Weather
Weather WisdomWeather Wisdom - Friday, September 4, 2009By Craig Koplien (WTMJ)
Our recent cool nights have led to me think about the inevitable changing colors of the leaves. Peak color in the southern Wisconsin doesn’t usually occur until mid to late October. Still, cooler weather caused by weak sunshine and longer nights lead some leaves to change earlier.
Leaves have 2 substances in them with a pigment, or color, and sometimes a third. They are: chlorophyll which is green; carotenoid which is yellow, orange and brown; and sometimes anthocyanins, which are red. Leaves are green during the spring and summer because chlorophyll is the most abundant substance in them. There is some carotenoid present, but its colors get overwhelmed by the chlorophyll. When it turns colder, leaves respond by producing less chlorophyll. When that happens, the green color fades and the yellow, orange and browns show through. Leaves sometimes turn bright red when the tree produces anthocyanins. These are produced only in autumn, usually when there are warm, sunny days. The sunshine allows the leaves to produce sugar, but the cool nights prevent the sugar sap from flowing from the leaves into the branches and trunk of the tree. Anthocyanins help rescue this sugar sap from the leaves before they fall off. |
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