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Terrain, Vegetation and Landscape Evolution of the R4D Research Site, Brooks Range Foothills, Alaska Author(s): D. A. Walker, E. Binnian, B. M. Evans, N. D. Lederer, E. Nordstrand, P. J. Webber Source: Holarctic Ecology, Vol. 12, No. 3 (Oct., 1989), pp. 238-261 Published by: Blackwell Publishing on behalf of Nordic Society Oikos Stable URL: http://www.jstor.org/stable/3682732 Accessed: 28/02/2009 19:06

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http://www.jstor.org HOLARCTICECOLOGY 12: 238-261. Copenhagen1989

Terrain, vegetation and landscape evolution of the R4D research site, Brooks Range Foothills, Alaska

D. A. Walker, E. Binnian, B. M. Evans, N. D. Lederer, E. Nordstrand and P. J. Webber

Walker, D.A., Binnian, E., Evans, B.M., Lederer, N.D., Nordstrand,E. and Webber,P. J. 1989.Terrain, vegetation and landscapeevolution of the R4D research site, Brooks Range Foothills,Alaska. - Holarct. Ecol. 12: 238-261.

Mapsof the vegetationand terrainof a 22 km2area centeredon the Departmentof Energy (DOE) R4D (Response, Resistance,Resilience to and Recoveryfrom Dis- turbancein Arctic Ecosystems)study site in the SouthernFoothills Physiographic Provinceof Alaska were made using integratedgeobotanical mapping procedures and a geographic-informationsystem. Typicallandforms and surfaceforms include hillslopewater tracks, Sagavanirktok-agetill deposits, nonsortedstone stripes, and colluvial-basindeposits. Thirty-twoplant communitiesare described;the dominant vegetation (51% of the mapped area) is moist tussock-sedge,dwarf-shrub tundra dominated by Eriophorum vaginatum or Carex bigelowii. Much of the spatial var- iation in the mapped geobotanicalcharacters reflects different-agedglaciated sur- faces. Shannon-Wienerindices indicate that the more mature landscapes,repre- sented by retransportedhillslope deposits and basin colluvium, are less hetero- geneous than newer landscapessuch as surficialtill deposits and floodplains. A typical toposequenceon a mid-Pleistocene-agesurface is discussedwith respect to evolutionof the landscape.Thick Sphagnummoss layersoccur on lower hillslopes, and the patternsof moss-layerdevelopment, heat flux, active layer thickness,and ground-iceare seen as keys to developingthermokarst-susceptibility maps.

D. A. Walker and P. J. Webber, Plant Ecology Laboratory, Institute of Arctic and Alpine Research and Dept of Environmental, Population and Organismic Biology, Univ. of Colorado, Boulder, CO 80309, USA. E. Binnian and E. Nordstrand, North Slope Borough GIS. Anchorage, AK 99501, USA. B. M. Evans, Office of Remote Sensing of Earth Resources, The Pennsylvania State Univ., University Park, PA 16801, USA. N. D. Lederer, Plant Ecology Laboratory, Institute of Arctic and Alpine Research, Univ. of Colorado, Boulder, CO 80309, USA. Present address of E.B., U.S. Geological Survey, EROS Field Office, Anchorage, AK 99508, USA. Present address of E.N., Environmental Systems Research Inst., Redlands, CA 92373, USA.

terrain and in a 22 km2 area defined the Introduction vegetation by boundaries of a 1:6000-scale geobotanical map centered A thorough knowledge of the foothills vegetation and on the DOE R4D research area (Fig. 1). This informa- its environmental controls is necessary for making tion is used to develop a hypothesis of landscape evolu- sound land-management decisions in the Southern tion with a view toward making terrain sensitivity maps Foothills Physiographic Province of northern Alaska of the Foothills region. (Wahrhaftig 1965). The trans-Alaska pipeline passes about 150 km of the foothills (Brown and Berg through Regionaldescription 1980), and future oilfields and transportation corridors will undoubtedly impact other foothill areas. This study The R4D site is representative of the Southern Foothills is the first detailed geobotanical study in this region. It Physiographic Province, a broad expanse of glaciated presents a classification, description, and map of the valleys and hills "...characterized by irregular buttes,

Accepted 1 February1989 ? HOLARCTIC ECOLOGY

238 HOLARCTIC ECOLOGY 12:3 (1989) Fig. 1. R4D study area. (A) a recently glaciated (Itkillik- age) surface, (B) glaciofluvial outwash plain of similar age, (C) bedrock outcrop, (D) floodplain deposit. Most of the other upland surfaces are mantled with Sagavanirktok-age glacial till and retransported hillslope deposits (see text for details). Also note well developed hillslope water tracks (E), colluvial basin deposits (F), and lowland water tracks (G). (CIR photo 1-4, 8-2-85).

Fig. 2. R4D Imnavait Creek watershed. View is toward the south into the Philip Smith Mountains of the central part of the Brooks Range. The mined area is Material Site 117. The crest of the low ridge to the right of the stream is the western boundary of the watershed.

HOLARCTIC ECOLOGY 12:3 (1989) 239 knobs and mesas, east trending ridges, and intervening procedures and copies of the sorted table can be ob- rolling tundra plains". (AEIDC 1975). The R4D water- tained from D. A. Walker (Walker et al. 1987a). shed is at the headwaters of the informally named Imna- The vegetation, surface forms, landforms, and per- vait Creek, which is situated in a shallow basin at the centage water cover were mapped at 1:6000 scale using foot of the central Brooks Range (Fig. 2). The 2.2 km2 an integrated mapping approach developed at Prudhoe watershed is 10 km north of Atigun Gorge, 3 km south Bay, AK (Walker et al. 1980, 1986). Field surveys for of the Dalton Highway, and located between the mean- the map were conducted in the summer of 1985 follow- dering Kuparuk River to the west and the beaded head- ing a preliminary classification of the vegetation data. waters of the Toolik River to the east. In this study, the Transects were established, and photographs and de- watershed is part of a larger 22 km2 area (Fig. 1). scriptions made of vegetation and surface forms at pre- The hills in the vicinity of the R4D site are generally determined points along the transects. This information gently rolling, rising less than 100 m from the valley was the basis for photointerpretation, which was done bottoms to the ridge crests, and elongated in a NNW on color-infrared (CIR) photographs (11 October 1984, direction. Two lines of steeper rounded sandstone and original scale 1:36,000 enlarged to a scale of 1:6000). shale outcrops are oriented perpendicular to Imnavait The surface forms (mostly periglacial features that Creek. The maximum elevation within the watershed is are superimposed over primary landforms, e.g. ice- about 945 m, and the lowest elevation along Imnavait wedge polygons, stone stripes, and frost scars) were Creek is about 875 m. The maximum elevation within mapped according to the legends developed by Everett the 1:6000 map area (Fig. 1) is 980 m near a small lake (1980, Walker 1985) at Prudhoe Bay with additions to on the eastern side of the area, and the lowest elevation include new units encountered in the foothills. The ter- is about 790 m where the Kuparuk River leaves the rain-unit classification is that of Kreig and Reger (1982), area. who mapped the route of the trans-Alaska pipeline. The designated northern boundary of the watershed These authors originally termed these units landforms, is a weir located in Imnavait Creek just south of the but have since used the term terrain unit to apply to road at Material Site No. 117 (MS-117). The east and elements of the landscape with definite composition. west divides of the watershed are two parallel NNW to Their use of the term landform differed from the tradi- SSE trending ridges. The southern divide is indistinct tional use which implies shape only (Kreig, pers. and occurs in the flat expanse of a colluvial basin and comm.). runs eastward up a gentle west-facing hill to the eastern Floristically-defined plant communities derived from divide of the watershed. table analysis (and field observation in a few cases The local hills are covered by glacial till of the Saga- where no detailed plot information was obtained) were vanirktok River Glaciation (Middle Pleistocene) (Det- grouped into mapping units based on site moisture and terman et al. 1958, Hamilton 1986). Most hill crests vegetation physiognomy. have till at the surface, providing rocky mineral sub- In several instances, it was possible to photo-interpret strate for plant communities, whereas hill slopes and units on the basis of dominant species. This was partic- valley bottoms are generally smoothly eroded and cov- ularly true for the dry dwarf-shrub, fruticose-lichen veg- ered by colluvium and shallow peat deposits. This con- etation types, where, for example, it was possible to trasts markedly with terrain of a nearby lobe of Itkillik consistently delineate Dryas-, Arctous-, Vaccinium-, (Late Pleistocene) till in the Sagavanirktok River val- and Cassiope-dominated communities. ley, where the deposits are generally stony and little eroded. Map analysis The mapped data were digitized and entered into a Methods geographic information system (GIS) (Evans et al. 1989), and computer-drawn maps of terrain units, sur- Classificationand mapping face forms, and primary vegetation were prepared using Field work was done during 1-10 August 1984 and 17 the ARC/INFO GIS software (Env. Systems Res. Inst., August - 4 September 1985. During these times, 73 Redlands, CA). The statistical analyses were conducted permanent vegetation plots were sampled, and geobo- using a grid-cell data base, and the correlation methods tanical surveys were conducted along transects within are described in Evans et al. (1989). the 1:6000-scale map area (Walker et al. 1987a). Plant The Shannon-Wiener index of diversity (Shannon and species identifications were verified by D. Murray (vas- Weaver 1949) was calculated to determine the relative cular plants) and B. Murray (mosses and lichens) at the vegetation diversity of five terrain-type groups (bedrock University of Alaska Herbarium, and we follow their outcrops, till deposits, retransported hillslope deposits, nomenclature. Vegetation types were defined by using basin colluvium, and floodplain deposits). The formula the Braun-Blanquet table analysis approach described for the index is: by Mueller-Dombois and Ellenberg (1974) and West- hoff and van der Maarel (1978). Details of the sampling Hi = - pi (log Pi)

