Why do autumn leaves change color and fall

As the process is gradual, individual leaves will be at different stages, so a tree will have leaves of many changing hues as autumn progresses. The trigger for autumn colour to develop is a combination of day length and night temperature. As days shorten, the amount of sugar generated by photosynthesis drops off, and hormones in the plant trigger the leaf sealing and shedding process.

This is accelerated by cold nights, but the lower temperatures also act on the compounds remaining in the leaf, breaking them down more quickly. A warm dry 'Indian summer' followed by colder nights is the best combination, keeping the leaves working later and then shortening the leaf drop process. That way, more compounds remain in the leaf and there is less time for them to slowly break down to brown before the leaves drop.

In a mild wet autumn, the whole process is much slower so leaves are often completely brown before they fall and individual trees, and even single leaves, change colour at different times, reducing the whole spectacle. The needle- or scale-like leaves remain green or greenish the year round, and individual leaves may stay on for two to four or more years.

Temperature, light, and water supply have an influence on the degree and the duration of fall color. Low temperatures above freezing will favor anthocyanin formation producing bright reds in maples. However, early frost will weaken the brilliant red color. The best time to enjoy the autumn color would be on a clear, dry, and cool not freezing day.

Apply Give Partner. Gateways for Advanced Directory. Search ESF. Once this happens, the green color starts to fade and the reds, oranges, and yellows become visible. Shorter days in the fall are a signal for trees to start preparing for winter.

Weather is also an important part of the color change. In the fall, the temperatures get colder and there is also more rain and snow.

Changes in these weather conditions can play a role in how early the leaves change and how long they keep their beautiful colors. Why might that be? It takes a lot of energy to make chlorophyll. If the plants break down the chlorophyll and move it out of their leaves before the leaves fall, plants save energy. The plants can reabsorb the molecules that make up chlorophyll. Then, when it's warm and sunny enough to grow again, the plants can use those molecules to remake the chlorophyll.

That way the plants don't have to make chlorophyll from scratch. There are other pigments in leaves called carotenoids. Carotenoids are yellow and orange. Anthocyanins are other plant pigments that are only made in the fall. These pigments cause red, pink, or purple colors.

Anthocyanins also protect leaves from being eaten or getting sun burned. So the different colors in leaves are caused by changes in the pigments. When the weather changes, some plants break down all the green pigment.