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Further Details on Holocene Treeline, Glacier/Ice Patch and Climate History in Swedish Lapland


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The present paper reports results from an extensive project aiming at improved understanding of postglacial subalpine/alpine vegetation, treeline, glacier and climate history in the Scandes of northern Sweden. The main methodology is analyses of mega fossil tree remnants, i.e. trunks, roots and cones, recently exposed at the fringe of receding glaciers and snow/ice patches. This approach has a spatial resolution and accuracy, which exceeds any other option for tree cover reconstruction in high-altitude mountain landscapes. The main focus was on the forefields of the glacier Tärnaglaciären in southern Swedish Lapland (1470-1245 m a.s.l.). Altogether seven megafossils were found and radio-carbon dated (4 Betula, 2 Pinus and 1 Picea). Betula and Pinus range in age between 9435 and 6665 cal. yr BP. The most remarkable discovery was a cone of Pice aabies, contained in an outwash peat cake, dating 11 200 cal. yr BP. The peat cake also contained common boreal ground cover vascular plant species and bryophytes. All recovered tree specimens originate from exceptionally high elevations, about 600-700 m atop of modern treeline positions. This implies, corrected for land uplift, summer temperatures, at least 3.6 °C higher than present-day standards. The current results, in combination with those from other Swedish glaciers, contribute to a new view on the early postglacial landscape and climate in high-altitude Swedish Scandes
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International Journal of Research in Geography (IJRG)
Volume 3, Issue 4, 2017, PP 61-69
ISSN 2454-8685 (Online)
International Journal of Research in Geography (IJRG) Page | 61
Further Details on Holocene Treeline, Glacier/Ice Patch and Climate
History in Swedish Lapland
Leif Kullman1
1Department of Ecology and Environmental Science, SE 90187 Umeå, Sweden
Abstract: The present paper reports results from an extensive project aiming at improved understanding of
postglacial subalpine/alpine vegetation, treeline, glacier and climate history in the Scandes of northern Sweden.
The main methodology is analyses of mega fossil tree remnants, i.e. trunks, roots and cones, recently exposed at
the fringe of receding glaciers and snow/ice patches. This approach has a spatial resolution and accuracy,
which exceeds any other option for tree cover reconstruction in high-altitude mountain landscapes. The main
focus was on the forefields of the glacier Tärnaglaciären in southern Swedish Lapland (1470-1245 m a.s.l.).
Altogether seven megafossils were found and radio-carbon dated (4 Betula, 2 Pinus and 1 Picea). Betula and
Pinus range in age between 9435 and 6665 cal. yr BP. The most remarkable discovery was a cone of Pice
aabies, contained in an outwash peat cake, dating 11 200 cal. yr BP. The peat cake also contained common
boreal ground cover vascular plant species and bryophytes. All recovered tree specimens originate from
exceptionally high elevations, about 600-700 m atop of modern treeline positions. This implies, corrected for
land uplift, summer temperatures, at least 3.6 °C higher than present-day standards. The current results, in
combination with those from other Swedish glaciers, contribute to a new view on the early postglacial
landscape and climate in high-altitude Swedish Scandes
Keywords: Treeline, glacier, megafossils, climate change, Holocene, Swedish Scandes, Betula pubescensssp.
czerepanovii, Pinus sylvestris, Piceaabies.
Recent glacier/ice patch recession in association with post-Little Ice Age climate recovery of the past
100 years or so has exposed a plethora of previously ice-entombed megafossil tree remains in many
parts of the world (Nicolussi & Patzelt 2000; Hormes et al. 2001; Schlűchter & Jörin 2004;Koch et al.
2007, 2014; Grosjean et al. 2007; Benedicht et al. 2008; Wiles et al. 2008;Scapozza et al.
2010;Nicolussi&Schlűchter 2012; Lee 2012). These ancient remnants, derive from subglacial
preservation sites and are currently exposed at the margin of basins presently occupied by glacier ice
and perennial snow. Theyoffer a unique opportunity to improve our understanding about past treeline
positions and associated plant cover characteristics and thereby indirectly provide clues to ancient
climates.This archive, also containing numerous human and cultural artefacts, has been widely
recognized and exploited by archaeologists (e.g. Nesje et al. 2011; Lee & Benedicht 2012; Reckin
2013), but in Scandinavia surprisingly little payed attention to by palaeoecologists.
