It happens every year about this time. Nature throws a switch and Kentucky's hills and plains light up with the neon colors of autumn. And that spectrum of colors painting the hillsides is part of a very green cycle - or more accurately, recycle.

"Trees do more than give us a spectacular color show," said Doug McLaren, University of Kentucky forestry specialist. "They also make an important contribution to an ongoing ecological system."

Nothing is ever wasted in nature; so minerals taken into the leaves during the growing season are recycled after the leaves drop to the ground. When the leaves decompose, their nutrients again are available to be taken up by the area's flora, and organic materials nourish the soil.

Year in and year out, the cycle continues, whether the season brings brilliant leaves or faded browns. Mother Nature doesn't care; it's all the same to her. We humans do, though.

Last year's fall display was breathtaking in many areas of Kentucky, despite temperatures that still pushed 90 degrees as late as October and a prolonged, extreme drought that strapped most of the state. This year could be much of the same, or we might see the effects of back-to-back dry summers. Though the winter and spring months brought above average rainfall, since June 1 the state is drier than it was last year.

"Two dry summers have put extra stress on the trees," said Tom Priddy, University of Kentucky meteorologist. "The moderate to severe hydrologic and agricultural drought being experienced around the state could end in a month, or it might not. There's nothing out there to indicate a major change. And we can't even blame it on El Nino or La Nina. We're at near neutral sea temperatures in that area of the Pacific, so that's not controlling anything."

On the plus side, this year the state did not experience the unrelenting extreme heat of last year.

So what does this autumn hold in the way of color? McLaren put on his prognosticator's hat while he took into consideration temperature and moisture levels.

"Usually with bright days and cool nights the trees will continue to make sugars in their leaves. But because the leaves have sealed off from the branch for the wintertime, none of those sugars get to the roots. The retained sugars in the leaves will make for brighter than normal color. Late summer and early fall have provided this for us in 2008," he said.

But it's not the temperature or moisture that actually triggers the onset of fall colors in deciduous trees. It's the amount of sunlight. Shorter days prompt the formation of a layer of cork cells at the base of each leaf. This restricts the flow of water and minerals into the leaf, which means that spent chlorophyll, the green pigment in foliage, cannot be replaced. As chlorophyll dies, it no longer masks other pigments present in the leaf and emerald transforms to crimson or saffron.

The amount of light also affects color brilliance. The production of one group of leaf pigments, the anthocyanins, is dependent on the breakdown of sugars in the presence of bright light in late summer.

It's early yet. On the calendar, autumn has just begun. The Kentucky Department of Tourism reports at present most areas of the state are in the earliest stages of fall color, with just a light stippling of reds and yellows across the landscape. McLaren said the best color in the state typically is between the second and fourth weeks of October. He predicts the best weekends to hit the state's highways and byways this year will be Oct. 11-12 and Oct. 18-19.

In the best of years, autumn foliage in Kentucky would stack up against any rival.

"Because we in Kentucky have such a diverse climate and soil composition, many tree species common to both northern and southern states grow here," McLaren said. "This provides a variety of fall colors."

The Kentucky Department of Tourism provides weekly updates on a fall color map at http://www.kentuckytourism.com/colorfall/map.htm.