Wood Macroanatomy
Wood Macroanatomy
Wood Macroanatomy
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FW1035<br />
Lecture 2<br />
Bowyer et al - Chapter 2, 25-40<br />
<strong>Wood</strong> <strong>Macroanatomy</strong><br />
• Planes of view in wood (again)<br />
• Growth rings<br />
• Sapwood and heartwood
Planes-of-View in <strong>Wood</strong> Samples<br />
Transverse Plane (Cross-Section)<br />
Tangential<br />
Plane<br />
Radial<br />
Plane
Appearance of the Different Planes in<br />
<strong>Wood</strong><br />
Transverse Plane<br />
(cross section)<br />
Radial Plane Tangential Plane
Two Basic Types of Boards<br />
A<br />
Radial Plane<br />
Tangential Plane<br />
B<br />
A - Quartersawn<br />
Radial plane on<br />
broad face<br />
B - Flatsawn<br />
Tangential plane<br />
on broad face
Log Cutting Patterns<br />
Flatsawn<br />
Quartersawn
Flatsawn<br />
Quartersawn
Quartersawn lumber is used in some<br />
furniture styles:<br />
• Mission Oak<br />
• Shaker
Growth Rings<br />
• Mark annual growth<br />
boundaries in trees grown in<br />
temperate climates<br />
• Often composed of 2 distinct<br />
segments<br />
earlywood (springwood)<br />
latewood (summerwood)<br />
• Earlywood and latewood cells<br />
have different characteristics
Cell Differences Within Growth Rings<br />
Earlywood<br />
• Large Radial<br />
diameter cells<br />
• Lower density than<br />
latewood<br />
Latewood<br />
• Smaller radial<br />
diameter cells<br />
• Thicker cell walls<br />
Generally true for both hardwoods and softwoods
Effect of Growth Rate on Appearance –<br />
Ring Porous Hardwoods<br />
Slow Average Fast<br />
Growth rate can have a large affect on gross appearance.<br />
All pictures are of red oak (Quercus rubra) samples.
Irregularities in Annual Ring Formation<br />
False rings<br />
- Growth interrupted by environment (e.g. defoliation)<br />
- Slow growth may cause formation of latewood type cells<br />
Discontinuous rings<br />
- Cambium was dormant in one region<br />
- One-sided crowns, suppressed, or overmature trees<br />
Trees grown in tropical environments<br />
- Almost continual growth can limit occurrence of rings<br />
- In some climates, stopping and restarting of growth can give<br />
more than one growth increment in a year
Discontinuous growth<br />
rings in redwood<br />
(Sequoia<br />
sempervirens)
False growth ring in bald<br />
cypress (Taxodium distichum)<br />
Discontinuous growth<br />
ring in redwood (Sequoia<br />
sempervirens)
Sapwood and Heartwood<br />
• In mature trees, the xylem has both living and dead<br />
cells.<br />
- Sapwood contains the only living cells in the xylem (not all<br />
sapwood cells are alive either) and has a conductive<br />
function.<br />
- ~1% of the cells in a mature conifer are alive<br />
- Heartwood is composed of dead cells and lends mechanical<br />
support only.<br />
• Size of sapwood region is related to size of the tree<br />
crown<br />
- Generally, larger crown leads to more sapwood<br />
- Varies widely with species and individual trees<br />
- Sapwood requirements are lessened upon maturity and<br />
layer width may shrink with age
Sapwood<br />
• Contains all of the live cells<br />
in the xylem<br />
• Rays provide water and<br />
nutrient transport in from<br />
phloem<br />
• Nutrients stored in<br />
specialized cells called<br />
“parenchyma” cells<br />
• Also provides strength to the<br />
tree stem
Heartwood<br />
• Formation from reduced<br />
water and oxygen availability<br />
leads to death of<br />
parenchyma cells<br />
• Formation of “extractives” in<br />
the cells<br />
• Often (but not always)<br />
results in a coloring of the<br />
wood<br />
• Function is strength/support<br />
to tree stem
Live Cells in the Sapwood
Extractive Concentration<br />
Heartwood<br />
Sapwood<br />
Distribution of<br />
Extractives<br />
Across Stem<br />
Diameter
Heart Rot
What do extractives do?<br />
Extractives can impart valuable properties to the<br />
heartwood:<br />
Color - black walnut and black cherry (for decorative<br />
use)<br />
Decay resistance - cedars, Douglas-fir, redwood,<br />
cypress<br />
Low Water Permeability – Douglas-fir (may cause<br />
difficulty in drying, though)<br />
Odor - cedars (cedar chests, closet linings)