Glossary

Absolute cover
The percentage of the ground covered by the vertical projection of the plant crowns of a species or defined set of plants (also known as the vertical projection of foliage of plants) as viewed from above. Small openings in the canopy and overlap are excluded (SRM 1989). The absolute cover of herbaceous plants includes any standing (attached to a living plant, and not lying on the ground) plant parts, whether alive or dead; this definition excludes litter and other separated plant material. The cover may include mosses, lichens, and recognizable cryptogamic crusts (Bartolome et al. 2007a).
Abundant
Very likely to be encountered; an abundant species need not be dominant.
Alliance
A classification unit of vegetation, containing one or more associations and defined by one or more diagnostic species, often of high cover, in the uppermost layer or the layer with the highest canopy cover. Alliances reflect physiognomy as well as regional to subregional climates, substrates, hydrology, and disturbance regimes (Jennings et al. 2006, FGDC 2008). This term replaces series used in the first edition.
Association
A vegetation classification unit defined by a diagnostic species, a characteristic range of species composition, physiognomy, and distinctive habitat conditions (Jennings et al. 2006). Associations reflect local topo-edaphic climates, substrates, hydrology, and disturbance regimes.
Canopy cover
The percentage of ground covered by the combined crowns of all plants that form the outermost perimeter of the spread of foliage. Small openings are included (SRM 1989, USDA-NRCS 1997); applications often include spaces between plant crowns, in part because they are difficult to view or estimate from above. See Plant Crown Cover.
Chaparral
A shrubland adapted to summer-dry Mediterranean climate by having shrubs with evergreen, leathery leaves, such as chamise, manzanita, or scrub oak species. Compare Coastal Scrub.
Character species
A species that shows a distinct maximum concentration (quantitatively and by presence) in a well-defined vegetation type, sometimes recognized at local, regional, and general geographic scales. Character species are very strong differential species (Bruelheide 2000, Mueller-Dombois and Ellenberg 1974). See Differential Species.
Characteristically present
A species is characteristically present when it is important in distinguishing a type of vegetation, regardless of what cover it exhibits in a stand. See Character Species, Diagnostic Species, Indicator Species.
Class
The first (highest) level of classification in the natural vegetation hierarchy, in which each vegetation unit is defined by a characteristic combination of dominant growth forms adapted to a very basic set of moisture / temperature regimes (FGDC 2008). Compare Subclass, Formation, Division, Macrogroup, Group, Alliance, Association.
Classification
The grouping of similar types (in this case—vegetation types according to criteria (in this case—physiognomic and floristic). The rules for classification shall be clarified prior to delineation of the types within the classification standard. Classification methods should be clear, precise, and based upon objective criteria so that the outcome is theoretically independent of who applies the classification. (UNEP/FAO 1995, FGDC 1997).
Coastal scrub
A shrubland dominated by species having evergreen or deciduous, non-leathery leaves, such as California buckwheat, California sagebrush, coyote brush, or sages. Compare Chaparral.
Co-dominant species
Two or more abundant species with high cover in relation to other species in the layer with the highest canopy cover. We typically define co-dominant species as those with at least 30% relative cover. The term co-dominance replaces the term importance used in the first edition. See Dominant Species, Relative Cover.
Community
A group of organisms living together and linked together by their effects on one another and their responses to the environment they share (Whittaker 1975). See Stand.
Constancy
The percentage of samples (e.g., relevés) in a given dataset in which a species occurs (Jennings et al. 2006).
Constant species
In this book, typically, species with at least 75% constancy other workers use at least 60% constancy (Mueller-Dombois and Ellenberg 1974). Sometimes referred to as “constant companion” species.
Continuous
Having greater than 66% absolute cover. Compare Intermittent, Open, Sparse.
Crosswalk
A comparison of two or more classifications. The relationships may be one-to-one, one-to-many, or many-to-many.
Desert scrub
A shrubland found in the Colorado, Great Basin, Mojave, and Sonoran deserts; taxa are adapted to low rainfall and high summer temperatures.
Diagnostic species
A species or group of species whose relative constancy or abundance differentiates one vegetation type from another (Jennings et al. 2006). The term can include character, differential, constant, indicator, and dominant species, though some authors restrict it to include only character, differential, and constant species (Westhoff and van der Maarel 1973).
Differential species
A species that is distinctly more abundant and with more cover in one of a pair of vegetation types than in the other, although it may be still more successful in other communities not under discussion (Bruelheide 2000, Curtis 1959). See Character Species.
