a list of scientific terms relating to the Arctic


An alphabetical list of scientific terms used in the website and publications. Some of the words are specific to the Arctic, and some are more general scientific terms.



Active layer: The layer of ground above the permafrost which thaws and freezes annually. Synonym of supragelisol.

Alluvium: A general term for all detrital material deposited or in transit by streams, including gravel, sand, silt, clay, and all variations and mixtures of these.


Basal area: (1) For trees, the area of the cross section (measured outside bark at d.b.h.) of a single tree, or of all trees in a stand, expressed in square meters/hectare or square feet/acre. (2) For range plants, the area of ground surface covered by the stem or stems of a range plant (usuallly measured 1 inch above the soil) in contrast to the full spread of the foliage. Compare canopy cover.

Beaded: See paternoster lake.

Bog: (1) A mire (peat-forming ecosystem) influenced solely by water which falls directly on to it as rain or snow and generally dominated by Sphagnum mosses. See ombrotrophic. Compare fen. (2) That stage in the physiographic succession of an area during which its surface is entirely composed of living Sphagnum, immediately under which is a fibrous brown peat composed mainly or entirely of partially disintegrated Sphagnum, the habitat exercising a distinctly selective influence on its flora. (3) A peat-covered or peat-filled area, generally with a high water table dominated by mosses, especially Sphagnum; although the water table is near the surface there is little standing water except in ponds. (4) In Alaska, bog vegetation may be dominantly herbs, shrubs, or trees. Sphagnum spp. are usually present, and often dominate the moss layer. Substrate is composed of very wet sedge peat or Sphagnum peat. Depth of peat may range from 30 cm to several meters.

  • Basin bog: A bog which has built up to the water level in a lake or an old river channel and the upper surface of the peat is either horizontal or gently sloping.
  • Blanket bog: Term used in the British Isles for a bog covering undulating semi-uplands. (1) Bogs of cool temperate regions formed under a maritime rainfall at lower elevations. (2) Bogs on hills developed under high rainfall and low temperatures as in Southeastern Alaska.
  • Dwarf shrub bog: A nutrient-poor, relatively dry bog covered with ericaceous dwarf shrubs and Sphagnum species.
  • Ericaceous shrub bog: Sites in Alaska on wet peaty soils on which ericaceous shrubs are co-dominant with sedges, mosses, other shrubs, and/or trees. Trees, when present, provide less than 25% cover. Peats may be either sedge or Sphagnum, and accumulations range from 15 cm to 12 m. The lowest peat accumulations are in Interior and Arctic Alaska (although some substantial peat deposits are also present in these areas); the deepest are in Southeast Alaska. Sphagnum spp. are usually present, whether or not they are the primary peat formers. These types are usually acid. The surface is usually hummocky and standing water may be present in the depressions, especially in early summer. In general, the surface is drier than wet meadows and the water table may fall several centimeters below the surface during dry spells. Peat-floored ponds one to several meters across are common in some bogs in Prince William Sound and Southeast Alaska. Mosses are present, if not co-dominant; lichens are frequently present, although usually not important. Erect shrubs, such as willows and alders, may be absent or common (but less than 25% cover). Aquatic plants are absent or non-dominant.
  • Flat raised bog: A bog which has a tendency for peat growth to extend up the sloping valley sides, leaving the boundary between bog and valley side poorly marked. There is a very weak rand and poorly developed lagg.
  • Floating bog: See quaking bog.
  • Lacustrine bog: The transitional stage in which some mineral water is still a major influence in the development of the bog.
  • Mesotrophic bog: A wet bog with a moderately poor to poor nutrient level. Sphagnum species are abundant but higher plants help to determine the physiognomy of the vegetation. Parts of the bog are influenced by somewhat richer water. Characteristic sites for mesotrophic bogs are bog boarders, surroundings of drainage channels in bogs, and shallow bogs.
  • Oligotropic bog: Wet, extremely nutrient-poor bog often ombrotrophic and dominated by Sphagnum species.
  • Paludification bog: Refers to a bog formed over previously dry land where a rise in the water table saturates the soil without forming a lake. See paludification.
  • Quaking bog: (1) Bog which has developed upon a mat of Carex or Sphagnum growing over a water surface. (2) A carpet of bog vegetation that is floating and sinks and quivers when walked on. Often called a floating bog.
  • Raised bog: (1) Ombrophilous mire in which peat accumulation at the center of the bog is greater than at its edges, giving rise to a cross-section resembling an inverted saucer. The central portion thus raised above the natural groundwater level, becomes solely dependent upon precipitation (ombrotrophic) and is therefore exceedingly low in plant nutrients. (2) A bog which has grown above its site of origin, whose center is higher than the margins and whose surface is convex. Growth is by Sphagnum proliferation and deposition of peat, water being supplied by airfall or capillary action in the peat. There is usually one or several very acid ponds near the center and around the rim is a sedgy channel (lagg) where water collects and flows away. (3) Bog with an elevated central area caused by peat accumulation. This central zone is generally isolated from the local water table and chiefly dependent on precipitation for water and minerals. (4) A bog with Sphagnum and associated plants that is typically convex and gently sloping from the center towards the steep margins and bordered by a ditch or a water course (lagg). Synonyms of Highmore, Hochmoor (German), hogmoose (Swedish), and red bog (Irish).
  • Spruce bog: A loosely applied term describing confined areas of organic terrain where coniferous trees (not always spruce) are a prominent feature of the vegetation cover. See muskeg.
  • String bog: A common taiga landscape consisting of alternating low bog ridges (German-Strange) and wet sedgy hollows (Swedish-flarke, English-flarks). The ridges and hollows are orientated across the major slope of the peatland at right angles to water movement. Synonym of Strangmoor (German) and more properly termed a fen since it is usually fed by waters from outside the mire.
  • Transition bog: A bog with a nutrient supply and vegetation type intermediate between the raised bog and low bog types.
  • Treed bog: A type of ericaceous shrub bog with a 10 to 25% cover of trees at least 135 cm tall. See muskeg.

Bog ridge: A ridge of peat moss supporting shrubs or trees and superimposed on a matrix composed primarily of sedges. The ridges are narrow, usually with their long axes across the slope and may form into net patterns. Synonyms of Strange (German), strangar (Swedish), and pounu (Finnish). See laniere.

Boreal: (1) Northern, or having to do with northern regions. (2) One of three transcontinental regions defined by Merriam. It extends from the northern polar seas south to southern Canada.

Braun-Blanquet name: The Braun-Blanquet (B-B) approach includes standard international protocols for sampling, analyzing, and publishing plant community names (Braun-Blanquet 1964, Westhoff and van der Maarel 1978, Weber et al. 2000). The B-B approach has a great many advantages for vegetation classification in the Arctic, where so many of the units have a circumpolar distribution and an international Arctic-wide classification seems achievable. It has been used extensively to describe Arctic vegetation in much of northern Europe (Dierssen 1996), Arctic Russia (Matveyeva 2006), Svalbard (Elvebakk 1994), Greenland (Daniëls 1982, Daniëls 1994), parts of Canada (Lambert 1972, Thannheiser 1976, Thannheiser and Hellfritz 1989, Thannheiser and Geesink 1990, Vonlanthen et al. 2008), northern Alaska (Walker et al. 1994, Schickhoff et al. 2002, Kade et al. 2005), alpine areas of Arctic Greenland (Sieg and Drees 2007), the Brooks Range, Alaska (Cooper 1986), and subarctic Aleutian Islands (Talbot et al. 2005).

The approach has not been widely used in the rest of North America because of its Latin nomenclature system and the generally poor understanding of the method. Braun-Blanquet Association names have an —etum suffix attached to the genus name of the dominant species and use various other protocols consistent with Latin naming conventions (e.g. Sphagno-Eriophoretum vaginati).) Much of the literature describing the method is in German and French and not generally accessible to English-speaking users. The recent development of a U.S. National Vegetation Classification (Jennings et al. 2009) will likely further reduce application of the method in North American. However, the sampling and analytical methods are similar in both approaches and lend themselves to units being described by both systems. We would strongly encourage this to promote international collaboration on the development of an Arctic-wide vegetation classification (Walker et al. 1994).

In this Atlas, all plant-community names used on the vegetation maps use a two-species form similar to that used in the U. S. National Vegetation Classification, but we also include Braun-Blanquet names where possible because we feel that these names are the gold standard that can be immediately identified and understood by vegetation scientists outside the U. S.

Broadleaf: A conventional term applied to trees and shrubs of the Angiospermae, in loose contrast with the generally needle-leaved Gymnospermae.

Bryophyte: A plant belonging to the phylum Bryophyta (mosses), Hepatophyta (liverworts) or Anthocerophyta (hornworts).

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Caespitose: Plants with short stems and branches usually covered with leaves and forming dense tufts or cushions, e.g. Silene acaulis. See cushion plant.

Canopy: (1) More or less continuous cover of branches and foliage formed collectively by crowns of adjacent trees, shrubs, or herbs depending upon the type of vegetation. (2) The cover of leaves and branches formed by the tops or crowns of plants as viewed from above.

