Quaternary Science Reviews 20 (2001) 135}147
Full-glacial upland tundra vegetation preserved under tephra in the
Beringia National Park, Seward Peninsula, Alaska
Victoria G. Goetcheus *, Hilary H. Birks
Department of Geology and Geophysics, University of Alaska-Fairbanks, Fairbanks, AK 99775, USA
Botanical Institute, University of Bergen, Alle& gaten 41, N}5007 Bergen, Norway
Abstract
The nature of the full-glacial vegetation of Beringia has been the subject of a great deal of investigation and debate. Here we present
a reconstruction of an intact example of the full-glacial upland vegetation of part of the northern Seward Peninsula at one point in
time. The area was blanketed by more than 1 m of tephra ca. 18,000 C BP (ca. 21,500 cal. BP), and the former land-surface was
preserved in the permafrost. The discovery of the land-surface provides a unique opportunity to study a fossil ecosystem preserved
in situ. Macrofossils were used to reconstruct the vegetation growing at several sites on the buried land-surface. The macrofossil
assemblages indicate a vegetation characterized by graminoids and forbs, with the occasional occurrence of Salix arctica. The
vegetation was dominated by Kobresia myosuroides, other sedges (Carex), and grasses, with a "ne-scale mosaic related to snow
accumulation and moisture availability. Overall, the vegetation was a closed, dry, herb-rich tundra-grassland with a continuous moss
layer, growing on calcareous soil that was continuously supplied with loess. Nutrient renewal by loess deposition was probably
responsible for the relatively fertile vegetation, and the occurrence of a continuous mat of acrocarpous mosses. Good physiognomic
analogues can be suggested, but no exact modern vegetational analogues have been found, probably because the full-glacial
environment and climate with loess deposition do not occur today. 2000 Elsevier Science Ltd. All rights reserved.
1. The Beringian background
Knowledge of the Beringian environment during the
last glacial maximum (LGM), 28,000}14,000 BP, provides a context for understanding species exchange between Asia and America, megafaunal extinctions at the
end of the Pleistocene, development of plant communities in the Arctic, life at high latitudes during glacial
stages, and the migration of humans from Asia to the
Americas (see Hopkins et al., 1982). Exploration of these
topics helps us understand how climate change a!ected
the arctic environment and in particular how vegetation
change can a!ect human and animal populations.
The nature of the full-glacial vegetation of Beringia has
been controversial (e.g. Cwynar and Ritchie, 1980;
Ritchie, 1984; Guthrie, 1990) due to disagreements about
reconstructions of the composition and productivity of
the vegetation and its ability to support the Pleistocene
megafauna. Schweger and Habgood, as early as 1976,
proposed the occurrence of a vegetational mosaic over
* Corresponding author. Tel.: 1-907-474-7329.
E-mail address: [email protected] (V.G. Goetcheus).
Beringia that was in#uenced by local and regional factors
such as altitude, aspect, and soil moisture. This idea was
developed further by Schweger (1982, 1992) and others
(e.g. Anderson, 1985, 1988; Anderson and Brubaker,
1996; Elias et al., 1997), supported by evidence of regional
variation from pollen analysis and other fossils (e.g.
Young, 1982; Ritchie, 1984; Anderson et al., 1994; Elias
et al., 1996, 1997). Anderson and Brubaker (1994) summarized available LGM pollen data across central
Alaska, and proposed an increase in mesic conditions
from east to west. This inferred gradient is supported by
records of late-glacial vegetational development following climatic warming ca. 14,000 BP, in which dwarf-birch
expanded eastward from central Beringia into the Yukon
(Lamb and Edwards, 1988; Elias et al., 1997). Local
vegetation reconstructions and insect evidence from the
now-submerged part of the Bering Land Bridge indicate
the presence of mesic tundra with fens and pools during
the full glacial (Elias et al., 1996, 1997). In contrast,
conditions appear to have been much drier in eastern
Beringia (western Yukon) (e.g. Cwynar, 1982; Cwynar
and Ritchie, 1980; Ritchie, 1984) and western Beringia
(eastern Siberia) (Lozhkin et al., 1993), where herb-dominated rather than shrub-dominated tundra covered
0277-3791/01/$ - see front matter 2000 Elsevier Science Ltd. All rights reserved.
PII: S 0 2 7 7 - 3 7 9 1 ( 0 0 ) 0 0 1 2 7 - X
136
V.G. Goetcheus, H.H. Birks / Quaternary Science Reviews 20 (2001) 135}147
Fig. 1. Map of Beringia. The full-glacial Bering Land Bridge is bounded by Russia on the west, Alaska on the east, and the 200 m isobath to the north
and south.
much of the upland landscape. Drier conditions on the
continental parts of Beringia may have resulted from
the regional in#uence of large icesheets, particularly the
Laurentide ice sheet over Canada (Barry, 1982; Bartlein
et al., 1991), on the atmospheric circulation, with the
southward displacement of the jetstream (Edwards and
Barker, 1994).
In this paper, we present palaeobotanical results from
the northern Seward Peninsula (Fig. 1), consisting of
plant macrofossil analyses from a land-surface buried
in situ by a deep layer of tephra at ca. 18,000 C BP. The
vegetation reconstructions and their environmental implications are considered in the context of previous fullglacial results and reconstructions from elsewhere in
Beringia.
