Reaction Wood
Reaction wood is formed
as a response by the tree
to a triggering event such
as tipping from the
vertical.
It is also known to
regulate the orientation or
angle of branches relative
to the main stem.
(Haygreen & Bowyer) 1
The terminology used to
describe reaction wood
formed in softwoods and
hardwoods comes from the
stresses normally present in
those locations.
However, those stresses
themselves are NOT
responsible for the formation
of reaction wood.
(Haygreen & Bowyer)
2
Compression Wood
Wind
(Haygreen & Bowyer)
(Hoadley)
3
Compression wood – characteristics and properties
Anatomy
• Wider growth rings
• More latewood
• Shorter longitudinal tracheids
• Rounded cells with intercellular spaces
• Helical striations (following S2Ө)
Ultrastructure
• Larger S2Ө
• S3 absent
• New S1L layer
Chemistry
• More lignin
• Less cellulose
• Hemicelluloses differ
Properties
• Higher wood density
• Compression strength ↑
• All other strengths ↓
• Brittle failure
• Greater longitudinal shrinkage
• Lower pulp yields
4
Compression wood – macroscopic appearance
Compression wood
(Hoadley)
5
Compression wood – characteristics and properties
Anatomy
• Wider growth rings
• More latewood
• Shorter longitudinal tracheids
• Rounded cells with intercellular spaces
• Helical striations (following S2Ө)
Ultrastructure
• Larger S2Ө
• S3 absent
• New S1L layer
Chemistry
• More lignin
• Less cellulose
• Hemicelluloses differ
Properties
• Higher wood density
• Compression strength ↑
• All other strengths ↓
• Brittle failure
• Greater longitudinal shrinkage
• Lower pulp yields
6
Compression wood – microscopic appearance
Light microscope
Scanning electron
microscope
Transmission electron
microscope
7
Compression wood – characteristics and properties
Anatomy
• Wider growth rings
• More latewood
• Shorter longitudinal tracheids
• Rounded cells with intercellular spaces
• Helical striations (following S2Ө)
Ultrastructure
• Larger S2Ө
• S3 absent
• New S1L layer
Chemistry
• More lignin
• Less cellulose
• Hemicelluloses differ
Properties
• Higher wood density
• Compression strength ↑
• All other strengths ↓
• Brittle failure
• Greater longitudinal shrinkage
• Lower pulp yields
8
Ultrastructure of longitudinal tracheids
(Josza)
9
Compression wood – microscopic appearance
Normal wood
Compression wood
Compression wood
10
Compression wood – characteristics and properties
Anatomy
• Wider growth rings
• More latewood
• Shorter longitudinal tracheids
• Rounded cells with intercellular spaces
• Helical striations (following S2Ө)
Ultrastructure
• Larger S2Ө
• S3 absent
• New S1L layer
Chemistry
• More lignin
• Less cellulose
• Hemicelluloses differ
Properties
• Higher wood density
• Compression strength ↑
• All other strengths ↓
• Brittle failure
• Greater longitudinal shrinkage
• Lower pulp yields
11
Tension Wood
Wind
12
Tension wood – macroscopic appearance
Tension
wood
13
(Hoadley)
Tension wood – microscopic appearance
(Hoadley)
G-layer
Aspen tension wood
Aspen normal wood
14
Tension wood – appearance of G layer
Microfibril orientation
15
*
Tension wood – characteristics and properties
Anatomy
• Fibers affected not vessel elements
• Gelatinous fibers (G-layer)
Ultrastructure
• SG - after S3
- replaces S3
- replaces S2 + S3
- replaces some of S1 + S2 + S3
• Microfibrils less closely packed
• Low Ө in G-layer
• Higher S1Ө
Chemistry
• More cellulose
• Less lignin
• Hemicelluloses differ
Properties
• Higher wood density
• Compression strength ↓
• Seasoning defects
• Higher pulp yields
• Poor workability (“fuzzy” grain)
16
Location of reaction wood formation
Compression wood
formation in horizontally
oriented stem.
Compression wood is
found on underside of
stem – not on side of
stem under
compression.
(Haygreen & Bowyer)
17
Location of reaction wood formation
Reaction wood formation in
growing looped stem.
a. Softwood
b. Hardwood
(Haygreen & Bowyer)
Compression wood is found
consistently on underside of
stem and tension wood is
found consistently on upper
side of stem (regardless of
the nature of the stresses
experienced in those
locations).
18