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Second Approximation (Version 2.6)
Information current as of July, 2013


The following list contains technical terms and abbreviations used in this report, as well as some additional terms commonly used in the practice of vegetation ecology. Definitions were generally adopted or paraphrased from the following sources: Allaby (1990), Allen (1990), Anderson et al. (1998), Bates and Jackson (1984), Cowardin et al. (1979), Driscoll et al. (1984), Frye (1986), Golet et al. (1993), Helm (1985), Johnson (1985), Mitsch and Gosselink (1986), Skinner and Porter (1987), and USDA Forest Service (1996).

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ac - acre(s).

acidic - as strictly applied to soils, having a pH value < 7.0, often indicating moderate or low fertility; in practice, the following degrees of soil acidity are recognized by the USDA: < pH 4.5 = extremely acidic; pH 4.5 to 5.0 = very strongly acidic; pH 5.1 to 5.5 = strongly acidic; pH 5.6 to 6.0 = moderately acidic; pH 6.1 to 6.5 = slightly acidic. As generally applied to soils and rocks, having low levels of base cation (calcium, magnesium) saturation indicative of low fertility; as applied to plants, indicative of species or vegetation types that grow in infertile substrates. See also circumneutral, alkaline.

actinolite schist - a schist containing abundant actinolite, an amphibole mineral rich in iron and magnesium. Ecologically, it can be considered a mafic metamorphic rock similar to metabasalt and amphibolite.

Al - aluminum.

alkaline - having a pH value > 7.0; in practice, the following degrees of soil alkalinity are recognized by the USDA: pH 7.4 to 7.8 = mildly alkaline; pH 7.9 to 8.4 = moderately alkaline; soils with pH > 8.4 have not been sampled by DCR-DNH ecologists and probably do not occur in Virginia. See also acidic, circumneutral.

allelopathic - of or pertaining to the release by an organism of a chemical substance that acts as an inhibitor to the germination or growth of another organism.

alluvial - of or pertaining to deposition of sediment by a stream.

alluvial fan - a body of alluvium forming a segment of a cone that radiates downslope from a point where a stream emerges from a narrow valley onto a less sloping surface (e.g., at the foot of a mountain).

alluvial swamp - a swamp occupying a poorly-drained floodplain habitat subject to periodic overland flooding; usually occupies a large slough, depressed area, or backswamp position in the floodplain, where water remains after flooding.

alluvium - unconsolidated sand, silt, clay, or gravel deposited by running water; see also colluvium.

amphibole - a group of dark, rock-forming minerals composed largely of silica, calcium, iron, and magnesium. Members of the group, including hornblende, actinolite, and tremolite, are common constituents of mafic igneous and metamorphic rocks. In chemical composition and general characteristics they are similar to the pyroxenes.

amphibolite - a metamorphic, mafic rock composed predominately of hornblende and other silicate minerals rich in iron and magnesium.

annual - a plant species that completes its life-cycle in one growing season.

aspect - the direction a slope faces (e.g., a north aspect).

B - boron.

backswamp - a depressed area of a floodplain between the elevated levee bordering a channel and a valley side or terrace.

bald - a non-forested, high-elevation mountaintop supporting shrubland or herbaceous vegetation.

bar - an elongated, ridge-like landform generated by waves and currents, and composed of sand, gravel, or other alluvial materials; usually runs parallel to the shore with water on two sides.

barren - an exposed, usually rocky, non-forested habitat in which shallow soils and drought-stress limit the establishment and growth of woody plants; typically dominated by warm-season perennial grasses and/or lithophytic forbs.

basal area - the cross-sectional area of a tree at breast height; extrapolated to a larger area, basal area is an estimated measure of how much of a site is occupied by trees.

basalt - a fine-grained, mafic igneous rock composed largely of plagioclase feldspar, pyroxene, and volcanic glass

base cation - the positively-charged ions of substances (e.g., calcium and magnesium) that in solution can bind and remove hydrogen ions or protons.

base-rich - as applied to soils, containing high levels of exchangeable base cations, particularly calcium, magnesium, and potassium, indicative of good fertility; nutrient-rich.

basic - as applied to soils, having high levels of base cation (particularly calcium and magnesium) saturation, along with iron, typically indicating high fertility; as applied to rocks, having high concentrations of iron, magnesium, and calcium; as applied to plants, indicative of species of vegetation types that grow in basic substrates. See also acidic .

basin wetland - a depression wetland with no or limited surface outlet.

biomass - the total weight of all living organisms in a biological community; in vegetation science, usually the total weight of all above-ground plant parts.

biotite - a common, iron-rich silicate mineral of the mica group usually found in igneous and metamorphic rocks

bluff - a steep, high slope or hill, typically subtending a stream, river, or estuary. Unlike a cliff, a bluff usually has substantial areas of surface soil and organic matter.

bog - in strict usage, an ombrotrophic peatland with organic soils > 40 cm deep; more generally (in the southeastern United States), any non-forested, oligotrophic wetland with groundwater-controlled hydrology. See fen, peatland, oligotrophic, ombrotrophic, and see Weakley and Schafale (1994) for additional discussion.

boreal - of or pertaining to subpolar and cold-temperate areas.

boulderfield - a sheet of coarse, loose, rock fragments mantling a slope; a collective term including talus, scree, block fields, and bouldery colluvium.

brackish - of or pertaining to water having salt concentrations between 0.5 and 30 parts per thousand; collective term encompassing oligohaline, mesohaline, and polyhaline regimes

breached foredune - an ocean-fronting dune that has been partly eroded or removed by ocean winds and water.

bryophyte - a nonvascular green plant; includes mosses, hornworts, andliverworts.

Ca - calcium.

calcareous - having high levels of calcium carbonate; applied to both soils and rock; in practice, DCR-DNH ecologists consider soils with calcium levels of >1000 parts per million to be calcareous.

calcareous fen - a fen developed over limestone or dolomite and saturated by calcareous groundwater. See also mafic fen.

calciphile - a plant restricted to or particularly characteristic of calcareous substrates.

carbonate rock - collective term for limestone and dolomite.

categorical variable - a property or quantity that is represented by discrete units, e.g., geologic rock types or vegetation types, rather than by a gradient.