In the Swedish Scandes, however, important findings of megafossil trees under above-mentioned
circumstances, high above current treelines, have been reported and discussed in some studies
(Kullman 2004; Öberg& Kullman 2011a; Kullman &Öberg 2013, 2015; Kullman 2017a). These
results have proven accuracy in time, space and species composition, going far beyond the resolution
of pollen analysis and other microfossil approaches (cf. Kullman 2017a) and lining up with inferences
originating from DNA-methodologies (Parducci et al. 2012; Parducci&Tollefsrud 2016). Late-glacial
and early-Holocene presence of boreal tree species are evidenced (megafossils) in this way for
restricted sites, situated much higher than current treeline elevations. Hereabouts peat deposits on the
open alpine tundra are rare and shallow, with little ability to preserve trees and other macroscopic
plant remains from ancient times. Therefore, little has been known about the highest treeline positions
and associated plant cover structure during the earliest part of the Holocene. The most promising
archives for that purpose are found in glacier cirques and nivation hollows, which were ice free before
Further Details on Holocene Treeline, Glacier/Ice Patch and Climate History in Swedish Lapland
International Journal of Research in Geography (IJRG) Page | 62
and became ice covered in accord with the mid-Holocene neoglacial cooling. In many cases, it is quite
obvious that the mega fossil tree remnants have been washed out by subglacial meltwater streams
from primary growing sites higher upslope. Some exceptional outlying records of 500-700m support
an even higher elevational origin as a more general pattern. The possible generality of this supposition
needs to be further elucidated in perspective of its implications for Holocene vegetation history and
paleoclimate (Öberg & Kullman 2011a,b; Kullman &Öberg 2013, 2015). With this background, the
present study reports efforts to sustain and further approach the uppermost limit of mega fossil trees
within an area previously well researched with respects to mega fossil tree remnants (debris wood)
occurring at glacier forefields at relatively modest levels above the present-day treelines (Öberg &
Kullman 2011a; Kullman & Öberg 2013, 2015).
For logistic reasons it has been judged impractical and dangerous (slippery bedrock, collapsing glacier
fronts and moving rock slabs) to investigate these higher potential source areas in search for mega
fossils. However, during the early autumn of 2017, the present author made a tentative approach, the
results of which are reported here.
The study was carried out within the central Swedish Scandes, in the southern part of the province
Lapland (Fig. 1). Focus is here on the forefield of the glacier “Tärnaglaciären”, which is located to the
Norra Storfjället massif (65° 51´N; 15° 16´E), with some peaks reaching above 1600 m a.s.l. and
valley floors at 700-800 m a.s.l. The glacier is contained within a cirque facing SE (Fig. 2). Currently
the glacier area is estimated to c. 0.2 km2, with an upper and lower margin at 1470 and 1245 m a.s.l.,
respectively. By the late 19th and early 20th century, the glacier was mapped by Gavelin(1897, 1910),
who estimated its area to 0.5 km2. Thus, the glacier has lost more than 50% of its area during the past
100 years or so, and the lower front has withdrawn by approx. 175 m in elevation. Figure 3 depicts the
maximum extent of the glacier by the late 19th century, manifested in the form of an incomplete
moraine bow in an outwash lake below the glacier, 1070 m a.s.l. (Fig. 3) (cf. Gavelin 1910; Lindgren
& Strömgren 2001).Substantial frontal retreat and thinning have taken place since the late 1990s and
up to the present day (Fig. 2)
On the slope below the glacier, a large snow/ice patch extends down to the outwash lake (Fig. 2). The
size of this patch varies on an annual basis, depending on prevailing weather conditions. Prior to the
present study, most megafossil recoveries have been made in association with melt water streams
close to the lower fringe of this patch.
The bedrock is of Cambro-Silurian origin, mostly mica schists. Quaternary deposits embrace
glacifluvial accumulations, till and peat. A weakly suboceanic climate characterizes the area. The
nearest meteorological station is Hemavan, 475 m a.s.l., situated in the Uman River Valley, c. 10 km
southwest of the study site. The mean temperature forJune-August and the year are 10.1 and -0.4°C,
respectively. Annual precipitation is 680 mm.
Currently, mountain birch (Betula pubescens ssp. czerepanovii) constitutes the upper treeline in this
area, 790 m a.s. l. (Fig. 4). The nearest treeline of Norway spruce (Pice aabies) and Scots pine (Pinus
sylvestris) are at 710 and 690 m a.s.l., respectively. During the past 100 years, the treelines of those
species have advanced by a maximum of more than 200 m (Kullman &Öberg 2009), which appears to
have taken them to a position uniquely high for the past 7000 years or so (Kullman 2017b).
Overviews of the structure and dynamics of the treeline ecotone in the Scandes are provided by
Kullman (2010) and Wielgolaski et al. (2017).
Fig1. Map showing the location of the study area (●) in northern Sweden.
Further Details on Holocene Treeline, Glacier/Ice Patch and Climate History in Swedish Lapland
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Fig 2. The glacier Tärnaglaciären, the snow/ice patch and outwash lake below (1070 m a.s.l.).
A. Prospect from southeast, 1999-09-06 (Photo: F. Lindgren & M. Strömgren). B. Virtually the same view
2017-09-01. The glacier has perceivably thinned since 1999 "Photo: 2017-09-01".
