UNDERSTANDING WOOD
Trees
CR O WN
T R UNK (B O L E)
R O O T SY STEM
Trees
EX CUR R ENT
SO FTWO O D S
GY MNO SP ER MS
D END R ITIC
HA R D WO O D S
A NGIO SPER MS
D EC ID UO US
C O NIFER O US
Hardwoods and Softwoods

Gymnosperms – Class of plants having naked seeds
including all softwood trees

Angiosperms – Class of plants having seeds
enclosed or covered. Includes all hardwood trees
Tree Cells


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Living cells (protoplasm)
Non living cells
Most cells are elongated
B A R R EL SHA PED
NEED L E SHA PE

The cell axis is oriented vertically
Planes And Surfaces
C R O S S S EC T IO NA L O R
T R A NS V E R S E FA C E
L O NGIT UD INA L
R A D IA L FA C E
T A NGENT IA L FA CE
Cross Section
B A R K (inner and o ut er )
CA MB IUM
P IT H
HEA R TWO O D
EA R L Y WO O D
A NNUA L R INGS
L A T E WO O D
SA P WO O D
RA YS
Annual Rings
Earlywood


Usually light in color
Usually softer than latewood
Latewood
Typically darker in color
 Typically has higher density
Uneven Grain - Pronounced difference in earlywood and
latewood (red oak)
Even Grain – Little contrast between early and late wood
(eastern white maple)

Earlywood and Latewood
Rays (Fleck or Flake)
RA Y


Strips of cells extending
radially within a tree and
varying in height from a
few cells in some species
to 4 inches or more in oak.
Rays serve primarily to
store food and to
transport it horizontally in
the tree
RA Y
Rays (Fleck or Flake)
More About Cells
Some cells are comprised of reproductive tissue. They divide
and form new cells.
 Apical meristematic tissue – growth tips
 Lateral meristematic tissue – cambium
Cells are collectively called tissue
 Bark tissue
 Wood tissue
 Both are permanent tissue
Photosynthesis

Water and nutrients move up through the roots and sap
wood cells to the leaves.

Most of the water evaporates helping cool the foliage.

Water from the soil combines w/CO2 catalyzed by
chlorophyll and energized by the sun produces basic sugar.
Photosynthesis

Sap (sugar) is carried downward through the inner bark,
distributed to the cambium layer where new cells are built.
These facts are important because…….


During the primary growth season the cambium is fluid
and the cell walls are extremely thin.
During the dormant season cambial cells are thick and
rigid.
What does this mean to woodworkers?
If you were making clock faces or coasters from crosssections would you want cross-sections harvested in
the summer or winter?
If you were peeling logs to build log cabins when would
you want to harvest?
More About Cell Reproduction

Division of cambium cells takes place lengthwise.

Sister cells are created
O ne s ist e r c e ll b e c o me s
b a r k o r ne w w o o d c e ll
mo t her c ambium c ell
T he o t he r si st e r c e ll b e c o me s
a new c a mb i um c ell
More About Cells
New wood cells undergo a change


They develop a fixed size and shape.
They develop a secondary cell wall


Cellulose
Lignin – Comprises 25% of woods composition
Most wood cells eventually loose their living protoplasm


Prosynchyma – Cells whose function is to support the tree and to
conduct sap
Parenchema – A small percentage of cells found in the rays retain
living protoplasm and can assimilate and store food
Sapwood & Heartwood




Twigs – All sapwood
As twigs grow they no longer need all of the wood tissue to
conduct sap
Near the pith sapwood cells cease to transport sap and
become heartwood
As sapwood becomes heartwood, extractives are formed
giving heartwood its darker color
Extractives In Heartwood


Formed in cell walls
Give heartwood a distinctive brown, red color


There are exceptions – Spruce extractives are non
pigmented
Properties of Extractives



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Fungal and decay resistance
Make wood impermeable (acts as a preservative)
Make wood denser
Makes wood more stable
Can be abrasive
Causes surface hardness
More About Heartwood

As the tree’s girth increases a proportionate amount of
heartwood is created as new sap wood is created.

The amount of heartwood varies from species to species and
growing environment
Density & Specific Gravity of Wood

Density = weight/unit volume

Specific Gravity – The ratio of the density of wood to the
density of water.
Example:
White Ash weighs 37.44 lb./ft3
Water weighs 62.4 lb./ ft3
37.44/62.4 = 0.6
• So why should we care about
density and specific gravity?
Density and Specific Gravity

Single most important indicator of strength in wood

Hardness

Ease of machining

Nailing resistance

Generally denser wood shrinks and swells more creating
greater problems in drying
Resistance to Heartwood Decay
L i gn um V it a e
1 .2
1 .1
SP EC IFIC GR A V IT Y
O F WA T ER
1 .0
R o s e wo o d
0 .9
Specific gravity is a good indicator
of strength; the values in this table
are the average for each species,
based on oven-dry weight and volume
at 12% moisture content.
S a t inw o o d
0 .8
P a d a uk
S ha g b a r k hic k o r y
B la c k lo c us t
Whit e o a k
D O MEST IC SO FT WO O D S
0 .6
S o ut he r n ye ll o w p i ne
B la c k wa lnu t
T a ma r a c k
D o ug la s f ir
B eec h
R ed oak
Y e llo w B ir c h
Whit e a sh
0 .5
R e d g um
B la c k c he r r y
S a s sa f r a s
We st e r n he mlo c k
E a st e r n s p r uc e
0 .4
E a st e r n whi t e p i ne
C he st nu t
C a t a lp a
D O MEST IC HA R D WO O D S
0 .7
B ut t e r nut
B a s swo o d
C o t t o nwo o d
We st e r n r e d c e d a r
0 .3
0 .2
B a ls a
0 .1
G Y MN O SP ER M
A NG IO S PE R MS
0
Co pied from Understan ding Wood
by Bruce Hoadley
Hardwood Cell Types

Vessel Elements


V ESSEL ELEMENTS
FIB ER S

Fibers



T R A CHEID S
Relatively large in diameter
Form end to end forming
continuous pipelines for
sap conduction.
Small in diameter
Closed ends and thick walls
(poor for sap conduction)
Give strength to the wood
Hardwood Cell Types
Pores



When vessels are cut transversely (across the end
grain) pores are exposed. Because all hardwoods
contain vessels they are considered Porous.
Softwoods do not contain vessels therefore they are
considered non-porous
The size, location and number of vessel cells
determine the appearance, uniformity and hardness
of a hardwood
Annual Rings
L A T E WO O D
A NNUA L R ING
EA R L Y WO O D
Porosity of Hardwoods

Ring Porous
L A T E WO O D
Large pores concentrate in the
earlywood
Pronounced uneven grain
Distinct figure or pattern
Typical Species – Oak, Ash,
Elm and Chestnut
EA R L Y WO O D
Porosity of Hardwoods
Semi Ring Porous



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Large vessels in earlywood and
small vessels in latewood but
more evenly distributed than
ring porous
More even grained
Less distinctive figure
Typical species - Black walnut
& butternut
Porosity of Hardwoods

Diffuse Porous
Pours are evenly distributed in
earlywood and latewood
Most species have small
diameter pores,
(mahogany is the
exception)
Typical wood species – birch,
maple, poplar,
mahogany and basswood.
Porosity of Hardwoods
Another look
Tyloses


As some wood species
make the transition from
sapwood to heartwood
bubble like structures
form, blocking the passage
way between connected
vessels
White Oak – used for wine
barrels