CEC - cation exchange capacity, i.e., the total amount of exchangeable cations that a particular soil or material can bind at a given pH; exchangeable cations are held mainly on the surface of colloids of clay or humus; measured in milligrams per 100 g of soil.

circumneutral - having a pH ~ 7.0; in practice, soils with pH 6.6 to 7.3 are considered circumneutral. See also acidic, alkaline.

channery - thin, flat fragments of shale, limestone, or other sedimentary rocks < 15 cm (6 in) in diameter.

charnockite - a granitic rock containing abundant pyroxene, a dark silicate mineral. See also granite.

claypan - a hardpan composed of dense clay or silty clay that to some extent impedes drainage and root penetration.

clearing - an artificial opening such as a roadway, powerline right-of-way, a clear-cut, or small field that lies within a forested landscape.

cliff - a high, vertical or near-vertical exposure of resistant bedrock that usually subtends a river or high-gradient stream. A cliff is usually formed from erosional downcutting of streams and differs from a bluff in having a substrate consisting largely of exposed rock.

clone - a group of genetically identical individuals derived from a common ancestor by asexual division; applied in vegetation science to a colony or group of plants generated by vegetative sprouting from underground rootstocks. See rhizomatous.

clonal - producing clones by vegetative sprouting from underground rootstocks; rhizomatous.

cluster analysis - a method of numerical classification that evaluates the similarity of quantitative samples and, through an interactive statistical process, fuses into clusters those samples that are most similar; different types of cluster analysis have been used in vegetation ecology: DCR-DNH ecologists use agglomerative-hierarchical cluster analysis, which starts with each sample in its own group and progressively fuses them into larger groups.

cm - centimeter(s).

cohort - a group of individuals of the same age or generation.

collinearity - a numerical problem that results when variables in a regression model are highly correlated.

colluvial - of or pertaining to colluvium.

colluvium - unconsolidated earth materials deposited on steep slopes by direct gravitational action and local unconcentrated run-off. See also alluvium.

community - as applied to plants, any unit of vegetation regardless of rank or development; an aggregation of plants on the landscape; in broader terms, any assemblage of organisms that co-occur and interact.

community type - an abstract unit of vegetation representing concrete plant communities sharing a similar structure and floristic composition, and occurring under similar environmental conditions; more or less equivalent to the "association" used in traditional phytosociological studies and the National Vegetation Classification.

composite - a plant of the Aster or Sunflower Family (Asteraceae).

continuous variable - a property or quantity that could be any conceivable value within an observable or measurable range.

cover - the percentage of the ground covered by the vertical projection of above-ground plant parts.

crustose lichen - a lichen adhering closely to, and difficult or impossible to separate from, its substrate; crustose lichens abundantly cover most exposed rock outcrops.

Cu - copper.

dbh - diameter at breast height (1.4 m [4.6 ft] above the ground); the standard position at which woody stems are measured in forestry procedures.

dendrogram - a tree-like graphic that depicts the results of cluster analysis.

density - the number of plants per unit area; used more specifically in vegetation ecology as a measure of the number of woody stems = than a specified measure in diameter at breast height per hectare.

depression wetland - a natural, discrete basin wetland with no clear drainage outlet; most depression wetlands are seasonal ponds with a hydrologic regime controlled by seasonal fluctuation of groundwater levels. Depression wetlands occur in all physiographic provinces of Virginia and can be formed by varied geomorpholical processes, most often the sagging or solution of deep, underlying sediment or rock strata. See also sinkhole pond.

detritus - rock debris or litter formed from fragments of dead, organic material (e.g., leaf litter or pieces of wood).

Devonian - a period of the Paleozoic era, following the Silurian and preceding the Mississippian, from about 400 to 345 million years ago.

diabase - an intrusive, mafic, igneous rock composed largely of plagioclase feldspar and dark silicate minerals; similar to, and intermediate in texture between, gabbro and basalt.

dip slope - a side slope determined by and approximately aligned with the angle of the underlying bedrock plane.

diurnally flooded - alternately flooded and exposed by tidal water on a daily basis.

dolomite - a sedimentary rock composed of calcium and magnesium carbonate. See also limestone.

dominant - of or pertaining to an organism or taxon that by its size, abundance, or coverage exerts considerable influence on a community's biotic and abiotic conditions.

draw-down zone - an area of a seasonally flooded wetland or shoreline that becomes exposed when the water table drops below the soil surface, usually in the later part of the growing season.

dry-mesic - intermediate between dry and moist but well drained; submesic.

duff - the matted, partly decomposed organic surface layer of forest soils.

dummy variable - a binary variable of 0's and 1's, which is one if the observation belongs to a category and zero if it does not.

dune - a hill or ridge of sand formed by eolian (wind-driven) or sometimes alluvial processes.

dune scrub - a shrubland that occupies somewhat protected maritime secondary dunes and leeward dune slopes, generally along the inland edges of dune systems in zones sheltered from constant salt spray.

dune woodland - a woodland occurring on protected maritime secondary dunes sheltered from regular salt spray; this community often occupies the highest, driest, stabilized dunes situated a considerable distance from the ocean or bay.

ecosystem - a complete interacting system of organisms and their environment, applicable at any spatial scale.

ecotone - a transitional area where characteristics of adjacent communities or environments are intermingled or gradational.

edaphic - of or pertaining to the influence of soils on living organisms, particularly plants.

embayment - a broad ocean inlet or estuarine river and the landforms enclosing it.

endemic –geographically restricted; a species or taxonomic group restricted to a particular geographic region.

environmental gradient - a spatially varying aspect of the environment (e.g., elevation, slope position, soil pH) that is expected to be related to species composition.

environmental variable - a measure of the environment that is presumably related to an environmental gradient; environmental variables can be continuous, or they can be represented by ordinal or dummy variables. See continuous variable, dummy variable, environmental gradient, ordinal variable.

ephemeral seepage - brief groundwater outflow resulting from precipitation.

ericaceous - of the Heath Family (Ericaceae). See ericad.

ericad - a plant of the Heath Family (Ericaceae); for example, blueberries (Vaccinium spp.), rhododendrons (Rhododendron spp.), and mountain laurel (Kalmia latifolia).

estuarine - pertaining to an estuary; the Estuarine System, as defined in this report, extends upstream to the inland limits of tidal flooding, thus including a zone of strictly freshwater tidal habitats on coastal rivers.

estuary - a body of water that has a connection (open, partly obstructed, or sporadic) to the ocean and where fresh water from overland drainage is mixed with oceanic salt water; usually characterized by tidal activity.

eutrophic - enriched with nutrients; applied both to naturally fertile environments and to those that have been enriched by anthropogenic disturbances.

exotic - an introduced, non-native species.

Fe - iron.

feldspar - a very common, rock-forming, aluminum-rich silicate mineral.

feldspathic - of or containing feldspar.

felsic - geologically, containing large amounts of light-colored silicate minerals rich in silicon, oxygen, aluminium, sodium, and potassium, e.g., quartz, muscovite, and orthoclase. The term is a combination of the words "feldspar" and "silica" and is usually applied to igneous rocks such as granite and rhyolite, or by extension to metamorphic rocks such as gneiss. See also mafic.

fen - in strict usage, a minerotrophic, enriched peatland with organic soils > 40 cm deep; more generally (in the southeastern United States), applied to similar wetlands lacking, or with only superficial, organic soils. See bog, minerotrophic, peatland, oligotrophic, and see Weakley and Schafale (1994) for additional discussion.

fibric peat - partially decomposed organic material whose original structure is still visible.

