Autumn Leaves; The Science Behind The Scenery
It’s that time of year when our wonderful woodlands give us one last spectacle, with a glorious show of autumn leaves before the trees retreat into dormancy for the winter.
Did you know that the fresh vibrant green leaves that adorn our trees in summer already contain these autumn colours? Tree leaves are covered in a layer of green chlorophyll (the chemical that changes carbon dioxide and water into tree food), which camouflages the golds, reds, and yellows.
So why do leaves change colour in autumn?
As temperatures start to drop and days become shorter, leaves start to receive less sunlight. This triggers a clever reaction which causes chlorophyll to break down and stops the tree from making more. Now that the chlorophyll has gone, the trees are free to showcase their hidden colours!
There are two chemicals that contribute to this range of colours; carotenoids and xanthophylls. If these sound familiar, it’s because these pigments add colour to carrots, pumpkins, orange peppers, corn, and pink grapefruit.
Some species also have an extra stage to this seasonal transformation. Anthocyanins cause a red colour in some leaves. This is a normal stage for some species of tree, but it can also be due to a high level of sugary, energy rich tree food in the tree sap. If this is the case the tree will try it’s best to get as much of this energy as possible by releasing anthocyanins which help the tree use this energy efficiently before winter.
Where do the autumn leaves disappear to?
Once the leaves have served their purpose, the tree sheds them. They’re no longer needed the tree is dormant, so it isn’t using any energy. Plus, in spring, they’ll need to grow new ones as quickly as possible.
However, the leaves don’t go to waste! All these fallen leaves are rich in nutrients. In fact, they act as compost for trees, adding lots of goodness into the soil ready for spring growth. Bacteria, fungus, and detritivores like woodlice, slugs, millipedes, and worms eat their way through the leaves, transforming them into soil as they munch their way through winter.
Looking to see this spectacle for yourself? Why not take a autumn stroll on one of our circular walks.