Mt. Åreskutan Nunatak: An Arboreal "Roadmap" to the Paleobiogeograpy of the Swedish Scandes and a Possible Pointer Towards a Future Revival of a Richer and More Biodiverse Mountainscape

Abstract

In the context of proposed future anthropogenic climate warming, the present study accounts for arboreal responses to recent temperature rise, viewed in the perspective of Lateglacial and early Holocene climate and ecosystem variability. As an analogue to a future warmer world, the focus is on an early deglaciated nunatak in the southern Swedish Scandes, Mt. Åreskutan, with a well-researched arboreal history, embracing periods of climate warming of present-day extent. New research from this and adjacent localities challenges traditional historical narratives, which fail to provide a true picture of deglaciation and vegetation history. It is increasingly evident that common boreal tree species grew close to this summit in a climate, 2-3 °C warmer than at present, during the Lateglacial and early Holocene periods 16 800-6000 years ago. Based on minimal temperature requirements for tree growth, future warming of the same magnitude would be sufficient for trees to reclaim their lost ground close to this peak. Recent observations of tree saplings and the emergence of genuine "forest plants" at these high elevations, indicate that dispersal mechanisms will not constrain this progressive process. Conceivably, it will not manifest as advancement of a broad forest front. History suggests that pockets of trees, with a ground cover of boreal plant species, will establish in local favourable niches, e. g. sites of vanished glaciers and perennial snow beds. Much of the present-day alpine tundra may be more conservative and resilient to tree invasion, as evident from insignificant upslope movement of forest limits in response to modern climate warming. By and large, continued warming is no imminent threat to alpine biodiversity. An open and diverse high-mountain landscape is likely to prevail.

Full text

European Journal of Applied Sciences – Vol. 12, No. 1
Publication Date: February 25, 2024
DOI:10.14738/aivp.121.16320
Kullman, L., & Öberg, L. (2024). Mt. Åreskutan Nunatak: An Arboreal “Roadmap” to the Paleobiogeograpy of the Swedish Scandes
and a Possible Pointer Towards a Future Revival of a Richer and More Biodiverse Mountainscape. European Journal of Applied
Sciences, Vol - 12(1). 219-242.
Services for Science and Education – United Kingdom
Mt. Åreskutan Nunatak: An Arboreal “Roadmap” to the
Paleobiogeograpy of the Swedish Scandes and a Possible
Pointer Towards a Future Revival of a Richer and More
Biodiverse Mountainscape
Leif Kullman
Department of Ecology and Environmental Science
Umeå University, SE-901 87 Umeå, Sweden
Lisa Öberg
oldTjikko Photo Art & Science
Handöl 544, SE-837 71 Duved, Sweden
ABSTRACT
In the context of proposed future anthropogenic climate warming, the present
study accounts for arboreal responses to recent temperature rise, viewed in the
perspective of Lateglacial and early Holocene climate and ecosystem variability. As
an analogue to a future warmer world, the focus is on an early deglaciated nunatak
in the southern Swedish Scandes, Mt. Åreskutan, with a well-researched arboreal
history, embracing periods of climate warming of present-day extent. New research
from this and adjacent localities challenges traditional historical narratives, which
fail to provide a true picture of deglaciation and vegetation history. It is increasingly
evident that common boreal tree species grew close to this summit in a climate, 2-3
°C warmer than at present, during the Lateglacial and early Holocene periods
16 800- 6000 years ago. Based on minimal temperature requirements for tree
growth, future warming of the same magnitude would be sufficient for trees to
reclaim their lost ground close to this peak. Recent observations of tree saplings
and the emergence of genuine “forest plants” at these high elevations, indicate that
dispersal mechanisms will not constrain this progressive process. Conceivably, it
will not manifest as advancement of a broad forest front. History suggests that
pockets of trees, with a ground cover of boreal plant species, will establish in local
favourable niches, e. g. sites of vanished glaciers and perennial snow beds. Much of
the present-day alpine tundra may be more conservative and resilient to tree
invasion, as evident from insignificant upslope movement of forest limits in
response to modern climate warming. By and large, continued warming is no
imminent threat to alpine biodiversity. An open and diverse high-mountain
landscape is likely to prevail.
Keywords: Treeline, nunatak, climate change, megafossils, paleobiogeography, Holocene,
Swedish Scandes

