October 2003
The colours of autumn |
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| The colours of autumn |
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Nottinghamshire's trees are turning
a paler shade of green - even red.
Weather presenter Sarah-Leigh Barnett tells us why. |
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Why do the leaves change colour?
Deciduous trees make their own food through a process called photosynthesis.
In order to do this they need a chemical in their leaves, this chemical,
chlorophyll, is green. The green of the chlorophyll gives the leaves
their green colour.
In the winter, there isn't much sunlight to make food. But more importantly,
any liquid in the stems and leaves will freeze solid in cold weather.
Since the tree can’t rely on the leaves
during winter, it gets rid of them by sealing the leaf stem off from
the branch.
This encourages the leaves to fall, but before they do they lose their
green colour because they cannot get their supply of chlorophyll.
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| The colours of autumn |
New chemicals form in some leaves giving them their
distinctive red and orange colours.
As the stem cells die the stem becomes weaker and cannot bear the
weight of the leaf. The now colourful leaves are only supported by
tiny veins that can easily be broken when a gust of wind blows.
Once the leaves have fallen to the ground the chemicals held within
the leaves begin to disintegrate and the colours fade. The only chemical
left within the leaves eventually turns them brown.
Since the process of sealing off the leaf
stem from the branch is fairly synchronised throughout a tree, a once
bright and colourful autumnal tree can be reduced to bare branches
with just one prolonged period of wind.
As October moves in to November, the process of sealing off leaf stems
from branches is more widespread amongst the variety of deciduous
trees, so that the deep rich oranges and reds associated with autumn
can quickly be replaced by the bare branches associated with winter.
Autumn downfall
Once the leaves have fallen, and the colours
have faded we’re often left with some problems. Not only do gardeners
have the task of sweeping up the leaves only to have eager children
jump in the piles and disperse them all again, but we also suffer
from what is euphemistically known as, ‘Leaves on the Line’
syndrome.
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| The colours of autumn |
Each year Autumn brings its major challenge to the
rail infrastructure with the problem the press have labelled, 'Leaves
on the Line.'
Fallen leaves that lie on the side of the track are picked up in the
vortices of passing trains and then trapped and crushed between the
wheels and rail. The result, after several trains have passed, is
a thick, black, stubborn layer of contamination coating the rail running
surface. In the past this has been associated with delays and problems
on the rail networks.
One Nottingham resident is fighting to save
the trees that border his garden and that of the railway line. However,
because of the problems caused by leaves on the line it is highly
likely that the trees will face the chop.
This time next year, we’ll be able to see how the trams fare
with ‘leaves on the line’, but let’s hope not too many
trees will have to go. |
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