The Biology of Bark Pt.1
The ‘bark’ of a tree, in some ways, is similar to the skin of a human. Both regenerate and both offer protection from diseases and external attacks to the living tissue underneath. ‘Bark’ is the corky waterproof layer on the outside of a tree and is really a very untechnical term to use when discussing plant anatomy.
The term bark could refer to a couple of elements of a trees makeup. Underneath what most of us think of as ‘bark’ is another layer, which is known as the Cambrian bark layer. This is the main layer against the newly growing wood, where the phloem and xylem are produced, ensuring water and nutrients can be carried up to the top of the tree, allowing photosynthesis to occur. This internal layer of ‘bark’ produces new internal cells every season, which is what causes the ‘rings’ of growth inside a tree. The outer layer of the Cambrian ‘bark’ is the outer layer of the tree, and is what we see and call ‘bark’, which basically refers to all tissues outside of the living wood, or the outside bit of the tree – the covering on the trunk, the branches and the twigs.
When looking at bark you may notice that the colour, texture, density and markings of different trees can be quite different. Often the bark of a tree changes as the tree ages and may be dependant on whether you are looking near the base of the tree or the crown. Bark may even be a different colour or texture in their juvenile years compared with their semi-mature years.
Take a birch tree, it has much smoother peeling bark when young but it becomes much thicker and corkier as it ages, with different varieties of birch behaving in different ways. Similarly, the sycamore is smooth-barked when young but produces what look like scales as they age.