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INTRODUCTION
Global warming since more the 100 years is a meteorological reality, particularly amplified in
northern and high-altitude regions already by the 1920s -1930s. This course of change is
associated with large and predominantly progressive repercussions for biota, physical
landscape and human society. However, the common and widespread perception of this
development is that it represents a serious and imminent threat to man and planet Earth. This
alarmistic and dystopic view is purported to the public and media by the prestigious
International Council of Climate Change (IPCC) and its followers, which downgrade natural
climate history and rely more on immature and unvalidated numerical models. The latter fail
to reproduce recurrent natural climate changes in the long-term past (e.g., Karlén 1988;
Hormes et al. 2001; Bengtsson et al. 2004) and to deliver reliable and useful climate
projections for the future. In fact, modern warming is within natural Holocene climate
variability (Vinós 2022).
Alpine and subalpine regions are supposed to display early signal and account of
profound geoecological and phytogeographical changes attributable to putative
anthropogenic and unprecedented climate warming (Moen et al. 2004; ACIA 2005; Kaplan &
New 2006; Gottfried et al. 2012). This alarmistic climate view has prompted some scientists to
ventilate doubt as to the realism and strength of these model projections, often based on
“worst-case” climate change scenarios and neglecting robust paleoperspectives on climate
and vegetation (cf. Idso 1998; Bengtsson, Semenov & Johannessen 2004; Walther, Beissner
& Burga 2005; Karlén, 2008; Ljungqvist 2009: Humlum et al. 2011; Hausfather & Peters
2020).
With this general background, our objective is to provide the best available view of past and
recent climate-driven landscape change in the high-altitude Swedish Scandes and to
complement projective biogeographic models with robust observational and paleecological
data. As focus object, we chose Mt. Åreskutan, an iconic object in Scandinavian paleogeograhy,
also displaying detailed data on arboreal and general vegetation responses to recent climate
change (Kullman 2002a, b). In addition, an independent model has projected the future
treeline rise by 600 m, in the case of a 3 °C warming, on this specific mountain (Boer et al.
1990).
Moreover, Mt. Åreskutan has been in the centre of a controversy concerning the date of
deglaciation and late-glacial arboreal performance. Kullman (2000, 2002) presented robust
megafossil data, showing unequivocal presence of mountain birch (Betula pubescens ssp.
czerepanovii), spruce (Picea abies) and pine (Pinus sylvestris), as early as about 16 000 cal. a
BP, close to the summit 300-400 m higher than present-day treelines. This is about 6000 and
more years earlier than previous estimates of local deglaciation. These megafossil
dates also represent the first presence of tree growth in the Scandes, in conflict with
inferences by less precise methods, e.g., pollen analysis and terrestrial cosmogenic
nuclide (TCN) analysis (Tallantire 1977; Kleman et al. 1997; Johnsen 2010; Stroeven et al.
2016).
Not surprisingly, these new and unorthodox results were heavily attacked by defenders of the
old paradigm with the simple and negative argument that they deviated from established

