Ramble Report April 11 2019

Today's Ramble was led by Linda Chafin.

All the photos in this post, unless otherwise credited, were taken by Hugh and Carol Nourse, former leaders of the Nature Ramblers.

Today's post was written by Linda Chafin.

Today’s Focus: The Rock and Shoals Granite outcrop.

25 Ramblers met today.

Today's reading: No reading today.

Announcements: The Garden is participating in a "Plantapalooza" plant sale this weekend (Saturday). Click here for the details and a link to the species offered.

Today's route: Ramblers met today at the Botanical Garden and carpooled to the Rock & Shoals Natural Area off Barnett Shoals Road. Mid-April is peak blooming season for the Piedmont granite outcrop specialties and endemics.

Piedmont granite outcrops are found from SE Virginia to central Alabama, totaling about 12,000 acres, but 90% of them occur in the Georgia Piedmont. There are approximately 5,000 granite outcrops in Georgia larger than ¼ acre. Unfortunately, only 11 of them are protected, including Rock and Shoals (R&S), which is owned jointly by Athens-Clarke County and Georgia Department of Natural Resources. Though small, R&S supports many of the outcrop endemics and four rare species.

 

Hugh Nourse, Carol Nourse, and Liese Der Vartanian spent seven years conducting a thorough plant inventory of the entire Natural Area, including the woodlands surrounding the exposed rock that are not on private land. They ultimately compiled a list of nearly 380 species of plants and lichens – an amazing diversity for so small an area.

Grasses, rushes, and sedges = 14 species

Forbs (wildflowers and other soft-tissue plants) = 139 species

Ferns = 14 species

Mosses = 4 species

Trees, shrubs, and woody vines = 176 species

Lichens = 32 species

Although some granite outcrops are composed of true granite, an igneous rock, most are actually composed of metamorphosed granite – some form of gneiss. R&S rock is called Athens Gneiss.

Plants on granite outcrops contend with drastic environmental conditions: temperatures at ground level of up to 120⁰ F. in the summer, and freezing temps in the winter. Most of the rain that falls on the outcrops runs off, leaving the rock an “island of desert in a sea of forest,” according to Robert Wyatt, a local expert in granite outcrop plants. To survive the harsh summer conditions, outcrop plants have developed a variety of survival strategies.

Hairy Spicerwort

The first plant we saw today that has adapted to the heat and high light on the outcrops is Hairy Spiderwort, which shows up along the access trail to the outcrop as well as on the rock. Looking much like the common garden spiderwort, this species is covered with long, silky hairs that reflect light and trap moisture next to the stems and leaves. Flower colors seen at R&S include dark blue, violet, dark pink, and white – all the same species, just natural variation in flower color.

Diamorpha; also called Elf Orpine

Sandwort

 

Tiny Bluets

Emerging onto the outcrop, we were treated to the sight a rock outcrop in full spring glory – Diamorpha’s red stems topped by white flowers, Sandwort with its solitary white flowers atop wiry stems, and Tiny Bluets with their red “eye.” All of these species are annuals that survive summer on the outcrop as seeds. If they are not eaten by birds and rodents, the seeds will germinate in the fall when temperatures drop and steady winter rains begin. After germinating, the plants overwinter as tiny rosettes of leaves that are ready to spring into reproductive action once warm weather arrives. After flowering, fruiting, and setting seed, the cycle begins again.

Sunnybells

 

False Garlic

Another effective survival strategy on the rock has been adopted by two typical outcrop plants, False Garlic and Sunnybells. Both are bulb-bearing plants and, after flowering, go dormant to survive the summer underground as bulbs. False Garlic is so called because it lacks the odor characteristic of other plants in the onion genus, Allium. Sunnybells’ name is obvious, and so is the genus name, Schoenolirion, which means “pretty lily.”

Another sort of bulb plant that we saw is Piedmont Quillwort, a member of an ancient group of plants that reproduces by spores. We dug up and examined the swollen base of the plant (not a true bulb) where the spores are produced. Found only in the muddy edges of water courses on outcrops, Piedmont Quillwort’s spores are spread by the small rivulets of water that seep across the rock. With its narrow leaves, this plant looks much like an immature Sunnybell or False Garlic. Two other species in the Quillwort genus are extremely rare and federally listed but don’t occur at R&S. They occur on Arabia Mountain and Heggie’s Rock, two outstanding outcrops in Georgia.

An important strategy for survival on outcrops is succulence – the ability of a plant to store water in its stems and leaves. We could easily see this on the Diamorpha, whose bright red stems and leaves are swollen with water. Prickly Pear Cactus, Yucca, and Fame-flower are other examples at R&S of succulent plants that thrive during the hot summer months.

