Modern pollen rain and vegetation of the St. Elias Mountains, Yukon Territory

Canadian Journal Journal canadien of Botany de botanique Published by Publie' par THE NATIONAL RESEARCH COUNCIL OF CANADA LE CONSEIL NATIONAL DE RECHERCHES DU CANADA

Volume 55 Number 18 September 15,1977 Volume 55 numCro 18 15 septembre 1977

Modern pollen rain and vegetation of the St. Elias Mountains, Yukon ~erritory'

H. J. B. BIRKS* Limt~ologiccrlResearch Center, University of Mit~nesotcr, Mint~ee~polis, MN, U.S.A. trtrtl T11e Botutly School, University

of Cambridge, Crrtnbridge, Englcrnd

Received March 14, 1977

BIRKS, H. J . B. 1977. Modern pollen rain and vegetation of the St. Elias Mountains, Yukon Territory. Can. J. Bot. 55: 2367-2382.

The vegetation of the area east of the Klutlan Glacier in the St. Elias Mountains is described with the methods of European phytosociology. Four major vegetation types are recognized: Picea gln~rca forests, Poprrllis balsamifera forests, Betlrla glandrrlosa shrub-tundra, and Dtyas integrifolicr tundra.

The modern pollen assemblages deposited in these vegetation types are determined by pollen analysis of surface moss polsters, lake muds, and moss samples from sedge swamps. Numerical analyses of the surface spectra indicate that spectra from the Dtyus tundra and from the Poprrlrrs forests are distinctive in their pollen composition. The variation in the percentage pollen content of samples from the Picecr forests and the shrub-tundra is s o great, even when spectra from a single sample type are considered, that no reliable distinctions can be made in modern pollen spectra from these two community types.

BIRKS, H. J. B. 1977. Modern pollen rain and vegetation of the St. Elias Mountains, Yukon Territory. Can. J. Bot. 55: 2367-2382.

A I'aide des mtthodes phytosociologiques europeennes, I'auteur decrit la vegetation de la region situee I'est du glacier Klutlan dans les montagnes St-Elias. I1 reconnait quatre types majeurs de vegetation, soit les forCts i Picecr glarrcn. les fori ts a Poprrlrrs balsat?~iferct, la toundra arbustive a Betrrla glcrndrtlosn et la toundra h Dryas it~tegrifolio.

L a distribution et la composition des dep6ts polliniques modernes reGus par ces types d e vegetation ont kt6 determines par I'analyse pollinique a partir de la surface d e tapis de mousses, de boues lacustres et d'echantillons d e mousses provenant d e tourbieres a Ccrrex-. L'analyse numerique des spectres polliniques d e surface indique que les spectres de la toundra h Dryas et ceux des forCts a Poprrlus ont des compositions polliniques bien distinctes. La variation dans le contenu relatif (pourcentage) en pollen des Cchantillons venant des fori ts a Picecr e t de la toundra arbustive est tellement elevke, mCme lorsqu'on considere des spectres provenant d'un seul type d'kchantillon, qu'aucunes distinctions valables ne peuvent Ctre percues dans les spectres polliniques modernes de ces deux types d e communautk.

[Traduit par le journal]

Introduction mountains in North America, with peaks up to

~h~ st . ~ ~ l i ~ ~ ~~~~~~i~~ are situated on the 19 850 ft (6070 m) in elevation. At the northern

border between Alaska and the Yukon. The edge the Icefield Ranges, the peaks are

Icefield Ranges, which form the core of the St. between 6000 ft m, and l6 420 ft (5000 m,

Elias Mountains, are the largest group of high the highest ones supporting extensive cirque and valley glaciers and ice fields. The geology of the

'Limnological Research Center Contribution No. 159. area is consisting a eugeos~nclinal ZPresent address: The Botany School, Downing Street, assemblage of sedimentary, metamorphic, in-

Cambridge, CB2 3EA, England. trusive, and volcanic rocks ranging from

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2368 C A N . J . BOT. VOL. 5 5 . 1977

Devonian to early Tertiary in age. The most common rocks in the area include limestone, marble, granite, granodiorite, shale, sandstone, andesite, and basalt (Muller 1967). The area was extensively glaciated in the Quaternary and the glacial history of the area has been studied in detail by Rampton (1970, 1971a, 1971b). Most of the area is blanketed with the White River Ash, a coarse-textured volcanic ash deposited about 1220 years ago (Rampton 1970; Lerbekmo and Campbell 1969).

The climate of the area is cool, continental, and dry (Rampton 1970). Winter temperatures are low and the summers are short and warm (January mean at Snag is -28°C and July mean is 14°C (Driscoll 1976)). The mean annual precipitation a t Snag is 35.8 cm, and although there is no pronounced wet or dry season, most of this precipitation falls during the summer. Snag is at about 650 m altitude and is 90 km north of the Icefield Ranges, so the actual precipitation within the mountains is likely to be considerably higher because of orographic effects. The temperatures in the mountains are probably sub- stantially lower than at Snag.

The area has been little studied by botanists and much of the botanical work that has been done has been primarily floristic (e.g., Lijve and Freedman 1956; Murray 1970, 1971 ; Porsild 1951, 1966), with the exception of the excellent vegetational survey by Douglas (1974) of the Alsek River region to the east. This paper presents a brief phytosociological account of the major subalpine and alpine vegetational types occurring between 1200 m and 2000 m altitude in a small area of the Icefield Ranges just east of the Klutlan Glacier between St. Clare Creek and Mount Byron at about 61'32' N and 140°30' W (Fig. 1). It also discusses the modern pollen assemblages, recorded in surface lake muds and terrestrial moss polsters from these major vegetation types near the regional tree line,and the relationships between the modern pollen rain and the regional and local vegetation. With the exception of the preliminary study by Rampton (1971a) on modern pollen spectra in the Icefield Ranges, work on contemporary pollen assemblages near the tree line of western North America has all been farther north in Alaska (Livingstone 1955; Colinvaux 1964; Matthews 1970, 1974) or farther east in the Mackenzie Delta area (Ritchie 1972, 1974).

Plant nomenclature and taxonomy follow HultCn (1968) for vascular plants, Crum et al.

(1973) for mosses, Worley (1970) for hepatics, and Dahl and Krog (1973) for lichens.

