Ramble Report July 20 2017

Today's Ramble was led by Dale Hoyt.

The photos in this post, except where noted, came from Don's Facebook album (here's the link).

Today's post was written by Dale Hoyt.

33 Ramblers met today.

Today's reading: Today was Sandra Hoffberg's last Ramble. She recently completed her Ph.D. and is moving to a postdoctoral position at Columbia University. Sandra read the

following:

My first ramble was on June 6, 2013. I came because, at my comprehensive exams in January 2013, my committee realized I had no knowledge of natural history. At that point, I could hardly identify a single tree by its bark or leaves, and I had no idea what kinds of trees grew in the southeast. I lacked this sort of general knowledge that people seemed to have slowly acquired over their lifetimes, and the task of learning Natural History was daunting. The only thing that could get me started was an excuse to skip work on my birthday. So on June 6, my 26th birthday, i showed up to ramble in a perfect birthday outfit but perhaps not the best rambling outfit - a bright yellow dress and flip flops. Dale and Hugh broke down ferns into a dozen identifiable types, and I left having a new bit of knowledge. Really, I was hooked, and came every week for a couple years, eventually wearing much more appropriate clothes. I have learned so much from the nature rambles, and I have really loved them. Besides ferns and trees and mushrooms and butterflies, I have gained a new and strong appreciation for weeds, for the little things that are so easy to overlook, but so magnificent to see if you take the time. My favorite thing that I have learned is that experts can be self taught, can be hobbyists, can learn a lot just a little at a time. And repetition is key. I really want to thank this group of experts for teaching me that. As I head off to New York City, I want to say that I will miss the ramblers and the State Botanical Garden of Georgia.

Sandra, we will miss you too!

Today's route:  We first visited the carnivorous plant pool at the front of the visitor's center. From there we went to the Orange trailhead via the upper parking lot. We then walked down the Orange Trail to the Orange spur trail bridge over the creek, crossing the bridge and returning to the visitor's center.

Carnivorous plant pool

A floating mat of Azolla; the ring around it keeps it from spreading and covering the pool.

Closeup of the Azolla ferns above

Azolla fern – an aquatic fern, it covers water like duckweed. It reproduces vegetatively and can rapidly cover any open water surface. But the really remarkable thing about this plant is its symbiosis with a cyanobacterium, Anabaena azollae, that can fix atmospheric nitrogen. Anabaena lives in tiny pockets in the Azolla leaves and functions like the nitrogen fixing bacteria that live in the root nodules of legumes (plants in the bean family).

Azolla is used in China and other Asian countries to provide nitrogen compounds in their rice paddies. The tiny fern yields its nitrogen to the soils in two ways: directly, when it is turned into the soil when the paddy is drained and indirectly, when ducks eat the Azolla and their feces are mixed into the paddy water.

Nitrogen fixation – nitrogen is often a limiting element for plant growth and must be added to increase crop production. Organic farmers use cover crops of plants like clover that have symbiotic bacteria that can fix nitrogen. When these crops are plowed under the nitrogen compounds are added to the soil. Such crops are often called "green manure."

Originally animal manure was used to fertilize soils, but after the discovery of the New World guano deposits off the coast of Chile were mined and became a dominant source of fertilizer. But those were finite deposits and it became obvious by the early 20th century that another source of nitrogen fertilizer was necessary if the growing population of the world was to be fed.

A German chemist, Fritz Haber, invented a process that could do what bacteria had been doing for millions of years. The Haber-Bosch process was very expensive but it replaced the fertilizer from the guano deposits and is now the primary source of nitrogen fertilizer in the world. Haber and Bosch both received Nobel prizes.

Pitcher plants grow in nitrogen-poor soils such as bogs and wet areas of coastal plain savannahs. The pitcher is a modified leaf. It is like a large leaf rolled up to form a tube, closed at the bottom, open at the top, and the sides where the leaf edges meet sealed. Water collects in the pitcher and visiting insects fall into it and drown. The inner surface of the tube is coated with wax to make it slippery, so the insects cannot crawl out. In addition, there are often downward pointing hairs inside the pitcher that prevent an animal from climbing up. Eventually the struggling insects die and then begin to decompose.

Digestion of insects by pitcher plants mostly depends on other organisms that live in the pitcher fluid. This fluid is home to a rich mixture of bacteria and the larvae of many kinds of insects, some found only in pitcher plants. The insect larvae feed on the dead material (and some eat the bacteria) while bacteria decompose the remains. The nitrogen compounds released by decomposition are absorbed by the pitcher plant but the insect larvae, in effect, steal some of it for their own use. But some of that "borrowed" nitrogen is returned to the pitcher fluid when the insects defecate. Each pitcher, then, is a tiny ecosystem in which nitrogen and other elements are continually recycled. Nitrogen enters in the form of living insects. When they die nitrogen passes into bacteria, insects living in the pitcher and the pitcher plant itself. Then some nitrogen escapes in insects leaving the pitcher. But not before they have returned some of the nitrogen through their feces.

Some carnivorous plants do secrete digestive enzymes, but our common species mainly rely on the insects and bacteria living in the pitcher to do the digestion..

Pitcher in the background (L); side view of a pitcher plant flower

 (R)

Pitcher plant flowers are among the strangest in the plant world. A single flower grows on a long stem that curves over at the top, so the flower hangs upside down. Each inverted flower has five drooping petals.. From the center of the flower the female structure, the pistil, hangs downward and its end is flared out so it resembles an upside down open umbrella.

The inverted umbrella shaped part of the pistil is clearly visible in this closeup photograph.

This "umbrella" has five equally spaced stigmas, the female structures that receive pollen. Each stigma is located in the gap between adjacent petals. The male structures, the stamens, grow in a circle around the pistil. Because the flower hangs upside down the pollen shed from the stamens falls downward and collects as a layer of dust in the "umbrella".

Pollination occurs when a bee makes its way into the flower, entering between adjacent petals. This brings its body in contact with one of the stigmas. Pollen on its body it is transferred to the stigma as the bee brushes over it. When the bee is inside the flower it looks for nectar and in stumbling around on the floor formed by the "umbrella" it gets covered with pollen. It also gets coated with pollen when it bumps into the stamens. It then leaves the flower by forcing its way out through one of the drooping petals. Any pollen it picked up will be transferred to the stigma of the next flower it enters.

Upper Parking Lot

Fall webworm nest enclosing a Sourwood branch

 

Fall webworm caterpillars visible inside the nest

A single Fall webworm caterpillar removed from the webbing

Fall webworm caterpillars have built a large silken nest enclosing a Sourwood tree branch. This moth favors Sourwood but can also lays its eggs on other kinds of trees. When the caterpillars hatch they enclose the end of the branch they are on with silk. This silken nest protects the caterpillars inside it from attack by predators. As the leaves inside the nest are eaten the nest is enlarged by the growing caterpillars, covering more and more of the uneaten leaves on the branch. Sometimes, if eggs have been laid on nearby branches, two nests will actually fuse together.

The Fall webworm nest is sometimes confused with that of the Tent caterpillar. They can be easily distinguished – the Tent caterpillar nest is always located in the crotch of a tree, usually a cherry tree, and does not enclose a branch and its leaves. Tent caterpillars don't eat leaves inside their nest; they travel out of the nest to find fresh leaves, eat them there and then return to the nest to digest their meal. Tent caterpillars are only found in the spring whereas Fall webworm nests are seen throughout summer and fall (only rarely in late spring).

Neither of these caterpillars defoliate an entire tree. They mostly consume the leaves of one or a few branches and the damage they do is minor – they just look unsightly for a short period of time.

Numerous fruits on Sourwood tree
A few weeks earlier each fruit would have been a small white flower.

Sourwood trees flower in late spring, producing curved inflorescences with dozens of tiny white flowers. The small tree we saw today is finished flowering and we saw the fruits developing. The leaves of sourwood are much longer than they are wide and opposite edges at the middle of the leaf are approximately parallel.

The honey made from nectar collected from Sourwood sells for a premium price. Many honey aficionados regard it as the best honey there is. It can sit on the shelf for a year or more with crystallizing.

Orange trail to Orange spur

Dead cicada with the abdomen of a yellow jacket wasp sticking out of the thorax

We had a two-for-one event when a dead Cicada was found on the trail. Almost completely concealed inside it was a Yellowjacket wasp busily eating the interior. This the time of year that empty cicada "skins" are often found clinging to the bark of trees. These skins are the exoskeletons of cicada nymphs that have spent several years underground, feeding on tree roots. Once they have reached the size of metamorphosis the dig upwards and crawl up the nearest stationary object. The shell splits along a seam running down the middle of the back and the adult cicada slowly climbs out of its old exoskeleton. Its wings are small, wrinkled bags and its body pale and soft. Over the next few hours it will inflate the wings and gradually harden its exoskeleton. Then it will be free to fly off and begin broadcasting (if it's a male) the courtship sounds we hear on summer afternoons.

Some Ramblers noticed a small, perfectly circular hole in the soil. I didn't see it but the description sounded like the hole left by the cicada nymph after it has climbed out of the ground. 
Whenever I hear a cicada chorus I'm reminded of a line written by the Japanese poet Basho:

Nothing in the cry of cicadas suggests they are about to die. 

Dog vomit slime mold

A Dog vomit Slimemold was found on the surface of a dead tree. Usually these slimemolds are seen on garden mulch. Slime molds used to be considered fungi but it has been discovered that they have more in common with unicellular organisms. They begin life as microscopic amoebas that wander about in dead wood feeding on the bacteria they encounter. When they run out of food they begin to seek out other slime mold amoebas and fuse with them, eventually forming a large, giant amoeba that crawls like a blob of protoplasm, which it is, over the surface. This giant blob produces spores all over its surface and ultimately fragments into pieces that blow away.

Beech blight aphids in boogie=woogie posture

A nearby Beech tree had a surprise -- several branches carried large colonies of Beech blight aphids.  These aphids are fairly common in the Garden and we always have fun when we find them. Just touch the branch or wave your hand over the colony and they immediately start to "boogie-woogie." Each aphid secretes waxy threads that cover its back and rear end. When they start to dance they tilt their abdomen straight up and begin to wiggle. The waxy threads are sticky and it is thought that waving around the threads might fend off parasitic flies or wasps that would like to lay an egg on one of the aphids.

Sooty mold growing beneath the aphid colony

The aphid "poo" (also called honeydew) accumulates on objects beneath the colony. The sticky substance is colonized by the spores of a mold. The mold can develop into a structure the looks like a kitchen scouring pad. Maybe we'll see one later this fall.

Where the Orange trail creek begins is an example of Headward erosion. The water that forms the creek seeps out at the base of the moist soil face. The soil eventually slumps off and is carried away by the seepage at the base. The process repeats and, over time, results the upstream movement of the head of the creek. Since I've been walking the Orange trail this gully has extended at least 10 feet and probably more. No one has actually measured it. The same process is responsible for forming Providence Canyon in south Georgia.

Christmas ferns are the commonest ferns seen in the Garden. No one is sure of the origin of their common name but it may come from the fact that their fronds remain green during the winter, instead of dying back as most other ferns do. Another theory is that the shape of leaflets (pinnae, in fern-speak) reminds some people of the Christmas stocking that are "hung from the chimney with care."

All living ferns reproduce in two ways: 1) vegetatively; e.g., from a perennial rhizome, and 2) by spores. The Christmas fern produces spore from the terminal sections of some of its fronds. If you look at a frond you will notice that the pinnae are smaller and have rusty brown undersides. The brown coloration is due to spore producing structures. Different kinds of ferns differ in the patterns and locations of the spore producing structures, as seen in some nearby Rattlesnake fern and Grape fern. Both of these have two types of fronds: sterile and fertile. The sterile fronds are the green leafy parts and the fertile frond lacks leaves but is covered with spore producing structures.

Christmas fern

Rattlesnake fern

Broad beech fern
Tilt you head to the right
Does it look like a fox face to you?

