The Science of Autumn Colours

I’ve been watching the trees change colour over recent weeks. They are probably at their best around now. I always hope they’ll stay around for a long time, but invariably we get gales and the trees go bare overnight. Some of them that are growing in exposed spots have already lost almost all their leaves.

Others are still green.

Of those that have changed, I love the range of colours, from the buttery yellow of this willow…

…to the deep orange-red of this ornamental rowan (complete with bright yellow berries).

Some of the Acer (maple) family are the stars of autumn. This one positively glows!

Have you ever considered the science of this spectacle? The leaves are key to everything the tree does. In spring and summer, they are full of the green pigment, chlorophyll. This enables the tree to use energy from sunlight to convert the carbon in carbon dioxide to sugars (by the process of photosynthesis) The sugars fuel growth, flowering and seed production: everything else the tree does. Like a factory needs down time for maintenance and replacement of worn out parts, the tree’s leaves reach the end of their life in autumn. It is the breakdown of the green chlorophyll pigment that gives rise to the yellows, oranges and reds of autumn leaves.

Shorter day length stimulates the tree to produce a layer of weak cells at her base of each leaf stalk. This is called the abscission layer and causes the leaves to detach easily and fall.

The trees will now remain dormant during winter until fresh green leaves emerge in spring, ready to go into full production. Nature is pretty amazing!.

Having been out and about looking for autumn leaf colour, I forgot this in our own garden. It’s a little Japanese maple we’ve had for years that always looks stunning at this time of year.

How are the trees looking where you are?