Golden season: Why do trees lose their leaves in autumn?

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Everyone who sets out on foot or by bike today needs to be careful. There are leaves everywhere on the streets and the leaves are extremely slippery.

Why do they change color? Colorful leaves in autumn?

Each type of tree or shrub has its own internal clock. Individual species such as beech, mountain ash or horse chestnut begin to change leaf color in early autumn. Since September is now drier than normal, color change in the leaves begins earlier, especially at higher altitudes.

Why do trees lose their leaves in autumn?

Thanks to green leafy vegetables, trees get the glucose they need. Due to photosynthesis, carbon dioxide in the air and water is converted into nutrients. As the leaves change color, the trees are preparing for winter.

Shorter days and lower temperatures trigger the aging process in the leaves. The nutrients in the leaves are broken down. Chlorophyll, the green pigment responsible for photosynthesis, is broken down into building blocks and stored in the branches, roots and trunk.

When the green color disappears, other color pigments appear in the leaves, previously covered by chlorophyll: yellow, red and finally brown when they die. The process also involves the formation of a cork-like dividing tissue between the leaf and the branch. The next time there is a strong wind the leaf falls from the tree.

Conifers stay green

Conifers maintain their green color all year round. They generally need less water and their needles are also coated with a thin layer of wax so less water evaporates.

Three more facts about autumn leaves

1. 1500 tons of leaves in cities: Approximately two-thirds of our forests are coniferous trees and one-third are deciduous trees. It is unknown how many autumn leaves there are in total in Switzerland. However, around 1,500 tonnes accumulate each year in the cities of Bern and Zurich.
2. Color change 30 days earlier than normal: Dry summer and autumn have consequences: MeteoSwiss found that linden leaves change color on average a month earlier. Beech and horse chestnut trees also had a 21 to 25 day head start last year.
3. 4 trees herald autumn: Autumn is the time when horse chestnut, oak, ash and copper beech change their leaves. This happens when they lack chlorophyll, the green leaf. What remains are yellowish or reddish pigments. Then the trees cut off the water supply from the branches to the leaf stems and the leaves fall.

Source : Blick