< b>flatwoods - a colloquial term for a forest occupying an extensive, level or nearly level area of the landscape. In Virginia, flatwoods are best developed on the large, outer Coastal Plain terraces, on inner Coastal Plain interfluves, and in the Mesozoic basins of the Piedmont

flora - all the plants that make up the vegetation of a specified area. See also vegetation.

floristic - of or pertaining to the flora of an area and the geographic patterns of distribution represented by its taxa. See also floristics.

floristics - the study of a flora and the geographic distributions of its taxa.

fluvial - of, pertaining to, or produced by rivers.

floodplain - a nearly level alluvial plain that borders a stream and is subject to inundation (non-tidal) under flood-stage conditions.

floodplain forest - a forest community occupying well-drained to somewhat poorly drained floodplains bordering rivers and streams. Habitats are subject to inundation by temporary overland flooding, the frequency and duration of which vary greatly with stream size, elevation of the floodplain, and other factors. See also alluvial swamp.

floodplain pool - depressions in a floodplain that pond water for at least part of the growing season.

foliose lichen - a lichen typically lying flush to its substrate, but removable such that the ventral surface is visible; foliose lichens are attached to rocks and other substrates by numerous fine structures called rhizines.

forb - a broad-leaved herbaceous plant.

foredune - a dune fronting the ocean or an estuary; also called a frontal dune. Foredunes are subject to constant salt spray and frequent impacts by storm surges. See also secondary dune.

forest - vegetation dominated by trees (= 6m [20 ft] tall) producing a more or less closed canopy, typically with 60-100% cover; some forests may temporarily have < 60% canopy cover following disturbances such as windthrow, disease, etc.

freshwater - of or pertaining to water with salt concentrations of < 0.5 parts per thousand.

fruticose lichen - a lichen that grows erect or pendent, with thalli that have no clearly distinguishable upper and lower surfaces; includes species that are branched and shrubby, as well as those that form unbranched stalks.

ft - foot (feet).

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gabbro - an intrusive igneous, mafic rock composed primarily of plagioclase feldspar and pyroxene.

geomorphic - of or pertaining to processes that change the form of the earth (e.g., volcanic activity, running waters, glaciers).

gneiss - a metamorphic, foliated rock composed predominately of feldspar and showing color banding or alignment of mineral grains.

graminoid - grasses and grass-like plants (e.g., sedges and rushes).

granite - a felsic, igneous rock composed predominately of feldspar and quartz.

granitic flatrock - an exposed, level or gently sloping outcrop of granite or related rocks such as granitic gneiss or granodiorite. In Virginia, these habitats are restricted to the southern Piedmont. Most are located on gentle slopes bordering streams, where the erosive power of water over time has worn rock surfaces smooth and created small, gravel-filled depressions. Lichens and bryophytes constitute the predominant biota on granitic flatrocks, covering much of the exposed bedrock. However, vascular plants dominate locally in crevices, flats, and depressions where moisture and thin layers of organic matter accumulate.

granodiorite - a granitic rock composed of plagiocase feldspar, quartz, and various dark silicate minerals, including hypersthene, augite, biotite, hornblende, and garnet; contains a lower proportion of silica than true granite.

greenstone - a colloqial name for metabasalt of the Catoctin Formation; a mafic, metamorphosed basalt composed predominantly of plagioclase, chlorite, epidote, and albite

groundwater - water occurring below the earth's surface in bedrock and soil.

ha - hectare(s).

halophyte - a plant restricted to or particularly characteristic of saline environments.

hardpan - a dense, clay subsoil layer that impedes internal drainage and root penetration. See also claypan, shrink-swell clay.

hardpan forest - a forest community that occupies gentle to flat Piedmont uplands with impermeable clay subsoils, or in a few cases, shallow bedrock. Sites are usually underlain either by mafic rocks or by acidic slates. Surficial soils are silt or clay loams, with an abrupt transition to plastic clay hardpans at depths of 23 to 38 cm (9 to 15 in). See also claypan, shrink-swell clay.

heath - a plant of the Heath Family (Ericaceae); an Ericad; for example, blueberries (Vaccinium spp.), rhododendrons (Rhododendron spp.), and mountain laurel (Kalmia latifolia).

hematitic - containing an abundance of hematite, a reddish-brown to black mineral consisting of ferric oxide, an important iron ore.

hemi-parasitic - pertaining to a plant that obtains part of its sustenance from another plant. A hemi-parasite typically is attached to the root or stem of a host plant, but is also photosynthetic to some degree.

herb - a vascular plant lacking woody tissue at or above ground level.

herbaceous vegetation - vegetation dominated by herbs having = 5 % total cover; such vegetation with herb cover from 5 to 25% is referred to as sparse herbaceous vegetation.

herbivory - the consumption of plants by animals.

hibernacula - overwintering den sites used by animals such as bats, snakes, and insects that hibernate in a state of torpor.

high-elevation forest - a montane forest community occurring (in Virginia) entirely or mostly above 1070 m (3500 ft) elevation.

Holocene - an Epoch of the Quaternary Period of geologic time, from approximately ten thousand years ago to the present.

hummock - as applied to wetland microtopography, a small raised or mounded area lying above the general level of the wetland and ususally having at least somewhat better drainage. A hummock may form around tree bases or by the accumulation of organic matter and bryophyte colonies between muck- or water-filled channels (usually called "hollows").

humus - decomposed organic matter that has lost all trace of the structure and composition of the vegetable or animal matter from which it was derived.

hydric - wet.

hydromorphic - structurally adapted for life in aquatic habitats.

hydroperiod - the specific flooding cycle of a wetland habitat; usually applied to the more or less regular periodicity of seasonally flooded wetlands.

hydrophytic - pertaining to plants or vegetation adapted to wetland environments.

hyperhaline - of or pertaining to water with salt concentrations > 40 parts per thousand, or to wetland soils that contain > 15% exchangeable sodium, a level that interferes with the growth of most plants; usually applied to Salt Flats ("salt pannes"), depressions that accumulate salt through evaporation of tidal inputs.

igneous - formed by solidification of magma within the earth's crust or of lava on the surface.

in - inch(es).

indirect gradient analysis - an analytical technique in which gradients are unknown a priori, and are inferred from species composition data; in vegetation ecology, usually performed using an ordination technique.

interdune pond - a deep interdune swale or basin that is seasonally to semipermanently flooded and supports tall wetland graminoids or aquatic vegetation.

interdune swale - a depression or hollow between secondary dunes, seasonally or permanently saturated by a perched water table and shallow or temporary flooding. Interdune swales are predominantly influenced by fresh water from rainstorms, but may be periodically flooded by salt water from ocean storm surges. Low graminoid-dominated herbaceous vegetation is characteristic.

intertidal mud flat - low marsh areas of very fine sediments that are fully exposed only at low tide. Freshwater intertidal mud flats usually support dense, monospecific colonies of common spatterdock (Nuphar advena).

intertidal zone - the zone between average low tide and average high tide in an estuary.

interfluve - the elevated area between two drainageways that sheds water to them.

intermittently exposed - substrate usually flooded, but exposed occasionally and without detectable seasonal periodicity.

intermittently flooded - substrate usually exposed, but surface water present occasionally and without detectable seasonal periodicity.

interstice - an intervening space or crevice.

interstitial - of or pertaining to interstices.

irregularly flooded - flooded by tidal water less often than daily but at least once annually.

Jurassic - the second period of the Mesozoic era (following the Triassic), from approximately 190 to 135 million years ago.

