The mystery of the ages
By Andrew Smith

Like a beautiful woman, a fine bonsai has it's secrets. This is good, for a finer depth of knowing is reached by not knowing completely. Some mystery must remain in love, some tantalizing, unreachable truth, to keep the relationship fresh and alive.

With bonsai, one of the greatest charms is the incredible ages the trees sometimes live to. This is interesting, for age is an invisible quality. A hundred year old tree may look no different, or even worse, than a twenty year old tree. But the hundred year old tree brings with it the ghosts of another time. It is a continuation of another age. It is worthy, merely because it has survived so long. We may, or may not, be able to see the scars that time has wrought upon it, but we know that they are there.

One of the first questions most people ask when they see a bonsai is, "How old is it?" Conversely, many trees are displayed with their known, or estimated ages, especially if the tree is believed to be over 100 years old. This is particularly true with wild collected trees. From what I have observed, most collectors (probably including myself) tend to overestimate the ages of their trees, sometimes grossly so. It is rare to find someone who can resist sticking a few extra decades, at least, onto the age of his or her favorite tree. Because, after all, who's counting?

And the truth is, plants live to some incredible ages. We are all aware of the legendary bristelcones and yews that sometimes live to four or five thousand years old. Creosote bushes, I am told, are sometimes believed to live for eight to ten thousand years. And in 1996, scientists in Australia found a shrub that they believe is 40,000 years old! The thing had filled up most of a small ravine. Congratulations to the gardener, for not forgetting to water.

If you ever make a trip to the mountains, or some local rocky ledge, and collect some lovely and twisted little dwarf tree, how will you ever know how old it is? Besides just coming up with a really great age that sounds good to you, how can you make an accurate age estimate for what will surely become your favorite tree?

The only way to make reasonable estimates of tree ages is to take trunk cross sections from typical specimens and count the rings. On a good collecting site it is quite common to find nearly as many dead specimens as there are live ones. I try and gather cross sections of representative dead trees, that is, trees of the same species, size and growth form of the ones I'm collecting. And, of course, anything that does not survive the transplant attempt will become another sample.

The stem is sectioned to reveal the growth rings and then polished with successively finer grades of sandpaper. I go all the way up to 600 grit. After the core is polished, a drop of mineral oil rubbed into the wood will bring out the rings. The core may then be counted using a very bright light, a 20x or 30x magnifier, and a lot of patience.

Contrary to popular belief, a ring count does not provide an exact age for your tree. Trees grown under very harsh conditions will sometimes skip a year, or more,without putting on any growth rings. In a tree that is several centuries old there can be several decades of missing growth rings. To make matters worse, trees on harsh sites sometimes put on two growth rings a year. Some species of juniper are notorious for this. In my experience however, a ring count is accurate enough to use for all but scientific purposes.

Once you have sectioned and counted several trees, you should begin to get a rough idea of the average age/size/growth form ratio of your collecting site. In the Rockies it is commonly said that ponderosa pine put on about one inch of radial growth per 100 years. So a tree with a two inch diameter base should be about 100 years old. This does not mean that all two inch ponderosas are 100 years old. What it means is that two inch ponderosas, collected from very similar dry, rocky sites, and with similar growth forms, will average about 100 years old. The important thing to remember is that growth information is very site specific. A 200 year old, three inch diameter pine at the top of the mountain gives no indication whatsoever of how old a three inch diameter pine at the bottom of the mountain will be.

Growing sites are extremely specific. Two trees of almost identical size, growing not more than six feet apart on a mountain, can vary in age by more than 100 years. One tree may be growing in a slightly larger pocket of soil, or be situated more favorably to the sun, or the flow of runoff down the mountain.
In fact, one thing I have observed is that size, by itself, is the worst indicator of tree age. If a two inch diameter pine is 100 years old, then how old is a four inch diameter pine? I'd say anywhere from 50 to 500 years would be a safe guess. Size is only important when considered in relation to the specific growing site and the physical traits of the tree. In fact, I have frequently found that the very oldest trees on a site tend to be some of the smallest. They are extreme dwarfs. Botanist Doug Larson, studying white cedars on Canada's Niagara escarpment found one four inch tall tree with the diameter of a quarter that was nearly 750 years old!