Methods Vegetational At~alysis

The methods of European phytosociology, as modified by Dahl (1957) for describing alpine vegetation in Norway, were used in this study (see Birks (1973~) and footnote 3 for a discussion of the merits of these methods). A standard plot of 16 m2 was selected within stands of vegetation that appeared to be as floristically uniform as possible. All of the taxa occurring in each plot were identified and their cover-abundance values were esti- mated on the 10-point Domin scale (Dahl 1957). A set of voucher specimens of all plants found in the area was made and is housed in the Botany School, University of Cambridge. When more than one vegetational layer was present, each stratum was considered separately for estimating the cover-abundance values. The values were defined as proportions of the total vegetation in the plot and not as proportions of the total area of the plot. Taxa absent from the plot but present nearby in the stand were also recorded and are shown in the vegetation tables by a +. Aspect, slope, altitude, soil type, and other environmental factors were noted.

Plots of similar floristic composition are grouped together on Tables 1-4, and the taxa within each table have been grouped so that taxa of broadly similar occurrence are arranged together, thereby emphasizing the floristic variation within and between groups of plots. Taxa that occur in one plot only are listed at the bottom of the tables.

Pollerz A~~alysis Surface mud samples were collected from the presumed

deepest part of I I small lakes either by diving or by sampling from a rubber boat with an Ekman dredge or a plastic-tube piston corer.4 Surface moss polsters were collected from the vegetational plots. Each polster con- sisted of at least six small subsamples generally with a surface area of 5 cm2 collected within the plot. These subsamples were amalgamated for subsequent prepara- tion and analysis.

All samples were prepared for pollen analysis by a standard treatment (Faegri and Iversen 1964) with alkali digestion, treatment with cold 10% HCI, hot 40% HF, hot 10% HCI, Erdtman's acetolysis, staining with safranin, dehydration with tertiary butyl alcohol, and mounting in silicone oil (2000 cSt (1 St = 1 cm2/s)). The moss polsters were thoroughly washed in distilled water, sieved to re- move coarse debris, and centrifuged several times before being treated as above.

Pollen counting was done with a Leitz Laborlux micro- scope fitted with x 10 Periplan oculars and x 40 and x 90 apochromatic objectives. Whole numbers of slides with regularly spaced traverses across the cover slip were counted for each sample. The total number of pollen and spores included in the calculation sum (all determinable pollen and spores of all vascular plants (ZP) excluding

"irks, H. J. B. 1977. The present flora and vegetation of the Klutlan Glacier, Yukon Territory, Canada: a study in plant succession. Unpublished manuscript.

4Wright, H. E. 1969. Cores of soft lake sediment. Unpublished manuscript.

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FIG. 1. Map of study area showing the Klutlan Glacier (cross-hatched) and the approximate alti- tudinal limit of coniferous forest (stippled). The dots mark the sites from which surface pollen samples were collected. The inset map shows the general location of the study area.

obligate aquatic taxa) varied from 227 to 1094, with a mean of 547 and a median of 514. A total of 80 pollen and spore types are included in ZP and the number of types per sample ranges from 11 to 38, with a mean of 23 and a median of 23. Copies of the tabulated pollen counts are available from the author. Pollen and spore identifications were made by comparison with an extensive modern reference collection of Yukon t a ~ a . ~ Notes on the pollen identifications are available from the author.

5Birks, H. J. B. 1977. Modern pollen assemblages and vegetational history of the Klutlan Glacier and its surrounds, Yukon Territory, Canada. Unpublished manuscript.

The degree of certainty in these identifications is indicated throughout by a standard set of conventions (Birks 1973~). The processing of the pollen counts and the drawing of preliminary pollen diagrams were done by the University of Cambridge IBM 3701165 computer using the program POLLDATA MK4 written -in FORTRAN IV by the author and Dr. B. Huntley.

Modern Vegetation Boreal Forest

In the study area, Picea glauca - dominated forests cover flat ground and slopes of all aspects up to an altitude of about 1450 m, although

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CAN. J . BOT. VOL. 55 , 1977

TABLE 1. Composition of Picea glauca forests

RelevC number 73 74 75 102 Plot area (square metres) 16 16 16 16 Percentage vegetation cover 100 100 100 100 Altitude (metres) 1365 1375 1430 1500 Aspect S S N NW Slope (degrees) 1 2 5 1

Picea glouco 5 5 5 5 Betula glandulosa 7 8 6 7 Salix glauca ssp. acutifolia 4 3 7 4 Vaccinium uliginosum ssp. alpinum 6 5 4 5 Vaccinium vitis-idaea ssp. mitzus 4 4 3 4 Arctostaphylos rubra 4 2 3 2 Ledum palustre ssp. decumbetzs 5 5 4 3 Empetrum nigrum ssp. hermaphroditum 5 5 4 4 Pedicularis labradorica 3 3 3 1 Saussurea angustifolia 2 1 3 3 Hylocomium splendetzs 4 5 5 5 Dicranum muehletzbeckii 2 3 4 3 Dryas integrifolia ssp. itztegrifolia 1 3 3 Rhytidium rugosum 3 3 3 Arctostaphylos uva-ursi ssp. uva-ursi 1 2 4 Cladonia amaurocraea 3 4 2 2 Peltigera apthosa 2 3 3 f Pyrola grandflora 2 2 1 Aulacomnium palustre 2 1 1 Cetraria nivalis 2 1 Carex concinna 1 1 Eqliisetum scirpioides 3 3 Peltigera polydactyla 3 3 Polytrichum juniperinum 1 f Dicranum fuscescens 1 1 Stereocaulon tomentosum 4 4 Cladonia arbuscula 3 3 Cladonia pyxidata 1 3 Pohlia nutans 1 1 Dicranella heteromalla 1 2 Salix reticulata ssp. reticulata 1 2 2 Stellaria lotzgipes 1 1 Salix arbusculoides 3 2 Mertensia paniculata ssp. paniculata 3 3 Tomerrthypnum nitens 1 3 Equisetum arvense 1 3 Potentilla fiuticosa 3 3 Calamogrostis purpurescens ssp. purpurescens 3 2 Hedysarum alpinum 2 3

Total number of species 33 31 3 3 33

Additional species in relevC: (73.) Aulacomnium turgidum, 1; Tofieldia pusilla, 3; Ditrichum heteromallum, 1; (74.) Cladonia ecomocyna, 1; (75.) Salix lanata ssp. richardsonii, 4; Epilobium latifolium, 3; Saxifaga punctata, 1 ; Voleriano capitata, 1 ; Cassiope tetragona, 2; Orthothecium chryseum, 1 ; Salix glauca ssp. glabrescens, 5 ; (1 02.) Epilobium angustifolium, 3 ; Par- nassia palustris ssp. neogaea, 1; Luzula n~ultflora ssp. multflora, I ; Solidago sp., 2; Gentiana prostrata, 1 ; Pokmonium acutflorun~, + ; Rosa acicularis, 3.