K - potassium.

km - kilometer(s).

landslide bench - a sag between resistant and less resistant sedimentary bedrock units in areas of catastrophic slope failure and landsliding; expressed physiographically as a sub-level, mid-slope area.

layered pyroxene granulite - a high-grade metamorphic rock of the Blue Ridge basement complex that contains abundant calcium, magnesium, and iron weathered from plagioclase and various mafic minerals.

leeward - on or toward the side sheltered from the wind.

levee - a low ridge or embankment of sand and coarse silt, built up by a stream on its floodplain and located adjacent to its channel.

liana - a woody vine.

lichen - a symbiotic association between a fungus and one or more species of algae and/or blue-green algae; although not based on genetic relationships, lichen species, for the aid of identification, are divided into foliose, fruticose, crustose, and umbilicate groups based on their growth strategies. See crustose lichen, foliose lichen, fruticose lichen, umbilicate lichen.

limesand - sand containing significant quantities of calcium carbonate derived from finely weathered shell material.

limestone - a sedimentary rock composed predominantly of the mineral calcium carbonate (calcite). See also dolomite.

lithologic - of or pertaining to the physical characteristics of a rock.

lithology - the description of rocks on the basis of physical characteristics such as color, mineralogical composition, and grain size.

lithophyte - a vascular plant confined to or particularly characteristic of rock habitats (outcrop crevices, shelves, ledges).

lithophytic - of or pertaining to lithophytes.

liverwort - a nonvascular, chlorophyll-containing plant closely related to mosses and hornworts, but differing in reproductive structures; liverworts have two dominant growth forms, one which resembles moss with overlapping leaves, the other forming prostrate leafless bodies.

m - meter(s).

macroinvertebrate - an animal lacking a backbone (invertebrate) and visible without the aid of magnification.

mafic - geologically, containing large amounts of dark-colored silicate minerals rich in magnesium and iron, e.g., pyroxene, amphibole, olivine and biotite mica; The term is a combination of the words "magnesium" and "ferric", and is usually applied to igneous rocks such as basalt, charnockite, diabase, and gabbro, or by extension to metamorphic rocks such as amphibolite and metabasalt (greenstone); also applied to soils with high levels of magnesium and iron that are derived from these formations. See also felsic and ultramafic .

mafic fen - a fen developed over actinolite schist, amphibolite, or other mafic rocks and saturated by groundwater rich in iron, magnesium, and calcium. See also calcareous fen.

magnesiophile - a plant restricted to or particularly characteristic of magnesium-rich substrates, e.g., soils derived from dolomite or mafic rocks.

MANOVA - see multivariate analysis of variance.

marine - of or pertaining to the ocean and its waves and currents; the Marine System, as defined in this report, extends from the outer edge of the continental shelf shoreward 1) to the landward limit of tidal inundation on beaches and 2) to the oceanward limit of water bodies with salinities < 30 parts per thousand.

maritime - living or situated near an ocean; of or pertaining to an environment under oceanic influences.

maritime forest - an evergreen or mixed forest community occupying stabilized, oceanside and bayside dunes and sand flats that are protected from salt spray except during major storm surges.

maritime swamp - a swamp occurring in saturated or seasonally flooded coastal habitats that are subject to at least occasional oceanic influences such as salt spray and storm surges. Stands usually occupy large, protected interdune depressions, and flats, and creek bottoms just inland from tidal flooding. Includes both maritime shrub swamps and maritime swamp forests.

marl - lime-rich clay containing a high proportion of soft calcium carbonate.

marsh - a eutrophic, non-forested wetland characterized by emergent herbaceous plants and a hydrologic regime of overland or tidal flooding.

meander - one of a series of sinuous loops, with sine-wave form, in the course of a stream channel.

mesic - of intermediate moisture conditions (i.e., moist and well-drained).

mesic mixed hardwood forest - a mesophytic hardwood forest dominated by variable mixtures of Americana beech (Fagus grandifolia), tulip-tree (Liriodendron tulipifera), white oak (Quercus alba), and northern red oak (Quercus rubra), occupying ravines and deep-soiled uplands of the Coastal Plain and Piedmont.

mesohaline - of or pertaining to water with salt concentrations from 5 to 18 parts per thousand.

mesophyte - a plant characteristic of mesic environments.

mesophytic - of or pertaining to plants or vegetation adapted to environments of intermediate moistureconditions.

Mesozoic - an Era of geologic time, from the end of the Paleozoic to the beginning of the Cenozoic, or about 225 to 65 million years ago; includes the Triassic, Jurassic, and Cretaceous periods.

metabasalt - a mafic, metamorphic rock that was originally basalt. See also greenstone, a metabasalt underlying extensive portions of the northern Blue Ridge and western Piedmont foothills.

metagrawacke - a dark gray, metamorphosed sandstone consisting of angular grains of quartz, feldspar, and various rock fragments, set in a compact, clayey matrix having the general composition of slate.

metamorphic - altered in mineral composition, chemical composition, and structure by heat, pressure, and hot fluids at some depth below the earth's surface; applied to rocks of igneous and sedimentary origin.

metasedimentary - consisting of sedimentary rock that shows evidence of having been subject to metamorphism; examples include quartzite (= metasandstone) and metasiltstone.

metasiltstone - metamorphosed siltstone.

metavolcanic - consisting of metamorphosed rocks of volcanic origin, e.g., metabasalt.

Mg - magnesium.

mi - mile(s).

microclimate - the local climate of a small site; this may vary from the climate of the larger, surrounding area due to aspect, tree cover, elevation, wind exposure, and other local factors.

microhabitat - within a habitat, a subdivision or precise location that has distinctive environmental characteristics; e.g., a tree-base hummock in a flooded swamp.

microtopography - the fine-scale variation in topography within a habitat; e.g., the pattern of vertical rock faces, shelves, and crevices on a cliff.

minerotrophic - receiving water that has passed through mineral soil; usually applied to groundwater-fed, enriched peatlands (true fens). See fen, ombrotrophic.

Mississippian - a period of the Paleozoic era, following the Devonian and preceding the Pennsylvanian, from about 345 to 320 million years ago.

Mn - manganese.

monadnock - an isolated hill or range of hills, resulting from erosion of the surrounding terrain; usually underlain by relatively resistant rocks.

monospecific - consisting wholly or largely of a single species.

montane alluvial forest - a forest community occupying a small-stream floodplain in the mountains. Habitats generally have at least some zones of alluvial deposition but overland flooding may be very infrequent and soils are usually well-drained.

montane mixed oak forest - a forest community of dry-mesic, generally acidic, mountain slopes and crests that is dominated by variable mixtures of northern red oak (Quercus rubra), chestnut oak (Quercus montana), and white oak (Quercus alba), with moderately diverse understory and herb layers. This community generally occurs between 600 to 1200 m (2000 ft and 4000 ft) elevation.

montane oak-hickory forest - a forest community of dry-mesic or mesic mountain slopes and crests that is dominated by mixtures of hickories (Carya ovalis, Carya ovata, Carya cordiformis) and oaks (Quercus rubra, Quercus alba, Quercus montana), with diverse understory and herb layers. This community generally occurs from about 760 to over 1200 m (2500 to over 4000 ft) elevation in association with moderately to strongly base-rich soils. Stands on the more mesic, deep-soiled sites over mafic or calcareous rocks often have an extraordinarily lush herbaceous flora.

moss - a nonvascular chlorophyll-containing plant closely related to liverworts and hornworts, but differing in reproductive structures.

mudstone - a sedimentary rock formed by hardening of silt and clay in approximately equal proportions.

multivariate analysis of variance - a technique which simultaneously tests differences between more than one dependent variable by relating variation to a set of independent variables.

multivariate technique - any analysis that simultaneously examines the behavior of more than one dependent variable.

muscovite - a mineral of the mica group that is common in gneisses and schists; also known as "white mica."

