Gab wrote:

>In a similar way, the best wood comes from trees with slow growth, the
annual rings are closer.<

This is a common generalization with limited accuracy. In "ring-porous"
trees (typically hardwoods) the slower growth rate can actually produce
wood with lower density. Northern Red Oak is a good example of this
phenomenon.

Density is a better way to ballpark the strength of wood within a
species. In ring-porous species the longitudinal cells that conduct
water (sap) are produced by the "early" wood that develops annually. As
the growing season progresses the "late" wood is added which has a much
lower density of longitudinal cells. Rapidly grown trees tend to add a
higher relative amount of late wood than early wood, particularly in
their younger life.

"Diffuse-porous" species (typically softwoods) are less prone to this
phenomenon since the "pores" created by the water conducting cells are
more evenly distributed in the early and late wood.

Both ring-porous and diffuse-porous woods tend to be weaker when grown
in a non-competitive environment. This is due to the fact that trees
gown in a dense or mature forest will have a small "crown" of leafy
branches relative to the "stem" of the tree. Normally the stem of a
mature tree in a mature forest will be nearly devoid of branches until
it reaches the "canopy". A tree which grows up after a clear cut in an
open area will tend to branch out and form a large crown compared to its
stem volume.

Larger crowns require more longitudinal cells and low density "sapwood"
to support the leaf structure. For this reason rapidly grown trees with
large crowns tend to be weaker because their sapwood density is higher.
Tulip poplar is a prime example of this. When it grows in a mature
forest it is called "yellow poplar" because it as a high density of
chartreuse colored heartwood. When it grows in a re-growth environment
it is just called poplar, or "white" poplar and sometimes "hickory"
polar (by the Amish) because of its high proportional volume of creamy
white sapwood.

The challenge to preservationteers is how to replace historic wood with
"in-kind" like it says on the "documents." The species may still exist,
but the wood normally has much lower design values. Replacing a yellow
polar timber in a covered bridge with a white poplar timber will lead to
certain disaster even though it is the same species and "grade" as the
original. Luckily it will rot away quickly enough that the problem will
be short lived.

And remember what Confusedus said about identifying amputees in a crowd:
"Man with wooden leg one foot short."

Signed..must have been the Starbucks.

Rudy

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