above about 1250 m the forests become pro- glandulosa forms a conspicuous and often dense gressively more open. These forests (Table 1 and shrub layer along with Salix glauca. The ericoid Fig. 5A) are generally rather open, with widely dwarf shrubs Vaccinium uliginosum, V . uitis- spaced trees that are often rather stunted in their idaea, Ledum palustre, Empetrum nigrum, Arcto- growth (up to 10 m tall, with girths of up to 160 staphylos rubra, and A. uua-ursi dominate the cm, and with 150-250 annual rings). Betula field layer, and Hylocomium splendens, Rhytidium

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TABLE 2. Composition of Betula glandulosa shrub-tundra

Relev6 number 100 105 110 113 104 Plot area (square metres) 16 16 16 16 16 Percentage vegetation cover 100 100 100 100 100 Altitude (metres) 1535 1635 1465 1465 1500 Aspect - W W NE N Slope (degrees) - 3 2 1 5

Betula glandulosa 8 7 8 8 4 Vaccinium uliginosum ssp, alpinum 4 5 4 4 4 Potentilla fruricosa 4 3 4 3 2 Hylocomium splendens 5 5 4 4 9 Dicranum undulatum 5 3 3 3 2 Cetraria nivalis 2 3 3 2 3 Arctostaphylos rubra 4 3 1 + Ledum palustre ssp. decumbens 3 2 1 4 Empetrum nigrum ssp. hermaphroditum 4 4 5 6 Carex scirpoidea 3 3 3 3 Carex concinna 3 3 2 Salix glauca ssp. acutifolia 5 4 3 Pedicularis Iabradorica 2 2 3 Tornenthypnurn nitens 2 3 2 Vacciniurn vitis-idaea ssp. minus 2 4 2 Carex rnicrochaeta 4 3 1 Tharnnolia vermicularis 2 3 2 Salix lanata ssp. richardsonii 2 2 Calarnogrostis purpurescens ssp. purpurescens 3 3 Arctosraphylos uua-ursi ssp. uva-ursi 3 4 Gentiana propinqua ssp. propinqua 2 2 Cassiope tetragona ssp. tetragona 4 5 Aulacomnium palustre 4 3 Salix reticulata ssp. reliculata 3 3 Equisetum scirpioides 3 2 Dicranum muehlenbeckii 1 1 Lupinus arcticus 3 2 Cladonia arbuscula 3 1 Solidago sp. 2 1 Alnus crispa ssp. crispa 3 7 Pyrola grandiflora 2 3 Stellaria Iongipes 1 1 Pelrigera apthosa 2 + Total number of species 21 28 25 25 22

Additional species in releve: (100.) Epilobium angustifolium, 3; Hedysarum alpinum, 3; Cetraria richardsonii, 3; Juniperus communis ssp. nana, 3 ; Salix myrtillifolia, 3 ; Hypnum bambergeri, + ; Carex capillaris, 1 ; (1 05.) Tofeldia pusilla, 4; Dryas integrifolia ssp. integrifolia, 3; Pedicularis verticillata, 2; Rhytidium rugosum, 5; Stereocaulon tomentosum, 3 ; (1 10.) Aconitum delphinifolium ssp. delphinifolium, 3 ; Salix arbusculoides 4; Campanula Iasiocarpa ssp. lasiocarpa, 2; Parnassia palustris ssp. neogaea, 1 ; Artemisia arctica ssp. arctica, 1 ; Luzula spicata, 2; Silene acaulis ssp. acaulis, 1 ; Saxifraga hieracifolia, 1 ; (1 13.) Cladonia pyxidata, 1 ; C. amaurocraea, + ; (104.) Saussurea angustifolia, 3 ; Oxyria digyna, + ; Papauer macounii, + ; Boschniakia rossica, 3.

rugosum, Dicranum muehlenbeckii, Peltigera apthosa, and Cladonia amaurocraea are the major components of the ground layer. Saus- surea angustifolia, Pedicularis labradorica, and Dryas integrifolia also occur commonly in the field layer. Most of the soils are derived from the White River Ash and are coarse textured and well drained. Lichens are prominent on the forest floor, particularly Cetraria nivalis, Stereo-

caulon tomentosum, Cladonia arbuscula, C . pyxidata, and Peltigera polydactyla (relevks 73, 74; Table 1). Equisetum scirpioides and Carex concinna are characteristic of this rather xeric forest, together with the mosses Polytrichum juniperinum, Dicranum fuscescens, and Pohlia nutans. This forest type corresponds, in part at least, to Douglas' (1974) Picea glauca - Betula glandulosa - Empetrum nigrum community and

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TABLE 3. Composition of Carex aquatilis sedge swamps

Releve number 106 103 Plot area (square metres) 16 16 Percentage vegetation cover 100 100 Altitude (metres) 1600 1500

Carex aqlratilis ssp. aquntilis 8 9 Saxfiaga hircul~rs 4 3 Equisetum palrrstre 3 2 Aulacotnt~ium palustre 4 2 Totnetztl~ypt~r/n~ nitens 3 3 Calliergotz gignnteuttz 4 3 Drepanoclad~rs revolvens 4 4

Total number of species 9 14

Additional species in releve: (106.) Meesia triqrretrn, 1 ; Catnpyli~rnz stellntum, 3; (103.) Snlix latlata ssp. riclmrclsot~ii, 4; Par- nassia palustris ssp. t~eogaea, 3 ; Potetztilla fruticosa, 3; Marchatztia polyt~lorpl~a, 1 ; Drepano- cladus flrritans, 4; Climaciro~z detlclroides, 3 ; Carex rostrata, + .

to some of the spruce forest types described by Drew and Shanks (1965).

On damp flushed sites, usually on north- facing slopes (relevts 75, 102; Table l), willows are often prominent, including Salix glauca, S . arbusculoides, S . lanata, and S . reticulata, along with Potentilla fruticosa and Rosa acicularis. A variety of taxa are differential to these damper forests, including Stellaria longipes, Hedysarum alyinum, Mertensia paniculata, Valeriana capitata, Polemonium acuttj7orum, and the moss Tomenthypnum nitens. This forest type is broadly similar to the Picea glauca - Salix glauca community recognized by Douglas (1974).

Within the zone of Picea glauca forest, pure and often quite extensive stands of Populus balsamifera - dominated forest occur locally on dry, well drained soils in steep south-facing slopes, generally below 1350 m altitude (Fig. 5B). The trees can reach a height of 8 m with girths of up to 105 cm. A plot from one such stand is as follows:

Species No. Species No.