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Na - sodium.

NMDS - see non-metric multidimensional scaling.

non-metric multidimensional scaling - an ordination technique, based on indirect gradient analysis, that maximizes, to the extent possible, the rank-order (i.e., non-parametric) correlation between inter-sample dissimilarity and inter-sample distance in ordination space.

non-riverine saturated forest - see wet flatwoods.

non-riverine swamp - a seasonally flooded forest occurring on poorly-drained peatlands of the Coastal Plain. In Virginia, this community is restricted to the wettest terraces of the Embayed Region in and around the Great Dismal Swamp.

non-tidal swamp - a collective term for alluvial swamps, non-riverine swamps, maritime swamps, and seepage swamps.

nonvascular - lacking a structural system of tissue (xylem and phloem) that conducts water and soluble nutrients; nonvascular plants include mosses, lichens, and liverworts.

northern hardwood forest - a high-elevation forest community dominated by variable mixtures of sugar maple (Acer saccharum), American beech (Fagus grandifolia), and yellow birch (Betula alleghaniensis). In southwestern Virginia, yellow buckeye (Aesculus flava) is also characteristic while in northwestern Virginia, black cherry (Prunus serotina) is a ubiquitous co-dominant. The understory and herb layers contain many species characteristic of higher elevations and regions north of Virginia.

northern red oak forest - a high-elevation forest community strongly dominated by northern red oak (Quercus rubra), occurring on upper slopes and crests from about 1070 ft (3500 ft) in southwest Virginia, or 975 m (3200 ft) in northwest Virginia, to over 1370 m (4500 ft) elevation. American chestnut (Castanea dentata) was an important canopy dominant with northern red oak prior to the introduction of the chestnut blight fungus. Stands of this community often have a very open understory and an herb layer dominated by ferns.

nutrient-poor - infertile; oligotrophic.

oak / heath forest - a forest community strongly dominated by oaks in the overstory, and by ericaceous shrubs in the understory. Oak / heath vegetation occurs statewide and is represented by multiple community types, all characterized by dry, infertile soils and low floristic diversity.

oak - hickory forest - a forest community containing relatively high density and/or basal area of hickory (Carya) species in the overstory or understory; distributed throughout the Piedmont and mountain regions of Virginia. Oak - hickory forests are typically associated with soils of higher base status and/or moisture-holding capacity than those of co-ocurring oak / heath forests or montane mixed oak forests.

ombrotrophic - of or pertaining to wetlands, usually peatlands, that are fed by rainwater.

oligohaline - pertaining to water with salt concentrations from 0.5 to 5.0 parts per thousand.

oligotrophic - infertile. See also eutrophic.

olivine - a group of greenish, rock-forming minerals composed primarily of oxygen, silicon, magnesium, and iron, often with minor amounts of manganese and nickel present. Olivine occurs in both mafic and ultramafic igneous rocks and as a primary mineral in certain metamorphic rocks.

ordinal variable - a property or quantity that may be represented by an ordered or ranked scale of values that denote relative magnitude.

ordination - a multivariate technique that arranges vegetation samples in relation to each other based on compositional similarity and relative species-abundances. Ordination procedures summarize multidimensional data in a reduced coordinate system, extracting those axes that explain the most variation in the data. See non-metric multidimensional scaling.

Ordovician - the second earliest period of the Paleozoic era, following the Cambrian and preceding the Silurian, from about 500 to 440 million years ago.

orogeny - the process of mountain formation.

outcrop pavement - a steeply sloping, montane rock exposure, usually of sandstone or granite, with a relative uniform surface. Because a pavement lacks major crevices, ledges, and soil deposits, its vegetation tends to be patchy or sparse, consisting of specially adapted lithophytes, scattered patches of ericaceous shrubs, and occasional stunted pines or oaks.

overstory - the uppermost layer of trees forming the canopy of a forest or woodland.

overwash flat - a sand flat situated behind a beach or breached foredune and subject to flooding by high spring tides and storm surges. Substrates consist of unconsolidated sand and shell sediments that are constantly shifted by winds and floods, while low relief and constant salt spray maintains generally moist conditions. Dynamic disturbance regimes largely limit vegetation to pioneering, salt-tolerant, succulent annuals.

overstory - the uppermost layer of trees forming the canopy of a forest or woodland.

oxbow - a closely looping stream meander having an extreme curvature such that only a neck of land is left between the two parts of the stream.

p - the probability of observed data if a null hypothesis is true; if the p-value is small (typically, < 0.05), then the result is considered statistically significant.

P - phosphorus.

palustrine - of or pertaining to non-tidal wetlands; the Palustrine System, as defined in this report, includes all non-tidal wetlands dominated by woody plants and herbaceous emergents.

patch-dominant - a species that exerts dominance by forming dense but spatially discrete colonies; such a species typically varies from abundant to completely absent within a given habitat. pathogen - an organism that causes disease in another organism.

peat - an organic soil or deposit, often formed under anaerobic conditions associated with waterlogging.

peatland - a wetland with organic soils > 40 cm deep.

Pennsylvanian - a period of the Paleozoic era, following the Mississippian and preceding the Permian, from about 320 to 280 million years ago.

perched water table - groundwater whose surface, while normally well below ground, is periodically or seasonally elevated close to or above the soil surface.

perennial - a plant species with a life-cycle that lasts at least two growing seasons.

periglacial - specifically, of or pertaining to an area adjacent to a contemporary or Pleistocene glacier; more generally, any environment where the action of freezing and thawing is currently, or was during the Pleistocene, the dominant surface process.

pH - a value on the scale 0 to 14 that gives a measure of the acidity or alkalinity of a medium. See also acidic, alkaline, and circumneutral.

phenology - the study of periodicity of leafing, flowering, and fruiting in plants; leaf phenology refers broadly to the habit and duration of foliage.

phyllite - a metamorphic, sedimentary rock intermediate in grade between slate and mica schist; minute crystals of sericite mica impart a silky, silvery sheen to the cleavage surfaces.

physiognomic - of or pertaining to vegetative form and structure.

physiognomy - the form and structure of vegetation.

physiographic province - a landform region; an area delineated according to similar terrain that has been shaped by a common geologic history. Geographers and geomorphologists characterize physiographic provinces by their relative elevation, relief, lithology, and geologic structure. Specific types of landforms or other geologic features are found within a given province as a consequence of the region's history of rock formation, deformation, and erosion. It is often possible to subdivide the provinces into subregions based on the distribution pattern of these features.

phytogeography - the study of the geographic distribution of plants and vegetation , with an emphasis on environmental determinants of distribution.

pine - oak / heath woodland - a montane, pyrophytic woodland community co-dominated by variable combinations of pitch pine (Pinus rigida), table-mountain pine (Pinus pungens), stunted and shrub oaks (Quercus coccinea, Quercus montana, Quercus ilicifolia), and ericaceous shrubs. This vegetation type occupies the most exposed,xeric, infertile ridges, slopes, or clifftops, and is maintained by periodic burning or extreme edaphic stresses.

plagioclase - a series of common rock-forming minerals in the feldspar family, consisting of mixtures of sodium and calcium aluminum silicates.