2. Modern geology, vegetation, and climate of the
Northern Seward Peninsula
The Seward Peninsula forms the eastern side of the
Bering Strait, with the westernmost tip of the peninsula
only 75 km from Siberia. When sea level was lowered
during glacial stages, the Peninsula adjoined the central
section of the Bering Land Bridge (Fig. 1). The Peninsula
consists of lowlands in the north, rolling uplands with
some mountains in the centre, and lowlands in the south
(Wahrhaftig, 1965). Continuous permafrost '100 m
thick underlies the north and central parts of the peninsula (Hopkins, 1988; Beget et al., 1996). Lowland regions
are covered with thermokarst lakes and basins of drained
lakes, intermixed with yedoma hills and plateaux. Four
maar lakes and the shield volcano, Devil Mountain, and
its associated cinder cones, and three other volcanic
structures add to the diversity of the landscape (Fig. 2).
The tephra that buried the surface studied in this paper
erupted from the youngest of the maar vents, Devil
Mountain Lake, and is called the Devil Mountain Lake
tephra (Beget et al., 1996).
The modern vegetation of the northern Seward Peninsula coastal plain consists mostly of lowland tundra, with
communities ranging from cottongrass-dominated tussock tundra with scattered dwarf shrubs and mosses,
through Betula and Salix shrub-dominated vegetation
with fewer tussocks, to Betula and heath-dominated tundra communities in drier parts of the landscape. The
most common species in this vegetation complex are
Eriophorum vaginatum, Carex bigelowii, Betula nana and
B. glandulosa, and various shrub Salix spp. (Viereck et al.,
1992). Eriophorum and Carex spp. also dominate extensive fens. Dry upland-tundra communities occur on
Devil Mountain and other cinder cones, while birch and
V.G. Goetcheus, H.H. Birks / Quaternary Science Reviews 20 (2001) 135}147
137
Fig. 2. The northeastern Seward Peninsula, showing the Cape Espenberg * Devil Mountain area. The area contains abundant lakes, not all of which
can be shown here. The informally named lakes with sites where the buried surface was sampled are indicated. Tern, Plane, and Point sites are located
on Tempest Lake.
willow shrub-tundra occupies #oodplains and swales.
The dominant mosses across much of the region are
Sphagnum spp.
Kotzebue, 60 km to the northeast of the study area, has
a mean temperature of !6.03C (US Weather Bureau).
January temperatures average !20.23C and July temperatures average 11.93C. Summers in Kotzebue tend to
be slightly warmer than those near the north shore of the
Seward Peninsula. Average precipitation is approximately 230 mm yr\. More than half the precipitation falls
during July}September.
3. The buried surface
In 1968, David M. Hopkins discovered an ancient
buried vegetated land-surface on the Seward Peninsula,
within an area that later became part of the Bering Land
Bridge National Park and Preserve. Approximately
2500 km of the original land-surface had been buried by
the Devil Mountain Lake tephra, which over approximately 1200 km was more than 1 m thick. Where the
tephra was thicker than the summer-thawed active surface layer, it preserved the plant and animal remains
present on the surface by in situ freezing. Subsequent
loess deposition buried the tephra to depths of 6}300 cm.
Holocene thermokarst lakes have incised themselves
into the sediments by the melting of large, syngenetic
ice wedges. The resulting steep banks along the lake
shores expose the tephra as a distinct dark horizon separating two lighter coloured loess units. A typical site is
located on the eroding bank of a thermokarst lake and
many are underlain by ice wedges that were actively
growing when the tephra fell. The occurrence of a subnivian rodent nest (Goetcheus et al., 1994) and large ice
lenses that appear to be compressed snowbeds suggest
that the tephra fell either during the late winter or early
spring.
The buried surface lies near the mid-point of the
north-south axis of the Bering Land Bridge (Figs. 1 and
2) and preserves the vegetation near the time of the
thermal minimum of the last glacial period, ca. 18,000
radiocarbon years BP. A macrofossil record of the plant
community has been preserved intact by the burial of the
land-surface. The fact that the tephra fell during the late
winter or early spring limits the quality of the plant
tissues preserved on the surface. Plant material either
deteriorated or was eaten during the winter, leaving only
remains that were protected, sturdy, or very abundant.
But all the remains found on the surface are strictly local,
and can be interpreted directly in terms of the past in situ
#ora and vegetation.
138
V.G. Goetcheus, H.H. Birks / Quaternary Science Reviews 20 (2001) 135}147
The chance to sample fossil in situ upland vegetation is
unique as far as we know. Water-transported Laacher see
tephra buried late-glacial river-bank vegetation in Germany, where well-preserved fossils give a good representation of the community (Waldmann, 1995, 1997).
Other macrofossil assemblages have been preserved in
#uvial and glacio#uvial sediments (e.g. Miller, 1993, see
Jackson et al., 1997) or in glacial sediments (e.g. Rosendahl, 1948, Miller, 1976). Often these are lowland peaty
deposits laid down in shallow pools or poorly drained
areas (e.g. the Two Creeks Forest Bed; Miller, 1976), and
do not represent actual upland vegetation. However,
their often good preservation, together with well-preserved mosses, allows a detailed reconstruction of the past
vegetation to be made (e.g. Miller, 1976). Fens and bogs
are other examples where lowland vegetation is preserved in situ, but here the timelines are obscured by peat
growth, root penetration, and compaction, so that it is
very di$cult to reconstruct actual vegetation other than
by assemblage analogies.
4. Radiocarbon dates
Eighteen samples from the buried surface have been
radiocarbon dated during the last 21 years (Table 1).
