FIELD NOTES |
Plot Narratives 2021

The area of interest hosts remarkable natural soil integrity, and a natural plant community with county record and regionally rare species. Has varied conditions from dry and well-drained to poorly drained, and supports a diverse set of wetland and upland grassland heliophytes. We list the present vegetative structure as “prairie”, but recognize that under natural disturbance regimes (4-10 year fire intervals) the normal and natural historic and prehistoric structure of this landscape would be savanna/woodland at most points in time (widely spaced trees within a diverse indigenous grassland). A notable characteristic of the old growth areas is that the plants there are middle-to-late successional grassland species. In other words, the herb layer here is in a “climax” successional phase within the grassland structure. Early successional weedy natives, as seen on the highly disturbed floodplain below, are nearly absent. We also recognize that, while the herb layer and soil strata appear to be intact, the shrub and canopy layers of a would-be natural savanna have obviously been cut, removed, and prevented for at least a century. Site is a high conservation priority for Albemarle Co. (See plots MA001-MA005 for data) and one of the more interesting grassland types discovered during our efforts to identify old growth remnant grasslands in a 9 county area in 2021, both for its unique assemblage of flora and rare species, but also because of its large size, its lack of association with a utility corridor or colonial period road, and its occurrence over apparent river terrace deposits (alluvial residuum).

MA001B

Plot is positioned in representative location of north end of our study area that also has low abundance of exotic species. The young woodland surrounding plot consists of upland and alluvial shrub and tree species, but they occur minimally in the plot. Pinus virginiana exerts most influence, reaching out over the plot from the north. The plot location is notably flat and exhibits pooling during rain events. 1937 aerial imagery show that this location had a grassland structure and lack of exotic species at location suggests that a woodland or forest has not existed at this spot for more than than short lengths of time during the past few centuries. Low number of exotics suggests minimal subsurface disturbance. Soil maps suggest this location, though in the floodplain, is rarely flooded. Geologic maps document this portion of the land as being residuum from ancient alluvial deposition. Soil samples show strong soil development in the top 5 inches with a smooth gradient between the A and B horizons. Signs of agricultural ditching bordering east and west edges of meadow with streamlets exiting to the north and joining the Rivanna River 600’ away. Vegetation in the plot is low and patchy with Achillea borealis, Lespedeza procumbens, Kummerowia striata (exotic), Anthoxanthum odoratum (exotic), Pycnanthemum tenuifolium, Sorghastrum nutans, and multiple other warm-season grasses not identifiable at this time the dominant cover. Notable occurrences in the plot include Helenium flexuosum, Polygala sanguinea, Rhynchospora recognita. Outside the plot, notables include Tripsacum dactyloides, Cirsium pumilum, and the county record exotic Galium anglicum.

MA002B

Plot location captures the variety noted in a dry, well drained sloped portion of the plant community, and the location was chosen for its reduced abundance in non-natives. This spot was the initial location that the remnant vegetative character of the open space on the property was recognized (by Devin and Sarai, early 2021). This location is impacted by an undetermined historic land use event, likely associated with the original WWII airfield-and possibly a refueling and maintenance station. This activity appears to have had little impact on the soil column and served as an accidental mechanism for conserving the interesting grassland that is present. A springlet that has been straightlined for drainage in the past 80 years extends north about 75’ east of the plot. The grassland is an undetermined age, but probably contains a strong element of a 19th century grassland, and precolonial remnant mix of species. The Rivanna River is 600-700’ east. The plot is dominated by several species of forbs and graminoids, including an unidentified grass, Sorghastrum nutans, Pycnanthemum tenuifolium, and the exotic invasive Anthoxanthum odoratum. Scutellaria integrifolia and several unidentified Carex and Dichanthelium species are also abundant in the plot.

MA003C

Plot is located in an area to capture the unique patch dominant vegetation and exposed mineral soil in the center of the larger remnant grassland. The location is characterized by having a large, shallow semi-circular depression and "fluffy" friable surface soils that support unique annual native species and stunted perennials. Ground water upwelling occurs here and has likely sustained an unusual physiographic and vegetative feature for centuries or millennia (same pattern is evident in all historic arial imagery, including those that predate the airfield activity). Variation in the community occurs to the north in a small wetter section dominated by Juncus dichotomus, Dichanthelium acuminatum var. lindheimeri, and Scutellaria integrifolia, and immediately to the west of the plot a barren area with a large area of exposed soil. The vascular flora are dominated by numerous graminoids, including Danthonia spicata, Schizachyrium scoparium, Sorghastrum nutans, Scleria pauciflora, Carex glaucodea, and Eragrostis refracta. The dominant flowering perennial forbs in the plot are Lespedeza repens and Pycnanthemum tenuifolium. Helenium flexuosum, Packera anonyma, Juncus dichotomus, possible Scleria ciliata var. ciliata, Krigia virginica, and Spiranthes vernalis are some of the notable species in the plot. A moss species currently unidentified covers most of the bare ground in the plot. Noteworthy species outside the plot include Cirsium pumilum and Dichanthelium acuminatum var. lindheimeri. The depression at the west end of the plot (and extending beyond) is visible in 1937 aerial imagery; it seems to be collecting groundwater or runoff from above and channeling it to the small stream to the east, in addition to receiving regular upwelling from below. The fine gravel in that area appears to include limonite nodules, perhaps related to the base-rich parent material (gravels and sands transported from the catoctin formation upstream and deposited here during the Pliestocene). The soil is notably friable and fluffy in the bowl-shaped depression area, and somewhat compact in the east end of the plot. The Rivanna River is located 600’ to the east. The vegetative cover pattern has remained similar from 1937 to now (historical aerial imagery evidence), and convergent rivulets are apparent in 1937, draining east to the lowland. The sandy/gravelly, hardpan area retains significant plant-restricitve edaphic conditions due to the unique groundwater upwelling of that location. Soil samples indicate that the water source is predominantly from upwelling, rather than rain-water accumulated (88.85% base saturation - Calcium/Magnesium). There is a strong "coastal element" in the vegetation here, and this is likely due to the unique residual sandy/gravelly soil conditions. Conditions are more similar to the piney flatwoods east of the fallline in Virginia and barrens often found in acidic woods in the Piedmont, and the often xeric conditions at this site support significant numbers of an odd mix of plants including Hexasepalum teres, Hypericum gentianoides, Krigia virginica, Eragrostis refracta, Helenium flexuosum, Aristida dichotoma, and state rare Scleria ciliata, as well as examples of Asclepias viridiflora and Packera anonyma that warrant further study due to their miniature stature at fruiting time.

