Download HEARTWOOD

Wood with no living cells.
Hoadley: “The central core
of wood in mature stems that
was at one time sapwood but
no longer conducts sap or has
living cells.
In most species,
infiltration of extractives
imparts a perceptibly darker
color to this wood.”
NOT ALL HEARTWOOD
HAS A DARKER COLOR
THAN THE SAPWOOD
Some species have light-colored
heartwood
• Spruce (Picea)
• Aspen (Populus)
The number of sapwood
rings varies with species.
Catalpa
Walnut
Oaks
S. Yellow Pine
Tupelo
1-2
10 - 15
10 - 15
15 - 25
100+
Ponderosa Pine 150 - 200
Most ring porous species have 10 or fewer rings of sapwood
Changes Sapwood to Heartwood
• Nuclei in parenchyma cells
degenerate
• Decrease in nitrogenous materials
• Moisture content changes
• Decrease in starch
• Accumulation of extractives
These changes can be “abrupt” or gradual.
Death of the Parenchyma Cell
• Spatial control -- Distance from the
cambium & secondary phloem
• Temporal Control -- Age of the
parenchyma cell (programmed to die
after a certain age).
Which factor is most important varies from
species to species, and can be a combination
of the two.
EXTRACTIVES
• Organic compounds (e.g, gums,
tannins, oils) manufactured by the
parenchyma cells.
• Extractives can be removed
(extracted) by water, alcohol, or other
solvents
EXTRACTIVES
• Not “structural elements” of cell
walls
• May or may not be colored
• May be in the cell walls or in cell
lumens
Heartwood Properties
If extractives go into the cell wall,
If a lot of extractives deposited in
cell wall,
Then may be some increase in the
compressive strength of the
heartwood relative to “like-aged”
sapwood.
Effects of Extractives
Some, not all extractives are toxic to
decay organisms or insects.
Heartwood then will be more durable,
last longer than sapwood.
This may be heartwood gets
considered “stronger” than sapwood -in some species it lasts longer.
Extractive Effects
If extractives coat cell wall and pit
membranes,
Then will reduce permeability.
Sapwood Intervessel Pit
Heartwood Intervessel Pits
Undesirable Effects
of Extractives
• Increased chemical consumption for
pulping and bleaching
• Tannins can corrode metals
• Can interfere with setting of paints, glues,
and varnishes
• Can migrate during drying cause
discoloration.
Desirable Effects of Extractives
•Color
•Durability
•Dimensional
Stability