Conventional dates on 12 samples collected between
1968 and 1994 produced a surprisingly large scatter of
age estimates, 16,880 $ 120 to 18,140 $ 200 C years
BP (Table 1a), given that the tephra from the Devil
Mountain eruption would have buried the entire landscape within a period of a few hours to a few days (Beget
et al., 1996). Several possible explanations exist for this
large scatter: (1) signi"cant modern contamination may
have been introduced during sampling and subsequent
handling; (2) large fossil willow roots included in the
earlier samples may have been as much as several hundred years old when buried by the tephra; (3) undetected
inaccuracies in counting in conventional radiocarbon
dating techniques may have caused the wide scatter of
dates (Baillie, 1990; Lowell, 1995), and (4) inclusion of old
carbon from calcium carbonate in the loess. Consequently, a more rigorous protocol was adopted when six
new samples were collected for AMS dating in 1995
(Table 1b). Latex surgical gloves were worn while collecting and the trowel was rinsed in "ltered water and #amed
with alcohol before each sample was collected. Twigs and
roots were avoided. Plant material was scraped o! the
ground surface, avoiding the underlying soil. Each
sample was placed in a ziplock bag that was immediately
sealed. The AMS radiocarbon dates are much more
tightly clustered. The weighted mean of the six uncalibrated AMS dates was calculated using the CALIB 3.0
program of Stuiver and Reimer (1993), and is 18,070
$ 60 C years BP, with a range of 17,770}18,260 at 2r
(Table 1b). Using the calibration curve in CALIB 3.0 the
Table 1
(a) Bulk dates on material collected using older protocols, 1968}1994 (The older dates are from Hopkins, 1988)
Site
Laboratory number
Age
Material
Egg lake
Eh'cho lake
Nuglungnugtuk
Fritz lake
Lake Rhonda 1
White"sh thaw pond
Lumpy drained Lake
Tempest lake
Ulu lake
Ulu lake
Kiliwooligoruk creek
Eh'cho Lake
White"sh thaw pond
Beta-60716
Beta-23048
Beta-18632
Beta-79838
Beta-60718
W-3489
Beta-75731
Beta-75529
Beta-79839
Beta-81732
Beta-18549
Beta-79837
Beta-79840
16,880$120
16,980$170
16,990$150
17,360$130
17,420$260
17,630$800
17,740$110
17,740$220
17,850$100
17,880$110
17,910$110
17,980$110
18,140$200
Wood on surface
Roots from surface
Plant remains
Plant remains
Woody root
Plant remains
Woody stems
Woody stems
Plant remains
Subnivian microtine nest
Detrital twigs in tephra-rich alluvium
Plant remains
Plant remains
(b) AMS dates on plant remains collected using the rigorous sampling protocol of 1995 (see text)
Site
Laboratory number
Age
Calibrated age
Tempest lake
White"sh thaw pond
Lake Rhonda 3
Eh'cho lake
Egg lake
Lake Rhonda 2
Mean age
Beta-85125
Beta-85126
Beta-85127
Beta-85128
Beta-85129
Beta-85130
18,090$70
17,880$110
17,950$70
18,170$90
18,090$110
18,190$70
18,070$69
21,780
21,550
21,610
21,900
21,810
21,900
21,570
(21,600)
(21,330)
(21,420)
(21,700)
(21,600)
(21,725)
21,400
21,100
21,230
21,500
21,380
21,390
V.G. Goetcheus, H.H. Birks / Quaternary Science Reviews 20 (2001) 135}147
Table 2
Properties of the buried-surface soil. Data from Hoe#e (1995).
OC"organic carbon
Site
pH OC (%)
C/N CO (%)
Palaeo-active layer
depth (cm)
Rhonda
Ulu
Eh'cho
Egg
Tempest
Fritz
Foot
8.2
8.1
8.1
8.6
7.7
7.7
8.1
8
13
10
10
9
10
11
39
52
n.d.
64
61
40
43
139
animals were important for maintaining the carbonaterich substrate and the productivity of the vegetation
(Schweger, 1992, 1997; Schweger et al., 1982).
6. Methods
2.9
7.1
3.0
3.5
3.1
3.8
4.8
1.6
1.3
2.4
2.6
2.7
2.3
2.0
calibrated age of the weighted mean centres on 21,570 cal
BP. The new AMS dates place the age of the buried
surface more precisely within the time of the Last Glacial
Maximum.
5. Soil
The physical and chemical properties of a soil have
a large in#uence on the plants that are rooted in it, and
thus on the composition of the vegetation. The buried
soils developed on massive Pleistocene loess with a silty
loam texture. According to Hoe#e (1995) and Hoe#e and
Ping (1996), the pH of the 21,500 year-old soil ranges
from 7.4 to 8.6 with a mean of 8.0, and the presence
of carbonate along with other chemical properties of
the soil indicate that it formed under dry conditions
(Table 2).
Fine roots were found throughout the soil pro"le,
within both the palaeo-active layer and the palaeo-permafrost layer. These indicate the former presence of
abundant herbaceous vegetation with a large sub-surface
biomass. A dense network of "ne roots in calcareous soil
under an open, graminoid-dominated vegetation is characteristic of northern steppe communities (Yurtsev,
1982).
The high organic carbon content and the narrow C/N
ratios (8}11) (Table 2) suggest a high nutrient, or at least,
a high nitrogen availability that may have been maintained by the constant input of loess with new nutrients
into the system (see Jacobson and Birks, 1980), and the
recycling of plant material by annual turnover and by
grazing by small mammals (Schweger, 1992, 1997). Modern analogues on the Arctic Coastal Plain where loess is
currently being deposited, tend to remain alkaline and
places without loess input normally become acidic as
peat accumulates (Walker and Everitt, 1991). Studies in
the Kluane Lake Region of the Yukon Territory support
the idea that loess input increases plant productivity;
such areas might have supported grazing during the
LGM (Laxton et al., 1996; Smith, 1997). It seems probable that the continuing input of loess and manuring by
6.1. Sampling
During the summers of 1993, 1994, and 1995, the
buried surface was excavated at 18 sites located on the
banks of nine thermokarst lakes and beneath the bottom
of one recently drained thermokarst lake. None of these
lakes have formal names, so informal names were assigned in the "eld, and are used when referring to them in
this paper (Fig. 2). Material from 11 sites has been examined so far for macrofossils, and material from three sites
was studied in considerable detail.
