We are still on the subject of age and there is still a long way to go.To recap from the previous article, the 3 most important points to remember are :
Nebari is important for establishing age and stability.
Nebari can be worked on from the start - cuttings are a good idea.
We need to look at Nebari around us and in books so that we can develop our Bonsai skills and imagination.
The next section of our Bonsai to be discussed is the trunk, starting with the Tachiagari and extending through to the Apex. The Tachiagari is the section between the Nebari and the first branch.
This is the area that establishes movement and gives life and character to the tree. A trees movement starts at the base and the manner in which it rises from the soil and the degree of movement, i.e. dramatic or gentle, should be extended throughout the entire trunk line.
Looking back on Hiro's guidelines for an old and mature tree we know that in respect to styling, the characteristics of age can be achieved in the trunk by paying close attention to the taper of the trunk itself and to the taper of the curve lines that we shape into our designs. This article will address some of the issues concerning trunk taper and curve lines will be discussed in the next instalment.
Trunk line taper
Once again we need to look at what is growing around us and compare young trees with older mature specimens so that we can understand the different characteristics that a tree displays in its aging process. A young tree will generally have a straight trunk line emerging from the ground and it is not until the tree grows taller that natural forces start to impact on the overall shape and movement.
In its initial years of growth, a young tree is only interested in survival, height is of primary importance and provided the apex is not damaged, growth at the apex will be strong while side branch development will be a lot slower. Consequently the trunk line will be relatively straight with a limited branch structure.
It is not until a tree starts to reach a reasonable height for its type that the apical growth slows and lateral growth commences with greater intensity. As a general rule, the lower branches, being the first to have grown, will grow bigger and stronger than those emerging further up the trunk line. The branch structure will be discussed as a future subject so we won't go too far down that track for now.
However, what we do need to be aware of is that growth within the branch system is so important in developing the thickness of the trunk and more importantly the taper of the trunk line. It all gets back to the flow of sap and while we often refer to this, do we really understand it.
Water and dissolved nutrients are transported from the roots to the foliage via the xylem for the process of photosynthesis to take place. Here, sugars are manufactured and redistributed to the rest of the tree via the phloem. Some of this food is used to develop new growth and some is stored in various parts of the tree such as the trunk and the roots.
The medium used to transport the nutriments, water and sugars in a dissolved state is called sap. The greater the amount of foliage the greater the amount of food production, the more food that is produced the more the foliage can be grown and greater amounts of surplus food can be stored for future use. The increased area of foliage results in a greater loss of moisture from the leaves through transpiration. Some of the food produced in the foliage is transported to the roots.
Here it is used to grow more roots so that an increased amount of water can be transported back to the foliage to replace the water being lost via transpiration. As a consequence, more nutrients are transported to the foliage, more food is produced allowing more foliage to be developed and so the cycle continues on an ever increasing scale. In essence, the more foliage that grows on a branch the greater the volume of sap traveling to and from the branch. Therefore, if we have an increasing amount of foliage, the branches and trunk have no option but to increase in diameter in order to transport the sap. The lower branches being the oldest will generally have the most foliage and therefore require a greater volume of sap and as a consequence a thicker trunk line develops below the branch. As we travel up the tree, the sap requirement diminishes with the reducing amount of foliage and therefore the diameter of the trunk also reduces which results in taper.
The natural growth habit of trees creates taper in the trunk and we need to harness this natural process in order to improve the taper in our trees.
The most common and quickest method of increasing the trunk diameter is by using a sacrifice branch preferably in the lower third of the trunk line and at the rear of the tree so that any scaring is less visible. A sacrifice branch is allowed to grow unchecked with lots of foliage. By increasing the flow of sap between the branch and roots we are able to expand the girth on a particular section of trunk below the sacrifice branch. The more foliage there is on a branch the greater the flow of sap and the thicker the trunk needs to be to accommodate the increased flow.
Once the section of trunk has reached the desired thickness the branch is removed. We need to be careful that if the branch is allowed to grow too thick then often the line of taper can be spoilt with the trunk bulging at the point where the branch emerges.
Using a sacrifice branch is a quick fix but on a much slower scale, allowing the lower branches to grow and thinning out the top section of the tree will have the same affect and is the more preferred manner of improving taper with an established tree. The method of using the growth habits of a tree generally relates to improving the taper in the lower section of the trunk but there is often a need to improve the taper further up the trunk line. Here, increasing the flow of sap is not going to be of any use and can destroy any taper that already exists. In these instances it is often necessary to remove the top section of the trunk altogether and replace the apex with one of the side branches which should be of a smaller diameter than the section of trunk being removed. The result is instant taper and after the scar has healed you would hardly know the difference.
The use of a side branch is preferred as it will look more natural. Using a rear branch can leave a large scar in front of the tree and the line is not so good while the use of a front facing branch can leave a pigeon breasted affect on the trunk. Trees that have been established for many years may need to undergo this process every now and then just as matter of course to keep the taper of the trunk line in check and maintain the tree at a desired height.
The vast majority of trees grow more vigorously at the apex than at the base and unless this is controlled through pruning the foliage and thinning any unnecessary branches, then taper can be easily lost in the top section of our trees. A common example of this is on Chinese Elms where branch growth can be strong and when two or more branches are allowed to grow in close proximity of each other an unsightly swelling can easily develop in the trunk line.
When growing bonsai stock from cuttings or immature trees, taper can be introduced with a cut back and grow method and works best with deciduous and some evergreens. Essentially the tree is allowed to grow unchecked and then cut back to a point where the trunk line can continue to develop with the use of either a lateral branch or new shoots. The next season the trunk is cut slightly higher up at a suitable point and so on for consecutive seasons. The cut needs to be at an angle so that as it heals it will form part of the taper and curve in the trunk line. This process works best if the tree is growing in the ground using the plastic colanders and the root system left undisturbed.
There are plenty of great articles on this subject in the Bonsai Today magazines and while they generally apply to deciduous trees the technique can be used on many evergreens that respond well to heavy pruning.
During the autumn months, trees prepare for winter dormancy and this applies particularly to deciduous trees prior to leaf fall, or in the case of evergreens, the onset of winter. During this time the tree stashes away as much food as possible to get through the winter months and to ensure it has enough energy left to produce new growth in spring. The food produced is stored throughout the tree, mainly in the trunk and root system. These areas can fatten quite considerably in a short period of time and by not pruning foliage during late summer and autumn, the tree will be able to manufacture as much food as possible allowing us to take advantage of this natural fattening process that the tree undergoes.
So now we have two important points to consider when trying to improve the illusion of age in our bonsai - the Nebari and the taper of the trunk line. Taper is something that can vary from tree to tree and the different styles of growth. For example, a tall growing tree such as a Eucalypt will appear to have less taper in the trunk than say a squat Moreton Bay fig with a buttress base.
Regardless of what style the tree is growing in, taper exists in the trunk line of a mature tree and to improve the appearance of age in our bonsai we need to try to get this right.
I hope I have given you something to think about so far and as I've previously stated and will continue to state - look at the trees around you and in books so that you can see as many different styles of tree as possible. Take note of the varying degrees of taper that the different artists and more importantly, nature have used. Use what you see to help yourself imagine what you would like one of your trees to look like. That's the easy part, now work out a plan of attack to achieve it.