TRUE COLOURS

Summer may have gone but the trees are about to dazzle with an uplifting display

- Mike Dilger

OF ALL BRITAIN'S WILDLIFE spectacles, surely the hardest to miss is the fanfare of autumn colour marking both the end of summer and the long descent to winter. Providing the most fabulous fillip on any woodland walk, the precise reasons why so many of our trees undergo such a radical transformation at this time of year are still shrouded in mystery.

The woody parts of Britain's deciduous trees are more than able to survive the winter. But with light levels becoming too low to enable photosynthesis and trees needing to conserve water when the ground may be frozen, the leaves suddenly become an accessory that trees are simply unable to keep.

Photosynthesis is the process by which plants use the sun's rays to power the conversion of carbon dioxide and water  into sugars. This reaction occurs due to the presence of the pigment chlorophyll, quite possibly the world's most important compound. Chlorophyll absorbs the red and blue parts of the spectrum while reflecting green, which explains why green is the dominant colour from April to October.

Although chlorophyll is able to perform the magic trick of harnessing the sun's energy, its unstable nature means it is easily broken down, so in order to maintain a constant supply of sugars through the spring and summer months, the trees' production line of chlorophyll must be running 24 hours a day.