Division
The fourth level in the natural vegetation hierarchy, in which each vegetation unit is defined by a group of plant communities in a given continental or other broad geographic area exhibiting a common set of dominant growth forms and many diagnostic plant taxa (including character taxa of the dominant growth forms) corresponding to broad climatic and environmental characteristics (Westhoff and van der Maarel 1973, Whittaker 1975). Compare Class, Subclass, Formation, Macrogroup, Group, Alliance, Association.
Dominance
The extent to which a species or growth form has a strong influence in a stand because of its size, abundance, or cover (Lincoln et al. 1998).
Dominant species
An abundant species with high cover in relation to other species in the layer with highest canopy cover. We typically define dominant species as those with at least 50% relative cover within a particular layer. Compare Co-dominant Species.
Dwarf shrub
A creeping, matted, or cushion-forming shrub that is typicall < 30 cm tall at maturity because of genetic and/or environmental constraints, and generally small-leaved. The term does not include shrubs that are < 30 cm tall only because of young age (Mueller-Dombois and Ellenberg 1974). See Herb, Shrub, Subshrub, Tree.
Floristic
Plant species composition and abundance.
Forest
An area (or vegetation type) in which trees dominate in the overstory where their crowns generally overlap (with > 60% canopy cover). Compare Woodland.
Formation
The third level in the natural vegetation hierarchy, in which each vegetation unit is defined by a geographically widespread (global) plant communities of similar physiognomy and dominant growth forms, typically related to major topographic and edaphic conditions occurring within major climatic conditions (Whittaker 1975, Lincoln et al. 1998). Compare Class, Subclass, Division, Macrogroup, Group, Alliance, Association.
Group
The sixth level in the natural vegetation hierarchy, in which each vegetation unit is defined by a group of plant communities with a common set of growth forms and diagnostic species or taxa (including several character species of the dominant growth forms), preferentially sharing a similar set of regional edaphic, topographic, and disturbance factors (cf. Pignatti et al. 1995, Specht and Specht 2001). Compare Class, Subclass, Formation, Division, Macrogroup, Alliance, Association.
Growth form
The shape or appearance of a plant reflecting growing conditions and genetics. Growth form is usually consistent within a species but may vary under extremes of environment (Mueller-Dombois and Ellenberg1974). Growth forms determine the visible structure or physiognomy of plant communities (Whittaker 1973a).
Habitat
The biological and environmental conditions associated with a vegetation type. The conditions reflect topo-edaphic climates, substrates, hydrology, and disturbance regimes. Another classic definition is the location where an organism or vegetation type is found, and the role a biological “entity” (usually species) plays in an ecosystem.
Herb
A vascular plant lacking aboveground woody stems; may be annual or perennial. The term includes aquatics, both flowering and spore-bearing broadleaf plants, grasses, grasslike plants, and herbaceous vines. See Dwarf, Shrub, Shrub, Subshrub, Tree.
Indicator species
A species whose presence, abundance, or vigor is considered to indicate certain site conditions (Gabriel and Talbot 1984).
Intermittent
Having 33% to 66% absolute cover. Compare Continuous, Open, Sparse.
Layer
A structural component of a stand consisting of plants of approximately the same height and growth form. Compare Stratum.
Macrogroup
The fifth level in the NVC natural vegetation hierarchy, in which each vegetation unit is defined by a group of plant communities with a common set of growth forms and many diagnostic plant taxa (including many character taxa of the dominant growth forms) preferentially sharing a broadly similar geographic region, regional climate, and disturbance factors. (cf Pignatti et al. 1995, and Braun-Blanquet concept of “Class”). Compare Class, Subclass, Formation, Division, Group, Alliance, Association.
Mosses
A group of non-vascular plants. Mosses always have leaves, which typically are not rounded, and the leaves of most species have a distinct midvein. Mosses have a spore-producing, reproductive structue with a capsule (which contains the spores) that matures only after the seta (the stalk that bears the capsule) stops elongating (Malcolm and Malcolm 2006, Wishner 2011).
Non-vascular
Refers to a plant or plant-like organism without specialized water or fluid conductive tissue (xylem and phloem). Includes mosses, liverworts, hornworts, lichens, and algae (adapted from FGDC 1997).
Open
Having less than 33% absolute cover. Compare Continuous, Intermittent, Sparse.
Physiognomy
The visible structure or outward appearance of a plant community as expressed by the dominant growth forms, such as their leaf appearance or deciduousness (Fosberg 1961, Jennings et al. 2006). Compare Structure.
Plant community
A group of plant species living together and linked together by their effects on one another and their responses to the environment they share (modified from Whittaker 1975). Typically, the plant species that co-occur in a plant community show a definite association or affinity with each other (Kent and Coker 1992).
