Wednesday, 12 November 2008

Adversity can promote a long life

I was raised within the sylvan embrace of the Low Weald; a well-wooded strip of country that rests on an ancient geology, now exposed with the eroding away of its covering chalk dome. To grow up among trees has left its mark on me and I always feel more comfortable in their presence. Yet, as I have mentioned before, trees have become an almost unseen backdrop to our lives. Their size and longevity, coupled with the fact that they remain rooted to one spot, seemingly makes them inconspicuous to casual observers. This also means that we tend to treat them badly, using them as architectural features – hemmed in by roads and pavements, or cutting them back indiscriminately because they block our view or shed leaves where we do not want them.

It is also fair to say that we do not, by and large, understand trees or fully comprehend our impact upon their lives. We have this conception that trees mature, become full of decay and, by doing so, reach the end of their lives. However, decay is part of the normal development of a tree and many trees will undergo retrenchment, reducing the area over which new wood has to be laid down by shedding branches and twigs, before going on for many more decades. While trees lack both an immune system and a wound repair system, they can wall off and bypass damaged tissue, effectively allowing them to redirect growth in a new direction and to balance this against incoming resources.  This whole idea that trees have a defined lifespan and die of old age is something of a myth, for most trees are felled before they even reach middle age.

How long a particular tree has left to live, our intervention excluded, has little to do with how old it is but far more to do with its size and rate of growth. The truly veteran trees of Europe are not the oaks of landscaped parkland with their spread of great branches; instead they are the small twisted forms of cypresses, growing slowly on the high slopes of Cretan mountains. For those trees that have in some way been managed by Man, it is those that have been pollarded which tend towards longer life. In both cases, it is adversity which has prolonged life, by slowing the rate of growth. Since so much of a tree’s fortune will depend upon our influence, it is we who determine how they live and when they will die. Oliver Rackham, the great woodland ecologist, summed this up just perfectly when he said that when it comes to life expectancy in trees the ‘battlefield’ is a better analogy than the ‘almshouse’.

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