Why do leaves fall in the autumn?

In Autumn, leaves demonstrate a beautiful self-protection behaviour by falling.

Shortening of days and gradual descent of temperatures activate cellular receptors, signaling to the tree that the transition of seasons is near.

Evergreen plants produce dense protective waxes and resins to prevent leaf damage, while deciduous plants lack this ability and have thinner, vulnerable leaves. Without protection, the water in leaf cells would freeze and rupture, hindering photosynthesis in winter. This would threaten the plant's overall health and well-being.

Autumn leaves fall is regulated by hormones, such as a decrease in auxin production.

These hormones activate the abscission process:

1. Chlorophyll production stops and leaves start showing yellow and red coloration

2. Vessels that carry water to the leaf and sugars from it close

3. A layer of cells starts to grow between the leaf stalk and the twig

4. Slowly these cells will cut the leaf from the tree

5. The plant enters dormancy, saving energy for the next spring

Team Let's Biologue

References

Di Silvestro, R. (2014, September 5). Why Leaves Fall from Trees in Autumn. The National Wildlife Federation Blog. https://blog.nwf.org/2014/09/why-leaves-fall-from-trees-in-autumn/

Woodland Trust. Why autumn leaves change colour. Woodland Trust. https://www.woodlandtrust.org.uk/blog/2020/10/why-autumn-leaves-change-colour/