Forestry experts offer fall facts
As the days shorten and temperatures become crisp, the green palette of summer foliage is transformed into the vivid autumn palette of reds, oranges, golds and browns before the leaves fall off the trees. For years, scientists have worked to understand the changes that happen to trees and shrubs in the fall, according to information provided by the Pennsylvania Bureau of Forestry.
Forestry experts say three factors influence autumn leaf color – leaf pigments, length of night and weather conditions.
The timing of color change and leaf fall are primarily regulated by the calendar, and the increasing length of night, according to experts.
None of the other environmental influences – temperature, rainfall and food supply – are as unvarying as the steadily increasing length of night during autumn.
As days grow shorter and nights grow longer and cooler, processes in the leaf begin to paint the landscape with nature’s autumn palette.
Leaves need pigments to produce the color palette, and there are three types that are involved in the autumn color. They are:
– Chlorophyll, which gives leaves their basic green color. It is necessary for photosynthesis, the chemical reaction that enables plants to use sunlight to manufacture sugars for their food. Trees in the temperate zones store these sugars for their winter dormant period.
– Carotenoids, which produce yellow, orange and brown colors in such things as corn, carrots and daffodils, as well as rutabagas, buttercups and bananas.
– Anthocyanins, which give color to such familiar things as cranberries and apples, concord grapes, blueberries, cherries, strawberries and plums. They are water-soluble and appear in the watery liquid of leaf cells.
Both chlorophyll and carotenoids are present in the choloroplasts of leaf cells through the growing season.Most anthocyanins are produced in the autumn in response to bright light and excess plant sugars within leaf cells.
During the growing season, chlorophyll is continually begin produced and broken down and leaves appear green. As night length increases in the autumn, chlorophyll production slows down and then stops and eventually all the chlorophyll is destroyed.
The carotenoids and anthocyanins that are present in the leaf are then unmasked and show their colors. Certain colors are characteristic of particular species.
Oaks turn red, brown or russet; hickories, golden bronze; aspen and yellow popular, golden yellow; dogwood, purplish red; beech, light tan; and sourwood and black tupelo, crimson.
Maples differ species by species. Red maple burns brilliant scarlet; sugar maple, orange-red; and black maple, glowing yellow. Striped maple becomes almost colorless.
Leaves of some species, such as the elms, simple shrivel up and fall, exhibiting little color other than drab brown.
The timing of the color change also varies by species. Sourwood in southern forests can become vividly colorful in late summer while all other species are still vigorously green. Oaks put on their colors long after other species have already shed their leaves.
This means a particular species at the same latitude will show the same coloration in the cool temperatures of high mountain elevations at about the same time as it does in warmer lowlands.