Pleistocene - the first Epoch of the Quaternary Period of geologic time, from approximately ten thousand to two million years ago.

pocosin - an ombrotrophic, saturated peatland supporting pyrophytic woodland vegetation dominated by pond pine (Pinus serotina) and various evergreen shrubs. In Virginia, pocosins are mostly restricted to poorly drained terraces of the Embayed Region, in and near the Great Dismal Swamp.

polyhaline - of or pertaining to water with salt concentrations from 18 to 30 parts per thousand.

pond - a natural basin wetland or small artifical impoundment with no clear drainage outlet

prairie - an herbaceous community dominated by warm-season perennial grasses and often containing other species that occur in midwestern grasslands.

pyrophytic - of or pertaining to plants or vegetation adapted to environments in which fire is an important ecological process.

pyroxene - a group of important rock-forming silicate minerals of variable composition, among which calcium-, magnesium-, and iron-rich varieties predominate. See also layered pyroxene granulite.

quartz - one of the most abundant rock-forming minerals, in pure form composed of hard, crystallized silica (silicon dioxide). Clear and variously colored quartz is a common component of igneous, metamorphic, and sedimentary rocks. The whitish "milk quartz" or "milky quartz" is a common and conspicuous variety of crystalline quartz that can be found in large veins in many Virginia rock formations.

quartzite - metamorphosed sandstone.

r - correlation coefficient, a number which reflects the strength of the relationship between two variables; this value varies between -1 (for a perfect negative relationship) and +1 (for a perfect positive relationship).

r2 - correlation coefficient squared, a value between 0 and 1 known as the coefficient of determination; indicates the proportion of variance in a dependent variable that can be explained by its dependence on independent variables. In cluster analysis, the r2 cut-off level is a measure of within-cluster variance, which increases as more units are added to a cluster (i.e., r2 = 1 when all samples are in their own cluster, and r2 = 0 when all samples are in one cluster).

recruitment - generally, the trees involved in natural supplementation of a forest stand; more specifically, trees that have entered a particularly category (age or size class) during a given period.

refugia - sites where plants or vegetation that formerly had much wider distributions have survived locally through periods of unfavorable conditions in a region.

regolith - all unconsolidated earth materials above solid bedrock.

regularly flooded - alternately flooded and exposed by tidal water on a daily basis.

relict - an organism or community that has survived while related ones have become extinct; often applied to plants or vegetation that formerly had much wider distributions and have survived locally through periods of unfavorable conditions in a region.

rhizomatous - having a horizontal, creeping, perennial rootstock that produces smaller roots and vegetative shoots.

rhyolite - a felsic igneous rock composed predominantly of quartz and feldspar.

rill - a small streamlet or rivulet.

riparian - of the area beside a stream, especially a river.

riverine - of or pertaining to waters enclosed by channel banks; the Riverine System, as defined in this report, includes all non-tidal wetlands and deepwater habitats contained within stream channels, except those dominated by woody plants or herbaceous emergents.

riverside prairie - a prairie occupying gravel bars, bedrock shelves, and bedrock terraces along high-gradient mountain and Piedmont rivers.

rockhouse - a colloquial term for a shallow, cave-like opening at or near the base of a cliff or outcrop. In Virginia, rockhouses are most widespread in the nearly horizontal sedimentary strata of the Cumberland Mountains, where resistant cliff-forming sandstones are frequently undercut by softer, more erosive shales and mudstone.

ruderal vegetation - vegetation resulting from succession following anthropogenic disturbance of an area; generally characterized by unnatural combinations of species (primarily native though including small to substantial numbers of exotics) and relatively short persistence in the absence of additional disturbance.

A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z |

saline - in common parlance, pertaining to or characterized by salt; in strict, formal usage, this term isapplied only to terrestrial and inland wetland environments, whereas the term haline is applied to environments under the influence of oceanic salts.

salt panne - depressions or flats in a polyhaline tidal marsh that accumulate high levels of salt through evaporation of tidal inputs; characterized by patchy to sparse vegetation dominated by species tolerant of hyperhaline soils (e.g., glassworts, Salicornia spp.).

sandhill - a low ridge of deep sand deposits elevated above the surrounding landscape. In Virginia, sandhills are limited to the inner Coastal Plain of southeastern Virginia, where they occur in discontinuous belts along both sides of the Blackwater and Nottoway Rivers. These sandhills consist of ancient marine deposits that were later sculpted by fluvial processes during the Pleistocene. The substrate consists of deep, well-drained, infertile sands that lack profile development and are generally droughty. Topographic lows in the sandhills that have a shallow water table are referred to as mesic sandhills.

sandhill woodland - a dry, pyrophytic woodland community occupying sandhills of the southeastern Coastal Plain. This vegetation type is characterized by numerous plants that are unusual and restricted in Virginia, including longleaf pine (Pinus palustris), turkey oak (Quercus laevis), and pyxie-moss (Pyxidanthera barbulata var. barbulata). Prior to European settlement, most sandhill woodlands were dominated by longleaf pine, but two centuries of logging and fire exclusion has eliminated or greatly reduced this species at most sites.

sandstone - a medium-grained sedimentary rock composed of rounded sand grains cemented together by silica, iron oxide, or calcium carbonate. Most sandstones are acidic rocks; those with abundant calcium carbonate are referred to as calcareous sandstones.

saturated - wet for extended periods during the growing season, but never or rarely flooded by surface water; usually applied to wetlands maintained by seepage inputs or perched water tables.

savanna - a sparse woodland with little or no understory and a dense, graminoid-dominated herb layer. This physiognomic expression usually results from frequent burning that eliminates shrubs and saplings, and reduces opportunity for tree regeneration.

scalar - a synthetically derived measure of the environment that functions as a pseudo-continuous or ordinal variable; examples include Topographic Relative Moisture Index and Relative Slope Position (see Fleming 2007). See continuous variable, environmental variable, ordinal variable.

schist - a metamorphic rock containing abundant, visible platy minerals (e.g., mica), giving it a pronounced foliation and cleavage.

scrub - vegetation dominated by shrubs. See shrubland.

sea-level fen - a rare fen community of the outer Coastal Plain, occurring just above normal highest tide levels at the bases of slopes where abundant groundwater discharges along the upper edges of estuarine bays. The constant influx of fresh groundwater dilutes the impact of occasional haline inputs from storm tides and salt spray. The vegetation exhibits characteristics of both inland seepage bogs and oligohaline tidal marshes.