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Kullman, L., & Öberg, L. (2024). Mt. Åreskutan Nunatak: An Arboreal “Roadmap” to the Paleobiogeograpy of the Swedish Scandes and a Possible
Pointer Towards a Future Revival of a Richer and More Biodiverse Mountainscape. European Journal of Applied Sciences, Vol - 12(1). 219-242.
URL: http://dx.doi.org/10.14738/aivp.121.16320
truth (Birks, Larsen & Birks 2005, 2006; Johnsen 2010). These opinions were viewed in a
wider perspective and refuted by some authors (Kullman 2005, 2006, 2008; Parducci et al.
2012; Nota, Klaminder, Milesi 2022). To make doubly likely, late-glacial tree remains have
been recovered at widely distributed sites along the Swedish Scandes (Kullman 2002a, 2017b;
Öberg & Kullman 2011; Kullman & Öberg 2015, 2020). Taken together, these paleo-arboreal
results, based on megafossils, provide profound implications for the comprehension of
Lateglacial climate and paleogeography of the Scandes. In addition, the precision of some
traditional paleoenvironmental research approaches and biogeographical histories are
challenged in general. It needs to be realized that positive records of megafossils do
trump most other approaches concerning presence of species and deglaciation (cf. Paus
& Haugland 2017; Kullman 2018b; Odland & Paus 2021). The presented early dates of
arboreal presence represent a “roadmap” of fixed points, that future students of high-
mountain paleogeography have to relate to. The main objective of the present study is to add
detail to previous late-glacial records of megafossil tree remnants, recovered at high
elevations on Mt. Åreskutan (Kullman 2002a, b) and questioned by some authors (see above).
In analogy, and based on these data, the likely course of change in a putative warmer future
climate will be tentatively outlined. For that purpose, recent trends in treeline positions and
plant cover in general are highlighted and considered.
Radiocarbon dates are given as calibrated years BP (cal. a BP; present1950 calibrated in CALIB
8.20 (Stuiver et al. 2021) using the Intcal20 data set (Reimer et al. 2020). In the text, the
intercept values of radiocarbon age with the calibration curve are used for simplicity. Original
data are derived from Kullman (2002).
STUDY AREA
Mt. Åreskutan (1420 m a.s.l.), is an isolated massif, located somewhat to the east of the main
Scandes mountain change in central Sweden, 63° 26´N, 13° 06´E (Fig.1). The relief, built by
schists and highly fissured Seve amphibolite, is alpine in its upper parts. Adjacent valley
bottoms are about 1000 m below the summit. Proximity to the Norwegian Sea and low passes
to the west support a local maritime and humid macroclimate (Raab & Vedin 1995). The nearest
official weather station Storlien/Visjövalen (642 m a.s.l.) displays mean temperatures
(1991-2020) for the summer and winter periods; June-August, December-February and the
year, 12.3, -5.5 and 2.0 °C, respectively. During the years 1980-1998 an automatic weather
station was operated about 1 km to the west of the main study site, 1280 m a.s.l. Mean
temperatures for June-August, December-February and the year were 5.8, -8.2 and -2.2 °C,
respectively. The last-mentioned figures match temperatures extrapolated from the Storlien/
Visjövalen station and a lapse rate of 0.6 °C per 100 m altitude (Laaksonen 1976). Summer
(J.J.A.) and winter (D.J.F.) temperature evolution 1901-2023 displays regional warming by 1.4
°C and 1.9 °C, respectively (Kullman & Öberg 2023). Here concerned megafossils were
retrieved from a site, close to the summit, 1360-1370 m a.s.l. This locality is a flat surface at the
base of a steep south-facing slope, characterized as a minor glacier/ice patch cirque
(Borgström 1989). A rock wall provides protection from prevailing westerly winds and
enables accumulation of a huge and late-lying snowdrift, occupying a topographic niche in the
steep slope (1360-1400 m a.s.l.), and adjacent parts of the flat area below (Figs. 2-4). At the
present time, snow prevails here well into mid-July or early August. The melting snow feeds
two small pools, interconnected by a wet moss carpet area, predominantly, Warnstorfia

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tundrae (Arnell) Loeske). Conceivably, this feature is a primary successional response to
earlier melt out over the past 100 years. A block rampart indicates a larger extension
of the snowpack in the past (Fig. 5). Most on the megafossils originate from beneath this
moss layer and its transition into the slope above, right at the mid-summer melting front. The
snow patch was described by Hartman (1814), who retells traditions from the
local population, that this snow patch had existed for centuries. A later geologist
(Högbom 1897), found that this was one of largest and most conspicuous snow patches in
the region. Tentatively, he discusses the possibility of a local glacier located here in the
past (cf. also Enquist 1910). That option had been dismissed by Hartman (1814).
Figure 1: Upper. Location of the study site, Mt. Åreskutan, close to the border between
Sweden and Norway. Lower. Winter view of Mt. Åreskutan.

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Kullman, L., & Öberg, L. (2024). Mt. Åreskutan Nunatak: An Arboreal “Roadmap” to the Paleobiogeograpy of the Swedish Scandes and a Possible
Pointer Towards a Future Revival of a Richer and More Biodiverse Mountainscape. European Journal of Applied Sciences, Vol - 12(1). 219-242.
URL: http://dx.doi.org/10.14738/aivp.121.16320
Figure 2: The snow patch cirque and the plain moss-covered area below, with a carpet of
Warnstorfia tundrae. Many megafossils were preserved beneath this cover, fed by meltwater
from the snow accumulating cirque above, and subjected to primary succession following
earlier melt-out over the past 100 years. Photo: 2010-09-09.
Figure 3: Overview of the main study site with the two small pools and the intervening moss -
covered area in the centre (1360 m a.s.l.). In the background a steep ridge protects from
predominant westerly winds and enables the accumulation of late-lying snow, that has
promoted the long-term preservation of tree remnants growing somewhat upslope. Photo:
2013-08-30.

