As autumn approaches I am sure you are all dying to know the science behind why leaves change colour. You have to imagine leaves as mighty food factories providing sustenance to the rest of the tree. A highly important ‘cog’ in this food factory is chlorophyll, which is green.
Trees, like us, are very clever and they know when summer has ended because the days become shorter. They use sunlight to make food and during winter there isn’t enough light available. The trees begin to shut down and so they stop producing chlorophyll. This allows for the other colours in the leaves to finally show through. Yellows, oranges and browns are the colours created by carotenoids, a pigment which is always in the leaves but is hidden beneath the chlorophyll.
So where do red leaves come from? Warm, sunny autumn days and cool (not frosty) nights are the best. During the day the leaves produce sugars but the cool evenings stop the sugars from being transported to the tree trunk and roots. Rather then wasting this sugar when the leaves drop off, the leaves produce anthocyanins. These allow the plants to hold onto the leaves longer and recover the nutrients from the leaves. Anthocyanins give the leaves their bright red, purple and crimson colours.
The best autumn colours come from: a warm, wet spring, a summer that’s not too hot or dry and an autumn with warm sunny days and cool nights. So far so good, I think we’re in for a very good autumn. The Falls of Clyde looks amazing at this time of year, I urge you all to come along in the next few weeks to witness it for yourselves. You won’t be disappointed!
Laura Preston – Scottish Wildlife Trust, Falls of Clyde Ranger