The secrets behind falling autumn leaves, the muntjac deer and meet the gardener’s best friend
As summer drifts into autumn, we’re treated to a spectacular show of colour as the natural palette shifts from myriad shades of leaf green to a golden blaze of red and yellow.
This dramatic display is incredibly beautiful but it also serves an important ecological function as deciduous trees prepare for the perils of winter. By shedding their leaves they can conserve precious water, which can be in short supply when the ground is frozen, and also reduce the risk of being blown down or damaged by winter storms. Growth is halted and the trees enter a dormant state to ‘sleep’ through the worst of the wintry weather.
The reason the leaves change colour before they fall is linked to the production of chlorophyll, the green pigment that is vital for photosynthesis. Each leaf is like a miniature solar panel, using the energy from sunlight to produce the sugars that fuel new growth, and chlorophyll levels are regularly topped up throughout the spring and summer to make the most of the growing season. But as the days shorten and there is less solar energy available, chlorophyll production slows down and will eventually stop altogether. The green fades and the leaf pigments that were previously masked by chlorophyll are gradually revealed. The yellows and oranges are produced by carotene pigments, while reds, pinks and purples are created by anthocyanins.
Meanwhile, within each leaf, a wall of cells starts to form across the base of the stem. This process is triggered by a drop in temperature and a subsequent change in the tree’s hormone levels, and will eventually sever the leaf to send it drifting to the ground. But before this happens, the usual flow of sugars out of the leaf towards the trunk is blocked. With nowhere to go, the excess sugar is converted into more anthocyanin pigments, producing an even deeper red blush.
The autumnal colours are most impressive when there is a combination of low (but above freezing) temperatures, dry weather and plenty of sunshine. These conditions all serve to reduce chlorophyll levels and enhance the conversion of leftover sugars, producing more intense shades of red and a truly magnificent wildlife spectacle.