Into the Woods with Curio: Those Red Fall Colours!

Such knowledge is too wonderful for me; It is too high, I cannot comprehend it. Psalm 139:6

Each fall the brilliant colours of the leaves have us talking about how they get these colours. It all starts with photosynthesis, of course, which is the incredible way in which the trees turn sunlight into energy through their leaves. Green chlorophyll is needed for this, and that is the predominant colour we see from ‘leaf-out’ in early spring until the late summer and early fall.

As the days get shorter, the trees start the process of losing their leaves for the winter. Tree leaves are like herbaceous plants, that is, they are not made for freezing temperatures, so the tree drops them before they are damaged by winter weather.

But before the leaves fall the tree re-absorbs the nutrients that are still left in the leaves, including the chlorophyll, taking them back down into their roots for the winter. The result is that the yellow and orange colours, which were always in the leaves but hidden by the dominant green chlorophyll, become visible. These are carotenoids, the same pigments that we see in such things as carrots and even egg yolks! If the fall weather is frosty there are more yellows and oranges, as the cold temperatures destroy the green chlorophyll in the leaves.

But what about the reds? This year the reds have been dazzling, and this is due to all the clear, sunny days we had in September, though the nights were not below freezing. The red, (and purple) colours in the leaves come from anthocyanin pigments, the same pigments found in different fruits and vegetables, including red cabbage, raspberries, blueberries, certain grapes and many others. Frosty nights weaken the red anthocyanins, so there are less reds when the fall nights are cold.

The tree produces these anthocyanins when there is too much sunlight in the fall, so it can protect the leaves during the re-absorption process. At least that is what we think is the role of anthocyanins. It may also be that the tree uses the red colours as a signal to parasitic insects that want to make the tree their home during the winter. Red indicates a higher chemical defense, so may serve as a warning to insects, similar to the bright colours of a monarch butterfly warning potential predators that it is not good to eat.

There are a number of other theories about anthocyanins in leaves, making it a little confusing, for sure. It may be that we really can’t know with 100% certainty why the trees produce these anthocyanins in the fall, though we certainly enjoy the show! God’s Creation is incredibly complex and amazing, demonstrating how worthy He is of our praise!

From the highest of heights to the depths of the sea
Creation's revealing Your majesty
From the colours of fall to the fragrance of spring
Every creature unique in the song that it sings
All exclaiming:
Indescribable, uncontainable,
You placed the stars in the sky and You know them by name.
You are amazing God.
All powerful, untameable,
Awestruck we fall to our knees as we humbly proclaim
You are amazing God.

(From ‘Indescribable’ by Chris Tomlin. CCLI Song # 4403076)