The Arb Academy has been recruiting again this week. Our irreplaceable Jodie Hodgkins has been tireless in organising interviews for apprentices and employers. Four of our prospective apprentices were taken on straight away by Birch Utilities on Thursday, and there are more applicants and interviews in the pipeline.
Next week, is week two of the block weeks, for our previous cohort, and they will be undertaking various chainsaw activities and assessments, and taking their ROLO test. If they haven’t read this, and it is very unlikely that they have- then it will come as a lovely surprise!
However, nothing could be further from the truth, there is an awful lot going on behind the scenes, and some very good reasons for the trees to put themselves through all this apparent hassle.
For a broadleaved tree to keep the leaves through the winter would be difficult and costly in energy terms. Losing them is actually a very clever survival strategy, and one that has served deciduous trees well for many millions of years. The vivid red, yellow and brown colours are simply what is left when all the useful stuff has been reabsorbed from the leaves, leaving only the skeleton of the leaf, and some waste products behind.
The leaves fall, and are broken down by the fungi and other microorganisms, and are then re-used by the trees to make next year’s leaves.
Deciduous trees tend to have large thin leaves generally, that continually lose water, and that water is replaced by the roots by a process known as ‘transpiration’. In winter, water sometimes freezes, and so is inaccessible for the tree, so the leaves could not be kept supplied. It’s called ‘physiological drought’- there is plenty of water around, it just isn’t in a form that the tree can use.
In addition, light levels are much lower, the Sun is lower in the sky, and the amount of light reaching the leaves is massively reduced. Leaves make the food that the tree uses to live, grow, and reproduce, but they still need energy to keep themselves going. The amount of energy used to keep the leaves alive, would not be offset by the amount of food produced by them at these reduced light levels, so it makes perfect sense to drop them, recycle them, and then put new ones out in the spring.
It also means you can ditch some annoying pests and diseases along with the leaves!
The new leaves have already been made by the tree this year, and are packed up like tiny parachutes inside the buds waiting for the cue to open. The cue varies between different trees, with some using light levels and day length as the trigger, and others temperature. That’s why trees come into leaf at different times, and sometimes earlier or later each year, the rhyme:
“Ash before Oak in for a soak, Oak before Ash in for a splash” illustrates that people understand this and at least have noticed that trees vary their habits according to variability in light and heat.
So trees may slow down a bit in the winter, but they are not in suspended animation, they are still very much alive and kicking, and monitoring what is going on in the environment around them- so much for dormant!
Although called ‘evergreens’ it doesn’t mean that they keep their leaves forever, they just tend to shed them all year round, and sometimes at particular times of year.
These adaptations, also means that conifers tend to survive in the wild at the extremes, such as altitude, or high latitude, where a lot of broadleaves couldn’t live.
Walking through the woods, along with thinking about trees and winter, it also got me thinking about Ash trees. I took this picture on Saturday afternoon. It is a relatively normal scene, one that is repeated all over Dartmoor, and the rest of Britain. However, with the advent of Ash Dieback, and its recent introduction to this country, scenes like this will disappear over the next decade or so.
Just try to imagine this scene with most of the trees taken out.
All of the main trees in the hedgerow to the left are Ash, as are the regenerating trees in the clear-felled area to the right. This picture without the Ash trees would look very different but unfortunately, that is exactly what is going to happen. It is quite sad to think that something so common, will become so rare. Plant health experts are working on a mortality rate of around 95%. A rough estimate is that there are about 12 billion Ash trees in this country, and the vast majority of them will be gone in the next few years. Whilst we can, unfortunately, do nothing to stop this happening, we do need to think about preventing other diseases coming in that affect other trees.
Imagine that picture above with not only the Ash missing, but also the Oaks, Chestnuts, Birches and Sycamores. We have to pay more attention to biosecurity, or the loss of our Elms, and now our Ash, will only be the start.