The sunlight becomes less during autumn season, the veins that carry sap into and out of a leaf slowly closes up. A layer of cells, known as the separation layer, develops at the base of the stem of the leaf. Slowly the leaf is separated from the tissue which is connected to the branch, and it falls.
In early autumn, due to short days and less intensity of sunlight, leaves start the processes of their fall Needles and leaves that fall doesn’t get wasted. They decompose and help the soil with nutrient forming the spongy humus layer of the forest floor which absorb the rainfall. These leaves provide food for numerous organisms found in the soil and is quite important to the ecosystem of forest.
Below Autumn Leaves info from Wikipedia (Read More):-
Autumn leaf color is a phenomenon that affects the normally green leaves of many deciduous trees and shrubs by which they take on, during a few weeks in the autumn season, one or many colors that range from red to yellow. The phenomenon is commonly called fall colors and autumn colors, while the expression fall foliage usually connotes the viewing of a tree or forest whose leaves have undergone the change. In some areas in the United States and Canada, "leaf peeping" tourism between the beginning of color changes and the onset of leaf fall, or scheduled in hope of coinciding with that period, is a major contribution to economic activity.
http://en.wikipedia.org/wiki/Autumn_leaf_color
