The trees will soon be giving us the annual autumn display. What causes the leaves to change colour

A.� What happens is this. The green pigments in leaves are the result of the production of chlorophyll, the stuff that converts carbon dioxide and nutrients into food for the plant to grow, which dominates the colour of the leaf most of the year round.

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A.� It is not known for sure, but a recent study suggests they may be there for more than our pleasure.

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The researchers found that many of the trees and shrubs that are most at risk of attack by a range of pests like aphids at this time of year produce the most spectacular autumn colours. Their suggestion is that for the plant to work hard to produce these complex pigments they must serve some purpose, namely to warn off pests tempted to attack them.

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A.� Anyone who has had the chance to compare the autumn colours of our native woodlands with those of the American 'fall', which is a tourist industry all in itself, will realise that the most spectacular colours tend to come from imported trees.

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Fortunately we have been bringing these back to our shores for centuries. For red and copper hues, the nation's favourites are the maples, acers, which range from Europe to Asia, especially the Japanese varieties (Acer palmatum).

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Other excellent imports are the American oaks (Quercus rubra and coccinea), the brilliant Liquidambar which seems to hold onto its leaves long after the rest have dropped theirs, and the Rowans (Sorbus) which usually have the added bonus of brightly coloured berries as well.

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A.� If you want to see trees then where better than an arboretum

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England's most famous arboretum is Westonbirt, near Tetbury in Gloucestershire. Over 100,000 people visited last October to see its autumn offerings, which include the famous Acer Glade.

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Gloucestershire is spoilt as it also boasts Batsford arboretum, near Moreton-on-the-Marsh, which also boasts a superb collection.

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Nearer London there is Adringly, near Haywards Heath, Sussex, where trees have been planted in geographical order, and in the Midlands the arboretum at the Bluebell Nursery near Ashby de la Zouch was only planted in 1992 and gives the visitor an idea of how various trees would develop in their own gardens.

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