seasonal pond - a depression wetland with a hydrologic regime of seasonal flooding and draw-down. The soils of such ponds are usually exposed during the late summer and fall, providing habitat for a number of specially adapted plants.

seasonally flooded - surface water present for extended periods during the growing season, but absent by the end of the growing season in most years.

secondary dune - a dune situated behind, and often at some distance from, dunes fronting the ocean or an estuary; also called back dunes. Compared to foredunes, secondary dunes are less regularly impacted by salt spray and storm surges, and are generally more stable with increasing distance from the ocean or bay.

sedimentary - formed from the deposition and compression of mineral and rock particles, and sometimes material of organic origin; examples of sedimentary rocks include sandstone, shale, and limestone.

seep - a small area of groundwater discharge, either non-forested or shaded by trees rooted in adjacent, upland habitats; seeps generally support characteristic herbaceous wetland species but are too small or narrow to support hydrophytic woody vegetation.

seepage swamp - a large area of groundwater discharge supporting wetland forest or shrublandvegetation.

semipermanently flooded - surface water present throughout the growing season in most years except during droughts.

seral - of or pertaining to an intermediate or transitional stage in plant succession.

serotinous cone - the cone of a pine (e.g., pitch pine, Pinus rigida) that remains closed for a period of time, sometimes years, following maturation; the opening of such cones are often triggered by the heat of fires; a reproductive adaptation that ensures seed dispersal under optimal conditions.

serpentinite - a metamorphic, ultramafic rock composed primarily of serpentine, a magnesium silicate mineral indicative of low-grade metamorphism.

shale - a fine-grained sedimentary rock composed of mud, silt, and clay grains and characteristically splitting into thin layers.

shale barren - a sparse woodland or herbaceous community occurring on steep, unstable exposures of Ridge and Valley shales and Blue Ridge metashales. Shale barrens are endemic to western Virginia, eastern West Virginia, west-central Maryland, and south-central Pennsylvania. Habitats are generally situated on south- to west-facing slopes that are continually undercut by streams and characterized by abundant loose channery, areas of exposed bedrock, and patchy vegetation. Less common, densely graminoid-dominated shale barrens occurring on more stable spur ridge crests and mountain summits are sometimes referred to as "shale ridge balds." Shale barrens are noteworthy among Central Appalachian vegetation types for supporting a number of endemic and near-endemic herbaceous species.

shale woodland - a more closed woodland community occurring on steep exposures of Ridge and Valley shales and Blue Ridge metashales. The usual tree dominants are Virginia pine (Pinus virginiana) and chestnut oak (Quercus montana).

shell-marl - a weakly consolidated, sandy, clayey, or limy subsoil deposit containing abundant mollusk shells and contributing very high levels of calcium to soils weathered from it; hard, strongly cemented exposures of similar material are referred to as shell-marl outcrops.

shell midden - an archaeological feature comprised mainly of mollusk shells; some middens (usually located adjacent to an estuary) represent areas where mollusks were processed directly after harvest; others represent dump sites in former residential areas. Larger shell middens may support distinctive and unusual vegetation due to very high levels of calcium contributed to soil by the shells.

shrink-swell clay - a clay, usually classified as a montmorillonite, that expands greatly in volume when wet. Such clays are locally common in constituents of impervious, hardpan soils weathered from fine-grained mafic rocks such as diabase; such soils are waterlogged during wet periods, and extremely hard when dry.

shrub bald - an ericaceous shrubland community occurring on high-elevation rocky summits. In Virginia, this vegetation is restricted to summit promontories of Wilburn Ridge, Whitetop, and the the Iron Mountains in the southern Blue Ridge, and a caprock summit on Clinch Mountain in the adjacent Ridge and Valley.

shrubland - vegetation dominated by woody plants < 6m (20 ft) tall and having = 5% total cover; such vegetation with shrub cover from 5 to 25% is referred to as a sparse shrubland.

siltstone - a sedimentary rock formed by hardening of silt particles intermediate in size between clay and sand.

Silurian - a period of the Paleozoic era, following the Ordovician and preceding the Devonian, from about 440 to 400 million years ago.

sinkhole pond - a depression wetland developed in a mountain valley, where alluvial fans or colluvium eroded from an adjacent ridge have covered a stratum of carbonate rocks. The pond is formed by slumping of the surface strata as the underlying limestone or dolomite is weathered out by solution.

slate - a fine-grained metamorphic rock that splits cleanly into thin slabs; metamorphosed shale.

slough - a linear depression or meander channel in a floodplain, usually with a seasonally flooded or semipermanently flooded hydrology.

snag - a standing dead tree.

soapstone - a massive, metamorphic, ultramafic rock composed primarily of talc and serpentine.

sp. - a species.

sphagnous - characterized by an abundance of Sphagnum spp.

sphagnum - a moss of the genus Sphagnum.

spray cliff - a constantly wet rock face, within the spray or splash zones of a waterfall or saturated by permanent seepage.

spring ephemeral - a plant that completes its reproductive cycle early in the growing season, typically before or during the period in which trees leaf out; such species usually die back and become dormant during unfavorable summer months when habitats are characterized by high temperatures and deep shade.

spruce forest - an evergreen, high-elevation forest community dominated by red spruce (Picea rubens) and occurring at the highest elevations, generally above 1220 m (4000 ft). In Virginia, this community is restricted to Allegheny and Jack Mountains (Highland Co.), Clinch Mountain (Tazewell and Russell Counties), and the Balsam Mountains (Grayson, Smyth, and Washington Counties). The understory and herb layers are composed of species characteristic of higher elevations and boreal regions north of Virginia.

spruce-fir forest - an evergreen, high-elevation forest community dominated by Fraser fir (Abies fraseri) or co-dominated by Fraser fir and red spruce (Picea rubens). In Virginia, this community is restricted to the upper slopes and summit of Mount Rogers in the Balsam Mountains of the Southern Blue Ridge, above 1700 m (5400 ft) elevation.

spp. - species (plural).

ssp. - subspecies, a taxonomic rank below species.

stratigraphy - the arrangement of bedrock strata, particularly their geographic position and chronological order of sequence.

stratum - a distinct vertical layer of vegetation defined by relative height (e.g., overstory, understory) and/or by a specific range of heights (see p. 20).

streamhead pocosin - a pocosin occupying a small, inner Coastal Plain stream headwaters or sandhill swale influenced by fluctuating groundwater and seepage inputs. In Virginia, this community is restricted to an area of deep sand deposits along the Blackwater River in Southampton County and the City of Suffolk.

sub-canopy - the understory tree layer immediately below the overstory.

submesic - somewhat moist but well drained, or intermediate between dry and moist; dry-mesic.

sub-shrub - a low, slightly shrubby plant, usually dying back annually to a woody base; such plants often are treated as herbs; examples include Chimaphila maculata (spotted wintergreen) and Hypericum hypericoides ssp. multicaule (St. Andrew's cross).

subxeric - somewhat dry and drought-prone; intermediate between submesic and xeric.

succession - natural change in the composition and structure of a plant community over time in the absence of disturbance.

successional - of or pertaining to the process of succession.

surface substrate - a collective term for the abiotic materials (e.g., leaf litter, rocks, dead wood) that constitute the ground cover of a site.

swale - a slight depression in a generally level or undulating landscape; or, in the case of an interdune swale, a long, narrow, trough-like depression between two beach ridges.