240 HOLARCTIC ECOLOGY 12:3 (1989) Tab. 1. Summary of R4D plant community types.

Physiognomic Units Plant Communities Other Common Plants Typical Microsite Permanent Plots (Walker et al. 1987a)

D1. Dry dwarf-shrub, a. Dryas octopetala- Vascular plants: Salix Windblown south-facing SW33, 52, 53, 54, fruticose- Selaginella sibirica phlebophylla, Minuartia slopes on sandstone and 58A lichen tundra obtusiloba, Antennaria shale outcrops alpina var. media, Saxifraga nivalis, Smelowskia calycina, Kobresia myosuroides, Oxytropis nigrescens, Saxifraga bronchialis, S. tricuspidata, Douglasia ochotensis, Bupleurum triradiatum Phlox sibirica, Potentilla uniflora, Poa glauca, Carex obtusata Mosses: Polytrichum piliferum Lichens: Cetraria spp., Thamnolia spp., Cornicularia divergens, Stereocaulon tomentosum, Alectoria spp., Sphaerophorus globosus, Asahinea chrysantha b. Dryas octopetala- Vascular plants: Arctous Windblown glacial till SW42 Vaccinium vitis-idaea alpina, Salix phlebophylla and outwash deposits Mosses: Polytrichum piliferum Lichens: Cetraria spp., Thamnolia spp., Stereocaulon tomentosum, Alectoria spp., Cornicularia divergens, Sphaerophorus globosus c. Arctous alpina- Vascular plants: Vaccinium Glacial till with shallow SW09, 28, 38 Hierochloe alpina vitis-idaea, Salix snow cover phlebophylla Mosses: Dicranum elongatum, Polytrichum strictum Lichens: Cetraria spp., Alectoria ochroleuca, Cornicularia divergens, Sphaerophorus globosus, Thamnolia spp., Dactylina arctica, Cladonia amaurocraea, C. gracilis d. Vaccinium Vascular plants: Vaccinium Shallow south-facing SW51, 60 uliginosum- vitis-idaea, Dryas snowbeds Arctous alpina octopetala, Hierochloe alpina, Bistorta plumosa, Artemisia arctica, Pedicularis capitata Mosses: Rhytidium rugosum, Polytrichum strictum Lichens: Cetraria spp., Stereocaulon tomentosum, Cladonia spp., Peltigera malacea, Thamnolia spp.

16 HOLARCTIC ECOLOGY 12:3 (1989) 241 Tab. 1. Cont.

Physiognomic Units Plant Communities Other Common Plants Typical Microsite Permanent Plots (Walker et al. 1987a)

e. Cassiope tetragona- Vascular plants: Vaccinium Nonsorted stone stripes SW29A, 30A, 32A, Calamagrostis vitis-idaea, Salix with shallow snowbeds 39, 43, 44A inexpansa phlebophylla, Ledum palustre spp. decumbens, Carex bigelowii, Betula nana, Diapensia lapponica, Pedicularis lanata, Bistorta plumosa, Petasites frigidus Mosses: Rhacomitrium lanuginosum, Hylocomium splendens, Aulacomnium turgidum Lichens: Cetraria spp., Cladonia spp., Dactylina arctica, Thamnolia spp., Peltigera aphthosa f. Cassiope tetragona- Vascular plants: Vaccinium Minerotrophic SW26, 59 Dryas integrifolia uliginosum, Salix reticulata, snowbeds Carex bigelowii, Pedicularis capitata, Bistorta vivipara, B. plumosa, Parrya nudicaulis, Equisetum scirpoides Mosses: Hylocomium splendens, Dicranum angustum, D. acutifolium, Tomenthypnum nitens, Ptilidium ciliare Lichens: Cetraria spp., Cladonia spp., Dactylina arctica, D. ramulosa, Stereocaulon tomentosum, Thamnolia spp., Alectoria ochroleuca g. Betula nana- Vascular plants: Vaccinium Till outcrops and dry None Hierochloe alpina uliginosum, Cassiope areas with moderate tetragona, Bistorta plumosa, snow cover Carex microchaeta, Arctous alpina, Artemisia arctica, Vaccinium vitis-idaea Mosses: Polytrichum strictum, Hylocomium splendens Lichens: Cladonia spp., Stereocaulon tomentosum, Cetraria richardsonii, Thamnolia subuliformis Dactylina arctica

242 HOLARCTIC ECOLOGY 12:3 (1989) Tab. 1. Cont.

Physiognomic Units Plant Communities Other Common Plants Typical Microsite Permanent Plots (Walker et al. 1987a)

Ml. Moist dwarf-shrub, a. Cassiope tetragona- Vascular plants: Vaccinium Moderately deep SW40, 55, 56, 57 moss, fruticose- Carex microchaeta vitis-idaea, Pyrola snowbeds, particularly lichen tundra, or grandiflora, Ledum palustre on north-facing slopes Moist dwarf-shrub, spp. decumbens, Salix fruticose-lichen rotundifolia, S. tundra phlebophylla, Pedicularis lanata, P. capitata, Luzula arctica, Senecio atropurpureus, Vaccinium uliginosum, Diapensia lapponica, Bistorta plumosa, Saxifraga nelsoniana Mosses: Hylocomium splendens, Aulacomnium turgidum, Rhytidium rugosum, Dicranum acutifolium, D. elongatum, Rhacomitrium lanuginosum Lichens: Cetraria spp., Cladonia spp., Dactylina arctica, D. ramulosa, Stereocaulon tomentosum, Nephroma arctica, Peltigera aphthosa, Thamnolia spp. b. Salix rotundifolia- Vascular plants: Poa Deepest snowbeds SW72, 73 Saxifraga nivalis paucispicula, Aconitum delphinifolium, Arnica lessingii, Luzula confusa, Artemisia arctica, Polemonium acutiflorum, Saxifraga nelsoniana, Arctagrostis latifolia, Poa arctica Mosses: Drepanocladus uncinatus, Polytrichastrum alpinum Lichens: Stereocaulon tomentosum, Cladonia chlorophaea, Solorina crocea M2. Moist tussock- a. Eriophorum Vascular plants: Vaccinium Stable, mesic sites with SW03, 04A, 50, 61, sedge, dwarf-shrub vaginatum- vitis-idea, Carex bigelowii, flat or gentle slopes 62 tundra, Sphagnum spp. Betula nana, Salix (Eriophorum planifolia spp. pulchra, vaginatum Ledum palustre ssp. dominated), or decumbens, Bistorta Moist nontussock- plumosa, Rubus sedge, dwarf-shrub chamaemorus, Petasites tundra, (Carex frigidus, Empetrum bigelowii hermaphroditum, dominated) Vaccinium uliginosum, Cassiope tetragona, Salix reticulata, Pyrola grandiflora, Saxifraga nelsoniana Mosses: Hylocomium splendens, Aulacomnium turgidum, A. palustre, Dicranum angustum, Polytrichum strictum, Tomenthypnum nitens, Ptilidium ciliare Lichens: Cetraria spp., Cladonia spp., Dactylina arctica, Peltigera spp. 16* HOLARCTIC ECOLOGY 12:3 (1989) 243 Tab. 1. Cont.

