♥ - Why Leaves Change Color in the Fall - ♥

.Why Leaves Change Color in the Fall

Temperature also plays a part in the ultimate vividness of the color.  However, as far as the timing goes, seems to play a very small role given that trees of the same species at very high elevations, where it is colder, will have their leaves change color at nearly the exact same time as those of the same species at lower elevations on the same latitude line.

Primarily though, as the length of day shortens, at a certain point which varies by species, some mechanism in the tree will trigger it to begin the process of closing up the veins to the leaves and eventually shedding them, lest they freeze while the veins are still open which can potentially harm the tree.

There are three main things that give leaves their color.  Those are: chlorophyll (green), which is necessary for photosynthesis; carotenoids, such as carotene and xanthophylls, which produce the orange and yellow colors, but whose roles are not entirely understood; and anthocyanins, which give us the shades of red and purple.

In the former two cases of chlorophyll and carotenoids, they are both present in the leaves during the summer, but the chlorophyll more or less covers up the carotenoids, so you see a mostly green leaf, rather than orange or yellow.  The anthocyanins, on the other hand, are primarily produced as a result of glucose that is trapped in the leaves when the veins are closed off.  These sugars then break down as a result of sunlight and produce the red and purple pigments.