Populrrs balsntrlifera 8 Arctostapl~)~los rrva-rrrsi 6 Jroziperus conlrnutlis 5 Hedysnruwz alpitzum 3 Potetztilla fruticosa 2 Gentiatza propitzq~m 3 Rosa ncicularis 3 Poa nrcticn 1 Epilobium nngustifoliurn 5 Solidngo sp. 1 Salix nlaxensis 2 Torfitla rrtralis 1 Shepherrlin canncler~sis 5 Tlzuidiunz abietinunz +

Plot area, 16 mZ; total vegetation cover, 100%; slope, 10"; aspect, SE; altitude, 1300 m; plot number, 116.

These forests have a closed canopy of Populus balsamifera and a tall shrub layer dominated by Juniperus communis and Shepherdia canadensis, with some Rosa acicularis, Salix alaxensis, and Potentilla fruticosa. The field layer is dominated by Arctostaphylos uva-ursi and Epilobium angus- tifoliurn. The ground layer is virtually absent. Interestingly no seedlings of Picea glauca were found in these forests. Although Populus tremu- loides also occurs in the study area, no extensive stands of it were found. It occurs as scattered trees on rather unstable south-facing xeric slopes growing with Juniperus communis and Shepherdia canadensis. The Populus balsarnifera forests correspond closely to the Populus balsamifera (dry phase) community delimited by Douglas (1974).

Shrub-Tundra Between about 1450 m and 1650 m altitude,

subalpine shrub-tundra dominated by Betula glandulosa (Table 2 and Figs. 5C and D) occur on a wide range of slopes and aspects. The B. gla17dulosa is often very dense and grows up to 1.5 m tall. Other shrubs in this community include Potentilla fruticosa, Salix glauca, and S . Ianata. Vacciniun? uliginosum, V . uitis-idaea, Arctostaphylos rubra, Ledum palustre spp. de- c~~tnbens , Empetrun? nigrum, Carex concinna, C. scirpoiclea, and Pedicularis labradorica commonly form the field layer. The ground layer is dominated by Hj~locomiuni splendens, associated with Dicranun? undulatum, Tomenthypnum nitens, Cetraria nioalis, and Tl7amnolia vermicularis. On damp, periodically irrigated, north-facing slopes, Alnus crispa is prominent (relevts 113, 104; Table 2) and Pyrola grand~jora, Stellaria longipes, and Peltigera apthosa are locally frequent. The interesting root parasite Boschniakia rossica grows in these alder stands. Occasional scattered and rather stunted trees of Picea glauca up to 150 years old occur within the shrub-tundra up to an altitude of 1500 m (see Fig. 5D). Related shrub-tundra communities are described by Corns (1974) from the Mackenzie Delta.

Within the zone of shrub-tundra, prairielike openings occur on steep, dry, south-facing slopes that have a considerable thickness of the coarse-textured White River Ash. Juniperus communis, Shepherdia canadensis, Calamogrostis purpurescens, Festuca altaica, Arctostaplzylos uva-ursi, and Epilobium angustifolium are frequent in these areas, and Mertensia paniculata, Acot~itum delphinifolium, Zygadenus elegans,

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TABLE 4. Composition of Dryas integrifolia tundra

Relev6 number 97 99 109 98 107 108 Plot area (square metres) 16 16 16 16 16 16 Percentage vegetation cover 50 60 100 100 100 100 Altitude (metres) 1930 2000 2000 2000 1765 1930 Aspect W S W W N NW Slopes (degrees) 15 8 2 1 10 10

Dryas integrifolia ssp. integrifolia 8 8 8 5 6 7 Vaccini~in~ uliginosum ssp. alpinum 3 3 3 5 3 3 Silene acaulis ssp. acaulis 2 3 1 2 1 1 Rl~ytidium rugosritn 3 2 3 2 1 3 Tl~atnt~olia vert?zicularis 4 4 4 3 4 2 Calamogrostis purpurescerls ssp. plirpurescetls 4 3 2 2 1 1 Lloydia serotitza 2 2 2 3 3 Salix arctica 3 2 3 3 3 Saxifiaga bronchialis ssp. futlstonii 3 4 3 2 3 Cassiope tetragotla ssp. tetragons 2 3 2 6 8 4 Saxifiaga flagellaris ssp. setigera 2 1 3 1 Pedicularis verticillata 2 + 2 2 Polygot~utn viviparum 1 1 3 Epilobium latifoli~im 2 2 1 Pedicularis kat~ei ssp. k m ~ e i I 2 + 2 Potentilla fruticosa 1 4 + Thuidium abietitzum 1 2 Gentiana prostrata 1 2 Kobresia t?~yosuroides 4 4 3 Aster grandiflorus + 3 2 Carex riipestris 3 5 4 Castilleja hyperborea 3 2 2 Cetraria tilesii 2 2 Saxifi.aga tricuspidata 3 3 Artemisia borealis 4 5 Potentilla utziflora 3 1 Getztiatm propinqua ssp. propinqua 2 1 Synthyris borealis 3 2 Setrecio ogotoruketzsis 3 4 Carex narditia 3 2 Carex bigelolvii 3 5 5 4 Salix retic~ilata ssp. reticulatn 3 4 G Aulacotnniunz turgid~rtn 2 4 4 Catnpatz~ila lasiocarpa ssp. lasiocarpo 3 2 Dactylit~a orctica 1 4 Saxrpaga hvurica ssp. grat~rl~elola 2 3 Pogonatutn alpitzum 3 4 3 Lycopodiut?~ selago ssp. appressutn 3 4 3 Hylocon~i~it?~ spletzrlet~s 4 4 3 Salix polaris ssp. pse~idopolaris 4 2 2 Dicran~itn fuscescetzs 5 2 Dryas octopetola ssp. alasketzsis 2 4 Antentzarin n~onocephala ssp. t?~ot~ocephala 1 2 Carex tnicrochaeto 2 3

Total number of species 29 27 29 27 29 34

Additional species in releve: (97.) Anenlone porvipora, 1 ; Herlysar~rtn alpit~~mz, 1 ; Astragalris alpitrus, 1 ; (99.) Erigeron purpriratus, 2; (109.) Oxytropis I~riddelsot~ii, 2 ; Setlecio resirlifolius, 2; Cetraria nivalis, 2; Min~iartia macrocarpa, 3; (98.) Enlpetr~itn nigr~rnl ssp. hernlaphroditrtn1, 3; Tonzet1fliypn1m1 nitens, 4; Saxifvaga re f ixa , 2; Rlracot?~itri~itn canescens, 3; Cetrario islatzdica, 2; Oxyria cligynn, 2; At~thelia juratzkatln, + ; (107.) Papaver nlaco~olii, 3 ; Cladonia arbriscrila, 3 ; Perlicularis capitata, 1 ; Ple~uoclarln albescens, + ; Lrmila arcuata ssp. ~it~atascl~a~sis, 1 ; Peltigera aptlrosa, 1 ; Calypogeia n~uelleriatza, 1 ; Annstrophyll~im mit~~itritn, 1 ; (108.) Luz~rla t~rriltiflora ssp. t?~ultiflora, 3 ; Carex scir- poirlea, 5; Potentilla diuersifolia, 2 ; Equiset~im scirpioides, 3; Sed~im rosea ssp. integrifolio, 1 ; Luzula spicato, 3 ; Sasifraga hieracifolia, + ; Mertensia paniculata ssp. paniculata, + .

