Science of Autumn Colours

The science of Autumn colours 

Have you been enjoying the autumn colours this year? The displays of red, yellow, orange and bronze lift the spirits on a walk through the wood, or a drive out in the countryside, and many people choose Autumn as their favourite season for this reason.

Rather than the change in temperature at this time of year, the process of colour change is triggered by the shortening of day length. Less daylight causes a layer of cells to develop at the base of the leaf stalk – the abcission layer – which slowly blocks the transfer of compounds like sugars or minerals from and to the leaf.
Chlorophyll, the green pigment, needs to be constantly replaced and when the leaf is blocked and no longer replenished, the chlorophyll breaks down in the light  revealing other pigments in the leaves such as yellow (xanthophylls) and orange (carotenoids). These pigments were present all through the summer but we couldn’t see them.

The red colour is due to the sugar remaining in the leaf which is used to make anthocyanins, creating the stunning red and purple colours we see in some trees.

The weather impact the vibrancy of Autumn colours

Lots of sunlight and low temperatures causes the chlorophyll to be destroyed more quickly – exposing those yellows and orange colours sooner, it also helps form the red and purple pigments.

Wind and rain causes leaves to fall before the colour is fully developed and heavy frosts will stop the production of red and purple pigments.

So for the best Autumn colours we want cool, sunny days, late frosts and not a lot of wind or rain please!

Ali

Site and Community Officer