hiya bucks in Bourne End, Flackwell Heath, Marlow, Wycombe, Wooburn October 2018 | Page 14

AUTUMN COLOURS EXPLAINED
There’s something about trees. They’re solid and dependable, yet
never the same. Their changing colours are a barometer of the
seasons, inspiring us annually with fresh green shoots in spring
and a glorious red-gold autumn display. But what causes their
extraordinary transformation at this time of year?
Autumn colour in the woodland starts with the
kind of summer we have. The leaves are busy
soaking up the sunlight of the long days for
the tree to use as fuel. The green pigment (cholorophyll) absorbs the light and uses it to process
carbon dioxide from the air and water from rainfall to create oxygen and glucose. Through this
process of photosynthesis, the sugar is used as energy to grow the tree and the oxygen diffuses
into the air that we breathe.
‘After a dry summer with lots of sunshine like this
one, autumn comes early and as long as there’s no
frost, we’ll get good autumn colour that lasts,’ says
National Trust forester Tony Knight.
As the daylight hours get shorter towards autumn,
the sun is at a lower angle and the air becomes
cooler. This triggers changes in the plant chemistry
of deciduous trees. The veins that carry fluids in and
out of the leaf gradually close off, the chlorophyll
breaks down and the strong green pigments fade
away. The yellow and orange pigments, which have
been there all along, but obscured by the bright
green, are freed to flame into colour.
Some of the best trees for rich red and purple colours are maples, oaks, cherries and dogwoods.
These red and purple shades appear when glucose is trapped in the leaves when photosynthesis
stops. Under autumn sunlight and cool nights, the glucose is chemically broken down, causing
those bright crimson and plum colours. The brighter the sunlight in the autumn, the greater the
production of anthocyanin (red and purple) pigments and the more brilliant the colour display.
Different trees, even different parts of the same trees, pass through these changes at slightly
differing rates. This gives us the dynamic, shifting range of autumnal colours we enjoy each
year. Autumn can come as early as mid-September but if it stays dry, the colours can continue
well into November.
By Katy Dunn, National Trust
https://www.nationaltrust.org.uk/chilterns-countryside/lists/chilterns-countryside-walks
For more information and ideas for great seasonal days out visit: www.nationaltrust.org.uk
www.facebook.com/nationaltrust
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Autumn is when our native British trees come
into their own in the Chilterns countryside.
On a bright October day in the parkland at
Hughenden, or on the steep edge of the Thames
at Cliveden, our rolling woodlands are aflame
with colour and it’s the perfect time for a walk.