A tree's life is hard. It must stand against wind, hail and
ice. A multitude of pests wait to consume it. To live
decades, maybe even centuries, the tree must be tough.
To protect itself, a tree will wrap itself, inside and out,
in protective clothing. It has to. When environmental
problems or pests come to damage it, the tree must stay
still and take whatever comes.
Life conspires to kill trees. They try to survive by using a
unique defensive system.
Actually, a tree has a double-edged defensive system to deal
with the environment   one part passive and the otheractive.
The passive system is composed of wooden walls made from
strong, complex materials. These include cellulose fibers,
which are made of sugars so tightly welded together that few
living organisms on earth have the enzymes to break themapart.
Another material in wood is like epoxy glue. Called lignin,
it holds the cellulose fibers close together. Lignin is
composed of complex chemical building blocks, each connected
in a different way to each other.
Again, only a few decay organisms can degrade lignin. Very
few living things can decay both cellulose and lignin.
Cellulose and lignin are the main walls, floors and ceilings
of individual cells and groups of cells. These wooden cell
barriers prevent or slow pests and decay from rampantlyconsuming 
the tree.
As cells age and die toward the middle of the tree, chemical
reactions biologically strengthen the wooden walls. Old
cells generate a number of toxic materials in their dying
gasps. These materials slow pest and decay organisms.
The active defensive system of a tree includes special
biological poisons it makes when injured. It also includes a
host of blocking, plugging and sealing compounds.
The tree's active defenses try to slow the spread of pests
and decay by producing toxins dangerous to living things.
Some of these toxins are dangerous to humans at the correctdose.
Of all the materials the tree makes to protect itself, one
of the most versatile and effective is suberin.
Suberin is a waxy waterproofer and wooden wall primer.
Lightweight and low-density, it is made of many similar
building blocks the tree piles together.
Chemically, suberin is a complex polyester. The tree can
make it wherever it needs it to block passages or seal offareas.
The tree also uses suberin as a passive defense, like an
overcoat. That's because prevention remains the best way for
a tree to defend itself from infection or injury. So the
tree surrounds itself with the protective polyester suberin.
People may know polyesters as a clothing fiber. But trees
produce them to stem the tide of invading pests and decay.
Suberin is one of the most effective barrier or wall
materials in a tree. You can see it every day as bark.
Bark is composed of many things. It includes a large portion
of suberin to shield and protect the living portions of the
tree. Unfortunately, unthinking or unknowing humans can
easily damage these bark overcoats.
Don't be one of those careless humans. Support your local
trees and their important, polyester overcoats.