Physiognomic Units Plant Communities Other Common Plants Typical Microsite Permanent Plots (Walker et al. 1987a)

b. Carex bigelowii- Same as above except Mesic sites on steeper SW01, 06, 08, 12, Sphagnum spp. dominanted by Carex slopes with some 27, 31 bigelowii, with Eriophorum solifluction vaginatum much less abundant c. Carex bigelowii- Vascular plants: Minerotrophic mesic None Dryas integrifolia Eriophorum triste, Salix sites, often with arctica, S. planifolia ssp. cryoturbation pulchra, S. reticulata, Bistorta vivipara Mosses: Tommenthypnum nitens, Aulacomnium turgidum, Dicranum elongatum Lichens: Thamnolia spp., Dactylina arctica, Cetraria spp. M3. Moist dwarf-shrub, a. Betula nana- Vascular plants: Vaccinium Palsas, high-centered SW15, 17 moss tundra or Rubus chamaemorus vitis-idaea, Carex bigelowii, polygons, margins of Moist dwarf-shrub, Ledum palustre ssp. water tracks, hillslopes moss, lichen tundra decumbens, Salix planifolia ssp. pulchra, Bistorta plumosa, Petasites frigidus, Eriophorum vaginatum, Pedicularis lapponica Mosses: Sphagnum spp., Aulacomnium turgidum, A. palustre, Hylocomium splendens, Dicranum angustum, D. elongatum, Drepanocladus uncinatus Lichens: Thamnolia spp., Cetraria spp., Cladonia spp., Dactylina arctica b. Betula nana- Vascular plants: Vaccinium Palsas SW24, 67 Cladonia rangiferina vitis-idaea, Ledum palustre ssp. decumbens, Eriophorum vaginatum, Pedicularis lapponica Mosses: Sphagnum spp., Aulacomnium turgidum, Hylocomium splendens, Dicranum elongatum, D. angustum M4. Moist low-shrub a. Betula nana- Same as M3a. above, Hillslopes, water track SW05, 10, 13, 46, 48 tundra Rubus chamaemorus except dominated by Betula margins nana low shrubs b. Salix planifolia ssp. Same as M2a. above, Lower hillslopes SW07, 35A pulchra-Eriophorum except dominated by Salix vaginatum planifolia ssp. pulchra low shrubs c. Salix planifolia ssp. Closed canopy shrubland Riparian margins None pulchra with varied understories d. Salix planifolia ssp. Vascular plants: Salix Riparian areas along SW68 pulchra- chamissonis, Polemonium Kuparuk River Calamagrostis acutiflorum, Artemisia canadensis arctica Mosses: Hylocomium splendens

244 HOLARCTIC ECOLOGY 12:3 (1989) Tab. 1. Cont.

PhysiognomicUnits Plant Communities Other CommonPlants TypicalMicrosite PermanentPlots (Walkeret al. 1987a)

Wl. Wet sedge tundra a. Carex rotundata- Vascularplants: Carex Wet meadows,poor SW21A, 22A, 25B Sphagnum lindbergii rariflora, Eriophorum fens on colluvialbasin scheuchzeri, Salix deposits fuscescens, Eriophorum angustifolium, Pedicularis albolabiata Mosses: Sphagnum imbricatum b. Carex-aquatilis- Mosses: Drepanocladus Wet meadows None Eriophorum revolvens, Sphagnum spp. angustifolium c. Eriophorum Watertracks None angustifolium W2. Wet sedge, dwarf- a. Salix fuscescens- Vascularplants: Carex Hummocks,strangs, SW19, 20, 22B, 25A shrub, moss tundra Sphagnum lenense rariflora, Eriophorum and raisedmicrosites in or scheuchzeri, Betula nana, colluvialbasins Wet sedge, dwarf- Pedicularis lapponica, shrubtundra Andromeda polifolia, Carex rotundata Mosses: Aulacomnium turgidum, Sphagnum rubellum, S. aongstroemii b. Carex aquatilis- Vascularplants: Carex Marginsof colluvial SW14 Salix fuscescens rariflora, Salix planifolia basis ssp. pulchra, Betula nana, Rubus chamaemorus, Andromeda polifolia, Pedicularis lapponica Mosses: Polytrichastrum alpinum, Sphagnum spp., Aulacomnium turgidum, A. palustre, Dicranum angustum, Calliergon stramineum c. Carex aquatilis- Vascularplants: Valeriana Streammargins with SW18, 47 Salix chamissonis capitata, Eriophorum deep winthersnow angustifolium, Aconitum delphinifolium, Anemone parviflora Mosses: Aulacomnium palustre, Sphagnum ssp., Bryum sp. W3. Wet low-shrub, Salix planifolia ssp. Valcularplants: Betula Watertracks, wet SW02, 11, 34, 36A sedge tundra pulchra-Eriophorum nana, Rubus chamaemorus, hillslopes angustifolium Carex bigelowii, Petasites frigidus, Saxifraga nelsoniana, Polemonium acutiflorum, Valeriana capitata, Bistorta plumosa Mosses: Drepanocladus uncinatus, Hylocomium splendens, Sphagnum spp., Aulacomnium palustre, A. turgidum, Tomenthypnum nitens Al. Aquatic marsh a. Carex aquatilis- Vascularplants: Streamchannels SW16, 23 Eriophorum Eriophorum scheuchzeri, angustifolium Carex rotundata Mosses: Sphagnum spp. b. Carex rotundata- Wet meadows None Eriophorum scheuchzeri

HOLARCTIC ECOLOGY 12:3 (1989) 245 Tab. 1. Cont.

PhysiognomicUnits Plant Communities Other CommonPlants TypicalMicrosite PermanentPlots (Walkeret al. 1987a)

c. Carex chordorrhiza Wet meadows,lake None margins d. Sparganium Mosses: Sphagnum Beaded ponds, oxbow SW35, 65, 66 hyperboreum- lindbergii, S. squarrosum, lakes Hippuris vulgaris Calliergon sarmentosum e. Arctophila fulva Lake margins None D2. Dry lichen Rhizocarpon Mosses: Rhacomitrium Blockfields,glacial SW63, 64 rockland geographicum- lanuginosum, erratics Cetraria nigricans Chandonanthus setiformis, Dicranum acutifolium Lichens:Cetraria spp., Cladonia spp., Cornicularia divergens, Alectoria spp., Umbilicaria spp., Xanthoparmelia centrifuga, Sphaerophorus globosus, Thamnolia spp., Parmelia omphalodes, Lecidea flavocaerulescens D3. Dry grassland Festuca rubra- Vascularplants: Trisetum Revegetatedareas None Poa glauca spicatum, Poa alpina, P. lanata, Epilobium angustifolium, E. latifolium, Crepis nana, Stellaria spp., Minuartia rubella, Equisetum arvense, Arctagrostis latifolia D4. Dry rush, forb, Juncus biglumis- Vascularplants: Cassiope Frost scars SW69, 70, 71 lichen barren Luzula arctica tetragona, Bistorta vivipara, Vaccinium vitis-idaea, Salix phlebophylla Mosses: Rhacomitrium lanuginosum Liches: Thamnolia spp., Cetraria spp., Cladonia spp.

where Hi is the index and p, is the fraction of the total vegetation maps prepared from the GIS data base. number of individuals belonging to the ith class. In this These black and white versions are for journal publi- study, high index values indicate terrain with many veg- cation, but color maps were also prepared and are avail- etation types and relatively high cover of each type, able from the North Slope Borough GIS, Anchorage, whereas low values indicate relatively homogeneous AK. The legends of the maps contain area summaries terrain. for each geobotanical type within the entire map and within the R4D watershed. Fig. 5 is a map of the pri- mary (i.e. dominant) vegetation. Maps were also pre- for the and types Results pared secondary tertiary vegetation (i.e. vegetation types occurring with secondary or terti- The floristically-defined vegetation community types ary importance in mosaics of vegetation). are grouped into physiognomically-defined units (Tab. For sake of simplification, many of the more minor 1) and into map units (Tab. 2-left-hand column). The terrain units in Fig. 3 were grouped with closely associ- vegetation types on the map (Fig. 5) are arranged along ated terrain units to form terrain-unit groups. For exam- a moisture gradient from dry to aquatic sites, and with ple, floodplain deposits include meander floodplains, barren and partially vegetated types listed at the bottom nonmeander floodplains, alluvial fans, and glaciofluvial of the legend. outwash deposits. Tab. 2 is a summary of the areas of Figs 3 to 5 are the terrain-unit, surface-form, and the dominant vegetation within the major terrain unit