The tephra was carefully removed from the surface
using trowels and paintbrushes. Each site was excavated
along the blu! face to expose 2}10 m;30}40 cm of the
original ground surface. At each site the percentage cover
of the di!erent vegetation components was estimated by
a point transect. The presence or absence of moss, woody
material, graminoids, and herbaceous material was determined for each point. Cover estimates commonly exceed
100% due to the presence of several plant layers at
a point. From each site on the buried surface numerous
areas of 5;10 cm were sampled with a trowel to a depth
of 2 cm (&100 cm).
6.2. Macrofossil analysis
Subsamples were taken in the laboratory. Their volumes were measured by water displacement and they
were sieved through 125 lm mesh with water to disaggregate the material and remove soil and tephra. The retained material was sorted using a binocular dissecting
microscope at 12;magni"cation into moss, insect remains, seeds, and organic debris. The organic debris
included an abundance of faeces of small mammals, such
as voles, etc. The few lichen remains found were classed
with the organic debris due to their decayed and fragmentary state. For convenience, both fruits and seeds will
be referred to here as &seeds'. By comparison with reference collections located in the Herbarium of the Museum
of the University of Alaska-Fairbanks, and at the Botanical Institute, University of Bergen, seeds were identi"ed
to the lowest taxonomic unit possible (several to species
level) based on their morphological characteristics
(Table 4) and counted. Although the concentration data
are available, they are not used here, as we are considering the relatively homogeneous vegetation as a whole.
The spatial variation over a few cm within the vegetation
of a site, or over a few km between sites, will be considered in a future paper. Therefore, we have estimated
140
V.G. Goetcheus, H.H. Birks / Quaternary Science Reviews 20 (2001) 135}147
Table 3
Moss taxa identi"ed from the buried surface. Habitat information is
from Steere (1978) and personal observations. Nomenclature follows
Steere (1978)
Moss taxa
Habitat
Abietinella abietina
Well}drained
calcareous
soils, xerophytic
On open calcareous soil
Moist soil
Wet-to-moist
calcareous
substrates
On moist soil and among
other mosses
On moist or wet soil, among
litter
On calcareous soil, often with
other mosses in moss turf
On moist calcareous soil
On moist calcareous soil
On moist calcareous soil
On moist to wet calcareous
soil
On open calcareous soil
On wet calcareous soil,
#ushes
On moist soil
On open calcareous soil, e.g.
frost boils, gravel, and in
moss turf
On calcareous soil and in
moss turf
On calcareous soil
Calcareous fens and tundra
depressions
On dry, open calcareous soil
On well}drained calcareous
soil
On "ne}grained silt on e.g.
frost boils and disturbed soil
Dry calcareous or acidic
substrates
On damp calcareous soil
On calcareous soil
Various
On calcareous soil and
other mosses
On moist calcareous soil
Mesic fens mixed with other
mosses
On moist to wet soil, e.g.
snow Melt}water #ushes
Various
On seasonally wet calcareous soil
Rich fens and damp calcareous soil
On calcareous silt on frost
boils
On calcareous soil
On calcareous soil
Mesic calcareous fens and
damp soil
On calcareous soil in late
snow}melt areas
Aloina cf. brevirostris
Amblystegium serpens var. juratzkana
cf. Amblystegium varium
Brachythecium groenlandicum
Brachythecium cf. nelsonii
cf. Bryoerythrophyllum recurvirostrum
Bryum cf. pseudotriquetrum
Bryum neodamense
Campylium hispidulum
Campylium stellatum
Desmatodon leucostoma
Dichodontium pellucidum
Dicranum bonjeanii
Didymodon rigidulus var. icmadophila
Distichium cf. capillaceum
Ditrichum yexicaule
Drepanocladus brevifolius
Encalypta alpina
Eurhynchium pulchellum
Fissidens arcticus
Grimmia sp.
Hypnum bambergeri
Hypnum vaucheri
Jungermanniales
Myurella julacea
Orthothecium strictum
Plagiomnium ellipticum
Pohlia cf. wahlenbergii
Pottiaceae
Pseudocalliergon turgescens
cf. Sanionia uncinata
Stegonia pilifera
Timmia austriaca
Timmia norvegica var. excurrens
Tomenthypnum nitens
Tortula norvegica
the abundance of the taxa on a 4-point scale related to
their percentage occurrence in the samples (see Table 4)
through the total data set. Most of the mosses were
identi"ed by Jan Janssens, and are listed in Table 3.
7. Macrofossil results
Macrobotanical remains found on the buried surface
can be classed in four groups: mosses, prostrate shrubs,
graminoids, and other herbaceous plants (forbs). Little or
no bare ground was observed during excavations of the
buried surface.
Mosses covered at least 60}70% of the ground at most
sites and often formed an understorey to the other plant
types. All the identi"ed mosses are listed in Table 3. No
lichens were seen on the buried surface in the "eld, but
some small remains were found when sorting the samples
under a microscope, growing on the surface of the moss
mat. They are too small to be identi"ed further than
thallose and foliose types. The mosses formed a carpet
across the land-surface with many di!erent species mixed
together. One small piece of the carpet (2;2 cm) consisted of a dense acrocarpous mat of Distichium cf. capillaceum, Encalypta alpina, and Didymodon rigidulus var.
icmadophila, with Drepanocladus brevifolius and Myurella
julacea creeping over it. D. rigidulus var. icmadophila,
Hypnum vaucheri, and Bryum spp. are the most common
moss taxa, occurring abundantly in most samples.
Abietinella abietina, Fissidens arcticus, and Stegonia pilifera are the least common taxa, occurring sparsely in
a few samples.
