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The Most Asked
Questions Of Autumn
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- Why do leaves change color?
Trees and plant leaves contain pigments that give them their color.
Three pigments are involved in fall color.
Chlorophyll-gives leaves their green color Carotenoids-provide the yellow, orange and brown colors
Anthocyanins-give the red and purple colors. In contrast to the other two
pigments anthocyanins are produced in autumn, in response to bright light
and excess plant sugars in the leaf cells.
During the growing season, most tree leaves are green because they are full
of chlorophyll. Plants use chlorophyll to capture sunlight for photosynthesis,
the process that enables them to manufacture their own food. The amount of
chlorophyll is so high during the summer that the green color masks all other
pigments present in the leaf. As the days grow shorter in the fall, chlorophyll
production slows down and eventually stops. The carotenoids and
anthocyanins that are present in the leaf then become visible.
- Do different types of trees turn different colors?
Certain colors of leaves are characteristic of particular species of trees.
Oaks turn red, brown or russet
Dogwood turn purplish red
Beech turn light tan
Red Maple turns brilliant scarlet
Sugar Maple turns orange-red
Black Maple turns glowing yellow
Aspen, Birch and yellow-Poplar turn golden yellow
Some trees, such as elms, have leaves that simply shrivel up and fall off
with a brown color. The timing of the leaf color change varies by species.
For example, oaks put on their fall color display long after many other trees
have lost their leaves. The timing of the color change for certain species
appears to be consistent regardless of local weather patterns or changes in
latitude and seems to genetically inherited.
- Why are some Autumns more colorful?
Temperature and moisture greatly influence autumn color. No two Autumns
are alike. A succession of warm, sunny days and cool, but not freezing nights
seem to bring about the most spectacular color displays. Since carotenoids are
always present in leaves, yellow and gold colors are fairly constant from year
to year. In order for the brilliant scarlet, purple and crimson colors to develop,
bright sunlight in the early fall is needed. Bright sunny days increases food
production in trees and plants. These sugars are trapped in the leaves spurring
the production of anthocyanin pigments, providing the red tint to foliage.
The amount of moisture in the soil also affects autumn color. A late spring,
or a severe summer drought, can delay the onset of fall color by a few weeks.
A warm period during fall lowers the intensity of autumn color. Trees
defoliated by insects during the growing season may also show less fall color.
- Why do leaves fall off?
In early autumn, in response to the shortening days and declining intensity of
sunlight, leaves begin the processes leading up to their fall. The veins that
carry fluids into and out of the leaf gradually close off as a layer of cells form
at the base of each leaf. These clogged veins trap sugars in the leaf and
promote production of anthocyanins. Once this separation layer is complete
the connecting tissues are sealed off, the leaf is ready to fall. Deciduous
trees drop their leaves in order to survive the harsh conditions of winter.
Stems, twigs, and buds are equipped to survive extreme cold. Tender leaf
tissues, however, would freeze in winter, so plants must either protect their
leaves or shed them. Evergreens are able to survive winter because they have
developed a way to protect their foliage. Their needle-like or scale-like
foliage is covered with a heavy wax coating and the fluid inside their cells
contains substances that resist freezing.
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