Protective Layers of Bark

The bark on trees has two layers: an outer layer of dead wood and an inner layer of living tissues. The inner layer is made up of living cells that are continually dividing. The inner cells need water to live. They take in water through pores and lenticels. When the cells are deprived of water, they die and become part of the outer dead layer, which serves as an effective barrier against injuries and environmental stresses. Since this layer consists of dead cells, it can no longer grow. It cracks or breaks away as the inner cells continue to grow and push the older cells outward.

You have certainly noticed that the bark on different species varies considerably. It can be sticky because resin or sap is secreted by the tree. The bark on fir trees, for instance, is covered with balls of resin that can be easily pierced with a fingernail. This represents a very useful criterion for identifying fir trees.

To identify a tree by its bark, you have to observe the texture, colour and pattern of the bark.

Some trees, like the red oak have smooth bark. Others like the white ash have rough bark. Bark may be thin as in the beech, or thick, like on the white oak.

There are four major characteristics to consider in observing bark. Some bark sheds in strips or flakes. Look at the white birch; it sheds in long horizontal strips. Bark can also be scaly as on the white spruce . Bark may also have shallow or deep grooves depending on the species. The white ash has straight grooves. Bark can also be covered in cracks as in the white elm.

To practise identifying bark, try feeling different types of bark with your eyes closed. Touching is an excellent way of developing your ability to identify bark.