246 HOLARCTIC ECOLOGY 12:3 (1989) groups. The left column of the table shows how the Mackay (1980) and Mackay and Mackay (1976) and community types of Tab. 1 are grouped within the vege- nonsorted circles of Washburn (1973)]. Glacial erratics tation map units. The second column contains the on the outcrops indicate that the bedrock outcrops were purely numeric vegetation codes that are in the GIS covered by Sagavanirktok-age glaciers. data base. Floodplain deposits are by far the most diverse (Hi = Vegetation 0.857) and retransported hillslope deposits are the least Vegetation on these knolls is complex due to the large diverse (Hi = 0.471) (Tab. 2). Bedrock outcrops, till variety of microsites; only the more common and dis- deposits, and basin culluvium have intermediate diver- tinctive vegetation types are described here. The sity (Hi = 0.624, 0.599, and 0.583, respectively). vegetation on these features is to a large extent con- trolled by the amount of winter snow cover and expo- sure to winds. Descriptions of the major terrain and vegetation units Exposed south-facing slopes are floristically the most Although the Arctic Foothills are largely dominated by interesting sites within the study area. These areas are tussock-tundra vegetation, there are local areas of high largely snow free during the winter due to southerly vegetation diversity due to bedrock outrops, and ripar- catabatic yiwinds blowing out of the Brooks Range val- ian systems, and regional variation due to influences leys. Dry Dryas octopetala, Selaginella sibirica dwarf- such as loess, glacial history, elevation and snow gra- shrub, fruticose-lichen tundra (Tab. 1, Community Type dients. Hillslope deposits dominate the local RAD wa- Dla has many herbs that are locally uncommon, such as tershed landscape, but the features that give the R4D Minuartia obtusiloba, Smelowskia calycina, Kobresia site its distinctive character are the sandstone outcrops, myosuroides, Oxytropis nigrescens, Douglasia ochoten- the site's position along the contact between Sagava- sis, Anemone drummondii, Bupleurum triradiatum, nirktok- and Itkillik-age glacial tills, and the floodplain Phlox sibirica, and Carex obtusata. The threatenedplant of the Kuparuk River. The vegetation descriptions that Erigeron muirii (Murray 1980) occurs on the exposed follow are organized according to the five terrain unit portions of some of the outcrops. Vegetation cover va- groups (Tab. 2), the results of which are appropriate for ries considerably depending on exposure to winds; the extrapolation to other foothill landscapes. most exposed sites are totally barren except for patches of Dryas octopetala, Polytrichum piliferum, and scat- tered lichens. Bedrockoutcrops South-facing snowbeds at the foot of the knolls have a Geology and surface forms complex variety of vegetation types. One of the more Several bedrock knolls of the Fortress Mountain forma- common types is dry Vaccinium uliginosum, Arctous tion (Chapman et al. 1964, Brosg6 et al. 1979) occur alpina dwarf-shrub, fruticose-lichen tundra (Commu- within the mapped area (Figs 1 and 3). These cover only nity Type Did) which occurs in relatively warm, well- 1% of the map but add considerably to the overall drained sites with early melting snow. Dry Cassiope topographic and floristic diversity. Thirty-two out of a tetragona, Dryas integrifolia dwarf-shrub, fruticose-li- total of 151 species recorded at the site (D. Murray, chen tundra (Community Type Dlf) is a snowbed com- unpubl. data) have been found only on the sandstone munity of relatively minerotrophic sites, such as shallow outcrops. The highest knoll is at the benchmark 'Gal' basins at the foot of knolls, where nutrients are concen- (Fig. 3), which is 68 m above the base of the knoll. Most trated from upslope. Numerous locally rare basophiles of the hills are oriented along an east-west axis with such as Salix reticulata, Astragalus umbellatus, Rhodo- steep north- and south-facing slopes. MS-117 is an dendron lapponicum, Salix arctica, Saussurea angustifo- open-pit rock mine on one of these knolls (Fig. 2); lia, Tofieldiapusilla, and Equisetum variegatum occur in material from this mine was crushed for gravel to con- these sites. Other shallow south-facing snowbed sites struct a portion of the Dalton Highway. The Fortress are dominated by Empetrum hermaphroditum or Arc- Mountain Formation is Lower Cretaceous in age and tous alpina. "...composed dominantly of thick units of dirty gray- North-facing slopes have deep late-lying snow drifts wacke-type gray to green sandstone and pebble-cobble (late June to early July). Well drained slopes with mod- conglomerate; thick units of clay shale and siltstone are erate snow cover have moist Cassiope tetragona, Carex interbedded with the sandstone and conglomerate" microchaeta dwarf-shrub, fruticose-lichen tundra (Com- (Chapman et al. 1964). munity Type Mla). These sites have a deep moss (Hylo- The surfaces of these outcrops range from smooth comium splendens) carpet that often occurs on talus gravelly slopes on the windward south-facing slopes to with very little soil development (Ranker soil of Tedrow talus slopes on the steep north-facing slopes. The south 1977). Salix planifolia ssp. pulchra or Betula nana can slopes are largely snow-free in the winter, and the north be locally important in these sites. slopes accumulate deep snow drifts. The summit ridges A variety of other more poorly defined vegetation and flatter areas of the outcrops have frost scars [Ever- types occurs in shallow snow beds, but more samples ett 1980 = nonsorted circles and mud hummocks of are needed to fully document the variation along the

HOLARCTIC ECOLOGY 12:3 (1989) 247 Tab. 2. Area of dominant vegetation and surface forms within the major terrain units groups.

Community Vegetation Map Unit Types (See Tab. 1) GIS Bedrock Outcrops (240) Till Deposits (650) Code(s)

Entire Map Watershed Entire Map Watershed

Ha % Ha % Ha % Ha %

Dla,b 671, 672 Dry dwarf-shrub, fruticose-lichen tundra 8.06 36.44 0.87 59.59 4.96 2.91 0 0 (Dryas octopetala) Dic 613 Dry dwarf-shrub, fruticose-lichen tundra 2.80 12.66 0.27 18.49 95.33 56.04 7.52 63.09 (Arctous alpina) Did 612 Dry dwarf-shrub, fruticose-lichen tundra 3.00 13.56 0 0 0 0 0 0 (Vaccinium uliginosum) Dle,f,g 453, 611, Dry dwarf-shrub, fruticose-lichen tundra 0.53 2.40 0.32 21.92 24.49 14.40 1.55 13.00 681 (Cassiope tetragona) Mla,b 451, 452 Moist dwarf-shrub, moss, fruticose-lichen tundra 7.26 32.82 0 0 0 0 0 0 (Cassiope tetragona) or Moist dwarf-shrub, fruticose-lichen tundra (Salix rotundifolia) M2a,b,c 411,412, Moist tussock-sedge, dwarf-shrub tundra 0 0 0 0 13.53 7.96 2.6 21.81 421 (Eriophorum vaginatum) or Moist nontussock- sedge, dwarf-shrub tundra (Carex bigelowii) M3a,b 461 Moist dwarf-shrub, moss tundra (Betula nana) 0 0 0 0 0 0 0 0 M4a 471 Moist low-shrub tundra (Betula nana) 0.47 2.12 0 0 18.09 10.63 0 0 M4b,c,d 431,441, Moist low-shrub tundra (Salix planifolia ssp. 0 0 0 0 5.96 3.50 0 0 472, 482, pulchra) 482 Wla,b,c 211, 212, Wet sedge tundra (Carex spp. or Eriophorum 0 0 0 0 1.18 0.69 0 0 213 spp.) W2a,b,c 241, 242, Wet sedge, dwarf-shrub, moss tundra or Wet 0 0 0 0 2.30 1.35 0 0 243 sedge, dwarf-shrub tundra (Carex spp., Salix fuscescens) W3 251 Wet low-shrub, sedge tundra (Salix planifolia 0 0 0 0 0 0 0 0 ssp. pulchra) Ala,b,c 031, 032, Aquatic sedge marsh (Carex aquatilis, 0 0 0 0 0 0 0 0 033 Eriophorum angustifolium) Aid 041 Aquatic forb marsh (Sparganium hyperboreum) 0 0 0 0 0 O 0 0 Ale 021 Aquatic grass marsh (Arctophila fulva) 0 0 0 0 0 0 0 0 A2 010 Unvegetated water 0 0 0 0 0 0 0 0 D2 821 Dry lichen rockland (Umbilicaria spp.) 0 0 0 4.11 2.42 0.25 2.10 D3 831 Dry grassland (revegetated) (Festuca rubra) 0 0 0 0 0 0 0 0 U 991 Unvegetated 0 0 0 0 0.17 0.10 0 0

Total 22.12 100.00 1.46 100.00 170.12 100.00 11.92 100.00

Shannon-Wiener Index 0.624 0.599

snow gradient. Dry vegetation (primarily Dryas-dom- (Hamilton 1986). On the ridge crests and at scattered inated) types cover 64.9% of the sandstone knolls, and sites on the hill slopes, till is exposed at the surface. most of the remainder (32.8%) is moist Cassiope snow- About 4% of the watershed and 9% of the total map beds (Tab. 2). have exposed till deposits. Flat exposed till deposits generally are rocky with gently undulating surface relief that includes blockfields (Washburn 1980) and sorted frost scars (Everett 1980). Till deposits Geology and surface forms Much of the watershed is covered by clay-rich glacial Vegetation till. Areas along the Kuparuk River and along the east- As on the sandstone knolls, the vegetation of till depos- ern side of the map are Itkillik till (late Pleistocene), its is largely controlled by the amount of winter snow whereas the deposits on most hill crests are from the cover and the degree of rockiness of the surface. The Sagavanirktok River Glaciation (middle Pleistocene), tops of small till knolls generally are blown free of snow which at other sites in the region is composed primarily in winter and are vegetated by dry Dryas octopetala, of Kanayut Conglomerate sandstones and limestones Vaccinium vitis-idaea dwarf-shrub, fruticose-lichen tun-