Fig3. The outwash lake below the glacier, 1070 m a.s.l. By the late 19th century, the lower glacier front was
located at the morainic ridges, protruding above the water surface (Gavelin 1910).
Fig4. The current treeline of Betulapubescens ssp. czerepanovii, 790 m a.s.l., right to the east and down slope
of Tärnaglaciären (arrow). The solitary birch copse is located at the bank of the main melt water stream from
the glacier "Photo: 2017-09-01".
Further Details on Holocene Treeline, Glacier/Ice Patch and Climate History in Swedish Lapland
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During the autumn of 2017 the fore fields adjacent to the lower and lateral margins of the glacier
Tärnaglaciären were thoroughly scrutinized for the presence of outwashed megafossils and other
identifiable plant remains. Recovered specimens were wrapped in aluminium foil and stored frozen
until delivery to the dating laboratory. Species identification was unambiguous in all cases, based on
bark fragments, cone and leaf characteristics. All recovered woody remnants were sampled and
altitudes were determined by a GPS navigator (Garmin 60CS), calibrated against distinct points on the
topographical map. Reported altitudes are rounded off to the nearest 5 m. The nomenclature of
vascular plants follows Öberg et al. (2017).
Radiocarbon dating of recovered specimens has been performed by Beta Analytic Inc., Miami, USA.
All original radiocarbon dates and time-scales in running text and figures are converted to calendar
years before present (cal. yr BP), with “present” = AD 1950, based on IntCal13 (Reimer et al. 2013)
and for the sake of simplicity, they are cited as “intercept values”. Outwash peat cakes and their
contained macrofossils (e.g. cones, leaves and bryophytes) were dated indirectly on the basis of 2 cm
thick bulk peat slices.
This study adds seven new dates of mega fossil tree remnants (4 Betula, 2 Pinus, 1 Picea) to a
previous sample of 21 specimens from the same glacier (12 Betula, 9 Pinus) (Kullman &Öberg
2015). Individual dates are given in Table 1 and the samples are depicted in Figures 5-7. They range
in elevation between 1410 and 1275 m a.s.l., which is about 600 and 700 m higher than the nearest
present-day treelines of these species. The ages all represent the early Holocene, c. 11 200 to 6700
before present.
Table 1. Radiocarbon dates of recovered megafossils. Relative elevation refers to the difference in altitude
between the sampling site and the nearest present-day treeline of the concerned species.
Fig 5. Recovered and dated mega fossils of Betula pubescens. A. 9365 cal. yr BP. B. 9450 cal. yr BP. C. 6665
cal. yr BP. D. 8780 cal. yr BP
Altitude Relative elevation Species Lab. code Radiocarbon age
Calibrated age
Intercept Size Material
m a.s.l. m
14C yr BP BP 1 SD cal. yr BP cm
1410 700 Betula Beta-474257
83330 9447-9273 9365 45 wood
1395 685 Betula Beta-474258
8400±30 9495-9397 9450 40 wood
1380 690 Pinus Beta- 474259
8020 ±30 9010-8848 8900 37 wood
1320 630 Pinus Beta- 474254
8380±30 9779-9371 9435 19 wood
1295 585 Betula Beta-474255
5850±30 6743-6603 6665 21 wood
1275 565 Betula Beta-474252
7910±30 8791-8602 8780 18 wood
1370 630 Picea Beta-474251
9760±30 11 238-11 167 11 200 14 Cone + peat
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Fig6. Recovered and dated megafossils of Pinus sylvestris. A. 8900 cal. yr BP. B. 9435 cal. yr BP.
A cone of Picea abies, contained in a peat cake, was dated 11 200 before present at an elevation,
almost as high as the uppermost dated birches and pines (Fig. 7).The cone contained a few heavily
decayed seeds.
This is the highest position, relative to its modern treeline, ever recorded for postglacial spruce. In
addition, this peat sample showed macrofossils of the following identifiable ground cover taxa:
Empetrum hermaphroditum, Vaccinium myrtillus, Vaccinium vitis-idaea, Rhododendron tomentosum,
Hylocomium splendens, Pleurozium schreberi, Dicranum sp., Sphagnum sp. All samples of Betula
and Pinus displayed a size and form which indicated that they originated from tree-sized individuals.
In the case of Picea abies(a cone) no such inference could be made.
Fig7. A. Peat cake which contained macrofossils of ground cover species, 1370 m a.s.l. B. Cone of Piceaabies
dissected from the peat cake.
The present study sustains a generic pattern for the entire Swedish Scandes(cf. Öberg & Kullman
2011a; Kullman & Öberg 2013, 2015). As evident from Fig. 5A, the highest date of Betula (1410 m
a.s.l,) is obtained from an outwash stream protruding from beneath the glacier. Obviously it originates
from a primary growing site further up valley, more than 700 m above today´s treeline.
