The state (Pennslyvanis) foresters just produced a booklet on trees. Common
Trees of Pennsylvania. It is very informative. However there is a couple
of half truths I think are worthy to mention.
The booklet points to the center of the tree and says trees form heartwood.
Yes, heartwood is a protection wood, however, all trees do not form
heartwood. Maple (Acer) trees are sapwood trees and they do not form
heartwood.

Second they state that the cambium zone produces wood to the inside. Not
so, the cambium forms xylem to the inside which is not lignified. Later the
cells differentiate and they take on lignin. Then and only then is it
correctly called wood. Wood is a substance made up of lignin, cellulose and
hemicelluloses. In the spring, when it appears that the bark slips, its not
the bark that slips its the xylem slipping. At that time if you take your
finger nail and scrape the material and you will get a jelly like substance
on your finger nail. That's xylem!

So, some trees form heartwood e.g., oak, pine.
Some don't e.g., maple, ash. maple is actually a sapwood tree often forming
discolored or color altered wood after a wound or injury. Remember
heartwood gets its color from an aging process and not from a wound or
injury. Ash on the other hand forms what we call false heartwood. Tulip
poplar trees form false heartwood that is thought to be the result of the
death of branches.

And, the cambial zone produces xylem to the inside and phloem (inner bark)
to the outside. The cambial zone does not produce wood. Just outside the
phloem is the phellogen which is sometimes called the bark cambium. It
produces the outer corky bark (phellem). It is interesting that all parts
of the tree are born alive. The outer corky bark is born alive but shortly
dies as it uses up its energy in forming suberin.

It also states that the soil bacteria and fungi make soil nutrients
available for the tree when actually it is essential elements that are
altered by soil microorganisms for absorption by the tree.

They claim the inner bark carries "FOOD" . This is true.
I remain optimistic.

--
Sincerely,
John A. Keslick, Jr.
Consulting Arborist
http://home.ccil.org/~treeman
and www.treedictionary.com
Beware of so-called tree experts who do not understand tree biology.
Storms, fires, floods, earthquakes, and volcanic eruptions keep reminding us
that we are not the boss.