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ARCTIC
VOL. 68, N O. 2 (JUNE 2015) P. 141 – 152
http://dx.doi.org/10.14430/arctic4480
New Aspects of High-Mountain Palaeobiogeography:
A Synthesis of Data from Foreelds of Receding Glaciers and Ice Patches
in the Tärna and Kebnekaise Mountains, Swedish Lapland
Leif Kullman1 and Lisa Öberg2
(Received 25 February 2014; accepted in revised form 7 August 2014)
ABSTRACT. Recent recession of high-mountain glacier ice and perennial snow and ice patches has exposed megafossil
and macrofossil tree remnants and peat, offering a new source of Holocene high alpine vegetation history in the Scandes.
Radiocarbon dates of 90 tree megafossils from Swedish Lapland, 29 of which had not previously been published, range from
11 980 to 1950 cal yr BP. During the interval 9500 – 8500 cal yr BP, mountain birch (Betula pubescens ssp. czerepanovii) and
Scots pine (Pinus sylvestris) grew 600 – 700 m higher upslope than they do today, which is a new and remarkable discovery.
Subsequently, tree density gradually declined at higher elevations, and as the tree line moved downslope, the ratio of Betula to
Pinus increased. Tree growth ceased around 4500 cal yr BP, presumably in response to the return of perennial ice and snow.
A short episode of resumed tree growth of Betula indicates conditions warmer than present around 2000 years ago. Between
c. 8500 and 7300 cal yr BP, Picea abies, Larix sibirica, Populus tremula, Sorbus aucuparia and Alnus incana were subordinate
species on a forest oor dominated by plant species characteristic of prealpine or subalpine woodlands. Growth of trees as
much as 700 m higher upslope than today around 9500 cal yr BP implies that summer temperatures at that time may have been
3.0˚C warmer than today’s temperatures (corrected for land uplift). This inferred temperature difference between the early
Holocene and the present concurs with changes in the Earth’s orbital parameters.
Key words: glaciers; tree growth; megafossils; macrofossils; Holocene; radiocarbon dating; climate change; Swedish Scandes
RÉSUMÉ. Le recul récent de la glace de glacier, de la neige pérenne et des bancs de glace en haute montagne a permis de
découvrir des mégafossiles et des macrofossiles de restes d’arbres et de tourbe, ce qui offre une nouvelle source d’histoire de
la végétation alpine des Scandes en haute altitude pendant l’Holocène. La datation au carbone 14 de 90 mégafossiles d’arbres
en provenance de la Laponie suédoise, dont 29 n’avaient jamais fait l’objet d’une publication, donne des résultats variant
de 11 980 à 1 950 années cal. BP. Au cours de l’intervalle allant de 9 500 à 8 500 années cal. BP, le bouleau de montagne
(Betula pubescens ssp. czerepanovii) et le pin sylvestre (Pinus sylvestris) poussaient à une hauteur de 600 à 700 m plus élevée
qu’aujourd’hui, ce qui représente une découverte à la fois nouvelle et remarquable. Subséquemment, la densité des arbres a
diminué graduellement en haute altitude, et au fur et à mesure que la limite forestière s’est mise à descendre, le rapport entre
Betula et Pinus s’est accru. La croissance des arbres a cessé vers 4 500 années cal. BP, probablement en raison du retour
de la glace et de la neige pérennes. Un bref épisode de reprise de la croissance des arbres de Betula indique la présence
de conditions plus chaudes qu’à présent il y a environ 2 000 ans. Entre 8 500 et 7 300 années cal. BP environ, Picea abies,
Larix sibirica, Populus tremula, Sorbus aucuparia et Alnus incana étaient des espèces subordonnées sur une couverture morte
dominée par des espèces végétales caractéristiques de terrains boisés préalpins ou subalpins. La croissance des arbres à une
hauteur de 700 m plus élevée qu’aujourd’hui il y a environ 9 500 années cal. BP implique qu’à cette époque, les températures
estivales pouvaient être plus chaudes dans une mesure de 3,0 ˚C que les températures actuelles (donnée redressée en fonction
du soulèvement de la terre). Cette différence inférée de température entre l’Holocène précoce et le présent converge avec les
changements caractérisant les paramètres orbitaux de la Terre.
Mots clés : glaciers; croissance des arbres; mégafossiles; macrofossiles; Holocène; datation par le carbone 14; changement
climatique; Scandes suédoises
Traduit pour la revue Arctic par Nicole Giguère.
1 Corresponding author: Department of Ecology and Environmental Science, Umeå University, SE 90187 Umeå, Sweden;
leif.kullman@emg.umu.se
2 Department of Applied Science and Design, Mid Sweden University, SE 85170 Sundsvall, Sweden
© The Arctic Institute of North America
142 • L. KULLMAN and L. ÖBERG
INTRODUCTION
Megafossil tree remains preserved in low alpine peats and
lake sediments have for some decades been successfully
used for paleo tree line reconstruction (Karlén, 1976; Aas
and Faarlund, 1988; Dahl and Nesje, 1996; Kullman, 1999,
2008, 2013; Paus, 2010). However, the virtual lack of these
archives at very high elevations in the alpine zone has pre-
cluded accurate reconstruction of the highest postglacial
elevation of tree growth, which hampers detailed under-
standing of past vegetation and climate evolution.
