Ramble Report October 31 2019

Today's Ramble was led by Dale Hoyt.

Here's the link to Don's Facebook album for today's Ramble. (All the photos in this post are compliments of Don, unless otherwise credited.)

Today's post was written by Dale Hoyt.

7 Ramblers met today. 

(Weather reports were for Thunderstorms, so many Ramblers waited until 10AM to attend a social hour in Café Botanica. But the thunderstorms never happened.)

Announcements:

Tuesday, November 5, 2019. Vote for SPLOST to support Sandy Creek Nature Center’s proposal.

Wednesday, November 6, 2019, at 9:00 AM

  Guided Walk at Sandy Creek Nature Center
Led by Dan Williams!! Meet at the visitor center. Free coffee, snacks and conversation afterwards.

Today’s Reading: Betsy read a poem by Kat LaMantia (from Alaska Women Speak, Fall, 2019).

She Listens

She listens easily, unstrained,

to the tiny scratches of lichens, the "pufh" of spores
to the lesser whispers of salamanders and spiders
She can silence the static, slow her pulse

and listen with a kind of vestigial inner ear

opened by prayer

She speaks all the dialects chanted by trees
hears the deep humming coming from hives
She knows when the exoskeletons detach
from growing cicadas and listens as

their papery skins split and fall to the grass

The rocks strain and the shells make their shushing sounds
She tucks their voices into the folds of her clothing,

this ancient opera written when light awoke,

when waters separated, when the stars

in His right hand took their first breath

and the world genuflected

She listens because her soul is hungry
She listens because this song is her bread

Today's route: Through the Shade Garden down the access road to the power line right of way. Return via the White Trail Spur.

Remember: Click on any photo to enlarge it. Click to return.

Arbor, Children’s Garden:

American Wisteria in bloom

American Wisteria. Before the construction of the Children’s Garden the Arbor fell into disrepair and had to be removed, along with the Chinese Wisteria that had covered it (and led to its decay). After the Children’s Garden was finished a potted American Wisteria was placed at the base of one of the supporting pillars. Today we noticed that the American Wisteria was blooming. Elsewhere in the Garden American Wisteria bloomed in late April and May. Why was this one at the Arbor blooming now?

Many plants are influenced by the length of night. Some will produce flowers only under short day-long night conditions, given that the temperature permits growth. This condition occurs in the spring and in the fall. If the fall is unusually warm some plants will be stimulated to produce a second flush of flowers. For example, some spring-flowering trees, like crab apples, also sometimes flower in the fall. Our American Wisteria, being a potted plant, may have its signals mixed up and thinks that the short days mean it’s spring.

The Ginkgo leaves are changing color from green to yellow. While looking at photos from earlier Rambles I noticed something interesting. Before I tell you what it is you should compare the two photos below.

October 31, 2019, Ginkgo Leaves

October 13, 2016 Ginkgo Leaves

In the 2019 photo the color change is almost complete, but you can still see a few leaves that have some green parts. Those green parts are near the petiole end of the leaf. What I noticed was that in the 2016 photo the base of the leaf closest to the petiole was turning yellow. In one photo the tree is withdrawing chlorophyll first from the base of the leaf blade. In the other, the chlorophyll is withdrawn from the furthest edge of the leaf blade. On our previous rambles I never noticed a difference. Maybe it's too subtle to notice? Is this just a difference between individual trees? If you have Gingko trees in your neighborhood take a look at them and let me know how their leaves are changing. Hopefully it is still not too late; otherwise we’ll have to wait until next year.

Ginkgoes are known for dropping all their leaves nearly simultaneously. All may be a little extreme – I’ve noticed that the Ginkgoes in my neighborhood don’t suddenly appear with naked limbs. Leaf drop for them is more gradual, but they still drop the majority of their leaves over a very short time period. One such Ginkgo was on the Earlham College campus in Richmond, Indiana. On a single day it dropped 95% of its leaves within one or two hours. One of my colleagues at the College predicted exactly when it would happen: the first morning after the first hard frost of the year when the sun was high enough to shine on the Gingko tree. Sure enough, the tree delivered up its leaves exactly as predicted. The ground beneath the tree was covered in fallen leaves to above your ankles! 

