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Getting to the root of a tree                                            December 2009 

GETTING TO THE ROOT OF A TREE

treesIf you ask anyone to name a key element of winter, along with colder weather a large number of people would answer – no leaves on the trees.

Certainly stark bare branches against a cold wintry sky is a very typical vision of winter and with or without leaves, trees make a huge difference to a landscape.

Some trees are now under threat; our poor elms have suffered immensely and now the beautiful horse chestnuts are suffering. But overall, trees are incredibly successful, inhabiting the widest range of land and climates and readily adapting to differing conditions.

Trees are actually the tallest free-standing organisms in the world; and they are the longest living organisms too. While in poor soils and weather, trees can be kept very small – the tiny Arctic Willow only reaches a few centimetres in height– in the right conditions trees can become giants. The tallest trees in the world are found in California where their huge coastal redwoods can grow well over 100 metres high. There is a record that an Australian eucalyptus tree reached over 114 metres and a Douglas fir in British Columbia, Canada an amazing 127 metres, but both trees have since died or lost their tops. Many flock to see the famous giant sequoia tree in California known as General Sherman which reaches over 83 metres high and is also over 24 metres around the trunk near the base, a real giant of a tree.

There are some trees that are incredibly old. Recently there were reports that the world’s oldest tree had been found in Sweden, a spruce tree that first took root at the end of the last ice age more than 9,500 years ago. Before that, pine trees in North America were considered some of the oldest at around 5000 years old. Certainly many trees live for a few hundred years.

Trees grow through photosynthesis. Their leaves absorb sunlight and carbon dioxide from the air which they convert into energy. As part of the process of photosynthesis, they also give out oxygen, a vital part of our existence.

There are basically two parts in a tree, the rigid trunk and a flexible crown of branches, twigs and leaves. It is this combination of rigidity and flexibility that plays a key role in the success of trees – they can flex under strong winds or a heavy snow fall but will never collapse under their own weight thanks to their sturdy central trunk. Tree trunks are tapered, thickest at their base and thinner towards the top, providing a solid anchor against the swaying upper branches and also helping to minimise the amount of wood needed to grow to height. Trees really are very clever!

One aspect we often don’t consider when thinking about trees is their root system, yet this is among the cleverest of all.

To begin with young trees put down tap roots which anchor the tree in the ground. Then lateral roots grow, radiating out sideways from the top of tap root and acting like the guy ropes of a tent, stopping the tap root from rotating.

As the tree grows, the tap roots become less important and the lateral roots become longer and thicker, branching out to produce a network of superficial roots that push outwards as far as the edge of the crown above them. These lateral roots take up nutrients but are not great at picking up water, especially in drought conditions when moisture is deeper down in the earth; and lateral roots aren’t very good at helping to anchor a tree either.

To counteract this, trees also develop sinker roots that grow vertically downwards from the lateral roots in by the trunk. These are usually predominant on the windward wide of the trunk to ensure maximum stability for the trunk.

In the tropics, especially in the rainforest, some trees develop huge buttress roots. These act as angle brackets, transferring forces smoothly down from the trunk to the sinker roots. It is all very clever engineering indeed.

The bark of a tree is another clever aspect; a comparatively waterproof layer which protects the tree from drying out and also gives protection against insects, pests and fungal diseases. Here in the UK because of our weather, trees do not grow all year and the seasonal growth pattern is shown by growth rings. These rings occur because in spring, a tree will lay down a lot of wide, thin-walled cells to help transport water up the stem; while later in the year narrower, thick-walled cells are generated to help strengthen the growing trunk. If you cut the trunk of a tree horizontally, you can clearly see the rings and these can give a good indication of the age of a tree.

Trees are so clever and so adaptable that it is surprising to learn than quite a number are under serious risk of disappearing. These include trees such as the Bristol Whitebeam, found in the Avon Gorge and sorbus leptophylla of which there are only 44 left in the Brecon Beacons.

The good news is that there are an increasing number of arboretum gardens around the UK, which are home to a wide variety of old and new trees. Many have active programmes to help protect rare or endangered trees and while our countryside will never be as covered with trees as it was in past centuries, nevertheless we should remain fairly confident that trees will remain a key part of our landscape for many years to come.

 


 

Nutricentre Discount for laterlife visitors If in any doubt about any of the information covered in health and nutrition related articles and it's relevance for you, consult your GP.

 

 



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