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Take a Walk on the Wild Side: Lincs Wildlife Trust's Rachel Shaw looks at the wonderful changing colours of autumn

In this month's column, Rachel explains the reason why the leaves on our trees change the colours they do:

Woodlands and trees are transforming; the once green leaves taking on fiery shades; bursts of red and purple berries and shiny brown acorns and nuts tempting thrushes and squirrels.

You don’t necessarily have to travel far to see this riot of colours. Trees in local parks, commons and alongside streets are all revealing their hidden colours. Inside the leaf there’s some complex chemical changes going on. The green pigment, called chlorophyll, converts sunlight into energy which is stored in the leaves as sugar. Within the leaf, red anthocyanin and yellow carotene are also present.

Oak leaves. (5111076)
Oak leaves. (5111076)

Over the summer, these colours are masked by the green chlorophyll but at the end of the summer as light levels and temperatures drop the leaves stop making chlorophyll and the red and yellow pigments are gradually revealed.

The intensity of the colours depends on the concentration of sugars in the leaves – the higher the concentration, the more vivid the colours.

The changes in weather and daylight also trigger the leaves to fall or, perhaps more appropriately, to be cut from the branch. Specialised cells form at the place where the leaf stem meets the branch. Slowly but surely, these cells push the leaf from the tree branch. This process is called abscission; from the Latin for ‘to cut’ (think of scissors).

The needle like leaves of a conifer are adapted to cope with winter. (5111078)
The needle like leaves of a conifer are adapted to cope with winter. (5111078)

The trees have shut themselves down for the winter. The shedding of leaves may also help trees to pollinate in the spring. Without leaves to get in the way, wind-blown pollen of trees such as oak and ash can travel longer distances and reach more trees.

In contrast, evergreen trees retain their green leaves through the winter. They maintain a thick, waxy coating on each needle. This waxy coating protects the leaves against cold and helps them conserve water.


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