16 Nebraskaland • October 2025
It's that time of year when trees start to dress for winter.
Maybe not in the same sense that we do — they can't
check the weather forecast and put on layers before a chilly
morning. But they prepare in other ways.
Inside their cells, tree leaves contain a pigment called
chlorophyll that absorbs sunlight and refl ects green light
waves during photosynthesis. This causes leaves to look
green. The UV rays in sunlight break down chlorophyll all the
time, so new chlorophyll must constantly be made.
As days shorten toward autumn, deciduous trees start to
store nitrogen and phosphorus in their woody parts rather
than continuing to supply leaves with nutrients, protecting
themselves and saving energy.
So, with fewer nutrients and less sunlight, leaves slow
down their chlorophyll production, and the green color fades.
This enables other pigments in the leaf to show through and
refl ect diff erent colors.
The red maple leaf, below, is a great example of this
phenomenon. You can practically see the tree withdrawing
nutrients from the leaf. Areas closest to the leaf stem and
veins have the most chlorophyll production happening so
they still appear green. Nutrients from the perimeter of the
leaf have already been pulled back into the branch to be used
for leaf production next year.
But why are there so many fall colors? In addition to
chlorophyll, other pigments are present in leaves. Diff erent
types of trees have genetic diff erences that cause certain
pigments to dominate their leaves in the fall and turn colors
characteristic to their species.
Bowhunters that favor hunting in river bottoms in early
fall will notice the golden yellow of cottonwoods. Hikers and
birdwatchers in oak hickory woodlands will enjoy red, brown
and golden bronze colors.
Of course, it doesn't happen all at once. Every tree is an
individual in a unique place in the forest. And just like people,
they get ready for winter in their own time.
IN THE FIELD
For deciduous trees like this red maple, chlorophyll production diminishes in the fall, revealing a number of other colors.
RENAE BLUM
By Jennifer Ruyle, Outdoor Education Specialist, NGPC
WHY SO MANY FALL COLORS?