Canopy closure: In a stand, the progressive reduction of space between crowns as they grow and spread laterally. A canopy in which the individual crowns are nearing general contact is termed a close canopy; and having achieved contact, a closed canopy. In general, closure indicates a process, while cover indicates a condition.

Carr: (1) A fen (minerotrophic mire) supporting a scrub or woodland vegetation. (2) A mire (permanently wet peat-forming organic soil) supporting a scrub vegetation and little or no Sphagnum.

Circles: One of the forms of patterned ground characteristic of earth subject to intensive frost action.

  • Non-sorted circles: (Also called frost scars or frost boils) Patterned ground whose mesh is dominantly circular and has a nonsorted appearance due to the absence of a border of stone such as that characterizing sorted circles. Spot medallions, cemetery hummocks, mud circles, frost scars, peat rings, and tussock rings are kinds of nonsorted circles. There seems to be no essential difference between unsorted circles and the centers of sorted polygons.
  • Sorted circles: Patterned ground whose mesh is dominantly circular and has a sorted appearance commonly due to a border of stones which have been segregated to a peripheral position around the surrounding finger material. When such sorted circles are adjacent to each other, the rock margins apparently coalesce forming nets, often of a polygonal pattern.

Cirque: Semicircular basin in an alpine landscape resulting from mountain glaciation. Progressive expansion of neighboring cirques results in the reduciton of the unglaciated slopes between them to sharp, knife-edged ridges or arêtes.

Climax: (1) Greek term meaning "ladder" and originally implying succession. It is interpreted to mean "the final step of the ladder." (2) In monoclimax theory, that state of a biotic community that is attained when population structures of all its species fluctuate rather than exhibit unidirectional change. Such a community will remain in a self-perpetuating state so long as present climatic, edaphic, and biotic conditions continue. See polyclimax and seral.

  • Climatic climax: (1) In polyclimax theory, the ultimate phase of ecological development of plant communities that the climate of a region will permit. (2) The apparently stable vegetation that terminates succession on zonal soils. See seral.
  • Edaphic climax: In polyclimax theory, any distinctive type of stable community that developes on soils different from those supporting a climatic climax.
  • Fire climax: (1) In polyclimax theory, any type of apparently stable vegetation whose distinctiveness depends on being burned at rather regular intervals. (2) In monoclimax theory, a disclimax maintained by burning at repeated intervals.
  • Zootic climax: (1) In polyclimax theory, any type of stable vegetation whose continued existence depends upon continuous stress from heavy use by animals. The animal components of all ecosystems play important roles as subordinates, but only in a zootic climax is an animal so influential as to be clearly a dominant. (2) In monoclimax theory, a disclimax maintained by heavy grazing.

Colluvial: (1) In soils, material that has been transported downhill and accumulated on lower slopes and/or at the bottom of the hill. (2) In geology, material consisting of alluvium in part and also containing angular fragments of the original rock; also talus and cliff debris; material of avalanches. (3) Pertaining to material transported and deposited by mass-wasting and local unconcentrated runoff on and at the base of steep slopes.

Community: (1) A general term for an assembly of plants living together and interacting among themselves in a specific location, no particular ecological status being implied. (2) A unit of vegetation that is relatively uniform in structure and floristic composition and consisting of competing plants of one or more species in a common location. The basic unit of vegetation.

  • Abstract community: (1) A generalized category comprising a number of similar units or stands of vegetation. A theoretical community. (2) Vegetation unit not yet placed into existing type concepts or categories and that is the result of grouping relevés or sample stands on the basis of floristic similarity.
  • Concrete community: Actual stands or real aggregations of plants (vs. abstract) of more or less similar uniformity in physiognomy, composition, etc. Concrete communities can be sampled or measured and then aggregated into abstract community-types and further abstracted into a general vegetation.

Congelifraction: The process of splitting rock by frost action. Also called frost-splitting, frost riving, frost-shattering and mechanical frost weathering. Synonym of gelifraction.

Congelifracts: Individual fragments (spalls) produced by congelifraction (frost-splitting).

Congeliturbation: (1) The process of stirring, thrusting and heaving of the earth's mantle by frost action. (2) Frost patterning by a freeze-thaw cycle including frost heaving and differential mass movements like solifluction. Synonym of cryoturbation.

Conifer: A plant belonging to the order Coniferales bearing cones and needle-like or scale-like leaves. Sometimes misleadingly referred to as a softwood.

Coniferous: Bearing cones.

Cover: (1) Any vegetation producing a protecting mat on or just above the soil surface. (2) The plant parts, living or dead, on the surface of the ground. Vegetal cover is composed of living plants, litter cover of dead parts of plants. (3) The area of ground covered by the vertical projection of the aerial parts of plants of one or more species. (4) The entire canopy of all plants of all sizes and species found in an area. (5) Plants or vegetation used by animals for nesting, resting, escape, or protection from adverse environmental conditions.

  • Basal cover: See basal area.
  • Canopy cover: (1) The proportion of the ground area covered by the vertical projection of the canopy. Expressed as a percent of area. (2) Sometimes used to mean a combination of canopy closure and crown density. Expressed as a degree of opacity. See shade density.
  • Crown cover: (1) The ground area covered by the crown of a tree or a shrub, as delimited by the vertical projection of its outermost perimeter. (2) The canopy of green leaves and branches formed by the crowns of all trees in a stand or forest. See canopy cover.
  • Thermal cover: Plant cover used by animals to ameliorate the effects of weather.

Creep: (1) Slow mass movement of soil and soil material down relatively steep slopes, primarily under the influence of gravity but facilitated by saturation with water and by alternate freezing and thawing. Under dry conditions creep constitutes a particular form of displacement brought about by thermal expansion and contraction. (2) The slow and imperceptible movement of finely broken-up rock-matter from higher to lower levels.

Crown: The upper portion of a tree or shrub, including the branches and foliage.

Crown closure: (1) The closing together of the crowns of trees in a forest as they age and grow. (2) By extension of the term, the proportion of the ground area covered by the aggregate vertical projection of all the tree crowns in a crown cover. Expressed as a percent of area. See canopy closure and canopy cover.

Crown density: The thickness or compactness of an individual crown, i.e. its opacity, as measured by its shade density. Collectively, crown density of all plants in a stand is termed canopy density.

Cryoplanation: (1) Molding of the landscape by frost action. (2) Land erosion or reduction by the processes of intensive frost action, i.e. congeliturbation including solifluction and accompanying processes of translation of congelifracts. Includes the work of rivers and streams in transporting materials delivered by the above processes. (3) The process of mass-wasting related to frost action and solifluction.

Cryoturbation: (1) Process of stirring, heaving, and thrusting of the earth's mantle by frost action including frost heaving and differential mass movements like solifluciton. Synonym of congeliturbation.

Cryptogam: (1) A plant (in the wide sense) that reproduces by spores, including mosses, liverworts, lichens, club mosses and horsetails. (Note: Lichens are not plants. Taxonomic reorganization of the old 'Plant Kingdom' now places the fungal and algal components of lichens in taxonomic clades separate from the Plantae. However, in vegetation studies they have been traditionally grouped and studied together as part of the cryptogamic layer of the plant canopy.) (2) Collective term for the Thallophytes, Bryophytes, or Pteridophytes. Compare phanerogam.

Cryptophyte: A plant in Raunkiaer's life-form classes in which the buds are covered with soil or water; includes geophytes, helophytes, and hydrophytes.

Cupola: The dome-shaped portion of an ombrophilous mire dominated by Sphagnum and flanked on one or both sides by the lagg. See bog and rand.

Cushion plant: An herbaceous or low woody plant so densely branched that it forms a dense resilient mat or cushion, e.g. Silene acaulis. See caespitose.

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D.b.h. (diameter at breast height): The diameter of a tree, measured outside the bark, at 4.5 feet (1.37 m) above average ground level.

Disclimax: In monoclimax theory, a distinctive type of climax community which retains its character only under continuous or intermittent disturbance such as heavy grazing or periodic burning.

Duff: (1) Forest litter and other organic debris in various stages of decomposition, on top of the mineral soil, typical of conifer forests in cool climates where the rate of decomposition is slow and where litter accumulation exceeds decay. (2) Decomposition products of litter lying on mineral soil, in which the identity of the original tissue can no longer be discerned. A product of litter decay. (3) A general term for vegetal matter including fresh litter and well decomposed organic material and humus lying on mineral soil in a forest.

Dystrophic: (1) Refers to habitats which are both low in basic nutrients and toxic. (2) Term used to denote high concentrations of humic acid in water. It generally refers to bog ponds with peat-filled margins which eventually develop into peat bogs. Compare eutrophic, mesotrophic, and oligotrophic.

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Ecesis: The process whereby a plant establishes itself in a new area, from germination or its equivalent (e.g., the rooting of some detached portion) to reproduction, whether sexual or vegetative. Synonym of colonization. The third of six steps in succession as described by Clements.