MA004B

Plot is located in an area of the southern part of the field that is representative of a semi-wetland, poorly-drained area. Specific location chosen to include as few exotic species as possible so the indigenous plant community could be fully measured. The soil in the plot is notably organic and silty, and basiphiles present indicate elevated levels of base saturation. Five separate samples were collected (one in each corner, and one in the center) and combined to form a representative sample for the plot. The ground surface had a strong moss component of several unidentified species.
While the shrub layer is notably reduced due to modern periodic mowing, the site does have a history of having a distinct thicket forming, savanna structure. The savanna tree saplings were removed intentionally in the 20th century by members of the Rivanna Radio Control Club. Representatives of that savanna, including Prunus americana, Acer rubrum, Juniperus virginiana, Pinus echinata, Quercus stellata, Diospyros virginiana and others grow very nearby along the edges in forest thickets. At the time of survey, the dominant shrub in the sample plot was Diospyros virginiana (9 individuals over 2' tall).
The herb layer is dominated by the grasses Agrostis perennans, Andropogon virginicus, Sorghastrum nutans, Setaria parviflora, and Shizachyrium scoparium, and the forbs Scutellaria integrifolia, Achillea borealis, and Pycnanthemum tenuifolium, Lespedeza procumbens, and Potentilla simplex. There is notable patch dominance of Coleataenia anceps in the plot as well. Helenium flexuosum, multiple Dichanthelium species, Cirsium pumilum, Penstemon spp, and Tripsacum dactyloides are some notable heliophytes species in the plot, while notable species immediately outside the plot included Asclepias tuberosa, and Clematis virginiana. The terrain here is very float and drains slowly and to the east, meeting a 20th century shallow ditch that eventually leads to the Rivanna river 400m to the East. The combination of silty/sandy soils and flat terrain create alternating dry-moist conditions, and therefor support species that can tolerate both sets of conditions.

MA005C

Sample plot positioned near the South end of the first large meadow east of the “hangar” at Milton Airfield. In a location most representative of the highest quality portion of the large grassland. This portion is the field is best characterized as having prairie structure as annual mowing prevents woody development. The plot is mostly characterized by upland species, however a few wetland associated species such as Onoclea sensibilis and Boehmeria cylindrica are present in the east end. The plot is dominated by Pycnanthemum tenuifolia, followed by Helenium flexuosum, Scutellaria integrifolia, Rhynchospora recognita, Dichanthelium acuminatum var. fasciculatum, and Andropogon virginicus. Exotic species occur rarely in the plot, except for Anthoxanthum odoratum, which cover 5-10% of the sample plot. The vegetation remains fairly consistent outside the plot, although it’s mowed to about an inch to the south of the plot. About ten meters to the north of the plot is a small hill, where invasives such as Anthoxanthum and Lolium become dominant. To the northwest of the plot is a small hardpan wetland about 100m squared, which is dominated by a nearly pure stand of an unid Carex sect. Ovales. Groundwater discharge and poorly drained soils effect the community type at this location. In fact most swale, divot, or other alternatively dry/wet portions of the grassland tend to host more native species relative to exotic invasives. This stand has some similarities to planted or restored meadows/prairies, where species like Helenium flexuosum and Pycnanthemum tenuifolium are frequently seeded. However, the elevated diversity of grasses, rushes, and sedges, as well as rarely planted or established species like Scutellaria integrifolia and Rhexia Virginia, are clear indication that the assemblage is not planted, but rather, self-assembled. The vegetation at this location is estimated to be a preserved piece of unplowed Pre-Colombian grassland (ca. 400-1,400 years old). The reason for its survival is unclear,
but a clue may be in the soil type observed and the position in the broader landscape. The soil appears to be decomposed, in-situ, and has clay in the matrix enough so that the area is poorly drained. Its position, 1000 ft away from the river and beyond a wetland are that separates it from the floodplain, which means it may have been avoided or spared incidentally. The soil sample produced a rubbery “fungal mat”, dense with roots and fungi. and a soil column with no signs of plowing (zero mottling), and a smooth and even fade in color from the A-horizon to the B-horizon.