Why do the leaves change colour?

There are three kinds of pigment in a usually green leaf: carotenes which are yellow, red and pink anthocyanins, and chlorophyll, which is the green that masks the other colours until autumn.

.o.

.o.

When the days get shorter and there is less daylight, the leaf stops making chlorophyll. The chlorophyll that is already in the leaf breaks down and disappears, the greens fade and the yellow, red and pink colours show through.

The shorter days and falling temperatures trigger the formation of a corky layer of cells between the leak stalk and the twig it grows on. This blocks the transfer of sugars from the leaf to the tree; the trapped sugars in the leaf break down and form more red-coloured anthocyanins so that as the autumn progresses leaves become increasingly orange, red and purple. The layer of corky cells becomes fragile as the chemistry of the leaf changes and eventually the leaf is blown from the tree or falls under its own weight.

.o.

.o.

There are advantages for a tree that sheds its leaves. Winter in temperate zones is a time of wind and storms: trees are safer without leaves. The Great Storm of 1987, which felled an estimated fifteen million trees in the UK, happened in mid-October, before the leaves had fallen.

Autumn is brief and beautiful; walk in the park and enjoy its colours.

.o.

Autumn leaves by DKGPictures by DKG

More trees:

Acorn

Autumn Leaves by DKG

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

Create a website or blog at WordPress.com

Up ↑

%d bloggers like this: