Ramble Report August 8 2019

Today's Ramble was led by Linda Chafin.

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 Linda Chafin.

Today’s Focus: How trees tell a story about the landscapes where they grow.

32 Ramblers met today.

Announcement: August 23 and 24 are the dates for the Great Georgia Pollinator Census.  UGA and the Bot Garden will be participating.  The Nature Ramblers will be contributing to this citizen science effort.  The August 22 Nature Ramble will be a dry run/learning experience to get the Ramblers ready for their participation.  Details will follow.

 

Today's reading: Bob recited a quote from Thomas Merton – “Nothing has ever been said about God that hasn’t already been said better by the wind in the pine trees.”

Today's Route:   We left the Visitor Center plaza and walked up the steps to the upper parking lot, then walked to the far end of the parking lot and crossed the road to the head of the White Trail.  We walked it to the ROW, and took a left back over to the road.  We then walked down the road to the Purple Passionflower vines and returned to the Visitor Center via the road.  The usual social hour followed at the Café Botanica.

OBSERVATIONS:

Sweetbay Magnolia
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Our first tree on this ramble was Sweet Bay Magnolia, planted near the entrance to the Visitor Center. A few fruits left on the branches reveal its Magnolia connection – their red seeds dangle on thin threads from the lumpy, fruiting “cone.”

Sweetbay Magnolia fruits with red seeds
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 The “cones” look like miniature versions of Southern Magnolia fruits that we are more familiar with. (The cone is actually an aggregate of many small fruits, each bearing a single red seed.)

The thin, smooth, pale gray bark tells us that this is a tree never threatened by fire, which would quickly destroy the bark and the underlying growth tissue, the cambium. Instead, it occupies wetlands called bayheads that develop at the springheads and upper stretches of Coastal Plain streams – bayhead for the three “bays” that grow there: Sweet Bay, Red Bay, and Loblolly Bay. Sweet Bay also grows in wetlands in the lower Piedmont.

American Beech trees
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Another smooth-barked tree grows just around the corner along the steps to the parking lot: American Beech. Common throughout most of Georgia, Beeches grow in moist soils on mid to lower slopes in north Georgia, where they are protected from fire. In south Georgia, they are a major component of the Beech-Southern Magnolia plant community that occupies moist slopes in ravines along large streams. This community is protected from the heat and fires of Coastal Plain uplands and supports a great diversity of “northern” species that require cooler, moist conditions.

Beech Blight Aphids doin' their dance, shakin' their waxy butts.
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This American Beech has a large colony of Beech Blight Aphids on one of its lower branches. These aphid colonies always bring joy to the hearts of Ramblers – merely touching the branch or waving a hand stimulates a choreographed boogie-woogie of performing aphids. The finest dance line south of Radio City Music Hall. Search Youtube for "beech blight aphid" and you'll find several movies of their performance. A bowl of popcorn is suggested.

The aphids, in spite of their name, never seem to do significant damage to the Beech trees. Their sugary droppings (aphid poo, AKA honeydew) make them ecosystem engineers for the Sooty Mold fungus that only grows on the droppings below a colony. (We saw the fully developed Sooty Mold fungus on our July 25, 2019, Ramble.)

One of the rarest tree species in Georgia, Yellow-wood, is planted at the top of the stairs to the parking lot. Its smooth, gray bark tells the same story that Sweet Bay and Beech do: it is native to areas protected from fire. In Georgia, it occurs in steep, north-facing coves in the mountains, plant communities that stay cool and moist, sheltered from droughts and fire. Yellow-wood is one of the few tree species in the bean family in Georgia, along with Redbud and Black Locust (there are many “bean trees” in the tropics).
 

Cross-section of Yellowood showing the yellow colorationPhoto credit: University of Kentucky/http://www.uky.edu/hort/Yellowwood(click to enlarge)

Yellow-wood does indeed have yellow wood; Jim, a new Rambler and a retired forester, described some beautiful furniture he’d seen made of cherry with yellow-wood inlay.

Virginia Pine
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Emerging into the parking lot, we encounter a very different tree, one adapted to frequent fires. Here, rows of Virginia Pine were planted around the Garden parking lots in the mid-1980s – a poor choice from an ecological point of view, since they don’t naturally occur in the mid-Piedmont, but a good choice for healing a construction site. Fast-growing Virginia Pines have been widely used to re-vegetate strip mines, road cuts, and the like. 

Virginia Pine distribution in Georgia
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This map from the USDA Plants web site shows the natural distribution of this species in Georgia:  primarily in the mountains and upper Piedmont. (The green counties shown further south in Georgia–Clarke, Oglethorpe, Greene–represent planted trees.) Virginia Pine grows as far north as Long Island, New York, in acidic, sandy or clayey soils. It has small cones and 2 twisted needles per bunch. Virginia Pine has an interesting relationship with fire. It lives in naturally fire-prone plant communities on ridge lines and hot, dry, south-facing slopes, but – it is killed by severe fire. 

Virginia Pine bark is thin and scaly
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Its scaly bark is much thinner than that of other pines and easily burns through to the cambium layer that produces new tree growth. But without fire, this prolific seed-producer will eventually die out in a given area because its seeds need bare, mineral soil to germinate. Fire burns off the layer of needles that blankets the ground, readying the soil for the huge seed crops that Virginia Pines produce. This kind of fire is called “stand-replacement fire” because it kills an entire stand of trees but prepares the way for the stand to follow. (During the ramble, I said this species has “serotinous” cones – cones that open and shed their seeds only after a fire. I was mistaken, confusing Virginia Pine with a similar tree in Florida called Sand Pine and two other Blue Ridge species that do have serotinous cones: Table Mountain Pine and Pitch Pine.)

For an interesting article on the role of fire in western pine forests, read this article:  https://www.allaboutbirds.org/old-flames-the-tangled-history-of-forest-fires-wildlife-and-people/

Sourwood leaves
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Sourwood is typically found in the same dry, acid-soil sites as Virginia Pine, in the so-called the “pine-oak-heath community.” The heaths referred to in that name are members of the heath family (Ericaceae) such as mountain laurel, rhododendron, blueberries–and Sourwood. It is top-killed by frequent or very hot fires but responds to fire by sprouting vigorously from the bases of burnt trunks. If fires are not too frequent, this strategy maintains Sourwood in the forest in about the same numbers over time.  

Undersurface of Sourwood leaf
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Sourwood is one of those plants that encourage us to engage senses other than sight: run your finger up the midvein on the back of the leaf and feel the line of stiff hairs; chew a leaf or twig and taste the oxalic acid stored in its tissues. Sourwood is in the genus Oxydendrum, which translates literally as acid-tree. (Oxalic acid also gives sorrel or sour-grass its acid taste–it’s okay to chew but don’t eat a lot of it.) Of course, sight is a good way to know this tree too–it has some of the most brilliant fall leaf color in our north Georgia forests and every June each tree produces many hundreds of small white flowers (Sourwood honey–MMM-mmm).

Post Oak
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Crossing the road to the White Trail, we encountered a Post Oak, another common species of dry, acidic soils in the Piedmont and throughout the southeast. Its heavily ridged and furrowed bark protects it from even frequent hot fires. Its leaves are leathery and have hairy undersurfaces, two traits that retain moisture. This is one species that will definitely thrive under the hotter, drier, fire-promoting conditions predicted for the southeast by climate change scientists. Post Oaks are in the “white oak” sub-genus: its leaves have rounded lobes and its acorns mature in one year: we could see them developing on this year’s twig growth. Acorns of oaks in the “red oak” subgenus take two years to mature; this time of year, they will have nearly mature acorns on older twigs and very small, immature acorns on this year’s twigs. Even though Post Oak leaves seem pretty tough, they are preferred host plants for a number of moths, including two especially beautiful species: Rosy Maple Moth and Cecropia Moth. A complete list of caterpillars that feed on Post and other oaks is at https://www.illinoiswildflowers.info/trees/tables/table266.htm.

Ecologists describe forests in terms of the layers of vegetation: the canopy (or overstory) contains the tallest trees that capture sunlight by raising their leaves to the highest levels in the forest; the subcanopy (or understory) contains shorter trees whose branches spread horizontally to catch the small flecks of sunlight that make it through the canopy; the shrub layer contains woody plants that are shorter than the subcanopy, usually with multiple trunks; and the herb layer that contains the soft-bodied plants that we usually call wildflowers.

Examples of subcanopy trees in the Garden’s forests include Flowering Dogwood and the ubiquitous (here at the Garden) Hop Hornbeam.

Red Mulberry leaves; notice the pointed "drip tip."
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On the dry slope along the White Trail, we were surprised to see a Red Mulberry, typically found in floodplains and moist lower slopes. Its leaves are distinctly heart-shaped, tapering to an elongated tip called a “drip tip.” A drip tip is an indicator that long-ago ancestors of Red Mulberry evolved in a wet forest environment (hmmm... like summer in Athens?). Drip tips let rain run quickly off the leaf, reducing the growth of fungi and disease-causing bacteria on the leaf surface. Studies have shown that removing the drip tip from a leaf leads to three times the amount of water accumulation on the leaf. Besides noting the heart-shaped leaves with drip tips, rub the upper leaf surface with your fingertips–Red Mulberry leaves have a sand-papery surface. Then tear a leaf–all members of the Mulberry family have milky latex in their tissues.

Hop Hornbeam leaf
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Hop Hornbeam is common on all the slopes at the Garden–whenever you see these calcium-loving trees in such numbers in the Piedmont, you know there is something interesting going on with the soil. Here that interesting factor is the presence of amphibolite, a bedrock that produces soil with a higher pH than typical acidic Piedmont soils. Amphibolite is a “mafic” rock – mafic being a “portmanteau” word formed from magnesium and “ferric,” i.e. iron. Amphibolite also contains calcium which, along with the magnesium, raises the pH of soils that form above it.

Hop Hornbeam sap wells (constructed by Yellow-bellied Sapsuckers)
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Hop Hornbeams seem to be especially attractive to Yellow-bellied Sapsuckers – many of these trees at the Garden have the telltale rows of their feeding holes.

Virginia Snakeroot
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Katherine spotted the “hard to spot” Virginia Snakeroot along the north side of the White Trail. Close kin to the Dutchman’s Pipevine, this inconspicuous herb couldn’t be more different in habit. But if you brush aside the leaf litter at the base of the plant in the spring, you’ll find a tiny “Dutchman’s pipe” flower blooming at the very base of the stem. Just like its large woody sister species, Virginia Snakeroot leaves support larvae of the Pipevine Swallowtail. We see these large, beautiful, blue and black butterflies occasionally at the Garden–they must be much better at spotting this small, uncommon plant than we are. Sometimes it seems that half the wildflowers in the SE are named “snakeroot.” In this case, the name is warranted–both stems and roots are zigzag (though, really, are snakes zigzag?) and the species name is “serpentaria.”

The White Trail winds its way through the classic Piedmont Oak-Hickory forest, dominated here at the Garden by White Oak, Scarlet Oak, Northern Red Oak, Mockernut Hickory, Pignut Hickory, and Red Hickory.

Transition between the undistinguished lower bark on a White Oak trunk and the characteristic vertical bark plates pulling away from the mid and upper trunk,
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Northern Red Oak with its long white furrows, aka “ski trails”
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Mockernut hickory leaves are compound, composed of 7-9 oval leaflets.
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The lower leaf surfaces and stalks of Mockernut Hickory are covered with pale hairs.
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Leaving the Oak-Hickory forest, we headed to the Passionflower vines to check the progress of the Gulf Fritillary population, passing some summer-flowering and fruiting plants on the way.

Mountain-mints attract many different types of pollinators with their white floral bracts and the nectar guides – lines of purple dots – on their flowers
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Swamp Hibiscus in fruit. Don peeled back the calyx to expose the short but otherwise okra-like fruit.

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Coastal Sweet Pepperbush in fruit and flower.

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It looks like this is another slow year for our favorite butterfly. Only a few Gulf Fritillary eggs and caterpillars were seen and most of the leaves are pretty intact. Katherine suggested that the vertically exposed position of the plants on this fence leaves the caterpillars especially vulnerable to birds.

Passionflower fruits are beginning to ripen.

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Don once again displays his photographer chops with this amazing photo of a Gulf Fritillary egg on the tip of a Passionflower tendril, a favored place for laying their eggs.

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SUMMARY OF OBSERVED SPECIES:

Sweetbay Magnolia	Magnolia virginiana
American Beech	Fagus grandifolia
Beech Blight Aphids	Grylloprociphilus imbricator
Ketucky Yellowwood	Cladrastis kentukea
Virginia Pine	Pinus virginiana
Sourwood	Oxydendrum arboreum
Elliott’s Blueberry	Vaccinium elliottii
Red Maple	Acer rubrum
Loblolly Pine	Pinus taeda
Post Oak/White Oak hybrid?	Quercus species
Red Mulberry	Morus rubra
Virginia Snakeroot	Aristolochia serpentaria
Eastern Hophornbeam	Ostrya virginiana
Cranefly Orchid	Tipularia discolor
White Oak	Quercus alba
Northern Red Oak	Quercus rubra
Mockernut Hickory	Quercus tomentosa
White Ash	Fraxinus americana
Climbing Milkvine	?????
River Oats	Chasmanthium latifolium
Post Oak	Quercus stellata
American Wisteria	Wisteria frutescens
Southern Mountain Mint	Pycnanthemum pycnanthemoides
Devil’s Walking Stick	Aralia spinosa
Coastal Sweet Pepperbush	Clethra alnifolia
Swamp Rose-mallow Hibiscus	Hibiscus grandiflorus
Purple Passionflower	Passiflora incarnata