The bark of a tree in bonsai is one of the most appreciated features. However, it is usually overlook its importance and it is one of the key elements that is dependent on time. As such is one that we cannot change easily and that requires the essence of time for it to develop.
Experience bonsai artist will immediately recognize between a tree that has been develop over the past few years as compare to one that has over 20, 30 or more years in pot development. This is simple because of the bark develop in the trunk, branches and exposed roots. The bark tells the story of how the tree has grown. Quick growth usually creates a thicker trunk, but the outer bark that we commonly call bark does not have the character of age. For this to occur, the trees have to slow down so the layers of dead cells accumulate and bind tighter to form an ancient look typical of the species of tree in question.
Part of the reason why bark is so appreciated among bonsai artist and collectors is because it provides the essence of WABI (The type of beauty given by a particular type of imperfection) and SABI (The type of beauty that only comes with age). Because of its important, many species and cultivars of different type of threes and scrubs have been selected for outperforming others in the time of bark formation. In Japan many cultivars like Black pine, maples etc may have the variety “arakawa” That we translate into rough bark, although “ara” really means “defect, flaw, blemish” however, in this case the “defects or flaw” are what is appreciated!
Over time we tend to observed that different species of trees when they mature form different types of barks depending on the species. They can be classified into : Ring bark, Scaly bark, Fissured bark, Smooth bark, Peeling bark, Green stems, Corky wings, Bark armature. No one can be said that is better than the other, Some trees with smooth bark do show a lot of character, as particular pigments do make some of this type of barks quite feminine in nature and attractive. Other Rougher barks may create twist and turns of age’s passes, while others with thorn like structures will warrant respect. With regard to its biological importance, the bark serves two very important functions.
The outer, mostly dead tissues (outer bark) form a protective barrier between the living cells and the abiotic and biotic environment. The inner tissue (secondary phloem), including living cells (inner bark), is where sugar transport for the plant occurs, and the inner bark also can have defenses against herbivores, such as cells with tough cell walls or cells filled with bitter or toxic chemicals. Some like the Quinine, found in the bark of the South American cinchona tree, has been used for many years to treat malaria, and others may hold the key for certain types of cancer as the bark of the pacific yew. They types of tissues from the outside to the deeper portion of the tree involve 1 Cork (2) Cork cambium (3) Phelloderm (4) Cortex (5) Phloem (6) Cambium (7) Xylem.
In young stems, which lack what is commonly called bark, the tissues are: epidermis, periderm, cortex, primary phloem, secoundary phloem, vascular cambium and then xylem. It is dependent on the type of species what number and organization of specific cells in the cork cambium, phelloderm and cortex it has for it to produce the different types of patterns seen in the bark. Some will produce chemicals that will allow a greater adherence and therefore create a thicker bark than others. Their organization may create different patterns that together with the flow of nutrients changing the growth pattern in different sections of the outer layer increase the effects of the patterns seen in the bark . It should be highlighted that the bark not only develops in the trunk but also in the branches and exposed roots. These are the real indicators that the branches are not newly develop and that the tree has acquired the age, maturity and respect.