Most folks who enjoy the outdoors especially
appreciate the coming of fall with the attendant color changes
in many plants. Aspen (Populus tremuloides) are among
the most colorful and wide-spread color-changing trees in
Rocky Mountain National Park. Experience suggests to us that
aspen produce more or less colorful leaves from year to year,
and that these differences seem to relate to weather patterns,
soil fertility, and the amount of moisture they received during
the growing season.
Recently scientists put forward an intriguing
alternative explanation for intense fall colors in some trees
(Ecol. Lett. 6, 807 (2003)). Mountain birches in Norway may
use intense fall colors to signal leaf-chewing insects not
to infest them. The intensity of color seems to be an indicator
of how much chemical defense compound the tree can produce.
In the case of the mountain birches, an inchworm (geometrid)
moth lays eggs on the trees in the fall. The following spring
the eggs hatch, and the moth caterpillars eat the trees' leaves.
Trees that can produce larger amounts of chemical defenses
to make their leaves unpalatable receive less damage. The
trees with the most intense leaf colors in the fall also have
the least damage the following spring, suggesting a direct
relationship between chemical defenses and intense colors.
Over time, perhaps the moths have learned to avoid laying
eggs on trees with the most highly colored leaves!
We don't know whether the same thing happens
in Rocky Mountain National Park's aspen or other trees. We
do know there are many different reprepresentatives of the
inchworm
or geometrid moth family in the park. However, whether
you enjoy fall colors because they are beautiful, or because
they may reveal scientific secrets, Rocky Mountain National
Park offers an excellent opportunity to experience a glorious
autumn.
Please
click on the photo captions for larger pictures
