As Earth continues its journey around the Sun, the chill of
northern climes creeps southward.

The air sweeps over us in waves, no longer from the summer Gulf,
but from the center of the
continent. Cool winds drive the rains. Your senses can see,
smell, hear, taste and feel the
coming of winter.

Trees sense winter’s arrival, too.

For trees, autumn is a time long expected and prepared for. From
the moment trees began to
expand their leaves and make food in the spring sunlight, a
biological timer has been running.

This timer is composed of sensors in buds, leaves and twigs that
measure light and dark, day
length and other environmental clues. The tree’s genetic
materials help define when and how a
tree will begin to shut down in fall.

For many people, fall is a time for harvest celebrations and
winter preparations. So it is with
trees.

Trees stay on their ageless cycle. Summer prepares them for
fall, and fall readies them for
winter. Winter’s resting time prepares trees for spring, and
spring unfolds the biological glory
of summer.

Fall is a time of reorganization. All of nature is making
changes, preparing for the coming
winter.

In trees, the topmost buds have sent a biological message that
signals senescence. That’s a big
word for the ordered shutting-down of summer growth and
conservation of valuable resources.
Senescence brings the fall colors and leads to winter
survival.

From soon-to-be-dead leaves, the tree withdraws many materials
it has made or collected. It
leaves waste materials behind.

The last bit of tree food is stockpiled in the living cells of
the outer few annual growth rings.
Twigs, branches and roots become the collection sites and
warehouses of materials needed for
another season to come.

Within the tree, biological doors and windows are being closed,
locked and weatherproofed.

People can enjoy the colorful rites of autumn in the forest,
across the landscape and with
individual trees. The process of senescence presents amazing
colors.

Some of the fall colors, such as the yellows and oranges, have
just been revealed after having
spent the summer wearing green cloaks. Other colors, such as
some of the purples and reds,
have been made just for autumn.

The pallet of colors in leaves is varied and rich. Individual
leaves actually can shift and change
colors over the senescence period.

Internal phosphorus and water contents, and external temperature
and sunlight, help blend and
mix leaf colors. From the first pale yellows of early fall
through the bright oranges of October
to the deep burgundies coloring the last oak leaf, autumn paints
a feast for the eye.

The scene changes daily and accelerates as winter comes closer.
The colors break over us in
three waves. The first is composed of yellows and yellow-browns.
Golden colors begin the
second wave, which ends with oranges and light reds. The third
wave is made of purples and
dark reds.

These color waves sweep down from the higher elevations and
farther north. Satellite images
show the moving color fronts. A short ride northward, and up in
elevation, is like taking a
time machine farther into the fall.

We live among great forests and stands of trees. Autumn is a
time to fully appreciate the
values they bring. The trees’ biological preparations are
colorful warnings of the winter to
come.