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2374 CAN. J. BOT. VOL. 5 5 , 1977

Artemisia tilesii, and Hedysarum alpinum occur more rarely.

In damp areas, such as along streams and in waterlogged hollows within the shrub-tundra, there are stands of tall herbs such as Valeriana capitata, Senecio sheldonensis, Polemonium acuti- florum, Petasites hyperboreus, Rumex arcticus, Luzula parvliJora, Potentilla diversifolia, and Polygonum bistorta.

There are numerous small lakes within the shrub-tundra zone, and their shores, consisting primarily of the White River Ash, provide habitats for a rich and varied flora. On dry stony and sandy shores, Artemisia tilesii, A . arctica, and Saxifraga hieracifolia are locally frequent, along with occasional plants of Gentiana prostrata, Carex leptalea, Parnassia palustris, Polygonum viviparum, Saxifraga punctata, S . bronchialis ssp. funstonii, Cerastium beeringianum, Rumex graminifolius (c f. Murray 1971), Oxyria digyna, Poa alpina, and Silene acaulis. Periodically moist gravels and silts and springs along the lake shores support Koenigia islandica, Juncus triglumis, J. biglumis, Eleocharis acicularis, Alopecurus aequalis, Saxifraga hirculus, Stellaria crispa, Ranunculus reptans, R. trichophyllus, Arctopkila fulva,Epilobium dauau- ricum, Selaginella selaginoides, Carex saxatilis, C. capitata, and C. loliacea. In sheltered bays and inlets of several of the lakes, sedge swamps dominated by Carex aquatilis (Table 3) occur on peats and lake muds. Saxifraga hirculus and Equisetum palustre are the major associates, and Aulacomnium palustre, Tomenthypnum nitens, Calliergon giganteunz, and Drepanocladus revolvens dominate the moss layer. Similar Carex aquatilis sedge swamps are described from Alaska by Hanson (1951) and Churchill (1955). There is sparse growth of aquatic macrophytes in these lakes, the only species noted being Hippuris vulgaris, Equisetum fluviatile, Ranunculus con- fervoides, Potamogeton gramineus, P. praelongus, Isoetes muricata, and Sparganium hyperboreum.

Dryas Tundra Above about 1650 m, the Betula glandulosa

shrub-tundra is replaced by a low-growing, species-rich Dryas integrifolia - dominated tundra (Table 4 and Fig. 5E). Common associates include Vaccinium uliginosum, Salix arctica, Silene acaulis, Cassiope tetragona, Saxifraga bronchialis, S . flagellaris, Calamogrostis purpurescens, Lloydia serotina, Pedicularis kanei, P.

verticillata, Epilobium latifolium, Polygonum viviparum, Rhytidium rugosum, and Thamnolia vermicularis. More local species occurring in this vegetation and not recorded on Table 4 include Campanula lasiocarpa, Rhododendron lapponicum, Mertensia paniculata, Gentiana al- gida, Stellaria laeta, Tojieldia coccinea, Zyga- denus elegans, Papaver macounii, and Saxifraga hieracifolia. Related communities dominated by Dryas spp. are described from Alaska by Gjaerevoll (1954), Spetzman (1959), Hanson (1 95 I), Churchill (1 955), and others.

In sheltered hollows, generally on north- facing slopes on which snow persists up to mid- July, Cassiope tetragona is abundant (relevis 98, 107, 108; Table 4 and Fig. 5E) along with lesser amounts of Dryas octopetala ssp. alaskensis, Carex bigelowii, Salix reticulata, S . polaris, Lycopodium selago, Antennaria monocephala, Carex microchaeta, and the mosses Hylocomium splendens, Dicranum fuscescens, Pogonatum alpinum, and Aulacomnium turgidum. More local species confined to these areas of late snow patches include Empetrum nigrum, Pedicularis capitata, Potentilla diversifolia, Papaver macounii, and the chionophilous hepatics Pleuroclada albescens and Anthelia juratzkana.

In north-facing gullies, generally above 1800 m, semipermanent snow patches occur. They support a varied flora on the damp silt and gravel near the snow, including Ranunculus nivalis, Dodecatheon pulchellum, Draba nivalis, D. longkes, Parrya nudicaulis, Castilleja hyperborea, Lagotis glauca, Synthyris borealis, Oxy- tropis huddelsonii, Pedicularis kanei, P. langs- dorflii, Anemone parvliJora, and an abundance of Luzula spicata, L. arcuata, Oxyria digyna, Salix polaris, and Dryas octopetala.

In exposed, wind-blasted sites at high altitudes (1900 m or above), the vegetation is open (50- 60% vegetation cover) and Dryas integrifolia fell-field (relevis 97, 99; Table 4) occurs. Several species are characteristic of these fell- fields, including Kobresia myosuroides, Carex rupestris, C. nardina, Artemisia borealis, Saxi- fraga tricuspidata, Aster grandliJorus, Castilleja hyperborea, Potentilla un$ora, Gentiana propinqua, Synthyris borealis, and the newly described Senecio ogotorukensis (Packer 1972). More local species in this vegetation include Oxytropis huddelsonii, Astragalus alpinus, Eri- geron purpuratus, Senecio residifolius, Minuartia macrocarpa, Luzula arcuata, and L. spicata.

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BIR

There are several species in common with the snow-patch communities (e.g., Castilleja hyperborea, Synthyris borealis, Luzula spp.), suggesting that their restriction to late snow patches and extreme wind exposure may result from their intolerance of competition in more closed communities.

Within the alpine zone there are several extensive limestone, basalt, and schistose cliffs and screes. These, especially those of northern aspect, support a rich and varied flora. Shaded cliff crevices provide habitats for Woodsia glabella, Cystopteris fragilis ssp. dickieana, Saxifraga nivalis, S. davurica spp. grandipetala, Oxytropis huddelsonii, Cyrtomnium hymenophyllum, Pohlia cruda, and Orthothecium chryseum. Cliff ledges support Lloydia serotina, Myosotis alpestris, Sedum rosea, Draba porsildii G. A. Mulligan, and Hedysarum alpinum.

