- Written by Nadia O'Carroll
Why and how does this phenomena occur? The leaves of deciduous trees are tender and unlike tough leaves such as pine needles, they would be vulnerable to the low temperatures of winter, so the loss of leaves is a means for the tree to shut down and avoid damage, and the autumn colours are a consequence of this strategy.
Deciduous trees are sensitive to the length of days and nights. When a threshold day/night proportion is reached, the cells at the leaf juncture divide rapidly to form a corky layer of cells that block the movement of materials between the leaf and the branch. One of the materials that require constant replenishment from the plant to the leaf is the pigment, chlorophyll. Chlorophyll is a strong green pigment that give leaves their colour, and plays a vital part in the process of photosynthesis. Chlorophyll breaks down in sunlight, and as the supply of chlorophyll is blocked, the green colour of the leaf fades. Other pigments always present in the leaves, such as yellows (xanthophylls) and oranges (carotenoids) can now be seen. Other colours are produced from the sugars that are trapped in the leaves, which may form red and purple pigments (anthocyanins) it is thought that these pigments may act as a sunscreen, repel insect pests or reduce water loss.
Some trees lose their leaves when they are quite colourful, and others retain their leaves until all the pigments in the leaves fade in the sun, and the only pigments that remain are tannins, which are brown. When the leaves fall to the ground, they decompose and form a rich layer of humus; this benefits both the individual tree and the entire forest.
Certain colours are characteristic of certain species eg maples are red and poplars are golden, but the change is also influenced by temperature, moisture, sunlight, drought, wind and soil conditions, so each autumn is different.
Here on Tamborine Mountain we have a number of exotic deciduous trees planted as street trees and in private gardens. Their colourful transformation gives us a hint of the change of seasons and represents autumn, even in our land of evergreen trees.