Plant crown cover
The area of ground covered by the crown of an individual plant See Canopy cover.
Plot
In the context of vegetation classification, an area of defined size and shape that is intended for characterizing a homogenous occurrence of vegetation. Compare Relevé.
Provisional alliance
An alliance is considered provisional when sufficient data exists to propose the vegetation type, but there may not be enough research and regional information to be confident about the status of the type in California's vegetation.
Relative cover
A measure of the cover of a species in relation to that of other species within a set area or sample of vegetation. This is usually calculated for species that occur in the same layer (or stratum) of vegetation, and this measure can be calculated across a group of samples (or across a space or time).
Relevé
A record of a sample of vegetation that is homogeneous in species composition and structure, is in a uniform habitat, and is sufficiently large to contain a large proportion of the species typically occurring in the stand being sampled (Mueller-Dombois and Ellenberg 1974). Compare Plot.
Semi-natural stand
A vegetation type that is dominated by invasive, non-native vegetation. Semi-natural stands are at an equivalent classification level as alliances and special stands.
Semi-natural vegetation
Vegetation in which past or present human activities significantly influence composition or structure but do not eliminate or dominate spontaneous ecological processes (Westhoff and Van der Maarel 1973). In a Semi Natural Stand classification unit, a non-native species is sufficiently dominant.
Seral
A vegetation type (or component species) that is demonstrably susceptible to replacement by other vegetation type (or component species based on its ecological characteristics (Daubenmire 1968).
Shrub
A woody plant that generally has two to several stems from base, giving it a broad crown and is usually below 5 m in height. Includes dwarf shrubs and low or short woody vines (adapted from FGDC 1997 and Box 1981). See Dwarf, Herb, Subshrub, Tree.
Shrubland
An area (or vegetation type) in which shrubs dominate, including chaparral, coastal scrub, and desert scrub.
Sparse
Having less than 10% percent but at least 1% absolute cove (FGDC 2008). Compare Continuous, Intermittent, Open.
Special stands
Specific patches of vegetation in the landscape that are unique from other patches; they may appear structurally distinctive as well as be rare. The presence of specific rare or threatened CNPS-list plants typically define a type.
Species composition
The species present and their relative dominance (commonly presented in terms of cover) of a relevé, stand, or vegetation type.
Stand
A spatially continuous unit of vegetation with uniform composition, structure, and environmental conditions. This term is often used to indicate a particular example of a plant community (Jennings et al. 2006). Compare Alliance, Plant Community.
Stratum (plural: strata)
A structural component of a stand consisting of plants of approximately the same height. Each stratum is named by the typical growth form in that layer (e.g., tree stratum). The stratum may be divided further into substrata of the same growth form, such as tall (canopy) and short (subcanopy) tree substrata (Jennings et al. 2008). See Layer.
Structure
The spatial pattern of growth forms in a plant community, especially with regard to their height, abundance, or coverage within the individual layers (Gabriel and Talbot 1984).
The spatial arrangement of the components of vegetation resulting from plant size and height, vertical stratification into layers, and horizontal spacing of plants (Lincoln et al, 1998, Mueller-Dombois and Ellenberg 1974). Compare Physiognomy.
Subclass
The second level in the natural vegetation hierarchy, in which the classification unit is based on growth form characteristics (Grossman et al. 1998). Compare Class , Division, Macrogroup, Group, Alliance, Association.
Subshrub
A plant with woody lower stems and herbaceous upper stems that die back seasonally; usually over 50 cm in height.
Taxon (plural: taxa)
In classification, a group of organisms at any rank (e.g. species, genus, family) (Hickman 1993), though in this manual ‘taxa’ is most commonly used in reference to species, subspecies, or variety.
Taxonomy
The science of classifying organisms
Tree
A woody plant that generally has a single main stem and a more or less definite crown. In instances where growth form cannot be determined, woody plants equal to or greater than 5 m in height at maturity shall be considered trees (adapted from FGDC 1997). Includes dwarf trees (Tart et al. 2005b) or “treelets” (Box 1981). See Dwarf Shrub, Herb, Subshrub.
Vegetation
The collective plant cover and floristics of an area (FGDC 1997).
Vegetation type
A classification unit of vegetation at any level in the NVC hierarchy (e.g., alliance, association), or a unit used when vegetation has not been classified formally to a specific level. A vegetation type is typically defined on the basis of shared floristic and/or physiognomic characteristics. It is comparable to a taxon in plant classification.
Woodland
An area (or vegetation type) in which trees occur in open stands where their crowns are open and generally do not overlap (usually with 10% to 60% canopy cover). Compare Forest.