Ramble Report November 3, 2022
Leader
for today's Ramble:
Linda
Author
of today’s Ramble report: Linda. Comments, edits, and suggestions for
the report can be sent to Linda at Lchafin@uga.edu.
Insect
and fungi identifications: Don Hunter, Bill Sheehan
Link to Don’s Facebook album for this Ramble. All the photos that appear in this report, unless otherwise
credited, were taken by Don Hunter. Photos may be enlarged by clicking them
with a mouse or tapping on your screen.
Number of Ramblers today: 26
Today's
emphasis: Changing leaf color and
other transitions from summer to fall in a Piedmont Oak-Hickory-Pine forest.
Reading: Catherine Chastain
brought in a poem: “Morning Talk” by Jarod K. Anderson, from his book, Love
Notes from the Hollow Tree (2022).
Morning
Talk
My
arm brushed a blue spruce on a gray hike.
I
spoke in a voice made of sparrows, stinging the quiet like sparks from a kicked
fire.
That
sudden sound hung a question on the air,
but
I did not answer.
I
knew that to answer would end a discussion
I
dearly want to stretch on
for
a lifetime.
Show and Tell:
 |
| The ginkgos near the arbor are
turning their glorious gold. |
Gary brought a fallen branch from a
hickory. One end of the branch is cut straight across
smoothly as if it were cut by clippers. It had been girdled by one of several species
in the Longhorn Beetle family (Cerambycidae) known as Twig Girdlers and Twig Pruners.
In late summer or fall, a female chooses a twig ¼ - ½ inch in diameter on which
to lay her eggs and chews a deep groove around it, leaving only a thin strand
of wood in the center and killing the twig, which soon breaks off. She lays her
eggs under the bark at the girdled point on the fallen twig. When the eggs hatch, the larvae feed
on the dead wood and live inside the twig until the following summer. The
larvae begin pupating late in the following summer; within two weeks, the adults emerge,
mate, and begin the cycle again with a new round of girdling and egg-laying.
 |
| Twig girdled by a
Longhorn Beetle |
Announcements/Interesting
Things to Note:
On
Wednesday, November 9, the Friends of the State Botanical Garden of Georgia are hosting the
annual Johnstone Lecture, this year featuring Dr. Cassandra Quave, a medical
ethnobotanist on the faculty of Emory University Medical School, and author of
“Plant Hunter: A Scientist's Quest for Nature's Next Medicines.” The book
chronicles her global search for plant compounds that may address the threat of
antibiotic-resistance microbes, as well as her struggles as a female field
researcher with a disability. The lecture will be held in the Visitor Center at
the Botanical Garden at 6:30 p.m., with a reception and book signing held at
7:30 p.m in the Museum. This event is free and open to the public, but pre-registration
is required here. https://botgarden.uga.edu/event/johnstone-lecture-2/
Gary
mentioned that the Oconee Rivers Audubon Society meets monthly, first Thursday
of each month, September through May, at 7:00 p.m., at Sandy Creek Nature
Center. There is always an interesting speaker.
Richard
extended an invitation to a garden walk and wood-fired pizza oven dinner at his
place on November 13 at around 4:30 p.m. His address is: Please RSVP at richard2191@charter.net.
There
is an interesting exhibit now at the Georgia Museum of Art on campus called “Longleaf
Lines.” The artist is Kristin Leachman; the exhibit is part two of her “Fifty
Forests” project, which documents the self-organizing patterns in trees in all 50
U.S. states. The show will be up till Sunday, Feb 12, 2023.
A lunar eclipse will be visible in the early hours of Tuesday, November 8.
Today’s
Route: After crossing the prairie, we entered the Blue Trail where it intersects
both the Green and White Trails. We wound through the successional and Oak-Hickory-Pine forests
along the Blue Trail and then turned north onto the service road that follows a
ridge east to the intersection with the Green Trail, which we took back to the
prairie, from where we returned to the Visitor Center.
How and
Why Leaves Change Color
Here in Georgia, we live at the southern end of the great Eastern Deciduous Forest, a renowned hot spot of biological diversity, especially when it comes to trees. In
the Piedmont of Georgia, we have more than 200 tree species, many of which contribute to a colorful show in the fall. In
New England, there are fewer tree species; the color displays are more intense than ours but shorter. The more diverse the forest,
the longer and more varied the colorful display.
 |
Piedmont mixed hardwood forest
(photo by Lee Shearer)
|
|
Leaves change color because
of the presence of four types of pigments: chlorophylls,
carotenoids, tannins, and anthocyanins. The first three of these
are present in leaves throughout the growing season – green chlorophyll is the pigment that facilitates
photosynthesis. Things begin to change as the nights get longer and the temperatures
drop, triggering the breakdown of chlorophyll. As the green pigment disappears,
the ever present yellow and golden pigments – carotenoids – are revealed, along with the tannins
that give leaves a brown or tan color at the end of fall.
 |
Hickories are giving a golden show right now.
