There are many reasons to love fall.

For me it's the season of harvest opportunity - a time to hunt deer, elk, ducks, pheasants and partridge and to spend hours on the river fishing for steelhead.

I also welcome the signs of its arrival and, like many, revel in the brilliant colors of the season. But like most people, I was unaware of the process behind the changing colors.

It all hinges, of course, on the tilting of the planet as it orbits the sun. As fall approaches, the Northern Hemisphere is hit with more of a glancing blow than a direct hit from the sun's rays. The days grow shorter and cooler, and plants respond by producing less chlorophyll.

In spring and summer, chlorophyll overwhelms other pigments, such as carotenoids, and so we see plants as mostly green instead of yellow and orange. In the fall, chlorophyll cedes power to carotenoid.

"In the fall, the tree stops producing as much chlorophyll because it's going dormant, and the green fades away and you are now able to see the oranges and yellows and the rich brown colors," said Yvonne Barkley, a University of Idaho Extension forester at Moscow.

At about the same time, another pigment not present earlier in the year is produced in the leaves of many trees and shrubs. This one, anthocyanin, is responsible for the vibrant reds, crimsons and purples.

Mix them together and you get the brilliant colors of fall. It's a show that is at its peak in many areas of north central Idaho and southeastern Washington. But it won't last long. In fact, it's already over at higher elevations, where the trees have mostly shed their leaves that are now tumbling with the wind, soon to decay into the building blocks of soil.

Not all years produce the same intensity of fall color. Conditions such as the amount of spring showers, summer heat and fall rain and cloud cover interact to influence the colors, especially the reds.

Barkley said a wet spring, a summer lacking prolonged heat waves, mixed with some July rainstorms and a fall with a good mixture of rain and sunny days, has produced fantastic fall foliage.

"We have had really good fall color this year and lots of reds and purples because the conditions were right. It's been stunning," she said.

The high winds predicted late last week turned out to be less severe than expected. That means there are still leaves on the trees and still time to take it all in. If you are out hunting, fishing, hiking or just going for a drive, be sure to take a moment or two and appreciate fall before the sun's angle is even shallower, the trees are bare and snow piles up in the mountains.


Barker may be contacted at or at (208) 848-2273. Follow him on Twitter @ezebarker.