Edaphic: Pertaining to the soil and particularly the influence of soil on organisms.

Epilimnion: The uppermost layer of water in a lake, characterized by an essentially uniform temperature that is generally warmer than elsewhere in the lake and by a relatively uniform mixing caused by wind and wave action; specifically the light (less dense), oxygen-rich layer of water that overlies the metalimnion in a thermally stratified lake.

Ericaceous: Refers to the heath family, Ericaceae, e.g., blueberry.

Erratic: A rock transported by glacier action from a distant source.

Esker: A narrow, winding ridge of stratified gravelly and sandy drift deposited between ice walls by meltwater channels flowing on, in, or under the glacial ice. See kame.

Eutrophic: (1) Literally, "well fed." Refers to habitats, particularly soils and water, that are rich in nutrients. (2) Applied to fens composed of plants growing in "hard waters" which are rich in nutrients. Compare mesotrophic, oligotrophic, and dystrophic.

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Fellfield: (1) From the Danish "fjoeld-mark," or rock desert. A type of tundra ecosystem characterized by rather flat relief, very stony soil, and low, widely spaced vascular plants. (2) Rocky habitats with a cover of low plants on exposed alpine summits and ridges, characterized by low mat and cushion plants and an abundance of surface rocks. (3) Those stony, sparsely vegetated alpine habitats which are intermediate between a boulder field and an alpine meadow. Compare felsenmeer.

Felsenmeer: German term ("sea of rocks") for extensive areas, usually fairly level or with only moderate slope, characterized by a chaotic assemblage of moderate to large size blocks of rock. Generally applied to polar regions where well-jointed bedrock is shattered by intensive frost action (frost riving) into jagged boulders and rock fragments, but may also refer to areas above timberline with similar characteristics. Synonym of blockfield. Compare fellfield.

Fen: (1) A general term for a mire (peat-forming ecosystem) with little or no Sphagnum and with a source of water and minerals outside the limits of the mire. Fens are, in comparison with bogs, less acid or even alkaline and mineral rich. Fens generally support a more varied vegetation composed of grasses, sedges, or reeds. Those supporting a scrub or woodland vegetation are termed a carr. See swamp. (2) A class of eutrophic mires lacking Sphagnum, with graminoids dominant. (3) A European term applied to grass, sedge, or reed covered peatlands. The water table is at the surface most of the time. The water and peat are not as acid as a bog and richer in nutrients. (4) A tract of low, wet ground containing sedge peat, relatively rich in mineral salts, alkaline in reaction, and characterized by slowly flowing water. Vegetation is generally sedges and grasses, often with low shrubs and sometimes a sparse cover of trees. Sphagnum mosses are absent or of low cover.

  • Eutrophic fen: Nutrient-rich fen (minerotrophic mire) where green sedges predominate and Sphagnum is absent. Usually on sites with nutrient-rich telluric ground water.
  • Forested fen: See alder swamp and swamp.
  • Mesotrophic fen: A moderately nutrient-poor fen (minerotrophic mire) where greyish-green sedges predominate and Sphagnum species occur. With an increase in Sphagnum it would become a bog.
  • Patterned fen: A mire (peat-forming ecosystem) characterized by low peat ridges alternating with parallel wet hollows, the pattern developing parallel to the contour (at right angles to water movement) on gentle slopes.
  • String fen: A patterned fen with long strings and flarks. See laniere.
  • Shrub fen: A type of mire (peat-forming ecosystem) usually flooded with slowly flowing water. Vegetated with low (less than 1.5 m) erect shrubs and generally open canopy. Trees may be present or absent. sedge peat is often present. See carr.

Fibric soil material: The least decomposed of all organic soil material. Synonymous with peat. Compare hemic and sapric.

Flark: A Swedish term referring to limited, usually elongated, wet areas of exposed peat having an algal film and sometimes a sparse cover of sedges. The flark may be several hundred meters in length. On sloping sites flarks are narrow, being only a few meters wide but on horizontal peatland they may be a hundred or more meters wide. The flark axis is always perpendicular to direction of the contours. Synonym of mare (French-Canadian), rimpi (Finnish), and kulju.

Flashet: Term used commonly in Newfoundland to denote any small pond found in bogs and fens. On raised bogs flashets usually form concentric circles outward from the center. Called seepages and rullen in other countries.

Forb: (1) An herbaceous plant other than a grass, sedge, or other grass like plant. (2) A broadleaf herbaceous plant, e.g., fireweed. Compare graminoid.

Forest: (1) Plant community predominately of trees and other woody plants, growing more or less closely together. (2) Ecosystem characterized by more or less dense and extensive tree cover, i.e., larger than what might be called a grove. (3) In the Preliminary Classification for Alaskan Vegetation, vegetation with at least a 10% crown cover by trees; i.e., single stemmed woody plants at least 5 m in height at maturity.

  • Broadleaf forest: In the Preliminary Classification for Vegetation of Alaska, forest vegetation in which 75% or more of the forest canopy is made up of broadleaf trees.
  • Closed forest: A community completely dominated by the tree stratum due to the closure of the crowns. See canopy closure.
  • Conifer forest: See needleleaf forest.
  • Gallery forest: A narrow fringe of forest closely confined to the margin of a stream running through otherwise unforested terrain. Synonym of galleria. See riparian.
  • Hardwood forest: See broadleaf forest.
  • Mature forest: A forest which has reached the age of utilization specified in a silvicultural plan. The meaning differs with the object of management.
  • Mixed forest: (1) A forest composed of two or more species of trees. (2) In Alaska, a forest composed of both needleleaf and broadleaf trees.
  • Needleleaf forest: In the Preliminary Classification for Vegetation of Alaska, forest vegetation in which 75% or more of the forest canopy is made up of needleleaf trees.
  • Open boreal forest: (1) A mosaic of trees (rarely krummholz) and a deep lichen mat (mostly Cladonia) with herbs and shrubs derived from a boreal-type vegetation. The proportion of trees to lichen mat gradually changes southward till trees become dominant and there is an economically useful, dense needleleaf forest with a moss, rather than a lichen understory. (2) The widespread forest within the subarctic zone between the forest line and closed boreal forest. Synonym of subarctic woodland, open woodland, and lichen-woodland.
  • Overmature forest: A forest in which net growth has almost ceased due to decay and deterioration of older trees. See old-growth stand.

Forest floor: A loose term for the deposit of dead plant matter on the mineral soil surface in a forest. Includes litter and unincorporated humus. See duff.

Forest limit (forest line): (1) The upper elevational or latitudinal limit beyond which natural tree regeneration cannot develop into a closed forest stand. (2) The general upper elevational or latitudinal limit of contiguous forest growth. (3) The limit of forest vegetation covering 50% or more of the landscape. Compare tree line and tree limit.

Frost action: (1) The weathering process caused by repeated cycles of freezing and thawing the ground in the presence of water. (2) Freezing and thawing of soil moisture.

Frost boils: Areas of bare soil which are sufficiently disturbed by frost action to prevent plant colonization. On slopes, fine material in non-sorted circles moves slowly downslope producing banked or "stepped" frost boils.

Frost heaving: The lifting of a surface by the internal action of freezing moisture. It generally occurs after a thaw when the soil is filled with water droplets and when a sudden drop of temperature below freezing changes the water to ice crystals with consequent expansion and upward movement of the soil. See congeliturbation and cryoturbation.

Frost scars: Small patches of bare soil often scattered through the vegetation in tundra areas; produced by frost action and thus a cryopedologic feature. See non-sorted circles.

Fruticose: Shrubby, as in fruticose lichens, e.g. Cladonia rangiferina.

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Geophyte: (1) Perennial herb with its perennating bud (s) located well below the soil surface. (2) Perennial plant with an annual shoot and perennial underground parts.

Glacial drift: Rock debris transported by a glacier and then deposited either directly from the ice or from the melt water.

Glacial outwash: Gravel, sand, and silt, commonly stratified, deposited by melt water as it flows from glacial ice.

Gleyed soil: A soil having one or more neutral gray horizons as a result of waterlogging and lack of oxygen. The term "gleyed" also designates gray horizons and horizons having yellow and gray mottles as a result of intermittent waterlogging.

Graminoid: (1) Grass-like in appearance, with leaves mostly very narrow or linear in outline. (2) An herbaceous grass or plant of similar growth form. (3) Plants which are grasslike in appearance even though they are not grasses in a taxonomical sense, such as sedges, reeds, cattails, and others, e.g., cottongrass. Compare forb.

Grass: (1) A member of the botanical family Poaceae, characterized by hollow stems that are circular in cross section and bladelike leaves arranged on the culm or stem in two ranks. (2) Vegetation composed mostly of grasses.

  • Medium-height grass: Grasses ranging from 0.5 to 1.5 meters in height.
  • Short grass: Grasses that grow only a few decimeters in height.

Grassland: (1) A landscape in which the existing plant cover is dominated by grasses. See meadow and savanna. (2) The continental scale landscape unit (biome) or ecosystem extending from Alberta to Texas and characterized by various species of grasses.

