Monday, 22 January 2007

Nature notes: From Acorns grow mighty oaks

Walking the dog last autumn I also gathered a bag of acorns for Richard, our pet pig. And while gathering them I pondered why there were so many acorns. A huge oak produces vast numbers of acorns year after year (does anyone know exactly how many?), and an oak may live for several hundred years. But in the grand scheme of life, all it really needs to do is reproduce itself. So why does it have so many acorns? One possible explanation is that it prevents a disease, such as Dutch Elm which devasted the largely clonal English Elms, from wiping the entire species out. But another idea which occurred to me is that it may be a mechanism for preserving a species over longer periods of time. Perhaps time on a geological scale. Is it possible, for instance that among those millions and millions of acorns that there is one that could grow into an oak that is adapted to tropical conditions? One that is not deciduous? One that is capable of surviving arctic conditions? One that can survive waterlogged soils? This seems highly probable. This means that over a period of centuries, when climate change becomes a reality, the odd oak would survive, to start new generations. Just a thought -- and not something it would be very easy to demonstrate experimentally.

There was a bumper acorn crop last year in Suffolk, and there was also a bumper crop of blackberries, which are now withered and dry on the bramble bushes. This latter is worrying -- where were all the birds that normally would have grown fat on the crop? A stretch of hedgerow that would have had perhaps 2 or 3 pairs of whitethroats, a pair of lesser whitethroats a blackap etc etc, had but a single pair of whithtroats nesting in it, and during the migration season no noticeable influx of birds. Where are all the birds? As I write, early in 2007 it is still noticeable how few birds there are around compared with previous years. But more worrying is if I think back over the 50 years I have been watching birds, there is a huge number of species, once abundant, now rarely seen, a huge number of birding localities disappeared under concrete. And that's without taking into account of the millions and millions of hectares of habitat that have disappeared in the wintering grounds of our summer migrants. In fact it's a miracle there are any summer migrants left.

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