248 HOLARCTIC ECOLOGY 12:3 (1989) Area and Percent of Terrain Unit Groups

Retransported Hillslope Deposits Bassin Colluvium (340, 890) Floodplain Deposits All Units Combined (330, 500) (400, 420, 440, 450, 711)

Entire Map Watershed Entire Map Watershed Entire Map Watershed Entire Map Watershed

Ha % Ha % Ha a % Ha % Ha % Ha % Ha %

0 0 0 0 0 0 0 0 4.54 2.04 0 0 18.7 0.87 1.1 0.39

7.74 0.54 0.13 0.07 0 0 0 0 27.57 12.36 0 0 146.6 6.80 7.4 3.34

0.05 0 0 0 0 0 0 0 0 0 0 0 3.2 0.15 0 0

187.00 13.12 44.03 25.22 0 0 0 0 3.13 1.40 0 0 229.7 10.65 35.3 15.44

0 0 0 0 0 0 0 0 0 0 0 0 7.7 0.36 0 0

1012.90 71.06 123.66 70.82 12.42 9.51 5.21 19.20 68.62 30.77 0 0 117.23 54.36 139.3 62.62

41.40 2.90 0 0 32.92 25.20 5.88 21.67 2.67 1.20 0 0 81.8 3.80 6.4 2.90 48.17 3.38 0.37 0.21 0.07 0.05 0 0 31.67 14.20 0 0 106.1 4.92 0.3 0.13 37.50 2.63 3.21 1.83 0 0 0 0 43.51 19.51 0 0 94.0 4.36 2.7 1.23

9.22 0.65 0.04 0.02 43.96 33.66 6.99 25.76 14.75 6.61 0 0 74.7 3.47 11.0 4.93

31.43 2.20 0 0 40.42 30.95 9.01 33.21 13.89 6.23 0.34 55.74 94.9 4.40 10.4 4.70

49.94 3.50 3.16 1.81 0.36 0.28 0 0 9.37 4.20 0 0 64.7 3.00 2.9 1.28

0 0 0 0 0.26 0.20 0 0 0.08 0.04 0 0 2.0 0.09 0 0

0 0 0 0 0.20 .015 0.04 0.15 1.73 0.78 0.27 44.26 1.4 0.06 0.2 0.08 0 0 0 0 0 0 0 0 0 0 0 0.5 0.02 0 0 0 0 0 0 0 0 0 0 0 0 0 0 15.0 0.70 0 0 0 0 0 0 0 0 0 0 0 0.33 0.15 0 0 5.2 0.24 0.1 0.03 0 0 0 0 0 0 0 0 0 0 0 0 12.6 0.58 0.9 0.42 0 0 0 0 0 0 0 0 1.16 0.52 0 0 25.4 1.18 5.3 2.39

1425.35 100.00 174.60 99.98 130.54 100.00 27.13 99.99 223.02 100.01 0.61 100.00 126.6 100.0 222.4 100.0

0.471 0.583 0.857 0.754

dra (Community Type Dib), which is similar to Dryas variety of vegetation types including those described vegetation on sandstone knolls (described above) but above for sandstone outcrops (especially Community without the rich assemblage of forbs. Type Mla). Dry Cassiope tetragona, Calamagrostis in- Dry Arctous alpina, Hierochloe alpina dwarf-shrub, expansa dwarf-shrub, fruticose-lichen tundra (Vegeta- fruticose-lichen tundra (Vegetation Type Dlc, Fig. 6) is tion Type Die, described below with "nonsorted stone one of the more common types on dry till deposits. The stripes") is common in depressions on clay-rich till and vegetation in most areas mapped as this type is actually on nonsorted stone stripes on the shoulders of ridges quite complex, and local small areas, not discernible at where there are shallow snowbeds. Dry stony areas 1:6000 scale, may be dominated by any of several plant often have communities dominated by Betula nana taxa including Arctous alpina, Salix phlebophylla, Cala- (Community Type Dig). Blockfields, sorted stone poly- magrostis inexpansa, Betula nana, or Vaccinium vitis- gons, and isolated glacial erratics are dominated by dry idaea. The dominance of one of these species over the Rhizocarpon geographicum, Cetraria nigricans lichen others at any particular site appears to be a function of barren. Like the sandstone outcrops, till deposits are subtle differences in the local snow and moisture re- covered primarily by dry vegetation types (73%), but gimes and depth of soil. with a preponderance of the Arctous-dominated types Snow accumulation areas on till deposits have a wide (Tab. 2).

HOLARCTIC ECOLOGY 12:3 (1989) 249 C;TTiQ DEPARTMENTOF ENERGYR4D PROGRAM ECOLOGICALRESEARCH SITE C,. IMNAVAITCREEK, NORTHERN ALASKA

1. 3 cn TERRAINUNITS _-

SYMBOL TERRAINUNIT (C0S CODE) WATERSHED ENTIRE ^AP (A HA 5 HA Bedrock:

2l S. 1.5 0.69 23.2 1.06 C/ Oondlton. ond .ho01 (240) P?- Clielal Depolts:

Till sheet (650) 9.3 4.20 118.9 8.76

FoIviol DOpoilt4:

oClcioIluvloo outwoosh (711) 0.0 0.00 93.9 4.36

No Inder floodploin (450) 0.0 O.aO 1 .9 3.80

0.7 0.30 51.1 2.37

0.0 0.00 9.4 0.44

Callviii l Dopealits:

Basin eolluvi um (340.1190) 35.9 16.14 13J .2 6.41

dlpOlit[i ![! 18.6 75.a3 1,513.2 70.17 H4iArutronoior olop1Dt.lft | toa d sits )

Loe?strli. Dipoilt.:

Emlrent loke bettom (810) 0.0 0.00 2.4 0.11

Water:

0.1 0.03 17.5 0.82 stern *r ,I ig9

Disturbted

Read or exeolation (980) 6.2 2.81 36.N 1.70

222.4 100.0 2156.6 100.00

d _ tloheroh boundaly

ul1hok: :olkr, 0.A. Institu.e R0 1r0tie snd AIlino Rsoolch Unoirity oiColorad. Bouldr, CO. 8030 Mop Automoation NrthBragoh Cog'Slop. ephie Intormation S tm 500 lost Soeond Aoenue,. 10. Anchrage, AK 99501 (107)27(-9505 Mop Projection: UOioerSol Tronnvrse Meraort. Zon. N Dote: Ioy 31. 1987

_a lNs . DOER40 STUDYAREA 10i /~I__ IILES cr_ DEPARTMENTOF ENERGYR4D PROGRAM ECOLOGICALRESEARCH SITE C IMNAVAITCREEK, NORTHERN ALASKA

n PRIMARYSURFACE FORM

SYMBOL SURFACEFORM (1CS CODE) WATERSHEID ENTIRE HAP HA l HA 1 Cf)Cl Perl9al etl F.atlo0le: o 1o0elids. onsodstd stone 1 tripes 0.2 0. 10 12.5 0.58

;D0 _NCnsaolted st0on stripes (18) 33.9 15.225 208.5 9.67

(08) 0 4 16 55.1 2.56 $ HummrIoin$ 0)

o Clt gil flutti t 0.Oures (26) 0.0 00 30.1 1.40 ??_ .

High-centered poly0ons (01.02) 7.3 3.: 29 12.9 0 60

P::los and elevoted trc.in in basi 0.4 0. 22.1 1.02 F111 7 0 1t 22) Frost 0., 44 1.43 sco$. (06) 14 30.9

01::.'-:, S1ranraligned hunotks in 12 6 5. 67 88.9 4.12

i1hro..ke ,st pito (14) 0 0 0 '.00 0.1 0.00

Strrnl m d Water TrIcks:

def ll-slope 75.3 33.86 697 .1 32.33 WeI:lycs. rtsrined thanh m woterf 1 tr- relief (15) 2 .8 1. 26 122.0 5 .66

_ I .reol4r th (1n ) 0.00 0.9 0.04 Incitedcits1 streamn dtfoine (17) 0 .0

01 p tIi floodplain olluvium (13) 0.0 0.00 2.8 0.13

0 .0 O 00 23.2 1 .08

Other:

Ra;ky t101oi (till .a.d e.diock) 7.3 3.30 171.7 7.96

74.7 33.59 616.0 28.56 FeotuIeless (10)

Pond complex (23) 0.2 0.07 7.6 0.35

- Wa4e, (99) 0.1 0.03 17.6 0.82

Disturbed (98) 6.2 2.81 36.6 1.70

222'4 100 00 215i?6 ao;.Oa

- atllrshld boundary

410 6A4th0ot1:88k1 r. D. Cntitute o1 Al ctic on80d l D R a ch IUn4iesi * Co *edo .I 8Bou4Ide1 C0 80359

Mop Au.tootion: No th Slope. 8 ou. G.eae1ph ic.t n.,ntio, S te 50 Sec4ond 11t P Aronue. 16. Anchoroge AK 99501 (947)27-9505 Mop Projection: Unive,rsl Tr.nsverse Mercotor. Zone 6

Dote: Moy 31. 1987 i......