Damp but well drained, fine-grained screes with bare soil support Saxifraga cernua, S. reflexa, S. serpyllifolia, Oxyria digyna, Chryso- splenium tetrandrum, Melandrium apetalum, Draba nivalis, D. cinerea, D. lonchocarpa, Cerastium beeringianum, Stellaria alaskana, S. longipes, and the moss Stegonia latifolia. Drier fine-grained screes are dominated by Saxifraga oppositifolia and S. tricuspidata, with Salix arctica, Senecio ogotorukensis, Erigeron grandiflorus, E. purpuratus, Arnica frigida, Artemisia borealis, A. arctica, Poa arctica, Minuartia rossii, M. rubella, M. obtusiloba, M. macrocarpa, Potentilla bifora, P. unifora, P . virgulata, Silene repens, Oxytropis huddelsonii, and Papaver la~~onicum. Areas of stable block scree are often colonized by Shepherdia canadensis (growing at an altitude of 1700 m) and Astragalus umbellatus. Crevices between the blocks ~rovide habitats for Androsace septentrionalis, Saxifraga serpyllifolia, and Moehringia laterifora.

Damp flushes by stream, springs, and snow beds above about 1800 m support Claytonia sarmentosa, Carex lachenalii, Saxifraga rivularis, S. punctata, Calliergon sarmentosum, and Pohlia wahlenbergii.

Modern Pollen Assemblages Introduction

The pollen and spore frequencies in the 30 surface samples analyzed are presented as histograms in Fig. 2. The samples are arranged according to the vegetation type from which they were collected. Within each vegetation type, the

spectra derived from lake muds, sedge swamps, and moss polsters are grouped together. The moss polsters were collected from many of the vegetational plots listed in Tables 1-4, and the sample numbers on Fig. 2 refer to the relevC numbers on Tables 1-4. The altitudes of the sampling sites are also shown in Fig. 2.

The pollen and spore types are grouped into five categories : trees, shrubs (Alnus crispa, Betula, Salix, Shepherdia canadensis, Juniperus), dwarf shrubs (Empetrum nigrum and all Ericaceae), herbs, and pteridophytes. Histograms for all the types identified and included in the calculation sum (CP) are presented in order of occurrence from the bottom to the top of the diagram within these five categories. All the histograms are drawn to a standard scale.

Pollen and spore preservation was generally good in all the samples; the percentage of total indeterminable pollen ranges from 0.9 to 20.3% per sample with a mean percentage of 4.2%. Crumpling and concealment (sensu Cushing 1967) are the major types of indeterminable pollen.

Picea glauca Forests The pollen assemblages from the Picea glauca

forests in the study area (Fig. 2) have variable values of Picea pollen (5-4373. Alnus crispa and Betula pollen attain values up to 14% and 56%, respectively. The highest Betula values are, however, in the three moss polster samples and thus they presumably reflect local pollen deposition (sensu Janssen 1973). The Alnus crispa percentages are surpsingly high considering the rarity of the shrub in the area. As discussed by B i r k ~ , ~ Ritchie (1974), Rampton (1971a), and Livingstone (1955), A. crispa is consistently over- represented in modern pollen spectra in the Yukon, in the Mackenzie Delta, and in Alaska. Pinus pollen values, in contrast, are very low (<2%). The nearest pine trees (P. contorta) occur about 150 km to the southeast (HultCn 1968). Populus cf. P . balsamifera, Skepherdia canadensis, and Juniperus pollen occur consistently in low amounts. Salix values are rather variable but generally low (<6%). Ericaceae pollen (mainly Vaccinium type, Ledum palustre, and Arctostaphylos) is well represented, especially in moss polsters, with values of up to 19.5%.

Cyperaceae pollen percentages are very variable. They are low (<5%) in the moss polster

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2376 CAN. J. BOT. VOL. 5 5 , 1977

samples and, not surprisingly, are very high (>50%) in samples from sedge swamps. Values of 14-33% occur in samples from surface muds. Gramineae percentages are generally low (< 14%), and other herb types are rare and of low frequency. Occasional grains of Pyrola grandlj7or.a type, Pedicularis labradorica type, Dryas, Saussurea angustifolia, Stellaria, Poten- rilla type, and Artemisia occur. Spores of Dryopteris type and Equisetum occur frequently but always in low amounts, reflecting the rarity of pteridophytes in the regional vegetation.

Populus balsamifera Forests Two surface samples were collected from one

of the largest stands of pure Populus balsamifera forest in the area. Sample 116 (Fig. 2) was collected from within the forest, and sample 115 was collected from a small damp hollow 10 m from the edge of the forest. The sample from within the forest has 67% Populus cf. P. balsamifera and 12% Juniperus pollen. These values closely reflect the abundance of balsam poplar and juniper in the vegetation. Shepherdia canadensis, although locally frequent in the forest, is poorly represented in the pollen rain (1.3%) and Arctostnphylos uua-ursi, although dominant in the field layer, is absent in the pollen assemblage. In sample 1 15, the Popul~rs and Juniperus pollen values are only 11% and 0.4%, respectively, indicating the poor dispersal of these pollen from the forest only 10 in away. Betula, Alnus crispa, Cyperaceae, and Gramineae form the major components of the spectrum derived from sample 1 15.

Shrub-Tundra Betula pollen values are generally high (10-

43%) but rather variable in sa~nples from the shrub-tundra (Fig. 2). Picea values are similar to those from samples in the Picea glnuca forest, ranging from 2 to 49%. Alnus crispa pollen frequencies are also similar (5-22%) to those in spectra from the other vegetation types. The exception is sample 104, where locally growing A. crispn (see Table 2) produced pollen values of 52%. In general, the pollen percentages for Ericaceae (0.5-1.57,) and Popul~rs cf. P. balsnmifera (0-0.7%) are lower than in spectra from the Picea forests, whereas Salix pollen values (1.5-8%) are slightly higher. Cyperaceae values are very variable (2-58%), with the higher values in spectra from lake muds and sedge swamps. Gramineae pollen frequencies vary little

(1.4-9%). Pollen and spores of other taxa are present in low amounts throughout, although Artemisia, Potentilln type (presumably derived largely from P. fruticosa), Pyrola grandiflora type, Saxifraga hirculus type, and Selaginella selaginoides are more frequent and more abundant in the spectra from the shrub-tundra than in spectra from the other vegetation types sampled.

