It's time to celebrate the awesome life-giving power of trees
AT THE TIME of writing, a dense sea fog has captured my town, after having wrapped it in a muffled embrace all night. In the park nearby, the trees stand gaunt and skeletal in the mist, their noble bones bare, waiting patiently for buds to crack open and leaves to thrust out.
Actually, I've no idea whether they are patient or not, and the sensible part of my brain says that they can't possibly feel emotion. But when they look like this, it's hard not to attribute to them some kind of deep and slow primeval animus.
In any case, it's undeniable that these wooden giants hold a massive life-force within them. Over the past weeks they have been slipping into wakefulness after their winter's slumbers. In the unseen darkness underground, tiny hairs - millions and millions of them - have been sprouting from the roots of every tree. Each hair grows from a single cell, and lives for only a month or two, when it is replaced by another (and come autumn, they all die, as the tree settles into dormancy). But this ever-changing, near-invisible fuzz of root-hairs is a vital part of the tree. Without them, it would expire. Every filament acts as a teeny pump, sucking in microscopic droplets of water from the soil, each with its tiny payload of nutrients.
When the tree is in foliage, that water is hauled upwards, ever upwards, into the highest leaves. It flows in a million gravity-defying streams, each drop connected to the next in an unbroken chain, and pulled upwards by the ensuing tension. Hydraulic valves on the undersides of the leaves, called stomata, help to regulate the flow. When they open, the flow is increased, and the leaves lose water and take in carbon dioxide, in a process called transpiration. The singular of stomata, incidentally, is "stoma", the Greek word for mouth - which might conjure up a fantastical image of a tree exhaling quietly through a billion sets of green lips.
Tree plumbing gets a lot more complicated than this, and although I would love to go into every infinitesimal detail of its sophisticated engineering, I will restrain myself. But, before I put a sock in it, let me just give my fellow anoraks another amazing fact to chew on. Different species move water at different speeds: beech, for example, takes an hour to pump water a metre up its pipes, but American red oak can shoot it along at a dizzying 28 metres per hour.
On this foggy day, when buildings, cars and other human emblems have been all but erased by the mist, only the trees have a definite presence. Their black, diagrammatic forms - like drawings in a blueprint by Gaia - make it easy to understand the sheer power they hold. And, as luck (or more likely, the county council) has placed a bench at the base of the largest one, where it is emphatically dwarfed by the woody colossus, we are supplied with a ready symbol of man's dependence on these largest of all growing things.
We all know about the tragedy of the rainforests: how their removal to make room for biofuels and animal feed releases catastrophic amounts of carbon dioxide into the atmosphere. But, equally important are the boreal forests: the tree colonies in the most northerly parts of Europe, Asia and north America. Logging for timber, pulp and paper is causing the clearfelling of great tracts of these crucial carbon sinks.
And while this may not seem like the place to bring this up, I make no apology. As gardeners, and people who are used to taking care of the earth, we should be concerned about these things. Or, if you need a reason: tomorrow is the start of National Tree Week.
The urban forest (that is, trees that grow in towns and cities) is also a doughty fighter in the war against climate change. Built-up areas are often subject to an "urban heat island effect": the temperature may be two to four degrees centigrade higher than the surrounding rural area, owing to the many ways that buildings can capture and manufacture heat.
Trees can bring down the temperature significantly: their shade cools buildings and pavements; and their leafy canopies absorb some of the sunlight (and use it for photosynthesis), and some of it they reflect back into the atmosphere. But one of their greatest feats in reducing heat is by transpiration. According to the US Environmental Protection Agency, a mature tree with a nine-metre crown can transpire around 150 litres of water a day. All that water has a wonderfully cooling effect.
The urban tree is - like its country cousin - a trapper of carbon dioxide, but it's also able to capture other noxious emissions such as pollution. Sulphur dioxide, nitrogen dioxide and carbon monoxide may all be lessened where there is tree cover. And particulate matter (the black grime that belts out of diesel engines) is caught by the foliage, and washed away when it rains. A well-placed tree can also filter the wind in winter, and reduce heating bills.
I talked earlier about trees transporting and dispensing water. Well, in order to give it out, they have to take it in. A deciduous tree in leaf (or an evergreen) can absorb 36 per cent of the rain that hits it - which means less stormwater running down the drain and into our hard- pressed sewerage system.
Did I mention that trees also prevent erosion? Indeed they do, by stabilising soil with their roots, which is especially important on river banks and hills.
All of the above means that we could be paying a little more homage to our trees. Planting them, minding them, revering them, and - why not? - hugging them.
Tree time
National Tree Week runs from March 2nd-8th with more than 300 events happening throughout the country. This year's theme is "Trees, Water, Life". See www.treecouncil.ie