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Heath: Community of grass-like plants and shrubs of one or more of the heath families Ericaceae, Empetraceae, or Diapensiaceae found on infertile sites. Frequently found on bogs in Alaska.

Heather: Common name for Calluna vulgaris found in Europe and the British Isles.

Helophyte: A cryptophyte that mainly grows in soil saturated with water or in the water itself, and from which leaf and flower-bearing shoots emerge. Helophytes do not include all the plants ordinarily known as marsh plants.

Hemic soil material: Organic soil material intermediate in degree of decomposition between the less decomposed fibric and the more decomposed sapric material. Synonym of mucky peat.

Herb: Flowering plant with no significant woody tissue above the ground, including both forbs and graminoids.

Herbaceous: In the Preliminary Classification for Vegetation of Alaska, vegetation with 5% or more crown cover in vascular and nonvascular (mosses and lichens) plants and less than 10% crown cover of woody plants.

  • Aquatic herbaceous: In the Preliminary Classification for Vegetation of Alaska, vegetation in which there is a predominence of cover in floating or submerged plants growing in water. It can include mosses and algae as well as vascular plants. In this classification scheme emergent plants are not included in aquatic vegetation, but are placed in the wet forb herbaceous and graminoid herbaceous units.
  • Bryoid herbaceous: In the Preliminary Classification for Vegetation of Alaska, a category of vegetation in which the predominance of cover is in mosses or lichens.
  • Forb herbaceous: In the Preliminary Classification for Vegetation of Alaska, herbaceous vegetation in which the predominance of cover is in nongrass-like plants. This includes forbs, ferns, and horsetails.
  • Graminoid herbaceous: In the Preliminary Classification for Vegetation of Alaska, herbaceous vegetation with the predominace of cover in grasses or sedges.

Hillock: See hummock.

Hollow: The lower wet areas between bog hummocks. The hollow may be characterized by a flashet or the remnants of a small pond with more hygrophilic Sphagnum sp. dominant. sedges also make up a major component of the plant cover in the hollow.

Horsetail drainage: Drainage patterns in which feathery or frondlike sets of tributaries feed small main streams on hillslopes or ridge flanks. Horsetail drainage patterns are characteristic of slopes subject to active solifluction in a permafrost environment. Because of active solifluction, the drainage courses are unable to maintain true channels, and they are marked instead by shallow depressions. The drainage lines generally are completely vegetated, and are defined by low willows. Intervening areas consist of lighter-toned grasses, sedges, etc.

Humification: (1) The process of decomposition whereby organic material is humified and becomes humus. (2) The degree of decomposition of organic matter. Three degrees of humification are recognized in organic soil materials: fibric, hemic and sapric.

Hummock: (1) A microtopographic elevated area on a raised bog, composed principally of hummock-forming species such as Sphagnum fuscum, S. imbricatum and S. flavicomans. (2) Structures built up by high Sphagnum cushions and usually covered by dwarf shrubs. This Sphagnum is later partially replaced by other bryophytes or lichens.

Hummocky: Refers to a landscape of hillocks, separated by low sags, having sharply rounded tops and steep sides. Hummocky relief resembles rolling or undulating relief, but the tops of ridges are narrower and the sides are shorter and less even. Often used to describe landslide deposition areas.

Humus: (1) The finely divided, amorphous organic matter that is diffused through mineral material in a soil profile. (2) That more or less stable fraction of the soil organic matter remaining after the major portion of added plant and animal residues have decomposed. (3) The well decomposed, more or less stable part of the organic matter in mineral soils. (4) The plant and animal residues of the soil, litter excluded, which are undergoing decomposition. See mull and mor.

Hydrarch: Of successions or seres which originate in aquatic habitats such as lakes and ponds and progress toward more terrestrial conditions, as in bogs and swamps. Can be observed in lakes and ponds on northern end of Kenai Peninsula. See hydrosere.

Hydric: (1) Relating to or containing hydrogen. (2) Sometimes used incorrectly in the sense of "wet" as a substitute for hydrophyte. See hygric.

Hydrophyte: (1) A cryptophyte which survives the unfavorable season by means of buds that live at the bottom of the water; the vegetative shoots remain submerged, only the flowers and inflorescences rising above the surface. (2) A plant usually found growing in water, or in soil containing water well in excess of field capacity most of the time.

Hydrosere: A time (not space) sequence of seral communities which starts with hydrophytes and eventually leads to a mesic climax community.

Hygric: Referring to sites or habitats characterized by decidedly moist or wet conditions. Compare hydric.

Hygrophile: Refers to organisms inhabiting moist sites.

Hygrophyte: A plant that is more or less restricted to moist sites, e.g., Drosera rotundifolia.

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  • Buried ice: In permafrost, includes buried glacier, sea, lake, and river ice and recrystalized snow.
  • Foliated ice: Large masses of ground ice which grow in thermal contraction cracks in permafrost. Also known as wedge ice, and the most conspicuous type of ground ice on the arctic slope of Alaska.
  • Ground ice: Term used to denote bodies of more or less clear ice in permanently frozen ground. Ground ice may occur as pore ice, segregated or Taber ice, foliated or ice-wedge ice, pingo ice, and buried ice.
  • Pingo ice: The ice core of a conical shaped mound formed under artesian or hydrostatic pressure. See pingo.
  • Pore ice: Formed by freezing of water filling small voids between soil granules, there is no addition of water required.
  • Segregated ice: Or Taber ice, forms films, seams, lenses, pods, or layers of ground ice which grow by drawing water from adjacent areas as the ground freezes. One of the most extensive types of ground ice, it represents 75% of the ground volume in some places on the arctic slope.

Ice wedges: Wedge-shaped vertical or inclined sheets of foliar ground ice which form in thermal contraction cracks in permafrost. Formation and active growth of wedges requires temperatures of -40° C to -45 ° C for creation of contraction cracks. Inactive wedges may be found in the discontinuous permafrost zone.

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Kame: An irregular short mound, hill, or ridge of poorly sorted sand and gravel deposited by melt water in contact with glacial ice. A long winding kame is termed an esker.

Karst: (1) Originally the name (from Serbo-Croat Krs for "waterless region") of a barren limestone plateau in Yugoslavia. Now any limestone or dolomitic region showing the pits, sinks, and other features characteristic of subterranean solution and diversion of surface water. (2) A limestone plateau marked by sinks, or Karst holes, and solution channels interspersed with abrupt ridges. Not a single feature, but a landscape. See thermokarst.

Kettle: (1) A depression in glacial drift formed by the melting of a detached block of stagnant ice that was buried in the drift. It often contains a lake or swamp (kettle lakes); Thoreau's Walden Pond is an example. (2) A pothole in a stream bed.

Kettle lakes: A body of water occupying a kettle.

Krummholz: (1) A german term meaning "bent wood" for the twisted and distorted woody vegetation characteristic of mountain timberlines. (2) Scrubby, stunted trees, often forming a characteristic zone at the limit of tree growth in mountains. (3) The belt of discontinuous scrub or groveland at alpine timberlines, composed of species which have the genetic potential of the tree life-form, but in this belt are both strongly dwarfed and misshapen.

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Lagg: (1) Marginal zone outside the rand containing fen vegetation and representing the transition between raised bog peat and mineral soils. (2) Fen belt which seperates a bog from mineral soil. (3) Natural ditch around the perimeter of a raised bog or confined muskeg.

Lanieres: In a fen or bog, the drier, low, winding peat ridges located between the flarks. They have a slight damming effect on the water drainage down the seepages. Synonym of strings, ribs, and banks.

Lichen: A symbiotic association of algae and fungi.

Limnology: The scientific study of fresh waters, especially of ponds and lakes. It deals with the physical, chemical, meteorological, and especially biological and ecological conditions pertaining to such bodies of water.

Litter: (1) A surface layer on the forest floor of loose organic debris consisting of freshly fallen or slightly decomposed plant parts. (2) Plant parts dropped on the soil surface so recently that the organ from which they originated can be discerned rather readily. See duff.

Loam: (1) Soil material that is 7 to 27% clay particles, 28 to 50% silt particles, and less than 52% sand particles. (2) A loose term for any non-sandy, non-sticky, friable soil.

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Marsh: (1) A periodically wet or continually flooded but nonpeat-forming ecosystem where the surface is not deeply submerged and supporting sedges, cattails, rushes or other hygrophytic plants. Subclasses include fresh and salt water marshes. Less acid and less continuously flooded than a bog, often only intermittently flooded. (2) An ecosystem dominated by herbaceous plants, and with the soil saturated for long periods if not permanently, but without surface accumulations of peat. (3) In Alaska sites are characteristically flooded with 15 cm or more of water, but may have no standing water late in the summer, but soils remain saturated. Vegetation is usually dominated by emergent herbaceous plants. Typical species are Arctophila fulva, Scirpus spp., Equisetum fluviatile, and Eleocheris palustris. Woody plants, lichens, and Sphagnum are absent or rare. Compare fen.