DOER4D STUDY AtA

- I J DOER4D0 STUDY AREA I ; v I Z NIM ~ .....~~~~~~~~~~~~~~~~~~~~~~~~~~~~ . - < a " "0 = -0 s r-; : 0 I ^ s.

3 - Ln o i - z - I I I) I Is 01 s.1 ^ + r ?? : ^a c ^c?=i -n 3 ' i b ';.s a 0 r 0j j^ S - * ;?. :? ir r. ^ ^ g ^ rr n I i _s :- I-c ^i Cow I gH ^:1K%t^: 5;.:i .Iil za: I~ 7TiU IIMUSIIii^a .. E]!II! I m i i 111: s hi? SS * Slin o-o6 So.2; .5 < ? ?SS ^ | a^ .. ". S- .-ls".ICC ^ s S ^5?^ 111 111111111 ni1~~~~~~~ W-l J s t5S ^1.~~~~~~~~~~~~~~~~~~~~~~~~~~~7t gg5MCIW 5s5~OL m - i!) .^i r- s ^ fi? i i ssn~~~~~~~~~~~- _-,Z

Fig. 5. Vegetationof the R4D site. Fig. 6. Till deposit with dry Arctousalpina, Hierochloe alpinadwarf-shrub, fruticose-lichentundra. Other visible species include Cladoniaspp., Dicranum elongatum,Vaccinium vitis-idaea,and Sphaerophorusglobosus.

ness, is often elevated above the level of the dry ele- Retransportedhillslope deposits ment because of the accumulation of organic matter. Geology and surface forms Vegetation on the dry portion of the stone-stripe Kreig and Reger (1982) have mapped most hill slopes in complex is primarily dry Cassiope tetragona, Calama- the region as "retransported deposits", which are "rela- grostis inexpansa dwarf-shrub, fruticose-lichen tundra tively fine-grained organic-rich materials moved down- (Tab. 1, Community Type Die, Fig. 8). The inter-stripe slope by slopewash, solifluction and piping. This unit is areas generally have a variant of the moist Carex bigelo- frozen and commonly contains massive ice". Till on wii, Sphagnum spp. nontussock-sedge, dwarf-shrub tun- most hill slopes of the R4D watershed is covered by clay dra, see 'hillslope water tracks' below). This variant loam that has been redistributed downslope and vege- contains Cassiope tetragona and a few basophilous taxa, tated with tussock tundra. Glacial erratics protrude up such as Dryas integrifolia, Tomenthypnum nitens and to a meter above the accumulated colluvium and peat. Salix reticulata. About 76% of the watershed and 70% of the total mapped area are mapped as retransported deposits. Surface forms associated with retransported deposits Hillslope water tracks include water tracks, frost scars, and nonsorted stone Most hill slopes have water tracks, which Everett de- stripes. The lower portions of stone-stripe complexes scribes as "...shallow channels that conduct snow melt- often grade into and may be the foundation for water- water and subsurface water during the thaw season... track complexes. giving the topography a ribbed appearance". (Walker et al. 1982). These 'hillslope water tracks' are distinct from the lowland 'water-tracks' described in mires of Minne- Nonsorted stone stripes sota, Labrador and northern Europe (Heinselman 1970, The shoulders of most hills have well-vegetated non- Glaser et al. 1981, Glaser 1983), where the term 'water sorted-stone-stripe complexes (Fig. 7), described by track' applies to minerotrophic drainage tracks in low- Washburn (1956) as "...patterned ground with striped lands through generally flat peatlands. Lowland water pattern and a nonsorted appearance due to parallel lines tracks occur in the R4D study area in colluvial basin of vegetation-covered ground and intervening strips of deposits (see Fig. 7, and below). relatively bare ground oriented down the steepest avail- The hillslope water tracks are subparallel channels able slope". Stripes at the R4D site consist of a dry to spaced tens of meters apart. Most water tracks within moist well-vegetated stony element 1.5 to 2 m wide and the R4D watershed are shallow with no clear drainage a comparably-wide moist to wet peaty element. The dry channel. There are a few well-developed water tracks elements usually have frost scars and well-developed within the watershed, but better examples occur north hummocks. The interstripe element, in spite of its wet- of the 'Gal' benchmark (Fig. 3) and on the lower part of

HOLARCTIC ECOLOGY 12:3 (1989) 253 .... Fi~:~!~ .. E~ ...... ? ~.:?,,,:~,:;,~.,~.~ ;~,,~:-:-.s ......

.:,~?:. 254 .0M~~? H EL (.) '~ . ~~~..I-~ ; -iR i

254 HOLARCTIC ECOLOGY 12:3 (1989) Fig. 8. Nonsorted stone- stripe complex. Plot in background is on drier element of the complex, and plot in foreground is on relatively wet element. The dry element has Cassiope tetragona, Calamagrostis inexpansa dwarf-shrub, fruticose-lichen tundra. The wet element is dominated by Carex bigelowii. Note the well-developed moss hummocks on both elements of the complex.

planifolia ssp. pulchra community (Tab. 1, Community nontussock-sedge, dwarf-shrub tundra (Community Type W3) along the margins of the channel. This same Type M2b) (see below). community also occurs on the wet east-facing hillslopes The somewhat elevated margins of water tracks often of the watershed, where there are water seeps but few have moist Betula nana, Rubus chamaemorus dwarf- clearly defined water tracks. These areas often have shrub, moss tundra (Community Type M3a). This same weakly defined solifluction features, with little differ- community also occurs along weakly developed water ence between the vegetation on the tops of the solifluc- tracks where water flows only briefly in interhummock tion hummocks and the interhummock areas due to the areas during storm events or for a short period during overall wetness. In these situations, this community of- the spring melt. It also occurs and is best expressed on ten grades into moist Carex bigelowii, Sphagnum spp. hummocks, palsas and high-centered polygons in collu-

_^ S IIS _ iiriiT I n

/ i : , -lbLi -'L i = L

Fig. 9. Interfluve with moist Eriophorum vaginatunm, Sphagnum spp. tussock- sedge, dwarf-shrub tundra. Other visible taxa include Carex bigelowii, Salix planifolia spp. pulchra, and Betula nana.