The explanation was that in the fall the leaves develop a weakness called an abscission layer at the base of the petiole where the leaf is attached to a twig. When the overnight temperature falls below the freezing point of water ice forms in the abscission layer, but the leaf can’t fall because the ice is holding it to the tree. In the morning, when the sun hits the leaves, it melts the ice. As the ice melts the leaves lose their connection to the tree and fall.

Why Ginkgo leaves shine golden in the sun.

Drizzling autumn sky

Under the ginkgo

The sun is shining

(Haiku by Dale Hoyt)

At this time of year, the Ginkgo leaves develop a beautiful lemon-yellow color. You may have noticed that in the sunlight they appear even brighter. There is a reason for this: a chemical compound called 6-HKA for short, is produced in the leaves as their green chlorophyll breaks down. 6-HKA absorbs the ultraviolet wavelengths of sunlight and re-emits them as the yellow wavelengths. This fluorescence, as it is called, increases the intensity of the yellow in the leaves. (A whitening agent in some laundry detergents works on the same principle. It absorbs ultraviolet light and fluoresces its energy in a broader range of the visible spectrum that appears white to our eyes.)

Shade Garden:

 

This is the Chinese Winterhazel, in the same family (Hamamelidaceae) as our native Witch Hazel. It blooms in late winter-early spring.

We stopped at the American and Ozark Witch Hazels, looking for their fall flowers but none were to be seen. (This is not the same group of Witch Hazels that we stopped at last week. They also show no signs of flowering this year.)

Bigleaf Magnolia leaves have turned yellow.

 

Several of us had not seen the Mayapple sculpture.

Road/Dunson Garden Deer Fence:

All the rain brought down many colorful leaves, nearly covering the road surface.

We stopped, as we often do, at the passionflower vines….no chrysalises or caterpillars were evident and there were still a few small fruits on the vines that were left.

Emily and Don were amazed by a tiny foliose lichen Don found growing on the deer fence. (Notice the reversal of twist direction in the Passionflower tendril.)

ROW:

Plant succession. The power line right of way (RoW) is a great example of the ecological process of succession interrupted by disturbance. Succession refers to the changes in plant species that occur over time in a specific area, like an abandoned field in the Georgia piedmont. Assuming you start with bare dirt the first few years you will see it colonized by annual plants. (Annuals germinate in the spring, grow, flower and set seed, all in one year.) As time passes perennial plants begin to arrive. Perennials, starting from seed, typically produce enough leaves to support the growth of a root system in the first year. The following spring their established root system enables them to grow rapidly, shading out their annual plant competitors. They may or may not flower in the second year, but will do so in their third. Each fall the above ground stems and leaves die back, leaving only the roots and rhizomes alive in the ground. Trees eventually invade the area with those species that grow rapidly at first, to overtop the perennials. Later tree colonists will be shade-tolerant and can survive in the understory until a gap is produced by the death of an earlier colonist.

This general pattern can be modified by climatic factors: temperature and rainfall. In the arid west the perennials are dominated by grasses. These grasses can be invaded by trees, but, where fires are frequent, the trees are killed and the prairie becomes the stable vegetation. When fires are prevented and/or controlled by man, the trees invade and replace the prairie vegetation. This has happened to the prairies of Ohio, Indiana, Iowa, Missouri and eastern Kansas, all of which had extensive prairies dominated by grasses.

The stems of all the floodplain RoW plants are dying for the season.

The RoW is a great example of the how the perennial stage of succession can be maintained by disturbance. The disturbance here is annual mowing and, in the RoW outside of the Botanical Garden, herbicides. The lower section of the RoW, between the access road and the river is dominated by wingstems and goldenrod. All these and other species have set seed and are now undergoing senescence of their above ground structures, leaving the roots and rhizomes alive in the soil. These plants are all perennials as are almost all the other species we find in the RoW.