The vascular plants identi"ed are listed in Table 4.
Prostrate shrubs are the least abundant component of
the buried surface vegetation. Salix arctica was identi"ed
at three sites where it covered approximately 30}50% of
the area sampled. Leaves and a catkin belonging to Salix
arctica were discovered at two sites located at Tempest
Lake; more leaves were found at the Egg Lake site. The
buried surface at the two Tempest Lake sites was covered
by large, horizontal ice bodies, evidently buried snow,
indicating a snow-bed environment for the shrubs. No
estimates of willow groundcover are possible at any other
sites due to a lack of shrub bases or leaves. Salix remains
such as buds and capsules have been found at other sites
but cannot be identi"ed to species level. The buds and
capsules indicate the transport of Salix parts by wind
from plants growing nearby but not in sampled sections
of the buried surface. Willow shrubs appear to have been
con"ned to patches on the landscape leaving most of the
surface without shrub cover.
Graminoid remains are abundant on the buried surface, but the dried bases and pieces of leaf and stem have
not been identi"ed to family. Gramineae and Carex seeds
have been identi"ed, but it has only been possible to
identify one seed type, Kobresia myosuroides, to species
V.G. Goetcheus, H.H. Birks / Quaternary Science Reviews 20 (2001) 135}147
141
Table 4
Plant taxa identi"ed from macrofossil remains. &seed' is used to indicate reproductive propagules, including fruits and seeds. Nomenclature follows
HulteH n (1968)
Plant taxa
Macrofossil
Sites present
Abundance in sample
Dwarf shrubs:
Salix arctica
Salix undi!.
Leaves
Capsules and Buds
TT, PT, EL
All but EL and PL
Uncommon
Uncommon
Graminoids:
Carex bigelowii type
Carex nardina type
Cyperaceae undi!.
Kobresia myosuroides
Seeds
Seeds
Seeds
Seeds
EH, UL and RH
All but EL and RL
All but PL, R3 and RH
All
Uncommon
Common
Uncommon
Abundant
Herbs:
Bupleurum triradiatum
Campanula uniyora type
Caryophyllaceae undi!.
Cerastium beeringianum
Compositae undi!.
cf. Artemisia
Cruciferae undi!.
Draba
Eutrema edwardsii type
Juncus
Luzula
Melandrium azne
Melandrium apetalum
Minuartia arctica
Minuartia obtusiloba
Oxyria digyna
Papaver sect. Scapiyora
Papaver walpolei
Polygonum viviparum
Potentilla hookeriana
Potentilla hyparctica type
Potentilla nivea type
Primulaceae
Ranunculus undi!.
Saxifraga oppositifolia
Taraxacum
Valeriana
Seeds
Seeds
Seeds
Seeds
Seeds
Seed
Seeds
Seeds
Seeds
Seeds
Seeds
Seeds
Seeds
Seeds
Seeds
Seed
Seeds
Leaves
Bulbils
Seeds
Seeds, whole Plant
Seeds
Seeds
Seeds
Seeds, leaves
Seeds
Seeds
All but R3 and RH
TT, UL, EH, RH
TT, PT, EL, UL, EH, R3
All but RL, RH and R1
TT, PT, RL, EH
PL
R2, R3, TT, PT, EL
All
TT, R3, EH, UL
TT, PT, RL, EL, UL, EH
UL, EH
All but PL, R1 and RH
TT, EH, R3
TT, PT, EL, UL, EH, R1, R3
All but PL and RL
UL
All but PL
TT
TT, RL, EH, UL
All
TT, PT, R1, R2, EH, UL, RH
R2, PT, UL, EH
All but R3
All but PL
UL, EH, R3
PL, EL, EH, R1, R3
TT, UL
Uncommon
Uncommon
Uncommon
Uncommon
Rare
Rare
Rare
Abundant
Uncommon
Uncommon
Rare
Uncommon
Rare
Uncommon
Common
Rare
Common
Rare
Common
Common
Common
Uncommon
Uncommon
Uncommon
Uncommon
Rare
Rare
&Undi!.'"undi!erentiated. The site abbreviations are as follows: TT"Tern, PT"Plane, PL"Point, R1"Reindeer 1, R2"Reindeer 2,
R3"Reindeer 3, RL"Rhonda 1, RH"Rhonda 2, EL"Egg, EH"Eh'cho, and UL"Ulu. Abundance rating is based on the percentage of
samples the taxon is found in: abundant '80%, common 50}80%, infrequent 16}49%, rare (16%.
(this taxon was misidenti"ed as Trichophorum caespitosum by Goetcheus et al., 1994). Kobresia myosuroides
is often abundant, and comprises the majority of the
Cyperaceae seeds (Table 4). It occurs in 98% of the
samples and averages more than 30 seeds per 100 cm.
Most of the other Cyperaceae seeds are Carex belonging
to two di!erent groups: Carex nardina type and Carex
bigelowii type (see Berggren, 1969). Carex nardina often
occurs with Kobresia myosuroides in the drier part of its
habitat range (Walker, 1990), although other species with
the C. nardina seed type occur in other habitats.
Graminoids covered approximately 30}50% of the
ground at each site.
The forb #ora on the buried surface is diverse. The
most commonly found seeds were Potentilla and Draba,
occurring in 90 and 98% of the samples, respectively.
Potentilla hookeriana, the most common of the three
Potentilla species found in samples from the buried surface, is locally common in subarctic steppe vegetation of
eastern and western Beringia today (Murray et al., 1983;
Eriksen, 1995). Papaver walpolei leaves were found at
only two sites, Tern and Plane, located on opposite sides
of Tempest Lake, but Papaver sect. Scapiyora (that includes P. walpolei) seeds were found at 10 sites including
Tern and Plane. Saxifraga oppositifolia is most common
at the Eh'cho site though it was found occasionally in
142
V.G. Goetcheus, H.H. Birks / Quaternary Science Reviews 20 (2001) 135}147
samples from other sites. The forb vegetation covered
approximately 25}40% of the ground at each site.
