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ONE OF THE initial fascinations
with bonsai is that of their age. But just how important is the
true age of a bonsai, and can true age be simulated? This article
is in two parts:
Part one: Natural
aging in trees
Part two: Simulation
of age in bonsai - including the "sphagnum
wrap" technique
PART
ONE - Natural aging of trees
Trees don't age in the
same "linear" way as animals. Animals transmute from
infancy to senility in a strict chronological progression. Their
physiological age - as marked by factors such as body shape,
skin texture, hair colour etc. - and their "reproductive"
age are precisely controlled by their chronological age. Animals
have, in a sense, only one growth phase - from birth to natural
death.
Trees, on the other hand, have
separate chronological, physiological and what Dr Peter Tredici
of Harvard University's Arnold Arboretum refers to as "ontogenetic"
aging processes. The three phases of maturity develop independently,
and at different rates in each individual tree, and even at different
rates on different parts of the same tree.
For example, the chronologically
oldest part of any plant is the cotyledal node, the section below
where the first two "seed leaves" were borne. Ironically,
this is also always and permanently the most juvenile part.
Conversely, if we take as an
example a hawthorn which flowers regularly, the flowering spurs
are the newest (chronologically youngest) parts of the tree,
but they are ontogenetically the oldest or most mature. As an
array of twigs begins to flower, they transmute from ontogenetic
juvenility to ontogenetic maturity. There will no longer be the
annual flush of extension growth unless the mature sections are
cut back to the juvenile buds at the base of the twigs. At the
top of the same tree, however, there may well be areas where
annual extension still occurs. In these juvenile areas there
will be no flowers.
With some species the growth
pattern is an indication of maturity - but not necessarily of
age. Larch, cedar and ginkgo all have two types of shoot growth:
vigorous extension shoots and short "rosettes" of foliage
borne on spurs which only extend by a millimetre or less each
year. Young seedlings have almost all extension growth, a sapling
will have many rosettes but still produces vigorous annual extensions.
An old tree will bear almost entirely spur growth.
PART
TWO - Simulation of age in bonsai
Some of the most common questions asked by the public at any
bonsai exhibition or nursery are, "How old is that tree?"
or, worse still "How old are some of these trees?"
After the umpteenth time, it's difficult not to become a little
irritated. John Yoshio Naka once came out with the perfect reply:
"But sir, you never ask a beautiful woman her age...."
This encapsulates the significance
of age in bonsai - at least as far as aesthetics are concerned.
It is how old a bonsai looks that is more important than old
it actually is. If the design is intended to represent a 500
year-old pine, then the bonsai should have all the characteristics
of a 500 year-old pine: fractured bark; fine, tight foliage;
open branches with angular bends; and, of course, a domed (rather
than pointed) crown.
Of course it helps a great deal
if you can start with a plant that already has some or all of
these characteristics. Old yamadori provide the quickest route,
but they can have their drawbacks. As often as not, it is necessary
to do heavy cutting and carving to reduce the size and to disguise
the removal of heavy branches. This is extremely difficult to
do convincingly, and once done badly, can never be rectified.
Additionally, the new branches that are grown and trained by
the artist are inevitably more juvenile in character, so the
problem is still not entirely solved.
There are some techniques which
can be used to increase the apparent age of a bonsai - some taking
more time than others to have an effect. None of them are quick-fire
solutions.
However, when we talk of the
appearance of age in bonsai terms, we are generally referring
the apparent evidence of physiological aging. These can be distilled
to five characteristics:
1. A domed crown
2. The poise of the branches
3. Angular branch ramification
4. Distinct, separated foliage
'clouds'
5. Mature bark texture
.........how
bark is formed
.........adding character
to bark
The first four are relatively
easy to impose with wiring and pruning, so they don't need to
be discussed in great depth here, but a few words may prove useful.
Then I will deal with bark texture in greater depth.
The Crown
To create a domed crown, it's necessary to forget the concept
of "wiring in a new leader". This is only done while
the trunk is being developed. Once that is finished all thoughts
of a leader are abandoned. The apex should then be thought of
as a central, apical branch. It should be constructed in precisely
the same way as any other branch, with one difference - the limb
that supports the apical branch structure approaches from below
rather than from one side.
Branch
Poise
Although the principles of branch positioning are straight forward,
it is something that is often compromised during the initial
design stages in the rush for a finished image. Old conifer branches
sweep downward and old broadleaved branches are more or less
horizontal - at least in the simplified world of bonsai. In neither
case will arching branches convey the impression of age. All
too often this realisation comes years after the branches have
set and have become too thick to change. The best advice is to
get the branches right at the outset.
Ramification
There's fine ramification and there's fine ramification. A broom
style bonsai may have millions of tightly-packed minute shoots.
It will look well-developed, mature, but never ancient. It simply
isn't that kind of image. So ramification alone doesn't achieve
the appearance of age, but HOW the branches ramify does. Sharp
angles, switch-backs, dramatic taper, are all indications of
age. The absence of thin laterals growing from the inner portion
of the main limbs, short distances between bends and forks, and
restricting short foliage-bearing shoots to the periferal areas
also contribute. Old trees do not have long central branches
with alternate laterals forming a triangular framework, any more
than they have pointed apices. Such branches are fine for the
initial stages of building a bonsai but they should be cut back
at the earliest opportunity. These are all points to consider,
not just during the initial shaping, but every time you prune
or wire. Regardless of the age or developmental stage of the
tree, there will always be opportunities for improvement.