The thing to remember is that a tree is a product of its growing site. Any growing site will either enhance or retard the growth of the tree. The best potential bonsai come from sites that have severely retarded the growth of the tree, resulting in a natural, ancient, dwarf. When looking at trees in the wild, always remember that they are a product of their environment, and be aware of what effects the immediate environment is having on them.

Some of the most common factors that limit plant growth are listed below:
* Lack of water. A harsh, dry site is probably the single most common source of dwarfism. Conversely, too much water may also limit growth in certain species.
* Poor soils. This includes things like poor soil drainage, poor water retention ability, lack of organic matter, improper ph, and excessive mineral content.
* Temperature extremes. Too much daytime heat, too many cold nights.
* Lack of sun. The shade of overstory trees may tend to dwarf certain understory trees growing beneath them. This is called suppression. Some trees however, like maples and spruces, tolerate shade well.
* Short growing season/ harsh climate. Plants that grow near treeline are naturally dwarfed simply because the growing season is so short there.
* Growth beyond a plants natural range. A site that may be perfect for a western ponderosa pine, may be marginal at best for an eastern white pine. Plants at the edges of their natural range often exhibit the symptoms of dwarfism.
* Animals. Repeated browsing by deer and cattle can force a plant to assume a dwarf form.

The mountain collecting sites I visit are typically very rocky and dry, with little or no soil, constant exposure to drying winds, sun and hail, and wild extremes of temperature. Mountain goats, porcupines and falling rocks frequently scar the trees. So the trees are exposed to many severe limiting factors, including lack of water, poor soils, short growing seasons, extreme temperatures and animals.

At any collecting site you should always pay attention to which, and how many, of these growth limiting factors are in operation. If there are no limiting factors in operation, then any bonsai-sized trees you find will be quite young. This doesn't mean they can't make good bonsai though, since bonsai itself is the art of limiting and directing plant growth.

After you have established some kind of a rough age estimate for your specific site, it is time to begin looking at the trees themselves. Old trees, whether dwarfed or full size, have distinct morphological characteristics that set them apart from younger trees. Some of the traits that are indicative of great age are:
* A large girth to height ratio, the tree appears somewhat short and fat. As trees get very old, they stop growing taller, but continue to put on girth.
* A flattened crown. Because the tree is no longer growing upwards, the crown tends to take on a flattened appearance, rather than the pointy top of a young, vigorously growing tree.
* Large diameter, old branches high up on the bole of the tree. The top of the tree is the youngest part. Old, thick branches high up in the tree indicate that the whole tree is of great age.
* A noticeable twisting in the grain of the wood. This is caused by stress due to wind and dry conditions. It indicates very slow growth.
* Large old dead branches, and dead wood on the stem of the tree.
* Deeply fissured bark.
* Large, exposed roots.
* Foliage that is sparse, and frequently smaller than average for the species.

Of course, these characteristics should be familiar to any bonsai addict, since they are the very characteristics we find desirable in our trees. They're also the characteristics we need to pay attention to when we attempt to estimate tree ages.

As a counterpoint, lets look at some traits that indicate relative youth in a tree:
* A small diameter trunk, that is thin for its height.
* Vigorous, healthy foliage, including leaves or needles that may be slightly larger than normal for the species.
* Long growth internodes on the branch tips, and a lack of refinement in the branches.
* Smooth bark.
* A pointy crown, indicative of fast growth.

Now, putting together information you have collected from ring counts, what you have observed of the specific growing site, and the physical traits of the individual tree in question, you should be able to start making some pretty good guesses about the actual age of your prize.

There's one last thing. Some trees are just going to fool you. I can estimate tree ages all day and be within 10% almost all the time, but there's always that one tree that is off the chart. Either it's 50 years old and I think it's two hundred and fifty, or it's three hundred and I think it's eighty. But that's just part of the mystery of bonsai.