(photo by Gary Crider) |
Leaves
undergo another change in response to longer, cooler nights – they prepare to
drop their leaves. Two special layers of cells form at the point where the leaf
stalk connects to the twig; this is called the abscission zone. One layer, the
layer nearer the twig, becomes impregnated with wax, forming a protective layer
between the twig and the outer world once the leaf falls. The other layer, the
layer at the base of the leaf stalk, breaks down, loosening the leaf’s
connection to the twig.
Sugars trapped in the leaf
when the waxy layer forms are converted to the fourth pigment, anthocyanin.
Anthocyanin is found throughout the plant world in the red of apples, the
blue of blueberries, and purple of eggplant (and so on). Some of the most
brilliant fall colors in the Piedmont are due to anthocyanin in the leaves of Sourwood, Sweet Gum, Dogwood, Red Maple, Black Gum, Dogwood, and Chalk Maple.
 |
| Sourwood |
 |
Sweet Gum
(photo by Lee Shearer)
|
How
leaves change color is pretty well understood. But doesn't it seem like a lot
of trouble just to brighten up leaves that are only days away from dropping to the forest floor? Which brings us to the question of why leaves change colors in the fall. Why don’t trees simply let their leaves fall to the
forest floor in the fall? Is there adaptive
value to the color change? Much to my surprise, scientists do not know. “Several
hypotheses have emerged to explain the evolution of autumn colors [but] the
adaptive value of this color change remains a mystery,” wrote a group of scientists
in 2009 and, as best I can tell, they haven’t figured it out yet. One theory is that, as the tree
canopy thins and more light penetrates the crown of the tree, anthocyanin
acts as sunscreen, protecting the leaves as they slowly wither. This
protection allows the leaf to stay functional long enough to withdraw the
maximum amount of nutrients – nitrogen, phosphorus, iron, and manganese – back
into the twigs and down into the roots, where they are stored.
Another theory relies on the fact that the color red is a warning
signal to some animals. Responding to this red flag, egg-laying aphids avoid
trees with red leaves. Since aphids can damage a tree during egg deposition by introducing
viruses and bacteria, a tree that
can produce red leaves in the fall has an adaptive advantage.
Yet another theory is that
red leaves act as a billboard to migrating birds: tasty berries are here – Exit Now! Take a
look at Flowering Dogwood (above), Black Gum and Virginia Creeper (below). Their leaves turn red when
their berries are ripe. Eating these berries on the fly, birds disperse
the tree's seeds across a wider range.
Whichever theory, or
theories, is proven correct, I am confident it will be more beautifully complex
than I ever dreamed.
 |
| Color is also
happening on the forest floor. Crane Fly Orchid leaves emerge in
the fall, and by flipping the leaf over, you can see the
lustrous purple of the lower leaf surface. |
What is the best weather
for producing brilliant leaf color?
The best combination of
weather for a spectacular show of red, orange, and purple is a wet spring
and summer followed by warm, sunny fall days and cool nights. Warm fall
days and moist soils ensure that leaves produce lots of the sugars that are converted
to anthocyanin. Cool nights trigger the formation of the abscission layer that
traps the sugars and pigments in the leaf. Since the yellow pigment in the
leaves of Hickories, Redbuds, and Tulip Trees is revealed primarily in response
to longer nights, these shades are revealed regardless of weather. However, if
there is a severe drought or cold snap, all leaves are liable to turn brown and fall
without going through a colorful phase.
Oak - Hickory - Pine: Matrix Forest of the Piedmont
The Blue
Trail and the Service Road that crosses the trail pass through classic Piedmont
Oak-Hickory-Pine forest. This forest covers most of the uplands at the Garden,
except for the prairie in the right-of-way and the cultivated gardens.
 |
Scarlet Oak is a typical species of the Oak-Hickory-Pine forest. The base of the trunk often has a crumbly, black appearance, while the upper trunk usually has narrow, vertical pale stripes.
|
 |
Scarlet Oak leaves have deep, C-shaped sinuses
and the base of the blade is more or less perpendicular to the leaf stalk.
|
