Tuesday 20 September 2005

Leaf Colour

Right now your leaves are losing their colour. The beautiful hues of fall have actually been there all summer long. The colors we see in the fall are normally masked by the pigment chlorophyll. Chlorophyll, the most common pigment, is responsible for the green colour in leaves. Sunlight is composed of many different colors of light. We can see the whole spectrum of light colours when they are broken up in a rainbow. Leaves absorb various wavelengths, or colours of light, and reflect back other colours. The green we see is reflected light that’s bounced back to our eyes. The light that isn’t reflected is absorbed is used to power the machinery of photo synthesis. Photosynthesis is the process that takes gases from the atmosphere, water and using energy from the sun creates sugar. Oxygen is a waste product of this reaction. Light of many wave lengths is used by other pigments, to a lesser extent to create other products in the leaf. Other pigments include caratenoids, that give the orange / red colours we see in carrots and maple leaves. Anthocyanins are pigments that give the blues and purples we see in plum leaves and chokecherry fruit. Many pigments blend together to give you dull brown, like the paint water in kindergarten class after you clean you brushes. At the end of summer, trees begin the process of shutting down for winter and much of the sugar in the leaves is transported elsewhere in the tree. The leaves vascular connections between the leaves and the trees are then plugged, with a layer of thick impervious cells called the abscission layer. The chlorophyll in the leaf degrades exposing the colorful accessory pigments. Only after the leaves have essentially died do we see their true colours. The leaves are then shed as the abscission layer plugging the leaf stem is complete. If we have a long frost free fall the leaves will have much more prominent colors. Trees will however lose there leaves with out frost as the process of abscission and leaf drop, is triggered by shorter fall days. The fall of 2002 was warm and then a sudden cold snap brought the first snow to Riding Mountain. I had the privilege of seeing thousands of still olive green aspen leaves fallen on fresh white snow. A painter could not have painted a more striking backdrop!
Enjoy the fall colors and know that spring is only months away!

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