Seed heads of one of the wingstems.

Seeds of Common Wingstem; notice the "wings" on either side of the seed and the tiny "antennae." They look like tiny nsects.

The three species of wingstems produce seeds (really fruits) with thin flanges, suggesting that the seeds could be wind dispersed. Goldenrod seeds have a short tuft of bristles at one end. Experiments have determined that they can be blown an average distance of about 5-6 feet. The RoW is so crowded with plants that reproduction by seed is probably not as important as the rhizomes that both goldenrods and wingstems produce. It is unknown how many of the stems of these plants are really genetically identical clones arising from the rhizomes of a single plant.

Here’s a handy way to remember the characteristic of perennial plants: Sleep, Creep and Leap. 

Sleep refers to the first year when the seed germinates, produces a few leaves and expends most of its energy growing a sturdy root system.

Creep is the second year in which the above ground stems reap the benefit of the root system establish in the sleep year. The plant may produce some flowers this year.

Leap is the third year and beyond. The plant should be a vigorous bloomer.

White Trail Spur:

Unidentified mushrooms

Cross Vine climbing up a tree.
If it reaches the top where the sunshine is it will flower up there.

On the way back to the Visitor’s Center we encountered a Crossvine and a number of mushrooms, both in the woods and growing in the mulch at the edge of the sidewalk around the Children’s Garden. 

Children’s Garden Sidewalk:

Leaves of Black Gum turn a rosy hue.

The leaves of the Black Gum trees between the Children’s Garden and the Administration Building are beginning to turn a light red. The shade of red is similar to the leaves of Sourwoods that are growing in the upper parking lot.

The change in color of autumn tree leaves is caused by the removal of chlorophyll from the leaves. Chlorophyll is green in color and there is so much of it that it masks the other colored compounds that are in the leaf. When chlorophyll is removed these other pigments are revealed. They are called carotenoids; pronunciation: kay-rotTEN-oids). It is because of them that many tree leaves turn yellow or orange in the fall. (Carotenoids get their name from carotene, the substance that gives carrots their orange color.)

The red coloration in many autumn leaves is due to a pigment called anthocyanin. (Pronunciation: ann-tho-SIGH-ah-nin.) Unlike the carotenoids, which are present throughout the summer, anthocyanin is made in the fall when the leaf is aging. There are many kinds of anthocyanins and they run the gamut from red through purple.

Why anthocyanins are synthesized in the autumn is something of a mystery. A plausible hypothesis is that they act as a sunscreen, shielding the photosynthetic apparatus from damaging ultraviolet light while it is being disassembled. They are also anti-oxidants and scavenge up damaging molecules that are produced by UV radiation.

Anthocyanins also appear at another time in the life of a leaf – when it is emerging from the bud in spring. You’ve probably noticed that new oak leaves are usually pink in color. The pink is due to anthocyanins and they may be protecting the photosynthetic apparatus as it is being constructed in the new leaf.

Another anthocyanin mystery: Why is the underside of the Tipularia leaf purple? If anthocyanins protect the photosynthetic apparatus you would think that the upper side might be a better location, wouldn’t you?

For a good technical review of the different hypotheses regarding the function of anthocyanins this paper is a good review, but it’s not aimed at a lay audience. If you’re curious you can read it for free and learn about the dozen or more ideas about their function.

SUMMARY OF OBSERVED SPECIES:

American Wisteria	Wisteria frutescens
Ginkgo	Ginkgo biloba
Winterhazel	Corylopsis veitchiana
American Witch Hazel	Hamamelis virginiana
Ozark Witch Hazel	Hamamelis vernalis
Bigleaf Magnolia	Magnolia macrophylla
Purple Passionflower	Passiflora incarnata
Common Wingstem	Verbesina alternifolia
goldenrod	Solidago sp.
Crossvine	Capreolata bignonia
Blackgum	Nyssa sylvatica