HOLARCTIC ECOLOGY 12:3 (1989) 255 vial basins (see below). In some sites, the birchis taller materialsby smooth gradationwith surroundingslopes than 20 cm, and the community is classed as moist and the highly variable and thin characterof accumu- low-shrubtundra (Community Type M4a). lated deposits"(Kreig 1985 pers. comm.). Interfluvesbetween hillslopewater tracksare gener- These basinshave complexmicrotopography consist- ally vegetated with moist Eriophorum vaginatum, ing of raisedfeatures, such as strangs(raised hummocks Sphagnum spp. tussock-sedge, dwarf-shrub tundra aligned in sinuous strings perpendicularto the line of (CommunityType M2a, Fig. 9) or a variantdominated drainage), palsas (ice-cored mounds), high-centered by Carexbigelowii (Community Type M2b). These com- ice-wedgepolygons and wet areas with lowland water- munities are not very variable with regard to species track patterns[sense of Glaser (1983)], flarks (ponded composition,but they are variablewith regardto spe- depressionsbetween raised strangsin strangmoorcom- cies dominance. Eriophorum vaginatum is usually dom- plexes), wet meadows,and thermokarstpits. Basin col- inant on the more stable hillslopeshoulders and on the luviumcovers about 16% of the watershedand 6% of upper backslopes. Shrubs (primarilyBetula nana and the total map. Rubuschamaemorus) tend to become dominanton the footslopesin associationwith deep Sphagnummats, and Vegetation Carex bigelowii-dominated communities tend to occur The vegetationin colluvialbasins is typicallycomplex. in areas with weakly developed solifluctionfeatures. A commoncharacteristic of most peatlandsis the occur- Frost scars occur on most slopes, particularlyon the rence of raisedmicrosites that are isolatedfrom mineral ridgecrests and shouldersand wherever there is mineral inputfrom waterflowing through the basin (Sjors 1948, materialnear the surface.These featurescan be totally 1963, Drury 1956, Damman 1977, Heinselman 1963, barrenor with communitiessimilar to CommunityType 1970, Glaseret al. 1981, Glaser 1983, Fosterand Glaser Die (see above discussionof nonsortedstone stripes). 1986). The details of water chemistryin the R4D collu- Luzula arctica, Juncus biglumis, and Rhacomitrium la- vial basin deposits have not been examined, but the nuginosum are characteristicspecies on frost scars Sphagnum-richbog vegetation(including numerous er- (CommunityType D4). icaceousshrubs and Betulanana,) on the raisedsurfaces About 71% of the retransportedhillslope deposits on indicaterelatively ombrotrophic conditions, and the oc- the total map and 71% of the hillslopes within the currenceof poor-fen species (e.g. Carexrotundata, C. watershedhave Eriophorumtussock tundra or one of its rariflora, Eriophorum scheuchzeri, Sphagnum lindber- close variants. Cassiope-dominateddwarf-shrub, frut- gii) in the water tracks and lower micrositesindicate icose-lichentundra covers 13% of hillslope deposits on relativelyminerotrophic conditions. the entire map and 25% of similardeposits in the wa- Low hummocksgenerally have wet Salixfuscescens, tershed. Moist low-shrubcommunities associated with Sphagnum lenense dwarf-shrub,sedge, moss tundra water trackscover only about 2% of the retransported (CommunityType W2a). Well drainedpalsas and hum- slope depositsin the watershedand 3% on slopes within mocks have moist Betula nana, Rubus chamaemorus the entire map. dwarf-shrub,moss tundra(Community Type M3a, Fig. 10, describedabove with water track vegetation). The best drained and hummocks have the variant Basincolluvium palsas moist Betula nana, Cladonia rangiferina dwarf-shrub, Genesis and surface forms fruticose lichen tundra (CommunityType M3b). This Imnavait Creek originates in a gently sloping basin type is similar to Type M3a except it is drier and has which collects water from weakly defined water tracks abundantfruticose lichens, dominatedby Cladoniaspp. in the headwatersof the basin (Figs 1 and 7). Similar Wet sites in the colluvialbasins have a varietyof wet basins are common throughoutthe Foothills Physiog- sedge tundra types that are dominated by any of a raphic Province. Kreig and Reger (1982) mapped the variety of sedges including Carex rotundata, C. rari- depositsof these featuresas "organicbasin fillings" and flora, C. chordorrhiza, C. aquatilis, Eriophorum have since called them "basincolluvium" (Kreig 1985 scheuchzeri, or E. angustifolium. Not all of these types pers. comm.). They are "generallyfine-grained, orga- were sampled. The most common type in the R4D nic-richdeposits with variableamounts of granularma- watershed is wet Carex rotundata, Sphagnum lindbergii terial present in basins occurring between smoothly sedge tundra(Community Type Wla). The marginsof rounded slopes on the Arctic Slope. They are usually many basins have Sphagnummeadows similar to wet associatedwith frozen upland silt... The origin of this Salix fuscescens, Sphagnum lenense dwarf-shrub, sedge, landformis not definitely known. However, the mate- moss tundra (CommunityType W2a describedabove) rial appearsto have moved into small basins from sur- or a variantwith Carexaquatilis. This type has an open roundingslopes by solifluction,creep and/orslopewash. cover of ericaceous shrubs, Betula nana, Rubus chamae- Other processesthat could have a role in the genesis of morus, and other bog species, and has a light color on this deposit are thaw basin formation and drainage, aerial photographs(note light marginsaround colluvial organicdeposit development,and perhapseolian depo- basinsin Figs 1 and 7). It gradesinto the tussocktundra sition. Basin colluviumis differentiatedfrom thaw lake on the lower slopes of the surroundinghills.

256 HOLARCTIC ECOLOGY 12:3 (1989) Fig. 10. Wet meadowin colluvialbasin with small ice-coredmounds (palsas). Vegetationon the palsas is moist Betulanana, Rubus chamaemorusdwarf-shrub, moss tundra.Vegetation in the wet meadowis a complex of hummocksand inter hummocks.Hummocks have wet Salixfuscescens, Sphagnumlenense dwarf shrub, sedge, moss tundra and the interhummockareas are dominatedby wet Carex rotundata,Sphagnum lindbergiisedge tundra.

The most common vegetation types in colluvial basins nity dominated by Carex aquatilis with Salix chamisso- are wet sedge tundra (34%), wet sedge, dwarf-shrub, nis and numerous species of forbs (Community Type moss tundra (31%) and moist dwarf-shrub, moss tundra W2c). Many streamside communities are similar to wet (25%) (see Tab. 2). Salix planifolia ssp. pulchra, Eriophorum angustifolium low-shrub, sedge tundra. Carex aquatilis and E. angusti- folium are common along stream margins and isolated stands of almost pure Arctagrostis latifolia also occur. Floodplaindeposits The banks of the Kuparuk River have well developed Floodplain deposits cover 11% of the total map, but are low-willow communities (Community Type M4b). relatively uncommon within the watershed (0.3%). The large floodplain of the meandering Kuparuk River con- trasts markedly with the small beaded Imnavait Creek. The colluvial basin gradually funnels into the narrow floodplain of Imnavait Creek. The stream "beads" are Landscape evolution small formed wherever the stream has eroded ponds Influenceof TerrainAge massive ground-ice deposits. The margins of the stream are predominantly peaty although there are short sec- The patterns of vegetation are controlled to a large tions with stony creek banks. extent by surface topography of the different-aged gla- cial units (see Figs 1 and 5). The terrain along the Kuparuk River and along the eastern edge of the map Vegetation are part of younger glacial till and outwash surfaces than Most of the small beaded ponds of Imnavait and Toolik that of the rest of the map. The Shannon-Wiener indices Creeks have aquatic communities with almost pure (Tab. 2) indicate that the more mature terrains, repre- stands of Sparganium hyperboreum (Community Type sented by the retransported hillslope deposits and basin Aid). Hippuris vulgaris, and aquatic mosses (Sphagnum colluvium, are less heterogeneous than the till or flood- lindbergii, Calliergon sarmentosum) also occur in most plain deposits. ponds. The edges of these ponds may have other species The younger Itkillik-age till surfaces are generally including Comarum palustris, and Carex aquatilis. The coarse-grained with irregular relief and relatively high streams linking the ponds are usually dominated by cover of dry vegetation types. The older surfaces tend to Carex aquatilis and Eriophorum angustifolium (Com- have Sagavanirktok-age till exposed on the ridge crests, munity Type Ala). but are dominated by tussock-tundra and colluvial-basin Stream margins are highly variable. The margins of deposits on the lower slopes. Idealized catenas based on small beaded streams have a distinctive sedge commu- vegetation and soils data from the long west-facing