In many parts of the world, recent glacier recession has
opened an entirely new window on the palaeoecology, veg-
etation history, and archaeology of sites at high elevations
(Dyurgerov and Meier, 2000; Farnell et al., 2004; Dove
et al., 2005; Nesje, 2009; Menounos et al., 2009; Nesje et
al., 2011; Andrews and MacKay, 2012; Callanan, 2012). In
foreelds of mountain glaciers and perennial snow and ice
patches, in most cases quite close to the tree line, exposure
of megafossil tree remnants of different species spanning
major parts of the Holocene is quite common (e.g., Nico-
lussi and Patzelt, 2000; Hormes et al., 2001; Schlüchter and
Jörin, 2004; Koch et al., 2007; Benedict et al., 2008; Joerin
et al., 2008; Wiles et al., 2008; Scapozza et al., 2010; Koe-
hler and Smith, 2011; Nicolussi and Schlüchter, 2012). In the
Swedish Scandes, reconnaissance surveys of these newly
emerging habitats have highlighted a surprising plethora of
debris wood currently being released from beneath reced-
ing perennial ice and snow bodies at unprecedented eleva-
tions high above the tree line (Kullman, 2004a; Öberg and
Kullman, 2011a; Kullman and Öberg, 2012).
Here we report and analyze the results of an intensied
search for recently exposed debris wood and peat from fore-
elds of glaciers and iceelds and snow patches in different
parts of Swedish Lapland and at very high elevations above
the tree line, presenting a comprehensive synthesis of new
and previously published data (Öberg and Kullman, 2011a;
Kullman and Öberg, 2012). The present extended sampling
effort adds to the understanding of the upper limit, general
structure, species composition of tree growth, and palaeo-
climate during earlier parts of the Holocene.
STUDY AREA
The study area includes two main areas in the prov-
ince of Lapland in the northern part of the Swedish Scan-
des: Tärna in the south and Abisko-Kebnekaise in the north
(Fig. 1). Geographical names are given in Swedish accord-Fig. 1). Geographical names are given in Swedish accord-
ing to ofcial topographic maps.
The highest peaks range between 1400 and 2100 m above
sea level (a.s.l.), while the valley oors are at 500 to 700 m
a.s.l. The bedrock is of Cambro-Silurian origin (amphibo-
lite, greenschist, and calcareous phyllite) and the Quater-
nary deposits consist of peat, till, glaciuvial, and loessic
accumulations. The climate is weakly suboceanic. More
detailed site descriptions and accounts of the physiography,
local climate, and Holocene glacier histories are provided
elsewhere (Gavelin, 1910; Svenonius, 1910; Ahlmann and
Lindblad, 1940; Schytt, 1959; Karlén, 1973; Holmlund et
al., 1996; Lindgren and Strömgren, 2001).
The general character of the foreelds fringing the gla-
ciers we focus on in this study is displayed in Figure 2.
Representative views of the investigated snow and ice patch
sites are presented by Öberg and Kullman (2011a) and Kull-
man and Öberg (2012).
The valleys and mountainsides are clad with an upper
forest rim of mountain birch (Betula pubescens ssp.
czerepanovii), with scattered specimens of Scots pine
(Pinus sylvestris) and Norway spruce (Picea abies). The
present-day (2010 – 13) local tree lines, set by Betula, Picea,
and Pinus trees more than 2 m tall (Fig. 3), are used as
modern references when calculating the magnitude of past
changes in tree-line elevation throughout the Holocene
(Appendix 1).
FIG. 1. Location of the study areas in Swedish Lapland: 1) Tärna, and 2)
Abisko/Kebnekaise.
SWEDISH LAPLAND GLACIERS AND ICE PATCHES • 143
METHODS
The surfaces of glacier foreelds were systematically
searched for megafossil tree and peat remains during the
late summer and early autumn of 2012 and 2013. Recovered
specimens were instantly wrapped in aluminum foil and
stored frozen until delivery to the dating laboratory. Only
complete and spatially well separated wood pieces were
dated. Thus, the risk of dating wood belonging to different
specimens is negligible. This kind of sampling cannot guar-
antee achievement of a perfectly true representation of tree
dates for each time; however, a large sample size may sub-
stantially reduce the uncertainty. This improved accuracy is
most relevant for the balance between pine and birch, since
birch decomposes more rapidly than pine.
Radiocarbon dating was performed by Beta Analytic
Inc., Miami (USA). Radiocarbon ages are calibrated to cal-
endar years before present (cal yr BP), with “present” = AD
1950. Dating was carried out after pretreatment with stand-
ard laboratory procedures. Calibration was conducted by
use of the INTCAL09 database (Reimer et al., 2009). In
cases when simplicity is needed (running text and Fig. 6),
the calibrated ages are quoted as the values of points where
radiocarbon ages intercept the calibration curve. We rec-
ognize that these estimates are not ideal. For the present
purpose, however, they are considered to be adequate, par-
ticularly since they provide data compatible with data from
previous studies (Öberg and Kullman, 2011a; Kullman and
Öberg, 2012). The discussion is based on the radiocarbon
time scale.
Outwashed peat cakes recovered on the foreelds were
dated on the basis of 2 cm slices of bulk peat samples. Some
of these were coarsely analyzed for the presence of mac-
roscopic tree remains, which were dated by accelerator
mass spectrometry (AMS). In some cases, macroremains
of Picea abies and understory species were dated indirectly
by the radiocarbon age of the thin peat slice in which they
were imbedded. In other cases, approximate ages of repre-
sentatives of the last-mentioned group were estimated from
dated wood samples contained in the same peat slices.
Great effort was devoted to searching alpine tundra
(lakes, soils, and mires) slightly below and above the fore-
elds here concerned for the presence of megafossils.
In most cases, the recovered megafossils had remain-
ing bark fragments or cone and leaf characteristics that
made species identication unambiguous. Some ambiguous
FIG. 2. Lower margins and foreelds of the glaciers concerned in this study. A) Tärnaglaciären, B) Kittelglaciären, C) Kårsajökeln, and D) Storglaciären.
144 • L. KULLMAN and L. ÖBERG
specimens were identied by wood anatomy analysis (Erik
Danielsson/Vedlab Inc.). Altitudes (m a.s.l.) and geographi-
cal coordinates of all retrieved tree remains were obtained
by a GPS navigator (Garmin 60CS) that was repeatedly
calibrated against distinct points on the topographical map.
Reported altitudes are rounded off to the nearest 5 m. The
nomenclature of vascular plants follows Mossberg and
Stenberg (2003).
RESULTS
General Character of Samples and Sites
The representative overview of the general character of
tree remains, peat samples, and their discovery sites provided
by Öberg and Kullman (2011a) and Kullman and Öberg
(2012) is complemented here by a few examples (Fig. 4).
Characteristically, detrital wood and peat cakes occurred
in close association with main glacier outwash streams,
originating from beneath glacier ice within a few hundred
meters of the ice fronts. Obviously, original growing sites
are still hidden by permanent ice upstream and at higher
elevations. Thus, the sampling sites represent minimum
elevations of the original growing sites. Some of the snow
and ice patches occur in relatively at terrain, indicating
that recovered megafossils are nearly in situ.
Most of the sampled wood remains were short sections
of logs, 0.2 – 0.5 m in length and 5 – 15 cm in diameter. As
a rule, they appeared to have been recently broken, often
displaying soft, rapidly disintegrating, and strongly com-
pressed wood indicative of subglacial burial and trans-
port. Usually, only fragments of the bark remained. In
some cases, macroremains of various tree species were
found as cones, bark, needles and leaf fragments embed-
ded in peat cakes with a size of 10 – 20 cm (Fig. 5). Their
rounded, somewhat compressed, and compact forms sug-
gest that they had been dislocated by streaming water from
their original growth positions, which were still covered
by ice. It is reasonable to suppose that many pieces of tree
remains were preserved in peat for some millennia prior
to the glacier inception, which further contributed to their
conservation.
In addition to wood fragments, peat cakes are regularly
recovered along the outwash streams. The small fraction of
these that have been dated range in age from 3900 to 8400
cal yr BP. As a rule, the peat contains plant macrofossils
easily identiable as common understory forest species and
tree species such as Picea abies (8450, 8380, and 8180 cal
yr BP), Larix sibirica (7320 cal yr BP), Sorbus aucuparia
(8640 cal yr BP), Alnus incana (8000 cal yr BP), and Pop-
ulus tremula (8590 cal yr BP) (Kullman and Öberg, 2012;
Appendix 1).
Chronology and Elevational Structure
In total, 90 tree remains, distributed among the seven
sampling sites, were radiocarbon-dated; ages ranged from
1950 to 11 980 cal yr BP (Appendix 1). Of these 90, 29 are
here reported for the rst time. Betula is the dominant spe-
cies (53), followed in order of abundance by Pinus sylvestris
(30), Picea abies (4), Larix sibirica (1), Populus tremula (1),
Alnus incana (1), and Sorbus aucuparia (1).
Figure 6 displays the calibrated radiocarbon ages of all
recovered birch and pine megafossils relative to their pre-
sent-day tree-line elevations in the study area. Except for
a pine remnant dated to 11 760 cal yr BP (i.e., right at the
Late Glacial/Holocene transition), no tree records originate
from the rst 2000 years of the Holocene. Around 9500 cal
yr BP, a distinct surge of pine and birch dates emerges in
the record at elevations 600 to 700 m higher than the pre-
sent-day tree lines of these species. Records from these
high relative elevations remained for about 1000 years.
Shortly after 8500 cal yr BP, an abrupt elevational dip of
approximately 200 m occurred. Thereafter, a more linear
descent of Pinus and Betula proceeded until about 4500 cal
yr BP, after which the records of pine and birch are virtu-
ally absent. During this later interval, birch appears to have
gained in dominance relative to pine. Notably, a single birch
log is dated to 1950 cal yr BP (Appendix 1, Fig. 6).
FIG. 3. The current tree line of mountain birch (Betula pubescens ssp.
czerepanovii) on the south-facing slope of Mt. Kebnetjåkka, 3.5 km southeast
of Kittelglaciären, is marked by this individual tree, growing at 910 m a.s.l.
Over the past century, the tree line has shifted 170 m upslope. Photo: 2013-
08-12.
SWEDISH LAPLAND GLACIERS AND ICE PATCHES • 145
DISCUSSION AND INTERPRETATION
High-Elevation Tree Growth and Landscape History
The virtual absence of megafossil tree records for the
rst 2000 years of the Holocene differs from the pattern
of other high-mountain parts of the Scandes, where scat-
tered trees grew during this period but exclusively at much
lower elevations relative to the present-day tree line (Kull-
man, 2002, 2013; Öberg and Kullman, 2011b). Apart from
sampling stochasticity, this feature may relate to the par-
ticular high-altitude habitats concerned here, where snow
and ice may build up quite rapidly as a consequence of
episodes with modest cooling (cf. Jansson et al., 1999),
making tree growth virtually impossible. In fact, short-
term glacier advances are inferred from this period in the
Norwegian Scandes (Nesje, 2009). Subsequently and until
the mid-Holocene, a diverse tree ora characterized gla-
cier and snow cirques without perennial ice and currently
situated several hundred meters above modern tree lines.
These results parallel the situation in the southern Swed-
ish Scandes (Öberg and Kullman, 2011a), suggesting a
more generic pattern, with a richer tree ora and wider
amplitude of Holocene tree-line and landscape change,
than is usually assumed when focusing on more traditional
palaeoarchives, such as peat bogs, soils, and lakes (e.g.,
Berglund et al., 1996; Karlén and Kuylenstierna, 1996;
FIG. 4. Megafossil tree remains sampled at different sites. A) Storglaciären, Betula pubescens 8490 cal yr BP, B) Kittelglaciären, Pinus sylvestris 9010 cal yr BP.
FIG. 5. A and B) Peat cake outwashed from Storglaciären, containing plant
macrofossils, C) Cone shell of Picea abies 8380 cal yr BP, D) Picea abies
needle 8380 cal yr BP.
A B
146 • L. KULLMAN and L. ÖBERG
Barnekow, 1999; Seppä and Birks, 2001; Bergman et al.,
2005; Mahaney and Kalm, 2012).
Tree growth 600 – 700 m above the modern tree lines
in 9500 – 8500 cal yr BP, as evidenced here for a particu-
lar type of habitat, is several hundred meters higher than
estimated for the same time interval in previous studies that
focused on low alpine terrain (e.g., Berglund et al., 1996;
Karlén and Kuylenstierna, 1996; Barnekow, 1999; Seppä
et al., 2004). Within an elevational zone 200 – 300 m below
the glacier cirques, no megafossil or macrofossil evidence
for tree growth could be found either in our study area or
in other parts of the Scandes (Kullman, 1995, 2013; Paus,
2010; Öberg and Kullman, 2011a). Thus, it appears that
between 9500 and 8500 cal yr BP, present-day glacier and
ice patch sites stood out as more or less isolated “wood
islands” in a virtually treeless landscape matrix. There-
after, these islands gradually contracted in size and began
to occur at lower elevations. In parallel, birch seems to have
gained in relative dominance, after a period when pine was
more prominent than previously presumed (e.g., Barnekow,
1999; Seppä et al., 2004).
Isolated multi-species tree islands, restricted to these
specic outlier habitats (glacier cirques) high above pre-
sent-day tree lines, may seem counterintuitive today. They
could be understood, however, primarily in light of their
particular concave (parabolic) local topography and associ-
ated climate, as suggestively illustrated by Öberg and Kull-
man (2011a). During warmer periods with less ice and snow,
sites of this character are likely to provide higher tem-
peratures, better wind shelter, and more stable soil mois-
ture than much of the surrounding and more exposed high
mountain landscape (cf. Elven, 1978; Anderson et al., 2009;
Scherrer and Körner, 2011). Some further support for the
latter contention is provided by frequent observations that
these habitats have been particularly targeted by upward
expansion of “forest species” in connection with the current
warm phase of the climate (Kullman, 2004b, 2010; Öberg
and Kullman, 2011a). With their propensity for snow accu-
mulation, these sites offer ideal preconditions for accumula-
tion of wind-driven seeds (Kullman, 1984, 2004b).
Today, tree growth of Betula reaches tree-line positions
about 200 higher than that of Pinus in the study region.
The present record provides no clear indication of whether
such a situation also prevailed during the early Holocene
within the habitats concerned here. It may appear that pine
extended somewhat higher relative to its present-day posi-
tion than did birch, i.e., the vertical separation between
birch and pine may have been smaller than it is today. How-
ever, it should be kept in mind that the present record is
somewhat fortuitous and incomplete, being composed of
wood remains that have been dislocated downslope from
their original growing sites. Thus, these samples (Fig. 6) at
best provide only a subdued view of the tree species zona-
tion pattern and the positional tree-line evolution through-
out the Holocene.
A virtually new discovery emerging from this and anal-
ogous earlier studies (Öberg and Kullman, 2011a; Kullman
and Öberg, 2012) is that during the early Holocene, high
alpine forest islands composed predominantly of birch and
pine were intermixed with scattered specimens of Picea
abies, Larix sibirica, Populus tremula, Sorbus aucuparia,
and Alnus incana. This relatively rich arboreal high moun-
tain ora is paralleled at lower elevations in the mountain
region with several warmth-demanding tree species that
currently are not growing in the region (Kullman, 2008;
Öberg and Kullman, 2011b).
The presence of Picea abies and Larix sibirica within
the interval 8500 – 7300 cal yr BP contributes to a grow-
ing recognition and insight that these species were regular
components of the high-mountain ora within the entire
extent of the Scandes, from south to north, during the early
Holocene and late Weichselian (Kullman, 2002, 2008;
Paus, 2010, 2013; Öberg and Kullman, 2011b; Paus et al.,
2011; Carcaillet et al., 2012). These features were previously
entirely undetected by traditional pollen analysis (cf. Elven
et al., 2013). Obviously, a much higher non-analogue biodi-
versity prevailed during the early Holocene than has ever
been supposed for high-mountain regions.
Given the rich tree ora in isolated high alpine habi-
tats during the early Holocene, when lower reaches of the
mountain valleys were still ice-covered (e.g., Kullman,
1995; Barnekow, 1999), it is reasonable to assume that
such populations have functioned as dispersal nodes for
downslope afforestation of the high-mountain landscape
(cf. Allen and Huntley, 1999; Kullman, 2002; Kullman and
Kjällgren, 2006; Carcaillet et al., 2012). This aspect adds
to the current discourse concerning the role of small out-
lier populations for understanding past, present, and future
arboreal biogeography (e.g., Feurdean et al., 2013).
Aspects on Glacier and Climate History
The striking and rapid surge of warming-induced
growth of Pinus and Betula at their highest Holocene levels
during 9500 – 8500 cal yr BP appears to be a common pat-
tern for the entire Scandes (Aas and Faarlund, 1988; Bjune
et al., 2005; Eide et al., 2006; Paus, 2010). Apparently, this
FIG. 6. Radiocarbon dates (intercept values) and corresponding elevations
of all birch (green) and pine (yellow) remnants, relative to their present-day
tree-line positions.
SWEDISH LAPLAND GLACIERS AND ICE PATCHES • 147
widespread phenomenon represents a release from the so-
called Erdalen 2 Event (10 100 to 9700 cal yr BP), which
was characterized by distinct cooling and major glacier
advance (Nesje et al., 1991; Dahl and Nesje, 1996).
The tight clustering of our dated tree remains suggests
that at the end of this period of rapid tree growth, the gla-
ciers and ice patches we are concerned with here did not
exist, or were much smaller than they are today, in response
to warmer-than-present summers. This situation prevailed
throughout most (or all) of the period 9530 – 4480 cal yr
BP, as inferred also in other studies in Scandinavia (e.g.,
Rosqvist and Østrem, 1989; Bakke et al., 2005; Nesje et al.,
2008; Öberg and Kullman, 2011a). It is reasonable to con-
clude that this circumstance reects a hemispheric climatic
situation related to higher-than-present insolation levels,
forced largely by the Earth’s orbital variations (Ekholm,
1901; Berger and Loutre, 1991). Obviously, this mechanism
has been the ultimate driver of a climate progressively more
amenable to glacier expansion throughout the Holocene.
Little support remains for repeated major glacier advances
and retreats during this period (e.g., Karlén and Kuylensti-
erna, 1996), as concluded in several other studies (e.g., Ber-
glund et al., 1996; Nesje, 2009).
The youngest peat date (3890 cal yr BP) constrains the
continuous “tree period” and approximates the inception of
perennial snow and glacier ice, which buried the last living
trees and further sealed with ice those peat repositories that
contained megafossils from earlier parts of the Holocene.
This inference agrees with several studies indicating a dis-
tinct shift to cooler and more snow rich conditions (Neogla-
ciation) around that time (e.g., Karlén, 1976; Caseldine and
Matthews, 1987; Snowball and Sandgren, 1996; Bergman et
al., 2005; Paus, 2010; Kullman, 2013).
Notably, a single medium-sized birch log was recovered
close to the lower, present-day front of the Kårsajökel and
140 m above the modern birch tree line (Fig. 4). Its date
of 1950 cal yr BP indicates that, at that time, the glacier
was more contracted upslope than at present and by infer-
ence, that this log may tentatively point to a period warmer
than the present. In fact, this contention is supported by a
reported nding near a glacier in SW Norway of a subfossil
birch log, also located 140 m above the present tree line, and
dating to about 2000 cal yr BP (Nesje et al., 1991). Futher-
more, an Icelandic glacier has released a birch log originat-
ing from virtually the same time (Ives, 1991). In line with
these ndings, several other climate proxies from northern
Europe indicate warmer-than-present conditions in the rst
decades of the Roman Empire (e.g., Hormes et al., 2004;
Ljungqvist, 2009; Humlum et al., 2011; Esper et al., 2012;
Kullman, 2013; Luetscher et al., 2013). Moreover, the dis-
covery of this birch log adds to the insight that present-day
glacier recession and associated warming are not unique
phenomena during the past 4500 years (cf. Kullman, 2013).
If we assume that the tree line and tree-line change relate
primarily to summer temperature (e.g., Körner and Paulsen,
2004; Holtmeier and Broll, 2005), former tree-line positions
may be used as proxy indicators of paleoclimate history
(cf. Karlén 1976; Tinner and Kaltenrieder, 2005; Kirdy-
anov et al., 2012; Kullman, 2013), drawing on a conven-
tional temperature lapse rate of 0.6˚C per 100 m in elevation
(Laaksonen, 1976). Given these assumptions, the Holo-
cene tree-line peaks, at 9500 cal yr BP and about 700 m
higher than present, may imply summer temperatures 4.2˚C
warmer than the rst decade of the present century. This is
a minimum difference, since most megafossils are down-
washed from elevations higher than their sampling sites.
As a consequence, the temporal record of dated megafossil
tree remains provides only a weak impression of long-term
summer temperature variations.
To some extent, the emerging evidence of multi-species
early Holocene tree growth at unprecedented high eleva-
tions relates to substantial glacio-isostatic uplift throughout
the Holocene. Since about 9500 cal yr BP, the land surface
in western Lapland has been lifted by at least 200 m (e.g.,
Möller, 1987; Svensson, 1991; Påsse and Andersson, 2005).
Thus, the total tree-line lowering attributable to general
climate forcing should be reduced to 500 m (700 minus
200), which reduces the inferred change in summer tem-
perature from 9500 cal yr BP to the present to 3.0˚C. This
lower estimate matches theoretical calculations based
on insolation variations in response to the Earth’s orbital
changes (cf. Berger and Loutre, 1991; Esper et al., 2012) and
compares well with multi-proxy reconstructions from adja-
cent parts of northern Lapland (Shemesh et al., 2001; Bigler
et al., 2003).
Despite the reservations and uncertainties outlined
above, there is little doubt that the Holocene thermal opti-
mum for the Scandes occurred in the earliest part of the
Holocene, which concurs with multi-proxy inferences from
other parts of Europe and Greenland (e.g., Paus, 2013; Luoto
et al., 2014). Other studies suggest a substantially later ther-
mal optimum (e.g., Berglund et al., 1996; Seppä and Birks,
2001). However, these reconstructions are based on pollen
analysis, an approach that is considered to provide less reli-
able temperature estimates (Paus, 2013; Elven et al., 2013).
The present study has provided a new and virtually
unexpected view of the general structure and species com-
position of the high-mountain landscape in northern Swe-
den during the Holocene. The methodological approach
depends entirely on rapid melting of perennial ice and snow
bodies, which makes them sensitive to annual weather
anomalies. Continued research and extensive eld invento-
ries urgently need to be implemented in order to gain even
more information from these rich sources concerning the
structure and species composition of the living mountain
landscape in the past.
ACKNOWLEDGEMENTS
This study was funded by a grant (to Leif Kullman) from the
Göran Gustafsson Foundation. We appreciate comments on the
manuscript by Atle Nesje and two anonymous reviewers.
148 • L. KULLMAN and L. ÖBERG
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APPENDIX 1. Radiocarbon dates of tree remains. Lab. codes marked with an asterisk (*) denote AMS dates. “Relative elevation”
refers to the difference in altitude between the sampling site and the nearest tree line of the concerned species. Source: 1 – Öberg and
Kullman, 2011a; 2 – Kullman and Öberg, 2013; 3 – this study.
Radio- Calibrated Sample
Relative Altitude carbon 1δ range Intercept size
Locality ˚N lat. ˚E long. elevation (m a.s.l.) Species Lab. code age (14C yr BP) (cal yr BP) (cm) Source
Tärnaglaciären 6550945 1516728 270 1070 Betula pubescens Beta-284450 5430 ± 60 6290 – 6190 6280 18 × 7 1
Tärnaglaciären 6558916 1516681 270 1070 Betula pubescens Beta-284449 4850 ± 50 5610 – 5580 5590 20 × 8 1
Tärnaglaciären 6550945 1516661 270 1070 Betula pubescens Beta-284455 5240 ± 50 6100 – 5930 5990 5 × 4 1
Tärnaglaciären 6550910 1516734 265 1065 Betula pubescens Beta-268653 5880 ± 60 6750 – 6650 6680 17 × 7 1
Tärnaglaciären 6550913 1516724 260 1060 Betula pubescens Beta-268654 6220 ± 60 7240 – 7020 7160 19 × 8 1
Tärnaglaciären 6550875 1517653 225 1025 Betula pubescens Beta-264395 5990 ± 70 6920 – 6740 6820 13 × 6 1
Tärnaglaciären 6550927 1516654 275 1075 Betula pubescens Beta-284467 4020 ± 50 4530 – 4420 4480 15 × 7 1
Tärnaglaciären 6550896 1516761 270 1070 Betula pubescens Beta-284447 4950 ± 50 5730 – 5610 5660 30 × 11 1
Tärnaglaciären 6550824 1516843 285 1085 Pinus sylvestris Beta-284448 8110 ± 40 9030 – 9010 9020 50 × 12 1
Tärnaglaciären 6550937 1516648 270 1070 Pinus sylvestris Beta-284453 5110 ± 50 5920 – 5760 5900 10 × 3 1
Tärnaglaciären 6550950 1516700 260 1060 Pinus sylvestris Beta-284454 7330 ± 60 8190 – 8040 8170 45 × 14 1
Tärnaglaciären 6550947 1516834 270 1070 Pinus sylvestris Beta-264394 8520 ± 70 9540 – 9480 9530 35 × 10 1
Tärnaglaciären 6550913 1516724 265 1065 Pinus sylvestris Beta-268655 7600 ± 60 8420 – 8370 8400 40 × 11 1
Tärnaglaciären 6550942 1516650 270 1070 Betula pubescens Beta-362589 5440 ± 40 6290 – 6210 6280 12 × 7 3
Tärnaglaciären 6550913 1516658 265 1065 Betula pubescens Beta-362590 7710 ± 40 8540 – 8430 8485 10 × 5 3
Tärnaglaciären 6550936 1516672 265 1065 Betula pubescens Beta-362591 8160 ± 40 9130 – 9020 9060 8 × 4 3
Tärnaglaciären 6550927 1516680 265 1065 Betula pubescens Beta-362592 8070 ± 40 9020 – 9000 9010 22 × 5 3
Tärnaglaciären 6550910 1516677 270 1070 Pinus sylvestris Beta-362585 8170 ± 40 9130 – 9030 9090 42 × 11 3
Tärnaglaciären 6550951 1516654 265 1065 Pinus sylvestris Beta-358468 4370 ± 30 4970 – 4870 4915 43 × 6 3
Tärnaglaciären 6550918 1516659 265 1065 Pinus sylvestris Beta-362587 5260 ± 40 6170 – 5940 5990 20 × 5 3
Tärnaglaciären 6550923 1516656 265 1065 Pinus sylvestris Beta-362588 6190 ± 30 7160 – 7020 7160 12 × 8 3
Östra Syterglaciären 6553748 1516984 390 1190 Betula pubescens Beta-284469 8080 ± 70 9030 – 8990 9010 29 × 6 1
Murtserglaciären 6550654 1514291 555 1355 Betula pubescens Beta-332297 7980 ± 40 8990 – 8770 8885 35 × 8 2