Mass movement: Gravity induced movement of a large mass of the land surface as a unit. Usually refers to a high velocity movement as in a landslide or slip. Does not usually include slow processes such as creep and solifluction. Compare mass-wasting.

Mass-wasting: (1) A general term for a variety of processes by which large masses of earth material are moved by gravity either slowly or quickly from one place to another. Includes mass movement. (2) A set of geomorphic processes which does not require a suspending medium (air, water, or ice) to carry away its detritus. (3) The slow downslope movement of rock and earth debris. See cryoplanation.

Meadow: Closed herbaceous vegetation, commonly in stands of rather limited extent, the term not usually applied to extensive grasslands.

  • Brackish marsh meadow: Coastal flats and lower beach habitats regularly inundated by tides. Soils are mineral (usually fine silts but sometimes sands or gravels), sometimes overlain by a tough sod of roots and rhizomes or by shallow (up to 20 cm) peat. Erect shrubs are absent or nearly so. Mosses and lichens are absent. See marsh.
  • Fresh marsh meadow: Fresh or essentiall fresh community types, predominately on mineral soils or less than 30 cm of peat. Where peat is present it is usually sedge peat. The full range of wet meadow soil pH conditions (3.0-9.0) is represented in this type. All wet meadow types occurring predominantly in tundra settings are included here. Common non-tundra sites supporting fresh marsh meadow vegetation are wet alluvium, margins of oxbow lakes, and silted-in sloughs. Erect shrubs are absent or nearly so, but small quantities of prostrate willows are present in some stands. Mosses may be common or absent, and lichens are absent or scarce. See fen.
  • Sedge meadow: A vegetation unit (usually in wet situations) consisting of low grass-like plants belonging to the family Cyperaceae; e.g. cottongrass.
  • Wet meadow: (1) In Alaska, sites characterized by saturated soils or by flooding to depths of of less than 15 cm and vegetation dominated by herbaceous species, usually graminoids. Moss cover varies, but is generally low. Soils are mineral but may be overlain by a shallow organic layer. Compare marsh and fen. (2) Sites with soils characteristically saturated or flooded with less than 15 cm water. The vegetation is predominantly herbaceous in most types but scattered erect woody plants are present in some types and prostrate willows are present in others. Aquatic plants may be absent, present or co-dominant. Lichens are usually absent or nearly so. This is the largest and most diverse class of wetlands, with a great variety of vegetation types occurring under a wide range of environmental conditions. Soils range from entirely mineral to deep peats. Soils pH ranges from 3.0 to 9.0. See fen.

Mesh: The unit component of patterned ground, such as circle, polygon, or net, but not a step or stripe.

Mesic: Refers to sites or habitats characterized by intermediate moisture conditions, i.e. neither decidedly wet (hygric) nor decidedly dry (xeric).

Mesotrophic: (1) Habitats of moderate nutrient capacity. (2) Used in European literature to describe bogs in transition between lowmoore and raised bogs. Compare eutrophic, dystrophic, and oligotrophic.

Minerotrophic: Sites which receive terrestrial mineral nutrition in addition to precipitation, indicating that nutrients are brought to the peat by water that has previously extracted them from a mineral soil. See soligenous.

Mire: (1) General term which embraces all those peat-forming ecosystems described in English by such other terms as bog, fen, carr, muskeg, moor,and peatland. Does not include marshes since they are, by definition, nonpeat-forming and are seasonally flooded. Mires are subdivided into fens and bogs on the basis of the origin and chemistry of their respective water supplies. Terms for conditions similar to mire in other languages are: myr (Swedish and Norwegian), Moor (German), myri (Icelandic), and suo (Finnish). (2) An ecosystem in which the rooting medium consists of wet peat.

Monoclimax: Theory which suggests that there can be only a single stable vegetation type as the result of succession within a climatic region. See polyclimax.

Moor: (1) A Germanic term applied to any area of deep peat whether acid or alkaline (bog or fen). (2) In English, the term is applied to high lying country covered with heather and other ericaceous dwarf shrubs, mainly Vaccinium. It is often used to refer to land having any of the oxyphylous communities.

  • Low moor (lowmoore): (1) Type of fen (eutrophic mire) composed of peat or muck soil, formed in eutrophic or mesotrophic waters (commonly a former lake) and, therefore, relatively rich in minerals, and supporting a rich vegetation. Compare to high moor which is poor in nutrients. (2) A common European term for fen peatland occupying basins or depressions and not elevated above their perimeter. (3) Peatland in which the peat is made up of sedges, reeds, and certain trees and shrubs, Sphagnum species are absent or rare. Occurs chiefly in river valleys and is fed by ground waters rich in mineral salts. Synonym of Flachmoor (German), niedermoor, and niederungs. See bog.
  • High moor: Type of bog in which both the vegtation and the peat have low nutrient status, the vegetation having developed either on basin sites receiving run-off water poor in minerals and nitrogen or on sites in a cool humid climate where heavy precipitation has leached most of the nutrients from the soil and caused waterlogging for much of the year creating a blanket bog. Sphagnum, Eriophorum, and ericaceous shrubs typically dominate high moor vegetation. Compare low moor which is rich in nutrients. Synonym of Hochmoor (German). See raised bog.

Mor: A type of forest humus layer of unincorporated organic material, usually matted or compacted or both, distinctly delimited from the mineral soil and generally overlain by litter. Formed in the absence of earthworms. See duff. Compare mull.

Moraine: An accumulation of glacial drift built within a glaciated region by the direct action of glacial ice. Examples are lateral, terminal, and recessional moraines.

Mottling, soil: Irregular spots of different colors that vary in number and size. Mottling generally indicates poor aeration and impeded drainage. Descriptive terms are as follows: abundance--few, common, and many; size--fine, medium, and coarse; and contrast--faint, distinct, and prominent. The size measurements are of the diameter along the greatest dimension. Fine indicates less than 5 millimeters (about 0.2 inch); medium, from 5 to 15 millimeters (about 0.2 to 0.6 inch); and coarse, more than 15 millimeters (0.6 inch).

Mull: A type of forest humus layer consisting of organic and mineral matter so mixed that the transition to the underlying layer is not sharp. Mixed mainly through the activities of earthworms. Compare mor.

Muskeg: (1) An old Algonquin Indian term applied to a large expanse of Sphagnum peatland bearing stunted black spruce and tamarack with ericaceous shrubs prominent. (2) A wet area usually moss-floored, characterized chiefly by an organic soil. Muskeg most often refers to a black spruce woodland with a thick mat of mosses (Hypnaeae and Sphagnum) underlain by peat. It can be used loosely to refer to a willow-grown sedge low place, and in loosest terms is any wet lowland such as a slough or bog. (3) A bog in northern North America characterized by an abundance of Sphagnum and a sparse cover of shrubs and small trees such as black spruce.

  • Flat muskeg: The surface of these muskegs is flat or concave and their development cannot go beyond a certain height nor can it spread laterally. Limited to lowlands, valley streams, and edges of lakes and ponds of which the water is more or less acid in reaction and relatively poor in soluable mineral salts.
  • Raised muskeg: Muskeg having a convex surface and hummocks of Sphagnum mosses which by their continual upward growth lead to accumulation of moss peat reaching several feet in thickness. Ledum, Kalmia, and Andromeda are the dominant shrubs. Raised muskegs develop in less extremely wet climatic conditions than those necessary for the formation of slope muskegs. Synonym of raised bog.
  • Slope muskeg: Muskegs which have a sloping surface and which usually develop in coastal regions where the peat-forming vegetation is dependent upon cool summers, high precipitation, and high humidity. Usually support mixed communities of sedge and moss vegetation with Scirpus, Eriophorum angustifolium, E. vaginatum, Rhyncospora alba, and several species of Sphagnum.
  • Smallpox muskeg: Areas of former lake and pond beds now free of water and characteristically saucer-like in shape. The former rims have a good growth of small trees and shrubs which produce a pock-marked effect.

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Needleleaf: Plant bearing stiff, linear, needle-like leaves, or vegetation composed of needleleaf plants.

Nets: One of the forms of patterned ground characteristic of earth subject to intensive frost action.

  • Non-sorted nets: patterned ground with a mesh intermediate between that of a nonsorted circle and a nonsorted polygon, and with a nonsorted appearance due to absence of a border of stones such as characterize a sorted net.
  • Polygonal nets: Honeycomb patterns in the soils of arctic and alpine regions, the borders of which are formed of relatively large stones of boulders, while centers consist of finer particles sorted by solifluction processes.
  • Sorted nets: patterned ground with a mesh intermediate between that of a sorted circle and a sorted polygon, and with a sorted appearance commonly due to a border of stones surrounding finer material.

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Old-growth stand: Not synonymous with old-aged forest and must be recognized on the basis of stand characteristics rather than age of trees. Old growth stands contain trees of a wide range of sizes and ages and have a deep, multilayered canopy. They contain large standing dead snags and large down dead trees and other coarse woody debris. Nutrient cycling is low and much energy accumulates on the forest floor.

