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 other active.

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 them apart.

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 rampantly consuming 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 correct dose.

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 off areas.

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.