Murtserglaciären 6550779 1514605 625 1425 Betula pubescens Beta-332288 8230 ± 40 9280 – 9130 9195 30 × 8 2
Murtserglaciären 6550727 1515561 500 1300 Betula pubescens Beta-332283 7660 ± 40 8450 – 8410 8420 11 × 5 2
Murtserglaciären 6550576 1514882 520 1210 Pinus sylvestris Beta-332287 8220 ± 40 9270 – 9120 9190 40 × 10 2
152 • L. KULLMAN and L. ÖBERG
Radio- Calibrated Sample
Relative Altitude carbon 1δ range Intercept size
Locality ˚N lat. ˚E long. elevation (m a.s.l.) Species Lab. code age (14C yr BP) (cal yr BP) (cm) Source
Murtserglaciären 6550527 1514787 515 1205 Pinus sylvestris Beta-332286 7910 ± 40 8770 – 8630 8675 13 × 5 2
Murtsernjuone 6550546 1513613 350 1150 Betula pubescens Beta-332290 7200 ± 40 8020 – 7970 8010 20 × 5 2
Murtsernjuone 6550387 1513589 285 1085 Betula pubescens Beta-322281 4640 ± 30 5450 – 5320 5380 12 × 5 2
Murtsernjuone 6550563 1513588 470 1160 Pinus sylvestris Beta-332280 7140 ± 40 8000 – 7940 7960 18 × 7 2
Murtsergure 6549623 1516427 355 1155 Betula pubescens Beta-332298 5300 ± 40 6180 – 6990 6095 30 × 7 2
Murtsergure 6549626 1516493 350 1150 Betula pubescens Beta-332295 7770 ± 40 8590 – 8520 8550 40 × 8 2
Murtsergure 6549606 1516568 330 1130 Betula pubescens Beta-332294 7740 ± 40 8580 – 8570 8540 15 × 13 2
Murtsergure 6549675 1516180 375 1175 Betula pubescens Beta-332292 6130 ± 40 7150 – 6950 7000 50 × 9 2
Murtsergure 6549590 1516568 330 1130 Betula pubescens Beta-332285 7340 ± 30 8180 – 8160 8170 30 × 6 2
Murtsergure 6549622 1516430 460 1150 Pinus sylvestris Beta-332296 8110 ± 40 9070 – 9010 9020 50 × 8 2
Murtsergure 6549605 1516672 425 1115 Pinus sylvestris Beta-332293 5980 ± 30 6860 – 6760 6800 45 × 8 2
Murtsergure 6549590 1516400 460 1150 Pinus sylvestris Beta-332282 7670 ± 40 8510 – 8410 8430 40 × 8 2
Kårsajökeln 6821610 1821096 80 930 Betula pubescens Beta- 250909 6130 ± 60 7160 – 6940 7000 40 × 7 1
Kårsajökeln 6821726 1820156 130 980 Betula pubescens Beta-250917 7920 ± 50 8960 – 8630 8710 60 × 9 1
Kårsajökeln 6821744 1819853 140 990 Betula pubescens Beta-264383 8160 ± 90 9260 – 9010 9060 30 × 12 1
Kårsajökeln 6821731 1820152 135 985 Betula pubescens Beta-264385 7250 ± 60 8160 – 8000 8030 18 × 7 1
Kårsajökeln 6821628 1820292 165 965 Betula pubescens Beta-264386 8290 ± 70 9420 – 9140 9290 20 × 8 1
Kårsajökeln 6821744 1819885 155 955 Pinus sylvestris Beta-250906 10130 ± 60 11980 – 11680 11760 30 × 8 1
Kårsajökeln 6821771 1819969 140 940 Pinus sylvestris Beta-250914 8270 ± 60 9400 – 9130 9280 30 × 12 1
Kårsajökeln 6821735 1819882 190 990 Pinus sylvestris Beta-264384 5980 ± 50 6890 – 6740 6790 40 × 15 1
Kårsajökeln 6821629 1820316 150 950 Pinus sylvestris Beta-264387 6130 ± 60 7160 – 6940 7000 7 × 4 1
Kårsajökeln 6821657 1820531 145 945 Pinus sylvestris Beta-264388 8250 ± 60 9380 – 9120 9260 15 × 5 1
Kårsajökeln 6821728 1819883 140 990 Betula pubescens Beta-362594 2020 ± 30 1990 – 1900 1950 15 × 6 3
Kårsajökeln 6821794 1819797 150 1000 Betula pubescens Beta-362596 7000 ± 40 7940 – 7730 7840 8 × 4 3
Kårsajökeln 6821680 1820065 445 965 Pinus sylvestris Beta-362593 8240 ± 40 9250 – 9150 9200 9 × 4 3
Kårsajökeln 6821714 1819868 470 990 Pinus sylvestris Beta-362595 7800 ± 40 8600 – 8550 8590 11 × 7 3
Slåttatjåkka 6821886 1841110 175 1025 Betula pubescens Beta-284457 4760 ± 50 5590 – 5460 5530 45 × 7 1
Slåttatjåkka 6821930 1841297 165 1015 Betula pubescens Beta-284458 6900 ± 60 7790 – 7670 7700 13 × 6 1
Slåttatjåkka 6821891 1841131 180 1030 Betula pubescens Beta-264392 8210 ± 70 9290 – 9030 9130 30 × 8 1
Slåttatjåkka 6821888 1841128 180 1030 Betula pubescens Beta-264391 8510 ± 70 9540 – 9480 9520 31 × 5 1
Slåttatjåkka 6821887 1841126 180 1030 Pinus sylvestris Beta-264390 8380 ± 80 9480 – 9300 9440 14 × 7 1
Slåttatjåkka 6821861 1841293 155 1005 Pinus sylvestris Beta-284456 7690 ± 50 8540 – 8420 8450 53 × 10 1
