Mountains and Forests
http://www.na.fs.fed.us/spfo/pubs/misc/leaves/leaves.htm Why do leaves change color
Directions: From Huntsville: Take Governor's Drive (Highway 431) heading east. Go up Monte Sano; when you reach the top elevation on this highway (which is rather brief) turn left onto Monte Sano Blvd. After climbing a bit in elevation, you'll pass through a residential area. Go about 2 miles from Highway 431, then turn right onto Nolen Avenue. You'll enter the park and veer right at a fork in the road; right around the corner is the Park Headquarters on the right.
Touch with the Nature:
The Forestry Commission is a State agency and manages the State's natural resources. The Forestry Commission provide assistance to private landowners in the management of their lands.

Trees are signaled to start changing colors in their leaves when days become shorter and nights become longer. As days get shorter, trees release a kind of hormone, restricting sap-flow to the leaves. As autumn approaches, certain influences both inside and outside the plant cause chlorophyll to be replaced at a slower rate than it is being used. Chlorophyll helps leaves turn sunlight into food all summer, but dwindles as fall progresses. When this happens, other pigments that have been present (along with the green chlorophyll) in the cells all during the leaf's life begin to show through. They give us the colorations of yellow, orange, brown, and other hues in between. The reds, purples, and their combinations come from another group of pigments that are not present in the leaf during the growing season. They develop in late summer in the sap of cells of the leaf. Their formation depends on the breakdown of sugars in the presence of bright light as the level of phosphate in the leaf is reduced. Phosphates and other chemicals and nutrients, moves out of the leaf into the stem of the plant. The brighter the light during this period, the greater the chances are for a more brilliant fall.