Bark is Beautiful

Article Tools

Image Gallery

Print

E-mail

Comments

RSS

But a trees bark is also influenced by outside forces unique to that particular plants lifetime: the soil in which it grows; the moisture it receives; the amount of wind and sun exposure; the overall climate; the animals, insects, fungi and other flora that feed or live upon it. So it is that, after a few years, the bark of every individual tree, though sharing basic botanic characteristics with others of its species, is as unique as a fingerprint.

More Than Skin Deep

Its remarkable diversity in texture, color and form is only half the story of barks beauty; the other half lies deeper, in its vital functions. To put it simply: no bark, no trees.

Most of us think of bark as a trees outer protective shell, covering the wood inside. Well, were right about that, but bark is far more than just a tough skin. Botanically speaking, bark consists of multiple layers of tissues that together make up the inner bark and the outer bark. Combined, the two layers of bark which in some species can reach more than 2 feet into the tree provide protection and deliver essential nutrients and life support.

In its infancy, a seedling trees stem is wrapped in a fragile outer skin, the epidermis. At its tip and the ends of its roots, the stem adds new cells and lengthens thus the seedling grows taller. Meanwhile, cells in a layer of the stems inner tissue, called the vascular cambium, divide on both sides of this tissue, producing wood cells (xylem) on the inside and a variety of cell types (phloem) toward the outside, widening the tree.

The vascular cambium produces far more new cells toward the inside than the outside, so the wood becomes thicker faster than the outer layer. If this were to continue for long, the little trees trunk would literally grow out of its skin, bursting the epidermis.

Instead, the outer tissues form a new layer of cells around the stem, just beneath the epidermis, called the cork cambium. This layer, like the vascular cambium, also generates new cells on both sides, but produces most of its new cells cork cells toward the outside. This is the trees initial layer of outer bark, which replaces the young plants thin epidermis with a tough layer of waxy, air-filled cork cells. As the outer bark thickens, the oldest cork cells die and toughen, creating a shell that insulates the tree from temperature extremes, keeps the plants inner tissues from losing water and presents an unappetizing barrier between the trees tender inner tissues and would-be insect invaders.

As the tree ages, more layers of cork cambium emerge and begin generating additional outer bark cells. Unlike the initial cork cambium, though, the new bark cells grow in arc-shaped patches or in overlapping patterns rather than in a continuous layer around the stem. So it is that each tree species, depending on the number, arrangement and growth characteristics of its cork cambia, produces the corky ridges, furrows, checks or cracks that are characteristic of its kind. The amount and nature of the outer bark cells are distinctive for each species, too. Some, such as cork oak, produce thick outer cork; in others, such as black locust, the outer bark is made up mostly of fiber cells that grow in deep fissured patterns. Trees with papery bark, such as birch, produce alternating layers of thick- and thin-walled cells; the fragile thin-cell layers peel or wear away, revealing the thicker layer below.

RSS | Comments | E-mail | Print