We have small samples from relatively few sites scattered in a small area (Fig. 2), so we are unlikely to have
sampled the full diversity of the regional upland vegetation. Macrofossils, as opposed to pollen, are locally deposited (Birks, 1973), especially so in this situation, where
the upland vegetation at a site is being sampled and there
is no sorting or blurring of the assemblage by
taphonomic processes. This local deposition means that
we have the potential to take adjacent fossil samples to
describe the vegetation variability, like sampling the variation in modern vegetation with quadrats. In the present
study, however, we have spot samples, and thus may have
missed recording species that occurred in the local vegetation, but not at our sampling points. However, there is
a large degree of homogeneity between our fossil assemblages, suggesting that a fairly uniform vegetation
may have occupied the landscape, with small variations
related to environmental factors, such as moisture
availability.
8. Reconstruction of vegetation and environment
The plant remains provide important information
about the environment of the northern Seward Peninsula
during the LGM. The vegetation was predominantly dry
tundra, rich in graminoids and forbs and lacking erect
mesic shrubs. The physiognomy of the vegetation resembled arctic steppe, a rare vegetation type today (Yurtsev,
1982; Guthrie, 1990, photo in Fig. 8.12; Walker, 1990;
Walker et al., 1991).
Most of the identi"ed taxa from the buried surface
share two characteristics: they grow on mineral soil and
they prefer calcareous substrates (HulteH n, 1968; Steere,
1976). The taxa di!er in their degree of drought tolerance (Tables 3 and 5), but all the vascular plants and
most of the mosses have some tolerance for drought
(HulteH n, 1968; Steere, 1976). The well-drained loess soil
would have dried quickly in the windy conditions, and
some of the vegetation may have been blown free of snow
in the winter (Schweger et al., 1982). Many of the moss
taxa require moist conditions, at least seasonally, but
several others are indicators of dry and/or disturbed soil
(Table 3).
The study sites fall into two main groups, those with
drought-tolerant plants and those with plants with higher moisture requirements (Tables 3 and 5), suggesting
some di!erentiation in moisture availability at di!erent
places. The latter group includes two sites where the ice
masses that are interpreted to be "rni"ed, late-lying snow
banks are found. Several of the moss taxa presently grow
in snow-bed habitats or areas with snow meltwater, and
it is probable that Salix arctica was also con"ned to areas
of snow protection in winter. Another possible source of
Table 5
Vascular plant taxa identi"ed from the buried surface and their habitats. The hatbitat information is from HulteH n (1968) and other references
in this paper, supplemented by personal observations
Plant taxa
Modern habitat
Bupleurum triradiatum
Carex nardina type
Dry grassy and open tundra, fell}"eld
Wind}exposed open grassy tundra on calcareous soils
Gravel and cli!s, soil disturbed by animals
Open, often calcareous, soil
Open damp soil on tundra, soli#uction
areas
Dry, calcareous tundra with stable soils
and little snow}cover in winter
Open soils, fell}"eld, screes and gravel
Dry places, open rocks and disturbed soil
Dry grassy slopes, open gravel and screes
Dry ridges and rocky slopes, on open soils
in grassy tundra
Dry slopes and snow beds
Snow beds on tundra, open gravel, screes
Dry calcareous soil
Dry and damp meadows and open grassland
Dry calcareous open grassland
Dry tundra with winter snow protection
Dry to moist exposed calcareous soils
Mesic grassland
Cerastium beeringianum
Draba spp.
Eutrema edwardsii
Kobresia myosuroides
Luzula spp.
Melandrium azne
Melandrium apetalum
Minuartia arctica
Minuartia obtusiloba
Oxyria digyna
Papaver walpolei
Polygonum viviparum
Potentilla hookeriana
Salix arctica
Saxifraga oppositifolia
Valeriana (capitata)
diversity of moisture requirements is irregularity in the
micro-topography, with 2}10 cm changes in the height of
the surface from the lowest point at some sites. Small
hollows would collect snow, and act as channels for
surface run-o!. The diversity and widespread distribution of the taxa present on the surface that require moist
conditions suggest that a moderate amount of water was
available during the growing season.
At other sites, lack of snow cover may have led to some
periglacial soil disturbance, as suggested by the occurrence of Fissidens arcticus and Stegonia pilifera. Mammal
grazing, trampling, and burrowing may also have resulted in open disturbed areas of soil. Many of the vascular
taxa also tolerate soil disturbance, e.g. Draba spp., Luzula
spp., Cerastium beeringianum, Minuartia obtusiloba, M.
arctica, Melandrium apetalum, Campanula uniyora, and
Papaver spp., and they can occur today where animal
disturbance by grazing, manuring, and burrowing is
strong (e.g. Walker, 1990).
The abundance of Kobresia myosuroides in the fossil
assemblages suggests that it was dominant in many places. In several samples, the seeds had been germinating,
suggesting good regeneration of Kobresia. It was usually
associated with herbs of open habitats, such as Potentilla
spp., Draba, Eutrema, Papaver walpolei, the Caryophyllaceae in Table 4, Bupleurum triradiatum, Campanula
uniyora, and Luzula spp. Kobresia myosuroides is a circumpolar species (HulteH n, 1968) that characteristically
V.G. Goetcheus, H.H. Birks / Quaternary Science Reviews 20 (2001) 135}147
grows on xeric to mesic wind-blown ridges, and in
meadows and heaths (Cooper and Sanderson, 1997), on
dry, usually calcareous slopes, gravel bars, and lichen
tundra (HulteH n, 1968) that are neither extremely windexposed nor covered by deep snow in winter (Gjvrevoll,
1954; Bell and Bliss, 1979). It is associated with many
of the above-mentioned taxa in its present-day communities.
