if the South is to increase production to the predicted levels. 

Figure 2. End view of a softwood showing growth rings. Each growth ring consists of a light and dark area. The light portion is called springwood or earlywood, and the dark area is termed summerwood or latewood. 15y ...

Figure 3. Softwood block showing three complete and part of two other growth rings in the cross-sectional plane lX). Individual springwood cells can be detected, whereas the smaller summer-wood cells cannot be seen as individual cells. Also note the absence of vessels and the uniformity of the wood. Two longitudinal surfaces (R—radial T— tangential) are illustrated. Food-storing cells can be easily detected on the radial surface (arrow). 47 X (Courtesy of N. C. Brown Center for Ultrastructural Studies, S.U.N.Y. College of Environmental Science and Forestry)...

At the beginning of the growth the tree requires an effective water transportation system. In softwoods thin-walled cells with large cavities are formed in hardwoods special vessels take care of the liquid transportation. Comparatively light-colored and porous earlywood is thus formed. Later, the rate of growth decreases and latewood is produced. It consists of thick-... 

The normal structure of the cell wall is broken by pits. Changes appear already in the growth period of the cell. For instance, early stages of pit formation in softwoods are visible in the primary wall just before the cell reaches its final dimensions (primary pit fields). The microfibril network is loosened and new microfibrils are oriented around these points. The structure in the middle of the circles is tightened and the radially oriented microfibril bundles finally form a netlike membrane, permeable to liquids (margo) (Fig. 1-17). The central, thickened portion of the pit membrane... 

Roy, C., Calve, L., Lu, X., Pakdel, H., and Amen-Chen, C. (1999) Wood Composite Adhesives from Softwood Bark-Derived Vacuum Pyrolysis Oils.In Biomass A Growth Opportunity in Green Energy and blue Added Products. 

Growth increments reach their most advanced form in temperate-zone trees where the norm is a single, generally distinct, and circumferential band of wood production each year (Figure 6). The appearance of these so-called annual rings varies between hardwoods and softwoods with species, tree age, and growing conditions. These factors, together with certain other environmental effects, can also... 

Within a growth ring, softwood interfiber pits are larger and more abundant in earlywood. In latewood they are fewer, smaller, and often appear slitlike in very thick-walled fibers (2). This same type of pit in hardwood fibers varies morphologically with the fiber type, changing from an obviously bordered pit in thin-walled cells to only a slitlike aperture in fibers with thick walls. 

Figure 1.3. The softwood Thuja plicata. Tracheids function in both sap conduction and stem support in softwoods. A growth ring is clearly visible with the thicker-walled latewood tracheids to the top left, and the thinner-walled and larger lumened early-wood tracheids to the lower right, x 275.

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