Oligotrophic: (1) Literally, "pooly fed." (2) Describing bog formed of plants growing in "soft" waters which are poor in nutrients as in a raised bog. (3) Pertaining to water that is poorly supplied with the basic nutrients needed by plants. Compare eutrophic, dystrophic, and mesotrophic.

Ombrotrophic: Term meaning "nourished by rain" and referring to areas exclusively dependent on nutrients from precipitation.

Oxbow lake: Semi-circular lake located in an abandoned meander river channel (loop) on a flood plain. See slough.

Oxyphylous: Refering to a habitat which is controlled by excessive acidity of the substratum.

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Palsa: (1) Peat-covered mound with a perennially frozen core. Usually ombrotrophic and generally much less than 100 meters across and from one to several meters high. In Fennoscandia, palsas are generally treeless but in North America they commonly have a few stunted larch or black spruce. (2) Large earth-hummock-like feature typical of parts of Scandinavia and Siberia. (3) Earth mounds, believed to be of periglacial origin and occurring in arctic and alpine regions. They are composed entirely of earth and persist long after amelioration of the climatic conditions that produced them. (4) Peat mounds. Compare pingo.

Paludification: (1) Literally, "swamping." Process of mire (peat-forming ecosystem) formation over previously forested land or grassland due to climatic or autogenic processes leading to waterlogging and anaeroby. (2) Conversion of previously dry land to swamp. Compare terrestrialization.

Paternoster lake: One of a linear series of small lakes occupying depressions in a glacial valley, connected by streams, rapids, or waterfalls.

Patterned ground: A group term for the more or less symmetrical forms such as circles, polygons, nets, steps, and stripes, that are characteristic of, but not necessarily confined to, ground subject to intensive frost action. Circles, polygons, and nets are most typically formed on level ground, and stripes and steps are found on slopes. Patterns may be sorted when the individual units of the patterns are bordered by coarse materials ejected from the fines by freezing and thawing. Two characteristics of patterned ground used in classification are (1) the pattern, and (2) the presence or absence of obvious sorting.

Peat: (1) Partially decomposed plant remains including both bog and swamp peat (formed under waterlogged conditions) and heath peat, mor, or raw humus (formed under well-drained conditions). (2) Layer consisting largely of organic residues originating under more or less water-saturated conditions through the incomplete decomposition of plant and animal constituents, and being due to anaerobic conditions, low temperatures and other complex causes. (3) Unconsolidated soil material, largely undecomposed organic matter, that has accumulated under conditions of excess moisture.

  • Acutifolia peat: Peat which is composed of Sphagnum species with nearly flat leaves, and in-rolled edges. It is generally dense in structure and has great resistance to humification. It is also characterized by low acidity and poor aeration.
  • Allochthonous peat: Peat of sedimentary origin. This peat is formed from the remains of plants brought in from outside the site of deposition.
  • Amorphous granular peat: Descriptive term applied to one of the primary macroscopic elements of peat which is granular in nature but to which no particular shape can be ascribed.
  • Autochthonous peat: Refers to true peat which has formed in place, that is, from plants growing in situ.
  • Basin peat: Referring to peat deposited in a water-filled basin. Begins with limnetic deposits up to the surface level of the pond and is succeeded by gradual formation of autochthonous peat.
  • Brown moss peat: Synonym of Bryidae peat and Hypnum peat.
  • Bryidae peat: Eutrophic fen peat composed predominantly of the non-sphagnaceous "brown mosses" such as species of Campylium, Amblystegium, Paludella, etc.
  • Carex peat: Peat developed on wet fens. In some fens and bogs it forms a lower thin layer, while in others it is quite thick, generally mixed with Amblystegium peat. See sedge.
  • Cymbifolia peat: Peat composed of Sphagnum species in which the leaves are not flat, but boat-shaped, and with rolled edges; it is generally loose and bulky with good water movement. This type of peat mainly comprises raised bog formation and is composed of such species as Sphagnum imbricatum, S. papillosum and S. magellanicum.
  • Drift peat: A peat deposit associated with or embedded in glacial drift.
  • Forest peat: Fluffy and somewhat fibrous forest mold or litter that is brown to dark brown. Its reaction is between pH 3.8 and 5.5. The total nitrogen is 1.0 to 2.5% on a dry basis, and the ash content is between 4 and 20%.
  • Limnic peat: Material deposited in water such as ooze, mud, detritus, shore and inundation peat, Equisetum, Scirpus, and similar peats stratified below the water.
  • Sedge peat: Peat composed of sedge species, primarily Carex, with Juncus, Eriophorum, and Scirpus. In some instances sedge peat is so termed because a unit proportion of peat has more than 50% sedge.
  • Semiterrestric peat: Eriophorum, Sphagnum and some broadleaf forest peat grown near the water surface and in moist conditions such as older peat.
  • Sphagnum peat: Peat which develops in drier areas than does Carex peat and forms thick deposits whose plant composition is exceptionally pure and homogenous. The mosses are chiefly cymbifolium and acutifolium and generally raw. Wood fragments may be more abundant in certain horizons. Synonym of bog-moss peat.
  • Telmatic peat: (1) Carex peat as well as those belonging to the Amblystegium and Sphagnum cuspidatum group of mosses. (2) A general term for peat developed on wet ground, such as Carex peat.
  • Terrestric peat: Peat consisting primarily of tree remnants.
  • Upland peat: Peat on slopes and undulating uplands. It has no particular water table.

Peatland: A generic term including all types of peat-covered terrain. May peatlands are a complex of bogs and fens, sometimes called a "mire-complex". A loose synonym of muskeg and organic terrain.

Pergelisol: Permanently frozen ground. See supragelisol. Nearly synonomous with permafrost, but permafrost refers to both phenomenon of frozen ground and the frozen material while pergelisol refers only to the material.

Periglacial: (1) Originally used to indicate the climate and climatically controlled features adjacent to Quaternary ice sheets. Now loosely used to refer to supposedly similar climates and features whether or not they are related to glaciers. (2) Refers to a family of phenomena which are a result of frost-weathering and which have developed in belts of terrain marginal to Quaternary ice sheets, including patterned ground in general. The influence of freeze-thaw oscillations is predominate. (3) Refers to areas, conditions, processes and deposits adjacent to the margin of a glacier.

Permafrost: (1) Perennially frozen ground, or ground in which a temperature below 0 degrees C has existed continuously for two or more years. Permafrost is defined exclusively on the basis of temperature and no moisture or ice need be present. The upper surface of permafrost is known as the permafrost table. The layer of ground above the permafrost which freezes and thaws each year is called the active layer. (2) Refers to both the phenomenon of permanently frozen ground and to the frozen material.

Permafrost table: The upper surface of permafrost.

Phanerogam: A seed-bearing plant; any of the Spermatophyta.

Pingo: An eskimo term for a perennial, conical-shaped ice-cored mound as much as 65 m high and 1,000 m in diameter. Generally found on the arctic slope, but open-system pingos also occur south of the Brooks Range. Compare palsa.

Plant functional types: Plant functional types (PFTs) are categories that define plants according to their function in ecosystems and/or their use of resources. Classification, analysis and modeling of vegetation often require that the great diversity of plant species be reduced to a much smaller number of logical categories. The PFT concept has gained favor particularly among modelers who are trying to predict how vegetation will respond to the effects of climate change (Smith et al. 1997). PFT approaches usually divide plants on the basis of phylogenetic characteristics (taxonomic groups such as willows, maples, sedges and grasses) and / or life-form characteristics. Life-form considerations include such things as whole-plant physiognomy (e.g., trees, shrubs, herbs, lianas, graminoids, etc.) or more specific properties, such as plant size (short vs. tall), leaf size (microphyll, macrophyll), leaf shape (needleleaf, broadleaf), seasonality of leaves (summer-green, evergreen, deciduous), leaf hardness (malacophyll, sclerophyll), light or shade tolerance, rooting depth, the position of the over-winter perennating buds (e.g., phanerophytes, hemicryptophytes). One of the most comprehensive approaches is that of Eugene Box (Box 1981), who defined 90 PFTs based on their environmental response to temperature and precipitation indices. This list was later grouped into 15 broader PFTs that were more appropriate for modelers to define the various global biomes (Box 1996).

Polyclimax: Theory which permits two or more simultaneously existing, stable, self-maintaining plant communities controlled by local environmental conditions in a larger climatic region. See climax and monoclimax.

Polygons: One of the forms of patterned ground characteristic of earth subject to intensive frost action.