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Figure 4: This has been the modal mid-summer situation of the snow-accumulation cirque
during the last century, where a majority of the recovered megafossils are supposed to have
grown. Photo: 2018-07-18.
Figure 5: At the end of most recent summers, the snow in the cirque has disappeared
completely. The block rampart in the foreground indicates a former larger extent and longer
seasonal persistence of the snow patch, which may also be inferred from lack of lichen cover in
the centre. Photo: 2023-09-14.

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Kullman, L., & Öberg, L. (2024). Mt. Åreskutan Nunatak: An Arboreal “Roadmap” to the Paleobiogeograpy of the Swedish Scandes and a Possible
Pointer Towards a Future Revival of a Richer and More Biodiverse Mountainscape. European Journal of Applied Sciences, Vol - 12(1). 219-242.
URL: http://dx.doi.org/10.14738/aivp.121.16320
Figure 6: The summer of 2012 was relatively cold and ice and snow did not disappear
completely, providing a faint hint of prevailing conditions during the” Little Ice Age”, prior to
the modern warming phase. Photo: 2012-09-16.
MEGAFOSSIL RECORDS DEPICTED
Under this heading we display in situ images of all recovered megafossils of Betula, Pinus and
Picea showing the wide frame of arboreal history at this high-elevation site from the Lateglacial
to early and mid-Holocene.
Birch (Betula pubescens ssp. czerepanovii)
Figure 7: Megafossil remnants of a birch that grow (1360 m a.s.l.) on the nunatak Mt.
Åreskutan, 16 815 cal. a BP. This is the earliest record of tree birch in the Scandes
and originates from a time when the Scandes, according the conventional wisdom,
should have been covered with a thick ice sheet. Photo: 2001-08-23.

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Figure 8: Another late glacial birch, recovered from the mud close to the front of the snow
patch. Radiocarbon dating yielded 15 500 cal. a BP. Photo: 2001-07- 27.
Figure 9: Remnants of a tiny birch tree, dated 12 330 cal. a BP. Photo: 2001-07-28.

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Kullman, L., & Öberg, L. (2024). Mt. Åreskutan Nunatak: An Arboreal “Roadmap” to the Paleobiogeograpy of the Swedish Scandes and a Possible
Pointer Towards a Future Revival of a Richer and More Biodiverse Mountainscape. European Journal of Applied Sciences, Vol - 12(1). 219-242.
URL: http://dx.doi.org/10.14738/aivp.121.16320
Figure 10: Stout parts of the root system, unearthed from beneath the moss cover and
belonging to a tree birch. Radiocarbon-dating gave 11 930 cal. a BP. Photo: 2001-07-28.
Figure 11: Megafossil remains of a tree birch trunk (1360 m a.s.l.), which dated 8380 cal. a BP.
Photo: 2001-07-27.

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Figure 12: Part of the root system of a birch (1375 m a.s.l.), dated 7980 cal. a BP. Photo: 2006-
09-03.
Figure 13: Part of a tiny birch stem exposed at the centre of the snow patch site, 1370 m a.s.l.
and dated 6010 cal. a BP. This is the youngest megafossil tree recovered on Mt. Åreskutan,
and possibly it marks the onset of the Neoglacial era, with climate conditions increasingly less
conducive to tree growth. Photo: 2006-09-03.

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Kullman, L., & Öberg, L. (2024). Mt. Åreskutan Nunatak: An Arboreal “Roadmap” to the Paleobiogeograpy of the Swedish Scandes and a Possible
Pointer Towards a Future Revival of a Richer and More Biodiverse Mountainscape. European Journal of Applied Sciences, Vol - 12(1). 219-242.
URL: http://dx.doi.org/10.14738/aivp.121.16320
Spruce (Picea abies)
Figure 14: Megafossil spruce and a keystone piece in Fennoscadian paleogeography, showing
that also spruce was part of the Lateglacial tree flora at high elevations. The radiocarbon
dating, 13 010 cal. a BP, is about 10 000 years earlier than previous inferences of first spruce
presence in the Scandes, based on the conventional pollen analytical approach. This chunk was
almost entirely covered by the moss carpet. Photo: 1998-08-02.
Figure 15: Megafossil spruce protruding from debris in the snow patch niche, 1380 m a.s.l
Radiocarbon dating yielded 12 000 cal. a BP. Photo: 2002-07-03.

