Montalto Prickly Pear Community ©Devin Floyd
Albemarle County, Virginia

With a strong and chilling mountaintop wind, fog lifting and sun dappled clouds racing by, we explored a very unusual habitat:

Catoctin Greenstone, Eastern Prickly Pear Cacti (Opuntia humifusa) community.

The prickly pear cacti in the larger Albemarle area is typically found on south facing and relatively horizontal rock outcrops. It also gravitates toward outcrops of granite, granulite, and related bedrock. These rocks are high in silica and decay to produce nutrient-poor acidic soils. The prickly pear cacti doesn't seem to mind. In fact, in keeping a tally of prickly pear sites in Albemarle County, all 5 have been on granite or granulite outcrops. Today I witnessed an abrupt shift in that trend.

Montalto reaches to the sky at the north end of Carter's Mountain. It is part of a strip of Virginia land that was preferred by early plantation holders (ie., Madison, Jefferson, Monroe, etc). The bedrock holding up this land (a meta-basalt known as Catoctin Greenstone) decomposes into soil that is very high in nutrients (esp. Calcium). It has a high levels of base cations, which means the soil retains nutrients and makes them available to plants.

The nutrient-rich soils of Montalto produce greater tree diversity here than at any other prickly pear habitat I've observed to date. It is likely that diversity is high in the herbaceous layer as well. (**Note: The site is maintained relatively treeless, and so we surveyed an outcrop in a forested area immediately next to it. Results are below).

Lat/Long.: 37.99949 / -78.464799

Elevation: 1272 feet
Size of the Habitat: The site is roughly 35' x 95' (+/- 5 feet)

Aspect: Relatively flat, mountain top. The prickly pear colony is most prevalent along the Southeast side of the outcrop, and the land slopes very gently toward the southwest.

Soils: Soil/silt trapped in small cracks and pockets in and around the greenstone outcrop.

Bedrock: Central Blue Ridge anticlinorium. Catoctin Formation - Metabasalt. early cambrian-age rocks (570-600 million years old).
Conditions: 50 degrees (going up to near 60) and very windy. The ground is saturated after a night of rain. The prickly pear at this site is unusually dense. I attribute this to the maintained lawn around it, giving it full access to sun, and high-nutrient soils.

Trees and Shrubs (This list was observed at an outcrop area immediately to the SW of the prickly pear habitat. The prickly pear habitat is in a maintained clearing.)
Dominants:

Chestnut Oak, Quercus prinus
Virginia Pine, Pinus virginiana
Honey Locust, Gleditsia triacantho
Eastern Redbud, Cercis canadensis

Other:

Black Oak, Quercus velutina
Scarlet Oak, Quercus coccinea
Black Locust, Robinia pseudoacacia
Red Cedar, Juniperus virginiana
Hackberry, Celtis occidentalis
Pignut Hickory, Carya glabra
Persimmon, Diospyros virginiana
White Ash, Fraxinus americana
Tulip Poplar, Liriodendron tulipifera
White Oak, Quercus alba

Other Flora noted:

Eastern Prickly Pear Cactus, Opuntia humifusa
Coralberry, Symphoricarpos orbiculatus

Non-native flora:

Japanese Honeysuckle, Lonicera japonica
Autumn Olive, Elaeagnus umbellata
Wineberry , Rubus phoenicolasius
Barberry, Berberis sp.

The cacti fruit (sweet and fermenting this time of year) is a valuable food source for wildlife including rabbits, deer. box turtles, and coyotes.

Thank you, Justin and Peggy, for a wonderful mountain-top morning!

I recommend the following plants for potential additions to this unique habitat. They are all regional basic outcrop plants (list compiled by Lonnie Murray and Devin Floyd of the Albemarle Natural Heritage Committee):

cliff stonecrop, Sedum Glaucophyllum
pale corydalis, Corydalis sempervirens
Allegheny stonecrop, Hylotelephium telephioides
wooly lip fern, Cheilanthes lanosa
small flowered phacelia, Phacelia dubia
rock spike moss, Selaginella rupestris
wild pink, Silene carolina
fameflower, Talinum teretifolium
woodland stonecrop, Sedum ternatum
skullcap, Scutellaria integrifolia
red columbine, Aquilegia canadensis