Why do leaves change color

Many people are transfixed by the process of leaves changing colors with the seasons and wonder just what causes this annual change to occur. Although the facts are not fully understood, there are three factors that influence autumnal leaf color, these being the leaf pigments, the length of night-time and the weather.

The timing of color-change and leaf fall are, however, mainly regulated by the increased length of nights, as the other environmental factors that influence the change are more variable. With the shorter days of Fall nights are longer and cooler, thus triggering the biomechanical processes in the leaf resulting in the changing of color.
The color change requires a palette which requires pigments. There are three different types of pigment involved in Fall colors, the first of which is chlorophyll which gives leaves their verdant green color. Chlorophyll is also required for photosynthesis, the process in which plants transform sunlight into energy and fuel carbon dioxide processing and respiration. The second are cartenoids, which result in the yellow, orange and brown colors we find in such things as bananas, carrots and daffodils. Finally we have Anthocyanins, which are soluble and give color to cranberries, cherries, strawberries and grapes.

During the growing season leaves consistently appear green as chlorophyll is constantly being produced and broken down. When Fall comes, heralding longer nights, chlorophyll production gradually slows and eventually grinds to a halt entirely. At this point the anthocyanins and cartenoids that are ever-present in the leaves are revealed, as are the colors they produce.

The actual timing of color change varies by species. Sourwood trees can become wonderfully colorful during late summer, during which time others species retain their verdant greens. This timing-related tendency may also be genetically inherited, as individual species located on the same latitude display the same colors at high altitudes in cooler temperatures as in the warmer lowlands.

Weather will also affect the variety and brilliance of the fall colors. After many warm and sunny days which ensures the production of sugars in the leaf the cooler, crisper nights result in the gradual closing of the veins traveling into the leaf which prevents the sugars from traveling out. This combination of increased sugar production and prodigious amounts of light encourage the production of the anthocyanin pigments which results in the brilliant red, purples and crimsons that abound at this time.

The levels of moisture in the soil will also affect Fall colors Either a late spring or summer drought can delay the coming of Fall by several weeks, whereas a warm and wet Spring, followed by a decent summer and Falls days abundant with warm sunshine and nights that are cool generally ensure the most wonderful and vivid Fall colors It is for this reason that many different colors can be seen in different environmental conditions, and while some changes can occur regularly in a particular style in one part of the world they may not necessarily be reproduced in exactly the same way elsewhere.