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Figure 16: Left. Old-established spruce growing in a steep slope, 975 m a.s.l. and marking the
treeline when this photo was captured. The stem was broken by a snow avalanche in the
1990s. Right. Wood remnants beneath the canopy gave an age of 6400 cal. a BP.
Photo: 2011-08-30.
Pine (Pinus sylvestris)
Figure 17: Lage megafossil pine, exposed from beneath the moss cover and representing the
Lateglacial epoch, 13 810 cal. a BP. Photo: 1998-08-02.

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Kullman, L., & Öberg, L. (2024). Mt. Åreskutan Nunatak: An Arboreal “Roadmap” to the Paleobiogeograpy of the Swedish Scandes and a Possible
Pointer Towards a Future Revival of a Richer and More Biodiverse Mountainscape. European Journal of Applied Sciences, Vol - 12(1). 219-242.
URL: http://dx.doi.org/10.14738/aivp.121.16320
Figure 18: Close to the megafossil depicted in Figure 17, another pine was unearthed. The
radiocarbon age was 12 840 cal. a BP, adding further evidence to the existence of trees on
this early deglaciated nunatak by the Lateglacial period. Photo: 1998-08-02.
Figure 19: Stout pine trunk emerging at the snow front, radiocarbon-dated 10 950 cal. a BP.
Photo: 2001-07-27.
MODERN TREELINE AND TREE SPECIES PERFORMANCE
At the present time, the upper treeline is formed by mountain birch (Betula pubescens ssp.
czerepanovii) at an elevation of 1015 m a.s.l., which represents a rise by 170 altitudinal
meters since the early 20th century. Analogous figures for spruce (Picea abies) are 1010 m a.s.l.
and 145 m, respectively (Kullman & Öberg 2009). Pine (Pinus sylvestris) is virtually
unrepresented in tree form on the slopes above the valley floor (380 m a.s.l.). Spruce is the
dominant species on this mountain up to about 750 m a.s.l. Higher upslope, a sparse birch
forest belt prevails. The upper limit of birch and spruce tree growth is currently about 350 m

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below the elevation of Lateglacial trees, concerned in this study (Figs. 20, 21). The slopes
above the present-day treelines are sparsely strewn by birch and spruce saplings up and
above the site of megafossils, 1360-1385 m a.s.l. (Figs. 23-25).
Figure 20: Left. The treeline of Betula, 1015 m a.s.l., has advanced by 170 vertical meters since
the early 20th century. Photo: 2023-08-25. Right. Birch sapling established 1365 m a.s.l.,
350 m above the local treeline. Photo: 2003-07-19.
Figure 21: The current Picea treeline (1010 m a.s.l.) is 145 meter higher than about 100 years
ago. Treeline rise is accomplished by phenotypic change of an old-established krummholz
individual. Photo: 2023-09-13.

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Kullman, L., & Öberg, L. (2024). Mt. Åreskutan Nunatak: An Arboreal “Roadmap” to the Paleobiogeograpy of the Swedish Scandes and a Possible
Pointer Towards a Future Revival of a Richer and More Biodiverse Mountainscape. European Journal of Applied Sciences, Vol - 12(1). 219-242.
URL: http://dx.doi.org/10.14738/aivp.121.16320
Figure 22: Left. Vigourous spruce sapling with an estimated age of 50 years and growing
1385 m a.s.l. Two small cones with viable seeds were retrived. Photo: 2001-07-27. Right. A few
tiny saplings were recovered in the close vicinity (about 4 m to the leeward).
Photo: 2003-07-19.
Figure 23: A young spruce sapling growing on the steep slope above the “megafossil site”,
1380 m a.s.l. Photo: 2016-08-06.