17 HOLARCTIC ECOLOGY 12:3 (1989) 257 slopes of the R4D site illustratethis sequence (Fig. 11). accumulationof ice at the interfacebetween the active These trends are consistentwith patternsdescribed by layer and the permafrostby ice-lensingduring the sum- Hamilton(1986) on end morainesof Sagavanirktokage. mer thaw period. Hamiltonused the surfacemorphology, weathering fea- It would be interesting to contrast the ground-ice tures, clast lithology,and vegetationcover on six differ- contents of acidic, Sphagnum-richfoothill tundraswith ent glacial deposits to help distinguishbetween these that of alkalinefoothill tundraswhere there is calcare- differentaged surfaces. ous loess. These areas lack Sphagnumand may show Jorgenson(1984a, b), has built on Hamilton's(1978) very different moss productivityand ground-ice pat- observationsto develop a concept of landscapeevolu- terns. Both of these tundratypes cover large areas of tion for three of these deposits [SagavanirktokRiver the foothills and have distinct spectral signatures on (>125000 ybp), ItkillikI (50-125000 ybp), and Itkillik aerial photographsand Landsat imagery (Walker and II (about 12000 ybp)]. He concludedthat as glaciated Acevedo 1987). landscapes mature, tussock tundra and bogs become increasinglydominant, and a varietyof factors, includ- Role of groundwater and snow ing colluviation, paludification, ice-aggradation,and eolian deposition, lead to the generally subdued hill- Another important consideration for Sphagnum growth slopes of the older surfaces. He also presents an hy- and massive ground ice is the amount of water avail- pothesis of organicterrain development based on ther- able. The degree of water-track development is a clue to mophysicalchanges to the surface.The centralconcept local subsurface water regimes. For example, at the is that as highly insulativepeat builds up on the older R4D site, the west-facing slopes have relatively few surfaces, heat flux is reduced and active layers are de- well-developed water tracks particularly below snow creased, leading to ice aggradationand terrain that is accumulation zones, except on the lower parts of the susceptible to thermokarst.Palsas and high-centered longer slopes. In contrast, north-facing slopes have polygonsin colluvialbasins are examplesof areaswhere well-definedtracks. [Comparethe tracks on the west- ground-icevolumes are high, and these peat plateaus facing slopes of the R4D watershedwith those on the are highly susceptibleto collapse if disturbed. north side of the sandstone knoll in the upper left corner Although the details of Jorgenson'sconcept of foot- of the mapped area (Figs 1 and 4)]. This is at least hills landscape evolution need to be expanded to in- partially related to snow distribution patterns (see clude the other glaciatedsurfaces of the Foothills, the Evans et al. 1989). The west-facing slopes have rela- basic concept has significancein relation to the terrain tively shallow winter snow that melts rapidly during the in the ImnavaitCreek watershedand the development first few days of the snow melt season (Liston 1986, of an approachto predictterrain sensitivity to disturb- Hinzman and Kane 1987, Evans et al. 1989), whereas ance. The lower hillslopesat the site should have grea- the steeper north-facing slopes have deep snowbanks ter quantitiesof groundice becauseof the deeper accu- that provide water well into the summerdry season to mulationsof Sphagnumpeat. Sphagnum,because of its the lower slopes where water tracks are common. The highly insulativecharacter and rapid growthrates, is a tracks, once established, also tend to trap snow and major factor contributingto large amounts of ground provide an additional source of moisture. The longer ice (see Sepalla 1986, Zoltai and Tarnocai1971, Hinkel west-facing slopes have well-developed tracks because et al. 1987 regardingthe effects of insulative organic they have larger source areas to collect summer precip- layers on massive ground ice). Paludificationof the itation for water-track formation. The details of sub- foothills landscapeis an importantprocess that needs a surface water movement are being explored by other fuller examinationwith regardto terrainsensitivity. investigators in the R4D project. Hill crests and shoulders along typical west-facing hillslopeson Sagavanirktok-agetill (Fig. 11) have rocky Terrainsensitivity maps mineralsoils with relativelyhigh heat flux, thick active layers(>80 cm), and low amountsof interstitialground In the Southern Foothills, it is clear that terrain sensitiv- ice near the top of the permafrosttable. This contrasts ity to disturbance can be related to landscape evolution markedlywith the lower slopes, whereSphagnum forms and that it should eventually be possible to accurately thickcarpets on the fine-grainedretransported deposits. predict thermokarstsusceptibility based on the age of The moss insulates the soil, creating a shallow active the landscape,surface morphology, existing vegetation, layer (20-30 cm thick) and ice-richsoil B horizons. At and hillslopegeometry. These are commonelements of this point in our investigations,it is uncertainhow deep geographic information system (GIS) data bases (Evans the ice-richzones extend becauseour observationshave et al. 1989) and would make derivationof terrainsensi- been limited to chippingfrozen soils in the bottom of tivity maps feasible. Detailed ground-ice studies in the soil pits. Deeper cores are needed to determinethe total R4D area and on slopes of other ages would help devel- ice content of the soils. A possible explanationfor the op models for predicting ground ice. Core data from ice-richzones could be the process of "upfreezing"de- long transects through a variety of till deposits [e.g. the scribed by Mackay (1981). This process involves the vertical support member (VSM) logs from the trans-

258 HOLARCTIC ECOLOGY 12:3 (1989) Crest Shoulder Upper Backslope Lower Backslope Footslope

Vegetation: - Dryprostrate-shrub, E Drydwarf-shrub, Moisttussock-sedge, Moist dwarf-shrub, tussock-sedge Moist (or wet) dwarf-shrub, CD truticose-lichentundra truticose-lichentundra dwarf-shrubtundra (or nontussock-sedge) tundra moss tundra 0. Dominant Taxa: ~0 Arctous alpina Carex Erlophorumvaginatum Eriophorumvaginatur Sphagnum spp tzl bigelowii Vacciniumuligirosum Cassiope tetragona Carex bigelowii Betula nana Betula nana (5 Vacciniumvitis-idaea Vacciniumuliginosum Salix planifolia Salix planifolia Rubus chamaemorus Saix reticulata Betula nana Eriophorumvaginatum 3=1 Diapensia lapprnica Sphagnum spp. Salix phlebophylla Dicranum Ledum palustre Carex bigelowii Ledumpalustre spp. Aulacomnium C,adoniaarbuscula Cladonia Cassiope tetragona Ledum palustre turgidum rangiferina Salix fuscescens 0 Sphaerophorus globosus aCD n (5 60 7.5YR WS6 to 7.5YR 3/3 oi " )'~~jphagnumand tussock bases) oeo i 7.OYR 2/1.5 - 0 (5C Oa 7.5YR 23 5 YR 5/6 a of -10 soa (Sphagnum) 10YRO 3/3 (5 40 Scale for Oe soil E 7.5YR2/3 profiles _ 20 Oi (cm) Oa 7.5YR2.5/3 0 Oe -30 'Z30 Bw -o IOYR43 0 Oa mott [es 7.5YR 4/6 C- 40O w Histic Pergelic Cryaquept Bw

N3.5/0

Pergeilc Cryaquept

0 0 100 300 400 700 Distance (in) Insulative Moss Mat (Oi + Oe): 2cm: <5 cm 5- 10 cm 10 20 cm > 20 cm

Active Layer: Moderate High Hig 60-80 cm 35 50 cm 25-35 cm 25 30 cm >70cm = c~~~~~~~~~~ Ground Ice: Low E Low Moderate Hligh High - Alaska would be invaluable for testing the 1986. Late Cenozoic glaciation of the Central Brooks pipeline] - In: of such models. Range. Hamilton,T. D., Reed, K. M. and Thorson, reliability R. M., (eds), Glaciationin Alaska: the geologic record. Alaska Geol. Soc., pp. 9-49. Acknowledgements - This study was funded by the Dept Heinselman,M. L. 1963.Forest sites, bog processes,and peat- of as of its R4D M. and D. landtypes in the GlacialLake Agassizregion, Minnesota. - Energy part program. Figgs Ecol. 33: Kallenbach were much field assistants. D. Monogr. 327-372. appreciated - 1970. Landscapeevolution, peatland types and the envi- Murray and B. Murray identified our voucher collec- ronmentin the Lake Agassizpeatlands Natural Area, Min- tions and assisted us with the plant taxonomy. V. Ko- nesota. - Ecol. Monogr. 40: 235-261. markova reviewed versions of this and Hinkel, K. M., Nelson, F E. and Outcalt, S. I. 1987. Frost early manuscript - made numerous valuable Discussions with mounds at Toolik Lake, Alaska. Phys. Geogr. 8: 149-159. suggestions. Hinzman,L. D. and Kane, D. L. 1987.Active layerhydrology K. Everett, D. Kane and all the members of the R4D for Imnavait Creek, Toolik, Alaska. - Preliminary data project were particularly helpful toward developing the reportfor R4D program,Dept Energy. M. T. 1984a.Controls of the ideas presented here. M. Walker provided numerous Jorgenson, geographicvariability of soil heat flux near Toolik Lake, Alaska. - M.S. thesis, helpful comments, analysis, and support during the Univ. Alaska. preparation of this manuscript. - 1984b. The responseof vegetationto landscapeevolution on glacialtill near ToolikLake, Alaska. - In: Inventorying forest and other vegetation of the high latitude and high altituderegions, Proc. Int. Symp., Soc. Am. Forest. Regi- References nal Tech. Conf., 23-26 July 1984, Fairbanks,AK, pp. 134- 141. AEIDC EnvironmentalInformation and Data Center, (Arctic Klinger, L. F. 1988. Bryophyte paludificationin southeast Univ. Alaska). 1975. Alaska RegionalProfiles, Arctic Re- - - Alaska. Ph.D. thesis. Univ. Colorado,Boulder, CO. gion. Atlas sponsoredby the State of Alaska in cooper- R. A. and R. D. 1982. and ationwith the JointFederal-State Land Use Com- Kreig, Reger, Air-photoanalysis Planning summaryof landformand soil propertiesalong the route of missionfor Alaska. the trans-Alaska - Div. Geol. W. H. N., Dutro, J. T., Jr. and Detterman, pipeline system. Geophysi. Brosg6, P., Reiser, Surv., AK, Geologic Report 66. R. L. 1979. Bedrock geologic map of the Philip Smith G. 1986. Seasonalsnowcover of the foothills of Mountains Alaska. - U.S.G.S. Misc. Field Liston, region Quadrangle, Alaska's Arctic Slope: A survey of propertiesand proc- StudiesMap MF-879B, Scale 1:250000,2 sheets. esses. - M.S. Univ. Fairbanks. 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