  • Ice wedge polygons: (1) Nonsorted polygons bounded by ice wedges. (2) Large-scale polygonal features commonly outlined by shallow trenches underlain by ice wedges. Synonym of tundra polygon and Taimyr polygon.
  • Cake polygons: Described from Russia by Antevs as a type of stone net with exceptional assortment, with sharply segregated stone-free clay fields. The clay cakes are frozen, harden nightly, and have become raised by frost heave.
  • High-centered polygons: Polygons bordered by eroding ice wedges that have permitted the polygon margin to collapse into the thermal contraction cracks. Generally, a later developmental stage of ice-wedge polygon associated with improved drainage.
  • Low-centered polygons: Polygons bordered by active ice wedges which are covered by low ridges of peat that cause the margins of the polygon to be higher than the surface of the center. Generally, an earilier developmental stage than the high-centered ice-wedge polygons.
  • Nonsorted polygons: Patterned ground whose mesh is dominantly polygonal and with a nonsorted appearance due to the absence of a border of stones or course materials such as that characterizing sorted polygons. Special varieties of nonsorted polygons are frost-crack polygons, ice-wedge polygons, and desiccation polygons.
  • Sorted polygons: Patterned ground whose mesh is dominantly polygonal and with a sorted appearance due to a border of stones or course material surrounding finer material.

Pteridophyte: A seedless vascular plant (with xylem and phloem), including club mosses, horsetails, and ferns.

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Rand: Outwardsloping margin at the perimeter of a raised bog. See cupola.

Relevé: A sample of a stand of vegetation in which characteristics such as species found, cover, density, etc. are determined. French for "abstract."

Rhizome: A stem, generally modified (particularly for storing food), that grows along but below the surface of the ground and produces adventitious roots, scale leaves, and suckers irregularly along its length, not just at nodes, e.g. Equisetum and Pteridium spp. Compare runner and stolon.

Riparian: (1) Pertaining to streamside environment. (2) Vegetation growing in close proximity to a watercourse, lake, or spring and often dependent on its roots reaching the water table. See gallery forest.

Runner: (1) An above-ground, more or less horizontal stem that forms roots and shoots at some of the nodes under favorable conditions, e.g., strawberry and Saxifraga flagellaris. Compare rhizome and stolon. (2) A slender aerial branch rooting at the tip and forming a new plant which eventually becomes detached from the parent.

Rush: Member of the plant family Juncaceae.

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Sapric soil material: Muck. The most highly decomposed of all organic soil material. Muck has the least amount of plant fiber, the highest bulk density, and the lowest water content at saturation of all organic soil material. Compare fibric and hemic.

Savanna: (1) A physiognomic type of vegetation in which tall, widely spaced plants, especially trees, are scattered individually over a landscape otherwise covered with low-growing plants, especially graminoids. (2) Closed grass or other predominantly herbaceous vegetation with scattered or widely spaced woody plants. The term implies not only a vegetation, but also a characteristic landscape, climate, and soils. Also spelled savana.

Scrub: (1) Vegetation dominated by shrubs. (2) Woody vegetation predominantly of shrubs, ranging between 0.2 and 3 m in height. (3) In the Preliminary Classification for Vegetation of Alaska, treeless vegetation (or with less than 10% tree crown cover) and with shrubs comprising 25% or more of the absolute crown cover.

  • Dwarf shrub scrub: In the Preliminary Classification for Vegetation of Alaska, scrub vegetation that is less than 20 cm tall and with 25% or more crown cover in dwarf shrubs. If tall and/or low shrubs are present their combined cover should be less than 25%.
  • Dwarf tree scrub: In the Preliminary Classification for Vegetation of Alaska, vegetation with 10% or more crown cover in dwarf trees which will not achieve heights of 3 m at maturity on those sites.
  • Low shrub scrub: In the Preliminary Classification for Vegetation of Alaska, scrub vegetation between 20 cm and 1.5 m in height and with 25% or more crown cover in shrubs.
  • Tall shrub scrub: In the Preliminary Classification for Vegetation of Alaska, scrub vegetation more than 1.5 m in height and with 25% or more crown cover in shrubs.

Sedge: A plant in the family Cyperaceae, grass-like in appearance, but with solid stems that are triangular in cross-section.

  • Non-tussock sedge: A sedge that does not form tussocks; usually growing with rhizomes, stolons or singly.
  • Tussock sedge: A sedge forming tussocks; refers mainly to Eriophorum vaginatum.

Seral: (1) Refers to sere. (2) Non-climax, i.e., a species or a community demonstratably susceptible to replacement by another species or community, usually within a few decades or a few centuries at most.

Sere: A sequence of plant communities that follow one another in an ecological succession on the same habitat from a pioneer stage to, and terminate in, a particular kind of stable (climax) association.

Shade density: (1) The percent of light passing through crowns, assuming uninterrupted light to have a value of 100%. (2) An expression of opacity. See crown density.

Shrub: A woody perennial plant differing from a tree by its lower stature and generally producing several basal stems instead of a single trunk. Subcategories are based on height:

  • Tall shrub: A shrub more than 2.0 m in height.
  • Low shrub: In the Preliminary Classification for Vegetation of Alaska, a shrub between 0.4 and 2.0 m in height.
  • Dwarf shrub: A shrub less than 0.4 m tall.
    • Erect dwarf shrub: Less than 0.4 m tall with erect stems.
    • Hemiprostrate dwarf shrub: Very short, generally less than 0.15 m tall, with a semi-erect or trailing stem (refers mainly to Cassiope tetragona).
    • Prostrate dwarf shrub: Lying flat on the ground.

Silvics: The life history and general characteristics of forest trees and stands, with particular reference to environmental factors.

Slough: (1) Wet or marshy area. (2) A former stream channel now containing standing water. See oxbow lake.

Soil horizon: A layer of soil, approximately parallel to the surface, having distinct characteristics produced by soil forming processes. The major horizons of mineral soil are as follows:

  • O horizon: An organic layer of debris and decaying plant residue at the surface of a mineral soil.
  • A horizon: The mineral horizon, formed or forming at or near the surface, in which an accumulation of humified organic matter is mixed with the mineral material.
  • A2 horizon: A mineral horizon, mainly a residual concentration of sand and silt high in content of resistant minerals as a result of the loss of silicate clay, iron, aluminum, or a combination of these.
  • B horizon: The mineral horizon below an A horizon. The B horizon is in part a layer of change from the overlying A to the underlying C horizon. The combined A and B horizons are generally called the solum, or true soil. If a soil lacks a B horizon, the A horizon alone is the solum.
  • C horizon: The mineral horizon or layer, excluding indurated bedrock, that is little affected by soil-forming processes and does not have the properties typical of the A or B horizon.

Solifluction: Downslope movement (flowing soil) of earth materials resulting from frost action characteristic of areas with cold arctic or alpine climate. A potent agent of mass-wasting, more effective than those generally operating in temperate regions, solifluction prevents the development of typical soil profiles and influences the development of plant cover. See mass-wasting.

Soligenous: (1) Referring to peatlands with water percolating through them that carries minerals into the peatland from outside sources. (2) Pertaining to muskeg formed on sloping ground where formation and development are controlled by the movement of surface water and by climate. See minerotrophic.

Steppe: (1) A landscape term referring to the broad, undulating, treeless and grassy plains of eastern Russia and Siberia. It implies a characteristic landscape, soils, climate, and vegetation similar to prairie in Northern America. (2) Temperate zone vegetation dominated by grasses and occurring in climates where zonal soils are too dry to support trees. Open grass or other herbaceous vegetation, the plants or tufts discrete but averaging less than their diameters apart.

Steps: Patterned ground with a step-like form due to a downslope border of vegetation embanking an area of relatively bare ground upslope.

Stripes: One of the forms of patterned ground characteristic of earth subject to intensive frost action.

  • Non-sorted stripes: Patterned ground with a striped pattern and a nonsorted appearance due to parallel lines of vegetation-covered ground and intervening strips of relatively bare ground oriented up and down the slope. Such stripes change their dimensions with changes in slope steepness and position on a slope.
  • Sorted stripes: Patterned ground with a striped pattern and a sorted appearance due to parallel lines of stones and intervening stripes of dominantly finer material oriented down the steepest available slope. Also called stone-bordered stripes, earth stripes and rock stripes.

Stolon: A horizontal stem which grows along the surface of the soil and which propogates vegetatively by forming new shoots and roots at its nodes. Compare rhizome and runner.

Succession: (1) The gradual replacement of one community of plants by another, the sequence of communities being termed a sere and each community a seral (successional) stage. A sere whose first stage is open water is termed a hydrosere, one whose first stage is dry ground is a xerosere. (2) Any series of vegetational communities following one another in an area, repeating themselves under similar conditions (habitat or environment) and clearly due in each case to the same or a similar set of causes. (3) The process of replacement of one plant species by another.

  • Allogenic succession: The kind of succession in which one kind of plant community replaces another because of a change in the environment which was external to and independent of that produced by the plants themselves. e.g., decrease in soil moisture by improved drainage. See autogenic succession.
  • Autogenic succession: A sere in which the replacement of one plant community by another results chiefly from the trasformation of the site by the plants themselves. Antonym of allogenic succession.
  • Primary succession: (1) Plant succession on newly formed soils or upon surfaces exposed for the first time, which have never borne vegetation. Primary succession is autogenic, or internally controlled by the developing vegetation. (2) The community formation process that begins on substrates that had never before supported any vegetation. Colonization is by pioneers. See ecesis.
  • Secondary succession: (1) Plant succession which is subsequent to the destruction of part or all of the original vegetation on a site. An allogenic succession. (2) All non-phenomenological vegetation changes that occur in already established ecosystems; originates only from a partial disturbance of an ecosystem.

