<P> During the summer growing season, phosphate is at a high level . It has a vital role in the breakdown of the sugars manufactured by chlorophyll, but in the fall, phosphate, along with the other chemicals and nutrients, moves out of the leaf into the stem of the plant . When this happens, the sugar - breakdown process changes, leading to the production of anthocyanin pigments . The brighter the light during this period, the greater the production of anthocyanins and the more brilliant the resulting color display . When the days of autumn are bright and cool, and the nights are chilly but not freezing, the brightest colorations usually develop . </P> <P> Anthocyanins temporarily color the edges of some of the very young leaves as they unfold from the buds in early spring . They also give the familiar color to such common fruits as cranberries, red apples, blueberries, cherries, strawberries, and plums . </P> <P> Anthocyanins are present in about 10% of tree species in temperate regions, although in certain areas--most famously New England--up to 70% of tree species may produce the pigment . In autumn forests, they appear vivid in the maples, oaks, sourwood, sweetgums, dogwoods, tupelos, cherry trees and persimmons . These same pigments often combine with the carotenoids' colors to create the deeper orange, fiery reds, and bronzes typical of many hardwood species . </P> <P> The brown color of leaves is not the result of a pigment, but rather cell walls, which may be evident when no coloring pigment is visible . </P>

When do the leaves start to change colors