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Fall Colors

The spectacle offered by Quebec’s deciduous trees in the fall is one of great beauty. Whether it’s the yellow or paper birches, the red and swamp oaks, or the red and sugar maples, all are adorned with extraordinary colors for a few weeks, just before the first snowflakes arrive.

This phenomenon, which has long puzzled and divided scientists, is now better understood.

Although considered primitive because their appearance on Earth predates that of deciduous trees, conifers have foliage that is very well adapted to cold and dryness. This is why the vast majority of conifers can retain their foliage all year round. Unlike them, deciduous trees renew their foliage every year and, each autumn, a veritable fireworks display precedes the abandonment of their fragile foliar mass.

The green color of leaves in summer is due to the presence of a particular pigment, chlorophyll. Its role is to capture sunlight and use this energy to ensure the tree’s photosynthesis. Thanks to its green color, chlorophyll reflects green sunlight and allows the absorption of red and blue radiation produced by it.

Photosynthesis is a process by which trees can perform their various vital functions. In the presence of sunlight, trees transform water and carbon dioxide from the air into sugars and oxygen through a complex chemical reaction.

The sugars thus produced allow trees to develop and ensure their growth. Obviously, the production of oxygen and water vapor associated with this reaction contributes to better air quality and the continuity of the hydrological cycle in nature.

Since chlorophyll is predominant in leaves in summer, it masks other pigments found there. At the end of summer, when the length of the day decreases, a small cork plug forms at the base of the leaf petiole, preventing the influx of water and minerals into the leaf. The level of chlorophyll present in the leaf is then increasingly low, and some other pigments previously masked by chlorophyll appear.

The 2 main pigments observed then are carotenoids and anthocyanins.

Very widespread in the plant kingdom, carotenoids are responsible for the color of carrots, daffodils, corn, bananas and egg yolks: these are therefore the pigments responsible for the yellow and orange color of birches, maples, ashes, poplars and alders. They are present all summer in the leaves.

As for the red, purple and violet colors of certain trees such as red maples, American ash and staghorn sumac, it is the anthocyanins that give them this incredible color.

Unlike carotenoids, they are only found in leaves in autumn. Some experts believe that they consist of both a means of protecting the tree by warning predators of the presence of toxic substances in the leaves, while also protecting the leaves from the sun’s insolation once chlorophyll has disappeared.

Once fallen to the ground, the leaves will renew the litter at the foot of the trees: decomposed by insects and microorganisms, they will increase the humus content and organic matter of the forest, which will have the effect of increasing the adsorption of essential nutrients for plants, allowing better water retention and improving the physical and chemical properties of the soil.