Slåttatjåkka 6821474 1841305 240 1090 Pinus sylvestris Beta-284461 7710 ± 70 8570 – 8420 8490 40 × 10 1
Kärkerieppe 6823189 1818025 370 1050 Betula pubescens Beta-284459 6090 ± 60 7140 – 6890 6950 18 × 7 1
Kärkerieppe 6823099 1817956 380 1060 Betula pubescens Beta-284460 4600 ± 50 5440 – 5300 5310 17 × 6 1
Kåppasglaciären 6821807 1834763 155 1025 Betula pubescens Beta-284462 6100 ± 60 7150 – 6900 6980 50 × 12 1
Kåppasglaciären 6821833 1834819 145 1015 Betula pubescens Beta-284463 3900 ± 60 4420 – 4240 4400 12 × 5 1
Kåppasglaciären 6821841 1834883 145 1015 Betula pubescens Beta-284465 4270 ± 50 4860 – 4830 4840 13 × 6 1
Kåppasglaciären 6821808 1824764 160 1030 Pinus sylvestris Beta-284464 6870 ± 60 7750 – 7660 7680 30 × 10 1
Låktatjåkka 6824603 1832415 295 975 Betula pubescens Beta-284472 5040 ± 60 5900 – 5710 5800 18 × 8 1
Låktatjåkka 6824590 1832372 300 980 Pinus sylvestris Beta-284471 8020 ± 70 9010 – 8770 8990 36 × 10 1
Kittelglaciären 6752996 1831010 320 1230 Betula pubescens Beta-358470 6760 ± 30 7620 – 7580 7610 30 × 9 3
Kittelglaciären 6753058 1830952 330 1240 Betula pubescens Beta-358475 8470 ± 40 9520 – 9470 9490 14 × 7 3
Kittelglaciären 6752971 1831002 300 1210 Betula pubescens Beta-358477 7310 ± 40 8180 – 8040 8160 13 × 8 3
Kittelglaciären 6752885 1831099 285 1195 Betula pubescens Beta-358478 7690 ± 40 8540 – 8420 8450 10 × 7 3
Kittelglaciären 6752885 1831099 285 1195 Betula pubescens Beta358684 7830 ± 40 8630 – 8590 8600 18 × 9 3
Kittelglaciären 6752885 1831099 285 1195 Betula pubescens Beta-358479 7920 ± 40 8930 – 8640 8720 21 × 7 3
Kittelglaciären 6753063 1830944 295 1205 Betula pubescens Beta-362592 8070 ± 40 9020 – 9000 9010 16 × 6 3
Kittelglaciären 6753038 1831019 330 1240 Betula pubescens Beta-358472 6040 ± 30 6940 – 6810 6890 14 × 8 3
Kittelglaciären 6753065 1830974 330 1240 Betula pubescens Beta-358473 5880 ± 30 6740 – 6670 6695 19 × 7 3
Kittelglaciären 6753066 1830945 655 1205 Pinus sylvestris Beta-358469 8050 ± 40 9010 – 8990 9000 23 × 8 3
Kittelglaciären 6753002 1831012 680 1230 Pinus sylvestris Beta-358471 7800 ± 40 8600 – 8550 8590 18 × 8 3
Kittelglaciären 6753066 1830945 655 1205 Pinus sylvestris Beta-358469 8050 ± 40 9010 – 8990 9000 12 × 5 3
Kittelglaciären 6753046 1831268 690 1240 Pinus sylvestris Beta-358474 8080 ± 40 9020 – 9000 9010 13 × 5 3
Storglaciären 6754189 1836540 205 1115 Betula pubescens Beta-358480 5650 ± 30 6430 – 6410 6420 15 × 7 3
Storglaciären 6754285 1836708 190 1100 Betula pubescens Beta-358690 7720 ± 40 8550 – 8430 8490 14 × 6 3
Storglaciären 6754205 1836701 195 1105 Betula pubescens Beta-358483 6110 ± 30 7000 – 6940 6980 19 × 8 3
Murtserglaciären 6550585 1514774 515 1225 Picea abies Beta-332275* 7360 ± 40 8190 – 8170 8180 Cone 2
Murtsernjuone 6550563 1513588 515 1160 Picea abies Beta-332274* 7690 ± 40 8540 – 8420 8450 Cone 2
Storglaciären 6754287 183670 555 1105 Picea abies Beta-366360* 7650 ± 40 8420 – 8340 8380 Cone shell 3
Murtsergure 6549599 1516574 510 1125 Larix sibirica Beta-332277* 6410 ± 30 7420 – 7310 7320 Cone 2
Murtsergure 6549599 1516574 1125 395 Alnus incana Beta-332278* 7280 ± 40 8170 – 8020 8000 Leaf 2
Murtsergure 6549625 1516669 1115 465 Populus tremula Beta 332276* 7790 ± 40 8600 – 8540 8590 Leaf 2
Murtsergure 6549599 1516574 1125 345 Sorbus aucuparia Beta-332279* 7890 ± 40 8750 – 8600 8640 Leaf 2
Tärnaglaciären 6550927 1516654 1075 Peat Beta-268652* 3590 ± 50 3970 – 3840 3890 13 × 11 1
Murtsergure 6549565 1516591 1115 Peat Beta-322289* 4500 ± 40 5300 – 5050 5175 15 × 15 2
Kittelglaciären 6757899 1830978 1230 Peat Beta-366365* 4650 ± 30 5340 – 5310 5380 14 × 14 3
Storglaciären 6754287 1836700 1105 Peat Beta-366360* 7650 ± 40 8420 – 8340 8380 17 × 12 3
Kårsajökeln 6821644 1820126 982 Peat Beta-366362* 6980 ± 40 7880 – 7700 7830 12 × 10 3