Dryas Tundra The pollen spectra from the Dryas integrifolia

tundra above 1700 m altitude (Fig. 2) have consistently high (17-27%) percentages of Picea pollen. The values of Betula (1 1-2273 and Alnus crispa (10-18%) pollen are also high. None of these taxa grows in the Dryas tundra. Rampton (19710) and Ritchie (1974) have also found similar high percentages of Picea, Berulr, and Alnus pollen in surface samples from tundra areas in the Yukon and in the Mackenzie Delta area. These pollen are all derived from long- distance dispersal from lower altitudes. Local pollen production in the tundra zone is probably so low (see Ritchie and Lichti-Federovich 1967; Fredskild 1973) that the regional pollen com- ponent from the lower vegetation zones domin- ates the pollen assemblages deposited in the tundra.

Cyperaceae and Gramineae pollen frequencies are rather low (2-16z and 3-9x, respectively), whereas Salix pollen values are surprisingly high (4-973 considering that willows are not abundant in the Dryas tundra (see Table 4) and that those present are all dwarf willows (S . nrctica, S . reticul(rtn, S . polaris). Several pollen types have higher values in these spectra than in spectra from other vegetation types, e.g., Cnssiope (0.4-11%), Senecio type (0.2-4%), Dryas (1.3-9%) and Saxifraga tricuspidntcr type (0.2- 13%). These values reflect the greater abundance of the corresponding taxa in the tundra vegetation, and these percentages indicate that they are all underrepresented in the pollen rain. There are several pollen and spore types that are virtually confined to spectra from the tundra, including Saxifragcr cf. S . bronchialis, Gentiana cf. G. prostrata, Tllalictrtm7, Castilleja, Saxifragcr hierncifolia type, Lloydia serotinn, Papaoer, Antennaria type, and Lycopodi~mz selago. The percentages of Arternisin pollen are surprisingly low (< 1 z ) considering the frequency of A. arcticn and A. borenlis in the vegetation.

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TABLE 5. Summary of selected pollen percentages in surface samples from the St. Elias Mountains. Upper figures are ranges of percentages; lower figures are mean percentages. All percentages are based on the sum of all determinable pollen and spores of non-obligate

aquatic taxa ( CP)

Vegetation type

Picea glaucn Populus balsamifern forest forest Shrub-tundra Dryas tundra

Picea

Betula

Alnus crispa

Populus cf. P. balsam$era

Salix

Ericaceae + Empetrun1 nigrunz

Gramineae

Cyperaceae

Discussion and Conclusions Values for the major pollen types in the 30

surface samples from the four vegetation types are summarized in Table 5 as percentage ranges and mean percentages. Inspection of this table and of Fig. 2 suggests that the pollen assemblages from the Dryas tundra can be distinguished from spectra from the other vegetation types by their high values of Dryas, Salix, amd Ericaceae plus Empetruin pollen, along with the occurrence of low amounts of pollen of several indicator species (sensu Janssen 1967) such as Sax(ficiga cf. S . bionchialis and S . hieiacifolirr type. The spectra from the Populus balsaniifercr forest are also distinct with their high frequencies of Popuhls cf. P. balsamgera pollen. There do not appear, however, to be any consistent diKerences in the pollen assemblages from the shrub-tundra and the Picea glauca forests.

These conclusions are confirmed by the results of canonical variates analysis of the data (see Birks et al. (1975) and footnote 5 for an account of the method and its applications to palynology). For the analysis, all taxa included in CP with a value of 5 z or more in any one sample were included, giving a total of 15 taxa in 30 samples derived from four vegetation types.

Each variable was expressed as a percentage of the total of these 15 taxa. The analysis was done on the University of Cambridge IBM 3701165 computer using the FORTRAN IV program CANVAR, much modified from the program of the same name written by Reyment and Ramden (1970). The first canonical variate axis accounts for 73.1% of the total variance and the second axis accounts for 24.4%. These two axes thus give a highly efficient (97.5%) summarization in two dimensions of the relationships between the samples from different vegetation types. The positions of the individual spectra and of the sample means for each vegetation type on the first and second canonical variates are shown in Fig. 3. The spectra from the Dryas tundra and from the Populus balsamfera forest are clearly distinct in their pollen composition, whereas there is no separation between spectra from the Picea gla~rca forests and the Betula glanduloscr shrub-tundra. Inspection of the third axis (2.5% of the total variance) shows no separation of these spectra on that axis. The correlations between the original variables and the canonical variates show that Snlix, Cassiope, Saxifraga tricuspidata - type, and Dryas pollen all have negative correlations with the first axis, whereas

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(3 S H R U B - T U N D R A

CAN. J. BOT. VOL. 5 5 , 1977

'1018

'1068

F r Populus bo lsom~fera FOREST

PlCeO F O R E S T

- 8.0

First Canonical Var iate Axis FIG. 3. Plot of the canonical variate group means for the surface pollen spectra from the four vege-

tation types (open symbols) and of the 30 individual spectra (solid symbols) on the first and second canonical variate axes.

Cyperaceae, Juniperus, Betula, and Populus cf. P. balsamifera pollen have positive correlations. These correlations indicate that the first canonical variate is discriminating between spectra with high Salix, Cassiope, Dryas, and Saxifraga tricuspidata - type pollen frequencies (i.e., samples from Dryas tundra) and spectra with high Cyperaceae, Betula, Juniperus, and Populus pollen. The second canonical variate axis has strong negative correlations with Juniperus and Populus pollen and positive correlations with Betula, Picea, and Cyperaceae pollen. It is thus discriminating between spectra from the Populus balsamifera forest and spectra from the shrub- tundra and the Picea glauca forests.