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Figure 24: The highest known (?) spruce in the Scandes (1410 m a.s.l.), close to the summit of
Mt. Åreskutan. That position is 400 m above the spruce treeline and 250 m higher than the
current upper limit of spruce saplings, recorded by the 1950s (Kilander 1955).
Photo: 2000-09-16. Source: Kullman 2002b.
Figure 25: Young pine saplings established 1365 m a.s.l.
Photos: Left. 2003-07-03. Right. 1999-07-07.
RECENT ELEVATIONAL PROGRESSION OF GROUND COVER SPECIES
In accord with regional rise of subalpine and alpine species richness since the
mid-1950s (Kullman 2007a, b, 2008), analogous progressive responses are recorded on
Mt. Åreskuran (Figs. 26, 27).

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Kullman, L., & Öberg, L. (2024). Mt. Åreskutan Nunatak: An Arboreal “Roadmap” to the Paleobiogeograpy of the Swedish Scandes and a Possible
Pointer Towards a Future Revival of a Richer and More Biodiverse Mountainscape. European Journal of Applied Sciences, Vol - 12(1). 219-242.
URL: http://dx.doi.org/10.14738/aivp.121.16320
Figure 26: The upper limit of Melampyrum sylvaticum along the perimeter of Mt. Åreskutan,
was recorded on 37 stations in the mid-1950s by Kilander (1955) (green dots). This endeavour
(golden stars) was repeated 2002-2003 by Kullman (2004). A spatially consistent upslope
average displacement of 130 m was recorded.
Figure 27: Left. The upper limit of Cornus suecica has advanced from 985 (Kilander 1955) to
1365 m a.s.l., since the mid-1950s (Kullman 2004). Right. A presumably young individual of the
fern Athyrium distentifolium (1355 m a.s.l.), recorded 20 altitudinal meters higher than
obtained by the mid-1950s (Kilander 1955). Photo: 2016-08-06
THERMOPHILIC TREE SPECIES
During the Holocene thermal optimum, 10000-8000 years ago, broadleaved deciduous tree
species, with thermophilic affinities, grew at scattered locations along the southern Scandes,
where subalpine forest prevail at the present time (Kullman 2008, 2013, 2020). A recent
tendency of resurgence of some members of this flora has been perceived in subalpine regions
of the Swedish Scandes (Kullman 2023). Observations in the present study area provide some
local facets of corresponding progression, in the form of elevational spread of saplings to the
subalpine forest (Figs. 28, 29).

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Figure 28: Relict outlier stands of Ulmus glabra ssp. montana, growing in a steep and boulder-
rich terrain on the south-facing slope (650 m a.s.l) of Mt. Åreskutan (Totthumeln). The oldest
stems are more than 300 years old and were mentioned by early botanists (Hagström 1752:
Lange 1938). Scattered saplings (0.5-1 m tall) occur in the stand, Photo: 2010-06-13.
Figure 29: Left. Sapling of Ulmus glabra ssp. montana, 970 m a.s.l., growing 320 m higher than
the nearest relictual stand and putative seed source (Fig. 28). Unfortunatly, it was extirpated
in 2004 by construction of a ski pist. Photo: 2001-07-28. Right. A newly established sapling of
Acer platanoides, 970 m a.s.l. Obviously this is a wildling from plantations in the nearby
village Åre, 400 m a.sl. Photo: 1998-08-02.

