The science behind the magic: Fall color explained

yellow-glory-by-scottie

Untitled, photo by Scottie

The Science of Color in Autumn Leaves from the United States National Arboretum is such an excellent explanation of the science behind the magic of Michigan’s fall color show that I try and share it every year:

The process that starts the cascade of events that result in fall color is actually a growth process. In late summer or early autumn, the days begin to get shorter, and nights are longer. Like most plants, deciduous trees and shrubs are rather sensitive to length of the dark period each day. When nights reach a threshold value and are long enough, the cells near the juncture of the leaf and the stem divide rapidly, but they do not expand. This abscission layer is a corky layer of cells that slowly begins to block transport of materials such as carbohydrates from the leaf to the branch. It also blocks the flow of minerals from the roots into the leaves. Because the starting time of the whole process is dependent on night length, fall colors appear at about the same time each year in a given location, whether temperatures are cooler or warmer than normal.

During the growing season, chlorophyll is replaced constantly in the leaves. Chlorophyll breaks down with exposure to light in the same way that colored paper fades in sunlight. The leaves must manufacture new chlorophyll to replace chlorophyll that is lost in this way. In autumn, when the connection between the leaf and the rest of the plant begins to be blocked off, the production of chlorophyll slows and then stops. In a relatively short time period, the chlorophyll disappears completely.

This is when autumn colors are revealed. Chlorophyll normally masks the yellow pigments known as xanthophylls and the orange pigments called carotenoids — both then become visible when the green chlorophyll is gone. These colors are present in the leaf throughout the growing season. Red and purple pigments come from anthocyanins. In the fall anthocyanins are manufactured from the sugars that are trapped in the leaf. In most plants anthocyanins are typically not present during the growing season.

As autumn progresses, the cells in the abscission layer become more dry and corky. The connections between cells become weakened, and the leaves break off with time. Many trees and shrubs lose their leaves when they are still very colorful. Some plants retain a great deal of their foliage through much of the winter, but the leaves do not retain their color for long. Like chlorophyll, the other pigments eventually break down in light or when they are frozen. The only pigments that remain are tannins, which are brown.

The explain that because the starting time of the whole process is dependent on night length, fall colors appear at more or less the same time every year and are not overly dependent on temperature, rainfall or other factors, other than the fact that weather can shorten or prolong the show by stripping leaves from trees.

Click through to the US Arboretum for more and also see Fall & Fuit from the Science of Color!

View Scotties’ photo bigger and see more in his Infrared slideshow.

Tons more fall photos on Michigan in Pictures!

Fall…ing: Michigan is Still Michigan Edition

Fall-ing Northern Marquette County

Fall…ing, photo by Thom Skelding

Yep. This photo pretty much sums up the weekend!! In Michigan gets bragging rights to first heavy snow east of Rockies, mLive meteorologist Mark Torregrossa writes:

Michigan now has bragging rights to the first heavy snow of the winter, east of the Rockies. Overnight Friday, October 16, 2015, and this morning, lake effect snow has been falling in part of the Upper Peninsula and a large area of northwest Lower Michigan.

The Kalkaska area, east of Traverse City, has officially reported 5.7 inches of new snow.

The northwest Lower Michigan snow belt has received areas of two to five inches of the winter wonder.

Click through for more, including some photos.

View Thom’s photo background bigtacular and see more in his slideshow.

More fall wallpaper and more winter wallpaper

The Science of Fall Color, Revisited

"Autumn Leaves" by Michael G.O'Callaghan

“Autumn Leaves”, photo by Michael G.O’Callaghan

Three years ago I posted this. It’s such good and useful information that I thought I’d share it again! #TBT?

The Science of Color in Autumn Leaves from the United States National Arboretum explains that process that starts the cascade of events that result in fall color is a growth process that starts in late summer or early autumn. When the nights get long enough, a layer of cells called the abscission layer forms that begins to block transport of materials from the leaf to the branch.

During the growing season, chlorophyll is replaced constantly in the leaves. Chlorophyll breaks down with exposure to light in the same way that colored paper fades in sunlight. The leaves must manufacture new chlorophyll to replace chlorophyll that is lost in this way. In autumn, when the connection between the leaf and the rest of the plant begins to be blocked off, the production of chlorophyll slows and then stops. In a relatively short time period, the chlorophyll disappears completely.

This is when autumn colors are revealed. Chlorophyll normally masks the yellow pigments known as xanthophylls and the orange pigments called carotenoids — both then become visible when the green chlorophyll is gone. These colors are present in the leaf throughout the growing season. Red and purple pigments come from anthocyanins. In the fall anthocyanins are manufactured from the sugars that are trapped in the leaf. In most plants anthocyanins are typically not present during the growing season.

As autumn progresses, the cells in the abscission layer become more dry and corky. The connections between cells become weakened, and the leaves break off with time. Many trees and shrubs lose their leaves when they are still very colorful. Some plants retain a great deal of their foliage through much of the winter, but the leaves do not retain their color for long. Like chlorophyll, the other pigments eventually break down in light or when they are frozen. The only pigments that remain are tannins, which are brown.

The explain that because the starting time of the whole process is dependent on night length, fall colors appear at more or less the same time every year and are not overly dependent on temperature, rainfall or other factors, other than the fact that weather can shorten or prolong the show by stripping leaves from trees.

Click through to the US Arboretum for more and also see Fall & Fuit from the Science of Color and Wikipedia’s entry on Autumn leaf color.

View Mike’s photo background big and see more in his Autumn slideshow.

Lots more fall color on Michigan in Pictures!