To investigate in more detail the patterns within the data, the information concerning the vegetation type from which each sample was collected was ignored and an ordination of the 30 individual surface samples was performed by means of principal coordinates analysis or metric scaling (Gower 1966, 1967; Reyment 1970). This was implemented by means of the FORTRAN IV program PCOORD, much modified from Blackith and Reyment's (1971) program of the same name. The method seeks to represent the distances or dissimilarities among all the spectra in a few dimensions so that the distances between the spectra in the low-dimensional model are, as nearly as possible, directly proportional to the

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A DfyUS TUNDRA: MOSS Polsters

I ,MOSS Polsters 0 SHRUB-TUNDRA surface Muds .I 0 sedge s w a m p s r Populus bo/sum/'fera FORESTS

Moss Polsters P~C~UFORESTS '1 sedge swamps

First Principal Coordinate Axis FIG. 4. Plot of the 30 individual pollen spectra on the first and second principal coordinate axes.

original distances between the spectra (see Birks and Xik is the frequency of pollen type I< in et al. (1975), Birks (1976), and Jijreskog et a/. sample i and Xjk is the frequency of pollell type (1976) for details of the method). In this anal- k in sample j (see Goodman (1972) and Krza- ysis, the same 15 taxa were used as in the nowski (1971) for a discussion of this distance canonical variates analysis, and the distance measure). measure used was the chord distance Dij where The results of the principal coordinates

analysis are shown in Fig. 4, where the positions of the individual spectra are plotted on the first

li= 1 and second principal coordinate axes. The

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FIG. 5. (A) View of Piceagla~tca forest at 1365 m altitude on a west-facing slope. Note the openness of the forest and the stunted growth of the trees. (B) View of the pure Populrts balsamifera forest at 1300 m altitude on a steep, dry, southeast-facing slope. (C) View of the regional tree line in the study area at about 1450 m altitude. The vegetation in the foreground is shrub-tundra with Betulaglandulosa and Salix glalrca. (D) View of Betula gland~tlosa - dominated shrub-tundra at 1500 m altitude. Note the scattered trees of Picea glauca that extend to this altitude. (E) View of Dryas integrifolia - dominated tundra at 1900 m altitude. In the foreground open Dryas fell-field occurs, whereas in the hollow nearby (dark area) Dryas- Cassiope tetragona snow-patch vegetation occurs. (F) View of Mount Constantine (3148 m) in the St. Elias Mountains.

mathematical efficiency of the anlysis is given by two axes provide a fairly efficient (60.2%) low- the proportion of the trace of the transformed dimensional representation of the original distance matrix accounted for by the eigenvalue distances. of each axis (Cower 1966, 1967). In this analysis, The two spectra from the Poplrllrs balsamgera the first axis accounts for 39.9% and the second forest (samples 115 and 116) are clearly dis- accounts for 20.3%, indicating that the first tinguished on the second principal coordinate

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B I R K S 238 1

axis, with high positive coordinates on that axis (Fig. 4). Similarly the six spectra from the Dryas tundra are distinguished by their negative coordinates on both the first and second axes (Fig. 4). There is, however, no separation between spectra from the shrub-tundra and from the Picea glauca forests. The first principal coordinate does, however, distinguish very effectively between spectra derived from moss polsters collected in the Piceu forests and the shrub-tundra (high negative coordinates on axis one) and spectra from samples collected in sedge swamps (high positive coordinates) in these two vegetation types (Fig. 4). Spectra derived from surface lake muds are positioned in the center of the first axis. Interestingly, spectra 106A, 106B, K16, and 1 12, which are positioned near the spectra from the sedge swamps, are all from small, shallow lakes (< 2 m deep), whereas the other mud samples (1 10B, 110A, K17, 103A, 101B, 101A) are from deeper ( > 3 m) lakes. The first principal coordinate axis thus groups together spectra from the shrub-tundra and Picea forests according to the type of sample (moss polster, lake mud, etc.) from which the spectra were derived and not according to the regional vegetation, and it is primarily a gradient from low to high Cyperaceae pollen values.

The 11 pollen spectra derived from surface lake muds collected within the Picea gluuca forest zone and the shrub-tundra zone were ordinated separately using principal coordinates analysis. No separation between spectra from these two major vegetation types emerged, indicating that even within a single sample type there are no consistent differences in pollen proportions from the Piceu gla~lcu forests and the subalpine shrub-tundra in the area studied. Davis (1969) and Davis and Webb (1975) discuss the problem of distinguishing between pollen spectra from forest-tundra and from northern open boreal forest in eastern North America and they conclude that the distinction is difficult when pollen percentage data only are available. Pollen influx data (e.g., Ritchie and Lichti- Federovich 1967) provide a means of distinguishing pollen spectra from these two major vegetation types.4

The low proportions (1-3%) of pollen that are undisputedly derived from outside the region of study (extraregional pollen sensu Janssen (1973); in this study mainly Pinus, Larix, Urtica, and Ostrya-Carpinus pollen) contrast with the high

percentages (20% or more) of extraregional Pinus pollen in modern spectra from tundra and shrub-tundra in central North America (Lichti- Federovich and Ritchie 1968; Webb and Mc- Andrews 1976). This difference is probably due to the prevalence of southerly winds in central North America during the early summer (Ritchie 1974), whereas in the Yukon the winds are mainly from the north and west, where pine is absent.

Comparisons between the modern pollen spectra presented here and fossil pollen spectra from the Yukon (Lichti-Federovich 1973, Rainp- ton 19710) confirm Lichti-Federovich's view that of the four major fossil pollen assemblages known in the Yukon, only the Picea-Betula- Alnus-Ericad assemblage of the post-Wisconsin age (zone 6 at Antifreeze Pond, Rampton 1971a) closely matches modern pollen spectra from the Yukon and elsewhere in Alaska and the Northwest Territories. No convincing modern analogues have yet been found for the distinctive assemblages of Wisconsin age in the Yukon or Alaska (Matthews 1970, 1974; Colinvaux 1964; Rampton 1971a).

Acknowledgments

I am indebted to Professor H. E. Wright, Jr. for providing the opportunity for me to work in the Yukon and for his encouragement and in- terest. I am also grateful to Dr. J. Platt Brad- bury, Dr. R. A. Watson, Dr. M. C. Whiteside, and Professor H. E. Wright for their assistance and companionship in the field, to Mrs. S. M. Peglar and Mrs. M. E. Pettit for their assistance in the laboratory, to Dr. G. A. Mulligan for his determinations of critical plant specimens, and to Dr. Hilary H. Birks for her helpful discussions and critical reading of the manuscript. The field work in the Yukon was financed by the National Science Foundation grant GB29063 to the University of Minnesota.

BIRKS, H. J . B. 1973rr. Past and present vegetation of the Isle of Skye-a paleoecological study. Cambridge Uni- versity Press, London.

1973b. Modern pollen rain studies in some arctic and alpine environments. In Quaternary plant ecology. Edited by H. J . B. Birks and R. G. West. Blackwell Scientific Publications, Oxford. pp. 143-168.

1976. The distribution of European pteridophytes: a numerical analysis. New Phytol. 77: 257-287.

BIRKS, H. J. B., T . WEBB, 111, and A. A. BERTI. 1975. Numerical analysis of pollen samples from Central Canada: a comparison of methods. Rev. Palaeobot. Palynol. 20: 133-169.

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BLACKITH, R. E., and R. A. REYMENT. 1971. Multivariate morphometrics. Academic Press, London.

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Documents

Modern pollen rain and vegetation of the St. Elias Mountains, Yukon Territory