![]() ![]() The formation and characteristics of reaction wood, compression wood in conifers and primitive nonporous angiosperms (wood lacking vessels), and tension wood in porous wood angiosperms (wood containing vessels) has been covered in the chapter on reaction wood in this volume by Donaldson and Singh (2016) and others elsewhere ( Wilson and Archer, 1977 Timell, 1986a, 1986b, 1986c Du and Yamamoto, 2007 Gardiner et al., 2014). Telewski, in Secondary Xylem Biology, 2016 Reaction wood Unfortunately the growth stress which is beneficial to the tree has undesirable effects on timber properties resulting in abnormal shrinkage and dimensional instability.įrank W. In tension wood, the additional cellulose is thought to generate tension on the upper side of the stem due to shrinkage during wood formation. The increased lignification of compression wood tracheids is thought to produce significant longitudinal swelling during wood formation, thus generating an expansion on the lower side of the stem, which attempts to correct the lean. Both compression wood and tension wood contains a β-1,4-linked d-galactan not found in normal wood. Compression wood lignin has a higher content of p-coumaryl units. Compression wood typically has more lignin, and less cellulose and galactoglucomannan, compared to normal wood, while tension wood has a higher cellulose content. Reaction wood occurs in two different forms, compression wood in softwoods, and tension wood in hardwoods. Reaction wood is produced as a response to stem lean, and has the function in the tree to generate growth stress to correct the stem lean, thus maintaining the most efficient position of the stem for photosynthesis. Donaldson, in Encyclopedia of Materials: Science and Technology, 2001 5 Reaction Wood Tension wood has a slower drying rate than normal wood, resulting in tension wood zones with a higher moisture content than surrounding normal wood.Ī.G. Tension wood fibers tend to pull out during sawing and planing operations, producing fuzzy or woolly grain. Tension wood will induce warp in the lumber, such as crook and bow. ![]() ![]() The tension wood zones in kiln-dried lumber tend to collapse. Most tension wood strength values are lower than normal wood of similar density. It is found on the tension or upper side of leaning trees and branches. The longitudinal shrinkage of compression wood is more than in normal wood, inducing warp in lumber, such as bow, crook, and twist.Ībnormal wood in hardwoods is called tension wood. However, it has lower strength than wood with a comparable density. It has a higher density than normal wood, but with comparable strength values. Compression wood properties are different from normal wood. It also has little contrast in color between earlywood and latewood within a growth ring. Compression wood has eccentric growth rings of varying width within the growth ring. It is induced on the compression or lower side of the leaning tree trunk and branch. Reaction wood in softwoods is called compression wood. Reaction wood is generally considered undesirable in sawn wood products, and is either not permitted or limited in structural grades of lumber. The function of reaction wood is to bring the main stem or branch back to its normal position. It is formed in the main stem of a leaning or inclined tree and in branches. Reaction wood is abnormal wood formed in response to the growth environment inducing mechanical stresses in the tree. Blankenhorn, in Encyclopedia of Materials: Science and Technology, 2001 1.2 Reaction Wood ![]()
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