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Kullman, L., & Öberg, L. (2024). Mt. Åreskutan Nunatak: An Arboreal “Roadmap” to the Paleobiogeograpy of the Swedish Scandes and a Possible
Pointer Towards a Future Revival of a Richer and More Biodiverse Mountainscape. European Journal of Applied Sciences, Vol - 12(1). 219-242.
URL: http://dx.doi.org/10.14738/aivp.121.16320
DISCUSSION
Images displayed in this paper, underline the robust character of Lateglacial and early Holocene
megafossil tree remnants and inferred past presence of trees close to the summit of Mt.
Åreskutan. No other approach has the same ability to pinpoint presence in space and time of
different tree species. In cases of conflict with other paleorecords, e.g. pollen analysis, priority
has to be given to megafossils (cf. Kullman 2018b). In general, it should be realized that
megafossils represent a higher level of evidence than e.g. the outcome of cosmogenic nuclide
dating of deglaciation, as performed by Johnsen (2010).
Our most common tree taxa in the Scandes (Betula, Picea and Pinus), were growing close to the
summit of Mt. Åreskutan already by the late glacial period 16 000-13 000 cal. a BP. A
reasonable analogue to the Lateglacial and early Holocene landscape is provided by Figure 30.
Figure 30: Today Mt. Grötmjölhögen (summit 820 m a.sl.), 30 km to the south-west of Mt.
Åreskutan, supports a cover of mountain birch, predominatly in snow-rich lee depressions. In
addition, clonal spruces and scatterd pines occur in the slope. The exposed character of this
site precludes a more dense tree cover over the entire area. Photo: 2010-04-06. Tentatively, the
Lateglacial and early Holocene landscape of Mt. Åreskutan had some resemblance with this
present-day view of Mt. Grötmjölhögen. Photo: 2015-08-14.
The megafossil dates, presented in this paper, constitute a corner stone to which present and
future students of Scandinavian paleobiogeography have to relate. These findings are
parallelled in other parts of the Scandes (Öberg & Kullman 2011; Paus, Velle & Berge 2011;
Kullman & Öberg 2015, 2020, 2021; Kullman 2017a,b, 2022; Paus 2021; Paus, Brooks,
Haflidason et al. 2023).
Lateglacial tree growth 350 m higher than present-day treelines is no big wonder, considering
the effect of land uplift. At the time of the oldest megafossils, i.e. the summit of Åreskutan
appears to have been about 300 m closer to the sea level than today (Eronen 2005; Påsse &
Andersson 2005). This implies higher summer temperature by about 2 °C, which translates to

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about 7.5 °C (see records above), and should have been sufficient for local tree growth at
favourable sites (Helland 1912; Körner & Paulsen 2004; Kullman 2021). The early dates of
Picea abies at this high altitude and and other analogous sites far to the west is particuarly
interesting since this species is assumed to have arrived about 3000 years ago. This gives credit
to inferences that a postglacial immigration stream came from the west (cf. Lindquist 1948;
Kullman 2001, 2008). Importantly, pollen analytical data point to the option of spruce
presence on the dry Doggerland during the Weichselian (Krüger et al. 2017), possibly an
underrated source area for biotic reclamation of Scandinavia following the Weichselian
glaciation (Paus et al. 2023).
By analogy, further warming by c. 2 °C would be sufficient to restore tree growth at the summit
of Mt. Åreskutan 350 m above present treelines, as modeled by Boer, Koster & Lundberg
(1990). That is a resonable option for the coming 100 years, based on the assumption of the
same pace of temperature rise as during the past 100 years, and the tight relationship between
temperature evolution and treeline displacement, documented for the past 100 years (Kullman
& Öberg 2009; Kullman 2018a). The realism of that vision is supported by the fact that saplings
of most boreal tree species are located right at formerly glacier/ice patch and megafossil sites,
as documented by this study. In other parts of the Scandes, groves of megafossil tree
assemblages are recovered in wind-protected ice-empty glacier niches, as much as 700
altitudinal meters above modern treelines (Kullman & Öberg 2015, 2020; Kullman 2017a).
Based on the above premises, the attainment of that postion would presuppose temperature
rise by about 4 °C. Most likely, such a course of change will not give rise to the emergence of a
closed tree cover over the entire summit area, due to a strong wind effect over the peak and the
prevalence of naked cliffs without a soil cover. Importantly, only future observations can
validate or refute these inferences.
SUMMARY
Megafossil tree remnants display that during relatively warm phases of the Lateglacial and
early Holocene periods, main members of the modern Scandinavian tree flora grew on an early
deglaciated nunatak, 350 m higher than present-day local treelines. These species were Betula
pubescens ssp czerepanovii, Picea abies and Pinus sylvestris. Based on a lapse rate of 0.6 °C per
100 m altitude, it may be inferred that summer temperature was at least 2 °C higher than the
early 21st century. By analogy, this historic situation may serve as a likely prospect of the
subalpine/alpine landcape evolution in the case of future warming by 2 °C over the present-
day level (early 21st century). With this background, it is reasonable to assume that tree cover
spots will arise in sheltered and scattered habitats on the alpine tundra, at least 350 m above
present-day treeline positions. This implies a more varied and richer mountainscape and a
revival of a more prosperous situation, prevailing during earlier and often warmer phases of
the Holocene.
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