The fertile frond in Grape ferns arises from the stalk near the ground. In the similar Rattlesnake fern the fertile frond arises from the stalk where the leaf blades are attached.

Another fern we saw further down the trail is the Broad Beech fern which grows in colonies. Each clump of ferns is probably produced by a common underground rhizome. The fern is easily identifiedby the two basal pinnae that point back toward the base of the plant. To some people the arrangement of the pinnae suggests a fox with the two basal pinnae becoming the ears. The sori (spore producing structures) are located near the margins of the pinnae.

Tree falls create light gaps – this Northern Red Oak has not only fallen, but it has taken several other trees with it, creating an opening in the canopy. This opening allows light to reach the plants that were in the undersory beneath the former oak. They now have a chance to bolt for the sky and fill the now empty space above. Many small trees linger in the understory, barely surviving, unable to grow because they don’t receive enough light. The formation of light gaps is an important way in which the composition of forests can change. For example the earliest trees to colonize an abandoned field are often shade intolerant. They will persist for a hundred years or more, but their seedlings will not be able to survive in the shade cast by their parents above. But any shade tolerant seedlings that appear in the understory or shrub layer will be able to replace the pioneer species when they succumb to disease or lightning strikes or disease. It is a time scale that is much longer than humans experience, so we seldom are able to perceive that it is happening around us.

While most plants can't survive without sunlight some can. They become parasites, an example of which can be found next to the trail: Beech drops – a parasitic plant living on Beech roots. Beech drops have no chlorophyll so they are totally dependent on their host plant, the Beech tree. They lack chlorophyll are are therefore not green. Why bother to make a substance that you don't need?

They are brown and inconspicuous stalks, hard to see against the background of dead leaves.

Tick-trefoil flowers with ripening "beggar's lice" (the triangular green objects)

If you have ever walked in the woods or fields in the fall you will be familiar with "stick-tights" or "beggar's lice," plant seeds that cling like velcro to your pants or socks. These are fruits of a plant called Tick-trefoil and most people have never seen or been aware of it. We saw a group of them by the trail near the bridge and some had developing fruits. Each stick-tight is a single segment of a larger fruit that the plant produces. Each segment contains a single seed. When you brush against them only one segment may break off or, more likely, the whole fruit, consisting of a string of stick-tights, may break off and attach itself to you clothing.

Five-lined skink

Golden garden spider feasting on Tiger swallowtail butterfly
Normally this would happen in the spiders web but the spider and its prey have been dislodged.

On the way back to the visitor's center some of us saw an unusual sight: a Tiger swallowtail butterfly killed by an Golden garden spider and being eaten by the same. Also running along one of the walls was a lizard with a blue tail and five yellow lines running the length of its body. There are three possible species it could be, but to identify it requires that it be caught, so we're going to have to be satisfied just calling it a Five-lined skink.

SUMMARY OF OBSERVED SPECIES:

Azolla	Azolla sp.
Pitcher plants	Serracenaceae
Blue dragonfly	Order Odonata
Map turtle	Graptemys sp.
Fall webworm	Hyphantria cunea
Cicada	Neotibicen sp.
Yellow jacket	Vespula sp.
Dog vomit	Fuligo septica
American beech tree	Fagus grandifolia
Beech blight aphid	Grylloprociphilus imbricator
Sooty mold	Scorias spongiosa
Katydid	Amblycorypha sp.
Christmas fern	Polystichum acrostichoides
Southern grape fern	Botrychium biternatum
Rattlesnake fern	Botrypus virginianus
American holly	Ilex opaca
Broad beech fern	Phegopteris hexagonoptera
Black velvet bolete	Tylopilus alboater
Northern red oak	Quercus rubra
Beech drops	Epifagus virginiana
Naked tick-trefoil	Hylodesmum nudiflorum
Downy woodpecker (seen)	Picoides pubescens
Acadian flycatcher	Empidonax virescens
Ruby throated hummingbird	Archilochus colubris
Tiger swallowtail	Papilio glaucus
Golden garden spider	Agriope aurantia
Five-lined skink	Eumeces (Plestiodon) sp.