Between October and December, London’s trees will lose many billions of leaves, weighing thousands of tonnes. If spread out as a single layer, the leaves would cover more than two-thirds of the capital.
The trees are saving energy as temperatures cool and the light fades. They are shutting down their leaves, which act as light-powered, food-making factories, and surviving on the sugars they stored during the summer. Green chlorophyll disappears first from the leaves, revealing the characteristic tints of autumn, a golden canopy of yellows, russets and browns.
After a tree has absorbed as many nutrients as it can from its leaves, specialized cells actively snip each leaf from its parent tree, helped by gusts of wind.
The trees may have finished with their leaves, but a whole host of wildlife awaits this golden windfall. Invertebrates, fungi and bacteria feast on the fallen leaves, which rapidly decompose, creating organic matter that enriches our soil.
Meanwhile, blackbird, robin and chaffinch flick through the leaves in search of tasty worms and insects. If you have a garden, creating a simple leaf pile is an easy way to help wildlife, and as the leaves break down, your garden soil benefits from a free nutrient top-up!
The loss of leaves may also help many trees, such as birches, alders, oaks and ash, to pollinate in the spring. Without leaves to get in the way, their wind-blown pollen can travel further and reach more trees, helping to produce the next generation of London’s urban forest.
First published as our Wild London column in the Evening Standard 17th November 2017.