Why do leaves change colour in autumn??

Why do leaves change colour in autumn??
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Autumn is characterized by the slow, beautiful change of colour of nature -green, vibrant reds, oranges, yellows, and purples. In another way, we can say it is a purposeful change of trees for their survival in adverse conditions. Here are the Pigments which are responsible for the colour-

  • Chlorophyll (greens)
  • Xanthophylls (yellows)
  • Carotenoids (oranges)
  • Anthocyanins (red and purple)

Stage 1: Green

Leaf colour comes from pigments that are natural substances produced by leaf cells. Chlorophyll pigment, which is green in colour, is the most important pigment, which is key to photosynthesis (the food-making process). In autumn as days get shorter, the temperature decreases, there is less sunlight, and as a result, less chlorophyll is produced in the leaves. Slowly, the green colour of the tree vanishes.

Stage 2:  Turning Yellow

Less sunlight triggers chlorophyll to break down, revealing the new, colourful pigments underneath and treating us to beautiful autumn yellows and oranges. The yellows and oranges which were previously masked by chlorophyll are called xanthophylls and carotenoids. These pigments are present year-round in the leaves but are usually hidden due to the presence of green chlorophyll. The leaves become a bright rainbow of glowing yellows and sparkling oranges that give a forest a jewel-like appearance in autumn.

Stage 3: Fiery reds

In some species and in certain special years, a vibrant red colour is also seen. This is due to the presence of anthocyanins. These reds are produced in years when lots of sunlight and dry weather have increased the concentration of sugar in tree sap, triggering the tree to release anthocyanins in an attempt to grab the remaining energy from its leaves, powering it up to get through the winter. Interestingly very cold weather, acidic soils, and other stress factors occasionally trigger higher levels of anthocyanins to be produced. The cool night temperatures prevent the sugar sap from flowing through the leaf veins, and down into the branches and trunk. Anthocyanins are produced as a form of protection. They allow the plant to recover nutrients in the leaves before they fall off.

Stage 4: The fall

At the end of this colourful process, leaves die. Trees shed their dead leaves because they are no longer able to get energy from them through winter. By shedding their leaves, trees can survive because they make room for new growth in the spring.


Trees are great at recycling! Fallen leaves contribute to the health of the forest after they fall, through decomposition. Though they have been released by the tree, some carbohydrates and sugars remain in the leaves. On the forest floor, these carbohydrates and sugars give nutrition for ‘feeders’ to flourish. Once fungi and bacteria have begun to break down the leaves, insects get in on the dinner party too. Once the leaves are broken down, they provide a source of fiber which helps the soil retain moisture and improve drainage.

Weather Affects Colour Intensity

Temperature, light, and water supply have an influence on the degree and the duration of fall colour. Low temperatures above freezing will favor anthocyanin formation producing bright reds in maples. However, early frost will weaken the brilliant red colour. Rainy and/or overcast days tend to increase the intensity of fall colours. The best time to enjoy the autumn colour would be on a clear, dry, and cool (not freezing) day.

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