The fascinating process of plant succession is continually taking place on rock outcrops, slowly changing the character of the outcrop with a fairly predictable sequence of plant species displacing one another as the conditions change cross the outcrop and also in microhabitats.

When the outcrop first emerged at the surface in the deep past, the bare rock lacked all organic life. Lichens arrived and began to break down the rock by secreting organic acids and contributing their dead tissues to the earliest stage of soil formation. The first true plants to arrive, the mosses, soon followed and continued the process of soil formation. Once there was an inch or so of soil, Diamorpha was able to get a toehold. As soil built up, Sandwort arrived, then Spiderworts, Dwarf Dandelion, Flatrock Pimpernel, and other forbs. Bulb-bearing plants need several inches of soil as do the grasses, and arrive when there are several inches of accumulated soil. The last stage of succession is seen in the “tree islands” that support woody plants such as Red Cedar, Loblolly Pine, Winged Elm, and Sparkleberry. At R&S, these islands have been invaded by Chinese Privet.

Granite Stonecrop

Thimbleweed with two dissected flower stem leaves

Thimbleweed; the basal leaves of the flowering stalk are in the lower right corner.

We saw two species of rare, state-listed plants at R&S today: Thimbleweed and Granite Stonecrop. The first we saw in the woodland on the edge of the outcrop as we entered. Thimbleweed is a strange plant, its cream-colored, 10-petaled flowers already gone to seed in the form of a compact, thimble-shaped spike. Its two stem leaves are deeply dissected, while its three-lobed basal leaves, which emerge inches away from the flower stalk, resemble those of Hepatica.

Granite Stonecrop is a close relative of Diamorpha and looks very much like it, except its fleshy leaves and stems are soft green in color and the stems occasionally branch. It often grows in wide patches with Diamorpha.

Two-flowered Melic Grass(Photo by Emily Carr)

Needle Grass
(Photo by Emily Carr)

Two pretty cool-season (spring-flowering) grasses are abundant in deeper soils under the trees here and elsewhere at the edges of the rock: Two-flowered Melic Grass and Needle Grass.

False Pimpernel

Purple Wood Sorrel

Dwarf Dandelion

Yellow Jessamin

On our way to the “top” of the outcrop, we passed Purple Wood Sorrel, Yellow Jessamine, False Pimpernel, and Dwarf Dandelion.

At the highest point on the rock, near where quarry explorations took place in the early part of the 20^th century, we looked at an area where a small slab of granite recently exfoliated. The rock that makes up the outcrop is still experiencing uplift from below, and the pressure occasionally lifts off a layer of rock, like a layer of onion. Exfoliation is another important process on outcrops, constantly exposing new, fresh rock where the process of succession can begin anew.

Evidence of exotic plant removal is obvious around the southeastern perimeter of the outcrop where ACC is using a masticator to kill Chinese Privet, Bush Honeysuckle, and Autumn Olive. Other invasive-removal plans including spraying the re-sprouts of these species and also spraying some of the aggressive natives, such as Dog Fennel. A European species, Silver Hair Grass, has shown up at R&S in the last decade, and has spread widely; methods for controlling it are not well developed, but Gary Crider will get on it!

SUMMARY OF OBSERVED SPECIES:

Hairy Spiderwort	Tradescantia hirsuticaulis
Diamorpha, Stone-crop, Elf-orpine	Diamorpha smallii
Sandwort	Minuartia uniflora (Syn. = Arenaria uniflora)
Tiny Bluets	Houstonia pusilla
False Garlic	Allium bivalve
Sunnybells	Schoenolirion croceum
Piedmont Quillwort	Isoetes piedmontana
Prickly Pear Cactus	Opuntia humifusa
Yucca	Yucca filamentosa
Fame-flower	Phemeranthus teretifolius
Red Cedar	Juniperus virginiana
Loblolly Pine	Pinus taeda
Winged Elm	Ulmus alata
Sparkleberry	Vaccineum arboreum
Yellow (or Carolina) Jessamine	Gelsemium sempervirens
Two-flowered Melic Grass	Melica mutica
Eastern Needle Grass	Piptochaetium avenaceum
Thimbleweed, Glade Windflower	Anemone berlandieri
Granite Stonecrop	Sedum pusillum
Purple Wood Sorrel	Oxalis violacea
Flatrock Pimpernel	Lindernia monticola
Dwarf Dandelion	Krigia virginica
Chinese Privet	Ligustrum sinensis
Bush Honeysuckle	Lonicera maackii
Autumn Olive	Elaeagnus umbellata
Dog Fennel	Eupatorium capillifolium
Silver Hair Grass	Aira caryophyllea