On the buried surface, the almost continuous moss
cover in the Kobresia-dominated communities was mostly a carpet of acrocarpous species, typically Didymodon
rigidulus var. icmadophila, Encalypta alpina, Distichium cf.
capillaceum, and rarely Desmatodon leucostoma and
Aloina cf. brevirostris, supporting creeping stems of
Myurella julacea and pleurocarps such as Campylium
spp., Pseudocalliergon turgescens, Tomenthypnum nitens,
and Drepanocladus spp. Small thallose and foliose lichens
also grew over the moss carpet. Such moss communities
are not recorded in modern Kobresia-dominated communities (as cited above) and may have no modern analogue, as loess deposition is a relatively rare process
today. The acrocarpous mosses were able to grow
through the accumulating loess, and may have e!ectively blocked competition from larger pleurocarps in
dry habitats.
Many taxa from the buried surface have a requirement
for calcareous soil today (Tables 3 and 5) (HulteH n, 1968;
Steere, 1976). The soil analyses (Table 2) (Hoe#e, 1995)
give direct evidence for a high carbonate content and
a high pH, resulting from loess deposition. In modern
tundra, the key environmental parameters in#uencing
#oristic composition are slope, aspect, substrate pH, and
moisture availability (Murray and Murray, 1975;
Schweger, 1982; Ritchie, 1984; Murray, 1992, 1997). Unfortunately, it was not possible to determine the palaeoslopes and aspects for the buried-surface sites, so their
in#uence on the vegetation of the buried surface is unknown. However, the majority of sites supported an
open, Kobresia-dominated community on calcareous soil
with high pH, maintained by the continuous addition of
small amounts of loess. Moisture conditions varied with
local topography and micro-topography, resulting locally in the occurrence of di!erent plant assemblages.
A number of taxa are conspicuous by their absence
from the buried surface. Ericads, Betula, Selaginella sibirica, and Dryas are all missing from the assemblages
recorded from the buried surface. These taxa are deciduous or semi-evergreen with leathery leaves. If they were
present on the landscape we would expect to "nd their
remains preserved and easily seen upon examination of
the surface. The absence of Ericads and Betula may
suggest that environmental conditions were beyond their
tolerance (i.e. dry, windswept, and cold). The absence of
Ericads can also be explained by the preference of the
majority of these taxa for acidic soils. Other taxa common in arctic vegetation today are also not recorded,
143
such as Fabaceae and Saxifraga other than S. oppositifolia. Potential fossils of many of these taxa are often
sparsely produced and poorly preserved. The moss
Rhytidium rugosum is also surprisingly not recorded from
the buried surface. It is very commonly associated today
with Dryas-dominated and open grass-herb communities
on calcareous soil in Alaska and the Yukon. Artemisia is
a prominent pollen type in full-glacial Beringian pollen
spectra, but we only found one doubtfully identi"ed seed
of Artemisia. Macrofossil remains of Artemisia are rare,
and may not be well preserved. However, Artemisia may
have been genuinely rare in our vegetation, and the
contemporaneous pollen recorded in upland Beringia
may be largely long-distance transported (cf. Birks and
Mathewes, 1978).
The absence of Dryas is one of the main di!erences
between modern calcareous tundra communities and our
fossil vegetation. Its apparent absence is di$cult to explain, as it is calciphilous and drought tolerant. Dryas
macrofossils were also rare or absent in full-glacial samples from Eastern Beringia examined by Matthews (1982)
though some Dryas remains have been found in older
deposits (Matthews and Ovenden, 1990). Dryas spp. are
widespread in modern montane and arctic communities
and on the Arctic Coastal Plain but are absent or are
minor components in steppe-like vegetation remnants
(e.g. Yurtsev, 1982; Cooper, 1986) and the graminoiddominated vegetation on pingos in northern Alaska
(Walker, 1990; Walker et al., 1991). Dryas spp. are typically pioneers on calcareous soils, but they need soil
disturbance by frost or soil erosion to regenerate. On
stable soils their abundance is reduced in time due to
competition with grasses and sedges (Elkington, 1971).
Dryas octopetala is a poor competitor in conditions of
high available phosphorus and nitrogen that encourage
the growth of graminoids (Je!rey and Pigott, 1973).
In the 21,500 year old ecosystem, phosphate may have
been continuously supplied by loess deposition (e.g.
Jacobson and Birks, 1980) and rapid turnover of dead
plant material and mineralization of nitrogen resulted in
the low C/N ratios (Table 2). The successful growth of
graminoids over thousands of years, combined with grazing of the #owers and seed heads of Dryas by the abundant small mammals, may have excluded Dryas from the
vegetation.
Another explanation for the absence of the above taxa
should be considered. We only have a few small samples
from a relatively large area, so we cannot exclude the
possibility that Dryas and the other species were locally
present but not sampled or recorded by us.
9. Discussion
The vegetation of the buried surface appears to have
no precise modern counterpart that has been described in
144
V.G. Goetcheus, H.H. Birks / Quaternary Science Reviews 20 (2001) 135}147
the literature. We can "nd analogues for the physiognomic vegetation type, but although the compositions of
the modern communities overlap in part, they do not
contain exactly the same species assemblages, and usually contain Dryas. The dry-soil vegetation of the buried
surface matches best with the dry meadow and Kobresia
meadow plant community-types described by Yurtsev
(1982, unpublished manuscript). The species compositions do not, however, exactly match that of the buried
surface, but similarities in structure and dominant plant
genera suggest that some analogy can be drawn between
them.