Supragelisol: (1) The zone above the pergelisol. (2) The active layer.

Swale: A moist or marshy depression, particularly in a grassland or prairie.

Swamp: (1) A loose term for a wetland area characterized by tree or shrub vegetation and saturated with water throughout much of the year, but with the surface of the soil not deeply submerged. Peat-forming ecosystems (mires) supporting a tree or shrub vegetation are properly termed fen or carr. (2) An ecosystem dominated by woody plants and with soils saturated for long periods if not permanently, but without a surface accumulation of peat. (3) A flat, wet area usually or periodically covered by standing water and supporting a growth of trees, shrubs and grasses; in contrast to a bog, the organic soil is thin and readily permeated by roots and nutrients. (4) Swamp is forested wetland, usually with little or no peat and waters having a slightly acid reaction. It is chemically allied with fens. (5) In the Preliminary Classification for Vegetation of Alaska, sites dominated by tall shrubs and occasional trees. Standing or flowing water is usually present. Although peat is generally absent, soils may be high in organic matter content. (6) A wooded fen whose mucky substratum is intermittently flooded; peat accumulation is not characteristic.

Swamp, alder: Wet, nutrient rich site, often with mucky soils and the vegetation dominated by alders. The nutrient-poorer alder swamps with abundant black spruce and poorly growing alder shrubs have been separated as mesotrophic alder swamps. Alder swamps often occur at bog borders influenced by seepage water.

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Taiga: (1) A Russian term meaning "land of little sticks," and originally applied to the open conifer lichen woodland between the boreal conifer forest and the tundra. (2) Ecosystems adjacent to arctic tundra in which Abies, Picea, Larix or paper-barked Betula are characteristic tree genera and muskeg, fen, and bog are prominent features of the landscape. Sometimes narrowly applied to just the arctic timberline transition zone; sometimes extended to all subarctic and even subalpine forests of the north temperate zone. (3) The wooded vegetation of boreal-subarctic latitudes that occupies the subarctic climatic zone adjacent to the treeless tundra.

Terrestrialization: Formation of a mire (peat-forming ecosystem) system by filling a water body with organic material. Usually occurs by gradual extension of peat-forming plant communities outward from the shore of a pond or lake. A common high school text example of succession. Compare paludification.

Thaw depressions: (1) Depressions which result from subsidence following the thawing of perennially frozen ground. (2) Hollow formed by the melting of ice in perennially frozen ground. See thermokarst.

Thaw lakes or ponds: (1) Lakes which occupy thaw depressions. (2) Lake or pond in permafrost region whose basin is formed by thawing of ground ice. See thermokarst. (3) A pool of water on the surface of sea ice or large glaciers formed by accumulation of melt water.

Thermokarst: A permafrost related landscape characterized by a peculiar topography of pits, hummocks, depressions, and small ponds caused by the melting of ground ice and the settling or caving of the ground surface. Considered to be a misuse of the work karst by most geomorphologists. See karst. "Cryokarst" has been suggested as an altermate term.

Timberline: (1) The upper altitude or latitude at which erect, marketable trees grow; not synonomous with tree limit. (2) Any altitudinal or latitudinal limit of forest growth. (3) Some consider the upper edge of continuous forest to be timberline, while others recognize it as the altitude of the highest tree, and still others accept a midpoint between these extremes. See tree line and forest limit.

Toposequence: Small-scale variations in topography determine the patterns of plant communities that exist within a mapped vegetation unit. Though these fine-scale patterns are too small to portray on a map, they can be understood conceptually and described. The idealized mesotopographic gradient consists of 5 microsites commonly found in arctic landscapes. From the highest to lowest elevation these are dry exposed ridges, snowbeds (sometimes divided into early- and late-melting), mesic zonal sites, wet meadows, and riparian areas (sometimes divided into stabilized and active floodplains). More information.

Tree limit: The point in latitude beyond which trees can no longer grow due to the interaction of their biological requirements with the complex of environmental factors. Compare forest limit and tree line.

Tree line: A loose term for the limit beyond which trees cannot or do not occur. Tree line is more generally used for the altitudinal boundary and tree limit for the latitudinal boundary. Compare timberline which is the rough limit of timber (forest) rather than isolated trees. See forest limit.

Tundra: (1) From the Finnish "tunturi," meaning a treeless plain and describing the landscape beyond the cold limits of tree growth. (2) A cold climate landscape having a vegetation without trees. The absence of trees is caused by a complex of conditions that is ultimately related to regional climate. This regional aspect distinguishes tundra from treeless bogs and similar local areas without trees due to edaphic extremes in areas that otherwise support a forest cover. (3) The landscape beyond the temperature limits of tree growth, both to the north and west of treeline in Alaska and at elevations above treeline on mountains. (4) The so-called "barren ground" north of the circumpolar coniferous forests. (5) Treeless areas where dwarf shrubs and low herbaceous plants predominate, often with many lichens and mosses, on a permanently frozen subsoil.

  • Alpine tundra: That portion of the landscape above the upper limit of tree growth in the higher mountain regions which supports a plant cover of dwarf shrubs and herbs.
  • Dwarf shrub scrub tundra: A tundra landscape (beyond the limits of tree growth) with a dwarf shrub scrub vegetation.
  • Herbaceous tundra: A tundra landscape (beyond the limits of tree growth) with an herbaceous vegetation.
  • Mat and cushion tundra: A tundra landscape (beyond the limits of tree growth) with a vegetation composed of mat and cushion plants. See fellfield.
  • Sedge-grass tundra: A tundra landscape (beyond the limits of tree growth) with a herbaceous vegetation of non-tussock forming sedges and grasses.
  • Shrub tundra: A tundra landscape (beyond the limits of tree growth) with a scrub vegetation.
  • Tussock tundra: A tundra landscape (beyond the limits of tree growth) with a herbaceous vegetation of tussock forming plants, particularly Eriophorum spp.

Tussock: A plant-form that is tufted, bearing many stems arising as a large dense cluster from the crown.

Tussock rings: See nonsorted circles.

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Water table: (1) The upper limit of the soil or underlying rock material that is wholly saturated with water. (2) The upper surface of ground water or that level below which the soil is saturated with water.

  • Apparent water table: A thick zone of free water in the soil. An apparent water table is indicated by the level at which water stands in an uncased borehole after adequate time is allowed for adjustment in the surrounding soil.
  • Artesian water table: A water table under hydrostatic head, generally beneath an impermeable layer. When this layer is penetrated, the water level rises in an uncased borehole.
  • Perched water table: The surface of a local zone of saturation held above the main body of ground water by an impermeable layer or stratum, usually clay, and separated from the main body of ground water by an unsaturated zone.

Water track: Term for vegetation types marking the path of mineral-influenced waters through a peatland. On airphotos, water tracks contrast sharply with the surrounding tussock tundra, bog forests, or muskegs depending upon the location.

Wetland: (1) Lands where saturation with water is the dominant factor determining the nature of soil development and the types of plant and animal communities living in the soil and on its surface. (2) A general term for sites which are permanently, seasonally, rarely, or never flooded, but which support plants characteristic of saturated soils. Dominant plants, or at least one co-dominant plant, are terrestrial or emergent, with subaerial stems and leaves. See bog, carr, fen, marsh, and swamp.

Woodland: (1) Vegetation in which trees, often small and characteristically short-boled in relation to their crown depth, are present but form only on open or sparse canopy, the intervening areas being occupied by shrubs or herbs. (2) In the Preliminary Classification for Vegetation of Alaska, forest vegetation with 10 to 25% crown cover of the tree crowns.


Xerarch: Refers to a successional sequence which begins in a dry habitat. See xerosere. Compare hydrarch.

Xeric: Refers to a dry habitat or site.

Xerosere: (1) A series of successional stages beginning on a dry habitat. (2) Primary succession emerging from geomorphological exposure of rock material, either solid bedrock, coarsely broken rocks, or fine rock and sand particles. See xerarch.


Zonal soil: (1) A soil having well developed characteristics reflecting the full influence of the prevailing climate, flora, and fauna, and, therefore, characteristic of that climatic zone. (2) Moderately deep to deep soil profile developed from loamy parent materials, having moderate internal and surface drainage, and, except in extreme environments, with evident horizon differentiaion. Soils in this category show the maximum correlation with climatic types.

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Glossary definitions excerpted from:
Bates, R.L. and Jackson, J.A. (eds.), 1984: Dictionary of Geological Terms. Garden City, New York: Anchor Press/Doubleday. 571 pp.
Gabriel, H.W. and Talbot, S.S., 1984: Glossary of landscape and vegetation ecology for Alaska. BLM-Alaska Technical Report 10. Anchorage, AK: US Department of the Interior, Bureau of Land Management, Alaska State Office. 137 pp.