|
The Facts About Fall
Foliage
With its crisp air and jewel-toned trees, autumn is a favorite
time of year for me. But why do the trees put on this spectacular show and
how do their leaves morph from green to vivid gold and red? Let’s
start with some basics.
Evergreen vs. Deciduous Trees
The shedding of leaves is a continuous process for all trees, including evergreens.
As leaves are damaged by insects, disease or weather, they are shed and replaced
by new ones. However, evergreens have specialized leaves that can withstand
harsh conditions. The tough needles of a ponderosa pine, or the waxy leaves
of a holly plant, for example, are adapted to resist cold and moisture loss,
and can therefore remain on the tree year round. By contrast, deciduous trees
shed all of their leaves as winter approaches. The thin, delicate leaf structures
of trees like gamble oak and aspen are more prone to freezing and drying out.
Shedding allows the tree to conserve water and protect itself from the elements.
But Why The Color Change?
All leaves contain special cells called chloroplasts, which capture energy
from sunlight and use it to produce food for the plant through the process
of photosynthesis. The best-known chloroplast contains the pigment chlorophyll,
which is green in color. However, there are food factories of other colors
in the leaf, as well. Carotenoids and xanthophylls are orange and yellow in
color, and can be found in foods like carrots, bananas, and egg yolks. Anthocyanin
pigments are red, and are found in radishes, roses, and geraniums. While the
chlorophyll in a leaf is active, it hides these other plant cells and leaves
appear green.
As winter approaches, environmental factors like shorter
days and less sunlight trigger subtle chemical changes in the tree. At the
base of each leaf is a specialized layer of cells called the abscission
or separation layer. In the fall, these cells swell and form a cork-like
material, which blocks the flow of fluids between leaf and tree. Food and
waste products become trapped in the leaf and the chlorophyll begins to
degrade due to lack of water. As the chlorophyll breaks down, the yellow,
orange, and red pigments that were previously masked are revealed.
What About Intensity?
A variety of factors, including precipitation, air temperature, and sunlight
contribute to the intensity of fall colors. The brightest colors are seen when
late summer is dry, and autumn has bright, sunny days and cool nights (in the
low 40s Fahrenheit). A fall with cloudy days and warm nights results in drab
colors and a less spectacular display. Peak foliage viewing time has arrived
in southwestern Colorado, so get out there and enjoy the fireworks!
MORE ARTICLES
|
