How old is that tree?

An early, and exact, method of ageing a tree was to fell it and then count the annual rings. Not a very satisfactory method from the point of view of the tree. Then some bright spark had the idea of using a long, thin, hand borer to take a core sample from the tree. This allowed the annual rings to be counted giving an exact age, without felling the tree. All went well until a student found what he thought was be the oldest tree in the world, a Bristlecone Pine in the Snake Mountains of Nevada. The student’s three foot long borer got stuck in the tree and he was given permission to fell the tree to retrieve his borer. At that time, it was the oldest tree in the world, at 4,900 years old!

They say “every cloud has a silver lining”. The great storms over the last few decades, especially the one in 1987, blew down tens of thousands of trees in England and France. Enthusiasts collected measurements of the girths of trees and then counted the annual rings. This exercise amounted to a database which allows the girth of a tree to be measured and a good proximity of its age given. There are three main categories in this database for many species of tree: open grown, woodland edge and woodland. There are three main categories as trees generally grow at different rates in the three situations. Even hollow trees can now be aged using this method.

In 1801, Walter Wade was the first to notice the “many very old dwarf oaks in the islands on Lough Corrib, particularly Bilberry Island.” Dwarf trees are a form of natural bonsai, with their root growth restricted. This has the effect of diminishing their growth potential. Bonsai is a word used to describe the cultivation of dwarf trees and Bonsai as a type of gardening was started by the Japanese a few centuries ago. There are many species of trees dwarfed in the hinterlands of Cong. Ash, Birch, Willow, Oak, Spindle, Mountain Ash, Beech, Sycamore, Crab Apple, to mention a few.

The only technical detail needed to roughly estimate the age of these trees is as follows. The top bud on a twig opens in the spring and a new twig emerges. When this happens the bud leaves a circular scar behind it on the twig. These scars are visible on the twig for a number of years. The distance between each scar represents one years growth. Have a look at the example of two years of growth in the photograph twig detail. The growth of a twig can vary from year to year.

It gives a better indication of growth, over time, to measure the length of the twig from the tip of the twig to the last visible scar, count the scars and you have the age of the twig you measured. Then measure the overall length of a branch/stem. Divide the total of the branch/stem measurement by the measurement of the twig and multiply by the twigs age in years. This will give you the approximate age of the branch/stem. This is easier to do in winter.

One particular Ash tree (tree 1) growing out of a grike, a shallow cleft, on a Limestone Pavement in Cong would be very easy for the casual observer to overlook. It is an excellent example of a dwarfed tree. This Ash is a mere 153cm from its base to the tip of its longest, uppermost twig. There are buds on this years’ growth only, and now that the leaves have fallen the matt black buds are clearly visible. The uppermost twigs increased by 1.5cm in length this year. A straight correlation 153cm divided by 1.5cm gives an age of around 102 years. But measuring back the twig to the last visible leaf scar, shows that the twig increased in length by 12cm in the last 9 years. 153cm divided by 12cm multiplied by 9 years gives 114 years. It would be reasonably safe to say that this tiny Ash tree is between 100 and 115 years old.

I have measured another, slightly larger, Ash tree (tree 2) that had everything which made it a serious challenge to age. It is growing out of a deep cleft in a limestone pavement, no soil visible, it is dwarfed, it has lost its leading shoot sometime in the past (giving it a bushy shape) and it is hollow. The ageing of this Ash tree was less straightforward, but using similar methods I have calculated an age range of between 130-170 years for this miniature Ash tree.

This summer I noticed a certain amount of dieback on the 100 and 115 years old Ash. A few of the taller branches had died. This may have been due to the severe winter we have just had. As the dieback did not happen to the other above tree, and as trees are self balancing systems, e.g. roots to shoots, etc, the reason for the dieback must have been one of the following:

 The diminutive branches were not hardy enough to withstand the winter weather,
 The small, restricted root system was damaged,
 The tree was self balancing.

What this means is that the trees may be older than my estimation, as there is no way to quantify dieback in previous years.