It’s tree hibernation time! Like many of you, my favourite thing about autumn is the colour change that we see in our woodlands

But do you know why leaves go yellow and orange? Or why deciduous trees lose their leaves in autumn?

(1/10)

(2/10) It’s a process so normal, so routine, that we rarely think twice about it. The woodland floor becomes a damp, earthy carpet of fiery orange and lemony yellow. It might seem like a passive process, but losing their leaves is actually a very deliberate act by these trees

(3/10) It basically comes down to food and water. The leaf is a food factory: it takes that delicious sunlight and uses a pigment called chlorophyll (the stuff that makes leaves green) to turn it into sugars, or plant food

(4/10) To do this, a leaf needs lots of water (among other things) which gets sucked up from the soil and transported all the way up to the leaves at the top via an internal plumbing system

(5/10) In the winter, when it’s colder, the water being transported around a tree like an oak or a maple is likely to freeze This would not only prevent water reaching the leaves, but ice crystals would form inside them too, causing irreparable damage

(6/10) Now trees are actually really clever They can detect that temperatures are dropping. They can detect that the days start getting shorter. They know winter’s on its way and so they initiate their leaf recycling systems before those damaging icy temperatures arrive

(7/10) In order to avoid losing all the energy and nutrients they’ve put into the leaves, trees recycle those nutrients, moving them down to the stem & roots. Here they’re stored safely until spring when they can be used to make new leaves.

(8/10) The most valuable bits are in the chlorophyll, so that’s the first thing to go (hence they lose their green-ness). The yellows & oranges you see are other pigments in the leaf called carotenoids Then they get recycled too & the leaf goes brown

(9/10) Once the tree has extracted everything it can recycle it ditches the rest and the leaf drops to the ground. The biodegradable brown leaf shell is essentially cheap to produce: the internal chemistry is much more expensive

(10/10) So just like hedgehogs go into hibernation during the winter , so too deciduous trees have a big old snooze until it’s warm enough for them get the water going again to make new leaves and more food