Wood Macroanatomy

FW1035
Lecture 2
Bowyer et al - Chapter 2, 25-40
Wood Macroanatomy
• Planes of view in wood (again)
• Growth rings
• Sapwood and heartwood

Planes-of-View in Wood Samples
Transverse Plane (Cross-Section)
Tangential
Plane
Radial
Plane

Appearance of the Different Planes in
Wood
Transverse Plane
(cross section)
Radial Plane Tangential Plane

Two Basic Types of Boards
A
Radial Plane
Tangential Plane
B
A - Quartersawn
Radial plane on
broad face
B - Flatsawn
Tangential plane
on broad face

Log Cutting Patterns
Flatsawn
Quartersawn

Flatsawn
Quartersawn

Quartersawn lumber is used in some
furniture styles:
• Mission Oak
• Shaker

Growth Rings
• Mark annual growth
boundaries in trees grown in
temperate climates
• Often composed of 2 distinct
segments
earlywood (springwood)
latewood (summerwood)
• Earlywood and latewood cells
have different characteristics

Cell Differences Within Growth Rings
Earlywood
• Large Radial
diameter cells
• Lower density than
latewood
Latewood
• Smaller radial
diameter cells
• Thicker cell walls
Generally true for both hardwoods and softwoods

Effect of Growth Rate on Appearance –
Ring Porous Hardwoods
Slow Average Fast
Growth rate can have a large affect on gross appearance.
All pictures are of red oak (Quercus rubra) samples.

Irregularities in Annual Ring Formation
False rings
- Growth interrupted by environment (e.g. defoliation)
- Slow growth may cause formation of latewood type cells
Discontinuous rings
- Cambium was dormant in one region
- One-sided crowns, suppressed, or overmature trees
Trees grown in tropical environments
- Almost continual growth can limit occurrence of rings
- In some climates, stopping and restarting of growth can give
more than one growth increment in a year

Discontinuous growth
rings in redwood
(Sequoia
sempervirens)

False growth ring in bald
cypress (Taxodium distichum)
Discontinuous growth
ring in redwood (Sequoia
sempervirens)

Sapwood and Heartwood
• In mature trees, the xylem has both living and dead
cells.
- Sapwood contains the only living cells in the xylem (not all
sapwood cells are alive either) and has a conductive
function.
- ~1% of the cells in a mature conifer are alive
- Heartwood is composed of dead cells and lends mechanical
support only.
• Size of sapwood region is related to size of the tree
crown
- Generally, larger crown leads to more sapwood
- Varies widely with species and individual trees
- Sapwood requirements are lessened upon maturity and
layer width may shrink with age

Sapwood
• Contains all of the live cells
in the xylem
• Rays provide water and
nutrient transport in from
phloem
• Nutrients stored in
specialized cells called
“parenchyma” cells
• Also provides strength to the
tree stem

Heartwood
• Formation from reduced
water and oxygen availability
leads to death of
parenchyma cells
• Formation of “extractives” in
the cells
• Often (but not always)
results in a coloring of the
wood
• Function is strength/support
to tree stem

Live Cells in the Sapwood

Extractive Concentration
Heartwood
Sapwood
Distribution of
Extractives
Across Stem
Diameter

Heart Rot

What do extractives do?
Extractives can impart valuable properties to the
heartwood:
Color - black walnut and black cherry (for decorative
use)
Decay resistance - cedars, Douglas-fir, redwood,
cypress
Low Water Permeability – Douglas-fir (may cause
difficulty in drying, though)
Odor - cedars (cedar chests, closet linings)