Foliage
Clouds
As time passes and ramification increases, the foliage on a mature
bonsai can become one solid mass if not properly attended to.
A solid green "blob" typifies a shrub or, at best,
a young tree - no matter how the trunk and branches are formed.
In general, as a tree reaches old age, the foliage masses become
more sparse and more isolated from each other. Each individual
"cloud" also becomes more fragmented, appearing to
consist of many smaller clouds. Spend some time studying some
of your more established and well-developed bonsai, and consider
whether removing one or two branches, or thinning out the clouds
to fragment them a little might not improve the image and add
apparent age. You'll be surprised at what you discover.
Bark texture
Mature textured bark is arguably the most precious feature of
almost any bonsai. With immature bark, few bonsai can appear
mature. The exceptions are species such as many acers. taxus,
fagus etc., where the bark remains smooth throughout the tree's
life. But most species produce a characteristic mature bark as
they mature, usually adopting a fissured or plated texture. Others,
such as pseudocydonia and platanus have bark which flakes in
patches to reveal many subtle shades of pink, green and buff.
Betula and many prunus species allow their bark to peel in colourful
layers.
How
bark is formed
New layers of bark are formed annually in much the same way as
the annual rings are formed beneath them. The single-cell thick
cambium layer produces new wood on the inside (the xylem) to
conduct water and nutrients to the leaves, and new tissue on
the outside (the phloem) to conduct sugars from the leaves to
the rest of the tree. As each new layer of phloem is formed,
the outermost dies and becomes bark.
The reasons why mature bark differs
between species is complex, and not yet fully understood. But
in bonsai terms, we're more concerned with discovering how to
accelerate its development.
Speed of growth is not the controlling
factor. If a tree grows very rapidly, it can reach a considerable
size and age but not display mature bark. The dying phloem remains
elastic, and the 'stretching' process associated with rapid trunk
expansion retards the development of bark texture. There are
two main influences on early bark maturation, one internal and
one external.
Internally, it is the amount
of phloem laid down annually in comparison with the trunk expansion
that determines how quickly the bark will mature. A slowly expanding
trunk, but with a heavy annual deposit of phloem, will produce
more bark. The bark becomes thick because it is not being stretched.
The amount of phloem produced is governed by the amount of foliage,
so a tree whose growth is retarded by external forces, but which
bears copious amounts of foliage will produce mature bark rapidly.
We can use this knowledge when
we grow material in open ground. Allowing unfettered extension
to thicken the trunk is only half the story. Once the trunk has
more or less reached the desired thickness, let it stay in the
ground a few more years. Build up as much weight of foliage as
possible without allowing long, vigorous leaders to grow. When
you finally pot up, you'll have material that has mature bark
character that would take decades to develop in a pot.
Adding
character to bark
Externally, the immediate environment around a trunk seems to
have an effect on the bark. With the exception of Betula, which
are colonisers of open ground and develop silver bark when grown
with their trunks exposed to full sun, most trees develop mature
bark quicker when their trunks are surrounded by vegetation.
The constantly moist ambient, where the bark is protected from
the scarifying effects of the elements, can dramatically accelerate
the process - and more so when trunk expansion is slow, as it
is likely to be when the tree is competing with the surrounding
vegetation for nutrients.
We can simulate
these conditions on a bonsai of any age or size to improve the
bark texture by following the three steps of the "Sphagnum
Wrap" technique:
ONE: With a piece of coarse abrasive paper,
very gently stroke the trunk in a vertical direction once or
twice to penetrate the outermost "skin". Don't go as
deep as the cambium, and remember that you're not trying to remove
the skin, just to score it in a few places. Go as high on the
trunk as you can and, if possible, include any heavy lower branches.
TWO: Take some moist sphagnum moss (or any
other dead, water retaining vegetable matter) and pack 20mm layer
LOOSELY around the scored area. Hold the moss in place with twine,
wire or open mesh of some sort, making sure it's not compacted
at all.
THREE: Keep the moss wet at all times, even
if this means placing the tree in the shade and heaping extra
moss around the trunk in dry weather. Inspect the trunk every
month or so to make sure you're not inadvertently layering the
trunk! If you see roots forming, break them off and remove the
moss for a couple of days, replacing it as soon as the bark appears
dry.
This procedure prevents the normal
drying and erosion of the outer "onion-skin" layers
and allows moisture to soak into and expand the still porous
spent phloem. The time required for fissures to appear will depend
on the thickness of the existing bark itself and the amount of
new phloem produced during the process, but be prepared to keep
the "sphagnum-wrap" in place for up to two years, possibly
longer. Allow the tree to bear as much foliage as possible to
maximise the phloem production. Balancing this need with the
need to maintain shape can be tricky, but even if you have to
spend a year or two re-refining the branches, the improvement
that mature bark will bring to your tree will be well worth the
wait.
(See the shohin hawthorn (Crataegus
monogyna), whose trunk is photogtraphed on the right, in
the shohin section of my Gallery.
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