1/3/2024 0 Comments Autumn leaf redIt's from this premise that scientists figured out what might be going on. Some scientists have even suggested that the red colors ward off pests that would munch on the leaves if they were a more appetizing-looking yellow. They also act as an antifreeze, preventing leaf cells from freezing easily in the autumn chill. These red pigments act as sunscreen for the trees by blocking out harmful radiation and preventing overexposure to light. The red color comes from anthocyanins, which unlike carotenoids are produced only in the fall. While this process has long been known to scientists, the mechanism that results in red hues has proved trickier to understand, particularly because of the energy the tree must use to produce them at a time when the leaves are about to die anyway. These pigments were always present in the background of the leaves' color, but can finally shine through as the green diminishes. As the green fades, yellow and orange pigments called carotenoids (also responsible for the orange color of carrots) take over. The contributing factors are still not well understood.When the weather begins to turn cool in the fall, chlorophyll, which is sensitive to the cold, stops being produced. It is therefore difficult to predict how the timing of leaf discolouration will evolve in the future with climate change. At low altitudes in Switzerland, beech trees are now changing colour almost five days later than they did in 1951, whereas in the mountains the discolouration is starting a few days earlier. The temperature increase that has occurred since the beginning of phenological observations in 1951 has varying impacts on leaf discolouration. In addition, the trees' level of productivity during the growing season also seems to play a role: The faster and stronger the trees grow in spring and summer, the earlier leaf discolouration occurs. A very warm, dry late spring and early summer can also bring leaf discolouration forward. A cool September usually leads to early leaf discolouration. Delayed leaf discolouration occurs when the months of August and September are very warm. Temperature and dryness also play a role in this process. When the days become shorter, this triggers the breakdown of chlorophyll and consequently the emergence of the yellow and red pigments. The timing of leaf discolouration is influenced by several factors, not all of which are precisely understood. What factors influence the timing of leaf discolouration? However, the intense reds do appear here on ornamental shrubs like the guelder rose, red dogwood and many others. Reds are not as common on Switzerland's trees as they are, for example, in the oak and maple forests of the USA and Canada, famed for their spectacular displays of autumn colour. Beech trees display yellow, orange and brown-red hues. For example, larch, birch, lime and maple glow golden yellow. The next strong gust of wind causes the leaves to fall to the ground, where they continue to decompose.Įach tree species has its own characteristic autumn hues. The brown colour only appears as the leaves begin to die.Ī cork-like tissue forms between the leaf and the twig in autumn. The red pigment (anthocyanin) is produced in the leaves in autumn to protect the dormancy processes from overly intense sunlight. Although these are also broken down in the autumn, this does not happen as quickly as with chlorophyll. Where do the autumn leaf colours come from?Īfter the green colour has disappeared from the leaves, colour pigments emerge that were hidden by the chlorophyll in spring and summer. The shorter days and cooler temperatures trigger an ageing process in the leaves whereby nutrients and chlorophyll – the green pigment responsible for photosynthesis in leaves – are broken down into their chemical components and stored in the trunk, branches, and roots. Foliage discolouration is a sign that the trees are preparing for the cold season.
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