The individualistic behaviour of steppe and tundra
species was proposed by Murray et al. (1983) and Walker
et al. (1991) in connection with the composition of the
full-glacial steppe-tundra of Beringia. The individual responses of tundra plants on the modern landscape to
changing conditions were demonstrated by Edwards and
Armbruster (1989) and Lloyd et al. (1994) along an altitudinal gradient in eastern Alaska. They showed how
species have the potential to combine in di!erent assemblages under di!erent environmental conditions. Present-day steppe-tundra communities are Holocene
combinations of species in situations where environmental conditions resemble those of the full-glacial,
namely open, calcareous, well-drained soils, and are the
current version of a continually changing community
(Murray et al., 1983). However, the full-glacial environment of strong continentality and aridity (Barry,
1982), combined with strong winds (Harrison et al.,
1992) and loess deposition in certain areas of Beringia,
including the Seward Peninsula (Hopkins, 1982), does
not occur today. Following their individual tolerances,
plants combine into di!erent communities under di!erent environmental regimes, as proposed by Gleason
(1926) and Griggs (1934), and demonstrated experimentally by Chapin and Shaver (1985) and Chapin
(1995)
Guthrie (1990), considered that no exact analogue
exists at the biome level for the environment of fullglacial Beringia, and proposed the occurrence of an extinct biome, the &mammoth steppe'. His reconstruction is
based on pollen evidence alone and the need of large
mammal populations for adequate grazing. If a biome is
de"ned as a community of plants and animals, then
Guthrie is correct that no analogue can exist because
so many of the mammals known to have inhabited
Beringia during the LGM are extinct. However, looking solely at the vegetation, analogues for the structure
and composition of the vegetation are possible. Our
macrofossil evidence, including the important evidence
from the mosses, together with the macrofossil and
Coleopteran evidence of Elias et al. (1996, 1997), and the
careful, taxonomically re"ned pollen analyses of Cwynar
(1982) demonstrate that the full-glacial vegetation
can be satisfactorily reconstructed, at least at a landscape
level (Schweger, 1982; Ritchie, 1984) using broad and
partial modern analogues, as found in diverse parts of
Beringia today.
The Kobresia-dominated vegetation on the Seward
Peninsula would have provided forage for grazing mammals, whose presence in Beringia during the full-glacial is
attested by the "nds of bones (e.g. Guthrie, 1990). Direct
evidence that large mammals ate grasses and sedges,
including Kobresia, is provided by the analyses of stomach contents of frozen mummies (Ukraintseva, 1993). The
ages of the animal fossils range through the full-glacial
period, and it is probable that the open steppe-like vegetation provided food for them and for smaller mammals
throughout this time. The relative roles of small and large
mammals in maintaining the Kobresia communities cannot be estimated, but the direct evidence of abundant
small-mammal droppings on the soil surface and the
discovery of the Microtus nest demonstrate that there was
a long-term balance between plant growth and grazing in
this ecosystem. Similar modern communities are able to
provide grazing for large animals such as Dall sheep
(Cooper, 1986), and for an often great density of small
mammals (Walker, 1990).
The full-glacial vegetation of the loess area of the
Seward Peninsula reconstructed here, almost in the
centre of Beringia, contrasts with the lowland mesic
shrub tundra reported by Elias et al. (1996, 1997) for
parts of the central Land Bridge, some of which are only
about 100 km away. The important environmental e!ects
of loess deposition may largely be responsible for the
di!erences, and point to the presence of a mosaic of
landscapes and environments across this part of Beringia
at this time, dependent on areas of loess deposition and
ground moisture.
10. Conclusions
The results of the macrofossil analyses of the samples
of in situ vegetation from a landscape that was buried
by deep tephra ca. 21,500 years ago show that the northern Seward Peninsula was covered by dry, meadow and
herb-rich tundra, often dominated by Kobresia myosuroides with a mixture of grasses, sedges, and herbs and
a continuous understorey of mosses. Prostrate shrubs
were a minor, though locally important, part of the
vegetation. Snowbeds and shallow hollows provided
damper habitats for more moisture-demanding species
assemblages. Acrocarpous mosses were an important element of the vegetation.
The vegetation seems to have no exact modern analogue, although it shares similarities with presently restricted vegetation types of dry graminoid and herb
tundra of open, arctic, and very dry habitats in Siberia
and Alaska today. The vegetation di!erences are probably caused by di!erences in the full-glacial environment.
V.G. Goetcheus, H.H. Birks / Quaternary Science Reviews 20 (2001) 135}147
Deposition of loess rich in basic cations (e.g. calcium)
played an important role in in#uencing the vegetation
composition. The occurrence of dry Kobresia- and
graminoid-dominated tundra in central upland Beringia
compared with the occurrence of mesic shrub-tundra on
the nearby lowland Land Bridge demonstrates the presence of a mosaic of landscapes and environments in
Beringia during the full-glacial period.
Acknowledgements
David Hopkins discovered the buried surface on the
Seward Peninsula, and recognized its potential value for
the reconstruction of the palaeoenvironment of fullglacial Beringia. To him we owe the greatest thanks
for originating and stimulating the work reported
here. We also thank the National Park Service and
the Centre for Global Change and Arctic System Research for funding this research, and Jeanne Schaaf
and Rich Harris of the Park Service who provided support for this project. Thanks are also due to David
Hopkins, David Murray, Mary Edwards, John Birks,
and Ken Wolf for their helpful suggestions to improve
this paper, and to Charles Schweger and Stephen Jackson for their constructive reviews of the manuscript. We
thank Jan Janssens for identifying most of the mosses,
Barbara Murray for identifying Desmatodon leucostoma,
and Hans Blom for his investigation of a small moss
community.
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