Swamp - a forested or shrub-dominated wetland with a hydrologic regime of seasonal, semipermanent,permanent, or tidal flooding; contrast with seepage swamp, which has a saturated, groundwater-controlled hydrology. See alluvial swamp, maritime swamp, non-riverine swamp, seasonally flooded, semipermanently flooded, tidal swamp.

talus - a sloping mass of loose rock fragments, usually formed at the foot of a cliff.

TBS - see total base saturation.

temporarily flooded - surface water, usually flowing, present for brief periods during the growing season, but water table normally lies well below the surface; applied to floodplain wetlands.

terrace - one of a series of platforms flanking and more or less parallel to a stream channel; originally formed near the level of the stream and representing the dissected remnants of an abandoned floodplain, stream bed, or valley floor produced during a former stage of erosion or deposition.

terrestrial - of or pertaining to upland (non-wetland) environments.

Tertiary - the first period of the Cenozoic Era of geological time, from approximately two million to 65 million years ago.

tidal aquatic bed - a community consisting entirely of submersed and floating herbaceous vegetation occurring in small guts, tributary creeks, large marsh pools, and shallow water of tidal rivers and bays. Mean water depths of these habitats are too great for emergent aquatics. The distribution and abundance of vascular plants in tidal aquatic beds are probably controlled by responses to water chemistry, water clarity and light penetration, the impact of currents and boat wakes, and herbivory by aquatic animals.

tidal marsh - an emergent herbaceous wetland occurring along estuarine rivers and bays that is subject to regular diurnal (lunar-tidal) flooding or irregular wind-driven flooding. Vegetation composition varies with halinity and microtopographic position.

tidal swamp - a shrubland or forest community occurring in narrow zones subject to regular flooding, primarily along upper reaches of inner Coastal Plain estuarine rivers and their tributaries in Virginia, Maryland, and Delaware. These habitats are usually situated between a tidal marsh and an upland. The are influenced by lunar tides up to 1 m (3 ft), but diluting freshwater flows from upstream often keep halinity levels below 0.5 ppt. An influential feature of tidal swamp habitats is a pronounced hummock-and-hollow microtopography, where raised areas above the highest tide level provide stable substrates for the establishment of trees and microhabitats for more mesophytic herbaceous species.

toe slope - the geomorphic unit that forms the outermost, gently inclined surface at the base of a hillslope.

total base saturation - the extent to which the exchange sites of a soil are occupied by exchangeable base cations (e.g., calcium and magnesium), expressed as a percentage of the total cation exchange capacity. See CEC.

travertine - limestone deposited around caverns, or in hot springs and waterfalls.

Triassic - the earliest period of the Mesozoic Era, from approximately 213 million to 248 million years ago.

TRMI - Topographic Relative Moisture Index, a synthetic environmental variable used to quantitatively estimate potential site moisture.

ultramafic - pertaining to igneous rocks with little feldspar and large amounts of mafic minerals; compared to mafic rocks, ultramafic rocks contain larger quantities of heavy metals and were formed deeper in the earth's mantle; examples include serpentinite, soapstone, and talc-tremolite schist.

ultramafic woodland - a rare woodland community occurring on xeric uplands underlain by serpentinite, soapstone, talc-tremolite schist, and other ultramafic rocks. In Virginia, this community type is restricted to three sites in the Piedmont (Amherst, Franklin, and Nelson Counties) and two in The Glades region of the southern Blue Ridge plateau (Grayson County). Habitats are relatively gentle, rocky uplands with very dry, shallow, magnesium- and iron-rich soil. Ultramafic Woodlands, along with closely related Ultramafic Barrens, are the only terrestrial communities documented in Virginia that grow in soils with Ca:Mg ratios < 1.

umbilicate lichen - a leaf-like lichen attached to rocks by a single cord; umbilicate lichens, especially those of the genus Umbilicaria, are often referred to as "rock tripes."

understory - collective term for the small trees and shrubs growing beneath the canopy in a forest or woodland.

upland depression swamp - a forested depression wetland of the Piedmont, occurring in shallow, seasonally flooded basins and elongate headwater depressions lacking active alluvial deposition. In Virginia, this community type is most frequent in hardpan soils of the Mesozoic basins and other areas underlain by mafic rocks or acidic slates. Hydrologic regime is characterized by shallow seasonal flooding from perched water tables during the winter and spring months. Mature stands are dominated by one or more hydrophytic oaks, especially pin oak (Quercus palustris), swamp white oak (Quercus bicolor), willow oak (Quercus phellos), and overcup oak (Quercus lyrata).

var. - variety, a taxonomic rank below species.

vascular - having a structural system of tissue (xylem and phloem) that conducts water and soluble nutrients; vascular plants include ferns and flowering plants.

vegetation - the plant life of an area, including its floristic composition, structure, biomass, and phenology. See also flora.

wet flatwoods - a non-alluvial wetland forest occupying extensive, saturated terraces of the Coastal Plain. These habitats are nearly flat, with seasonally perched water tables. Some sites experience periodic sheet flows of anastomosing seepage from adjacent slope-bases. Shallow, braided channels and depressions which pond water shallow and intermittently may be present. Soils are silt, sand, and clay loams, sometimes with a very thin mantle of coarse, fibric peat. Mature stands are dominated by hydrophytic oaks such as laurel oak (Quercus laurifolia), swamp chestnut oak (Quercus michauxii), willow oak (Quercus phellos), and cherrybark oak (Quercus pagoda). However, secondary stands dominated by mixtures of loblolly pine (Pinus taeda), sweetgum (Liquidambar styraciflua), and red maple (Acer rubrum) are more extensive in the contemporary landscape.

wind-tidal marsh - an emergent herbaceous wetland subject to irregular wind-driven flooding along the shores of estuaries that have been cut off from oceanic influences by the closure of inlets. In Virginia, this community type is confined to the North Landing and Northwest Rivers (tributaries of Currituck Sound) and Back Bay in the extreme southeastern part of the state. Although these systems are no longer influenced by lunar tides, wind-driven currents may produce as much as 1 m (3 ft) of variation in water levels and contribute to a salinity regime that fluctuates between completely fresh and about 5 ppt . Vegetation consists of a mixture of freshwater species and species more typical of mesohaline marshes.

woodland - vegetation dominated by trees (= 6m [20 ft] tall) producing an open canopy, typically with 5-60% cover; such vegetation with canopy cover from 5 to 25% is referred to as a sparse woodland; some woodlands may have > 60% canopy cover following elimination or reduction of natural disturbances (e.g., fire).

xeric - dry; drought-prone.

xerophyte - a plant or vegetation type adapted to dry environments.

Zn - zinc.