Conservatively drawing on the latter figure and a summer temperature lapse rate of 0.6 °C per 100 m
elevation (Laaksonen 1976), coulda priori mean that, summer temperatures were at least 4.2 °C
warmer than present around 9500 year before present. However, glacio-isostatic land uplift by at least
100 m since that time (Möller 1987; Påsse & Anderson 2005) implies that this figure has to be
Further Details on Holocene Treeline, Glacier/Ice Patch and Climate History in Swedish Lapland
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reduced to 3.6 °C higher than present-day levels, i.e. first decades of the 21st century. Evidently, this
was the warmth peak of the Holocene, hitherto. This inference concurs with paleoclimatic
reconstructions from Europe and Greenland (Korhola et al. 2002; Bigler et al. 2003; Paus 2013; Luoto
et al. 2014; Väliranta et al. 2015) and complies with theoretical calculations based on variations in
Earth´s orbital parameters and associated gradual change in summer insolation (Berger & Loutre
1991; Esper et al. 2012). It contrasts with common interpretations suggesting a much later thermal
optimum (Berglund et al. 1996; Seppä & Birks 2002). The latter inferences are based on pollen
analyses, which in some cases are proved to deliver less reliable vegetation history details and
temperature estimates (Paus 2013; Elven et al. 2013;Luoto et al. 2014; Kullman 2017a).
The youngest mega fossil date, 6665 cal. yr BP, suggests that the concerned glacier, like many others,
did not exist prior to that date (cf. Bakke et al. 2005). Dated peat remains indicated that neoglacial
instatement of this particular glacier ice took place after 3890 cal. yr BP (Kullman & Öberg 2013).
Available dates are too few to allow any firm conclusions as to the zonation patterns during the early
Holocene. Anyhow, Betula appears to have been the highest ascending tree species. Such a pattern
also emerges from earlier more extensive megafossil studies, although a distinct subalpine birch forest
belt, as we know it today, appears to have formed later on (Kullman 2013). In that context, it is of
some interest to note that the nearest living birches (tree-line markers), in the form of a dense and
isolated copse, are located within the main outwash stream furrow from the glacier here concerned
(Fig. 4). This pattern is compatible with an earlier inference, based onmega fossil performance, that
trees (and possibly other plant species, have in general spread downslope from primary “occurrence
sites at high elevations, e.g. empty glacier cirques (Kullman 2002).
Information from ground cover macrofossil plant species contained in a peat cake (Fig. 7A), indicate
that the recovered mega fossils grew in a matrix of dwarf shrubs and bryophytes with present-day
quite ordinary boreal forest affinities. Predominance of Sphagnum spp. could indicate that the
megafossils were preserved by peat growth prior to the final burial by glacier ice.
Recent data on early Holocene presence of Picea abies at high elevations in the Scandes comply
temporally with megafossil and some recent pollen studies from different parts of the Scandes
(Kullman 1996, 2000; Segerström & von Stedingk 2003; Öberg & Kullman 2011b; Paus et al. 2011;
Kullman & Öberg 2013, 2015).This pattern contrasts with traditional inferences from pollen data,
suggesting a mid- or late Holocene wave-like spread of spruce from the east (e.g. Moe 1970; Hafsten
1992; Huntley & Birks 1983;Giesecke 2005;Seppä et al. 2009).Recent DNA analyses in lake
sediments and emergent patterns in genetic structure of extant spruce populations support the
contention of Late-glacial andearly Holocene presence of spruce enclaves in western and northern
Scandinavia (Parducci et al. 2012). Furthermore, multimillennial old prostrate spruces, prevailing high
above the current treeline in some mountain areas, provide support to the latter option (Öberg&
Kullman 2011b; Kullman 2015).
Apparently, these peripheral spruce occurrences were confined to restricted, widespread and
particularly favorable habitats, acting as dispersal nodes during later parts of the Holocene. This
option was originally inferred from megafossil spruce data gathered along the entire Swedish Scandes
(Kullman 1996, 2001, 2008, 2017a; Kullman &Engelmark 1997), a mechanism reiterated by
Väliranta et al. (2011) on evidence from north-eastern European Russia.
Importantly, mega fossil data of the kind accounted for above, in combination with DNA analyses in
soils and lake sediments, urge pollen analysts to adopt a less conservative attitude when interpreting
trace amounts of pollen. Evidently, much of the commonly narrated pollen-based postglacial history
of subalpine/alpine regions has to be reconsidered in the light of emerging megafossil evidence. These
latter results, in combination with those, analogously derived, from other Swedish glaciers, provide a
new view on the early postglacial landscape and climate in high-altitude Swedish Scandes.
Paleoecologists are forced to reconsider standard views on Late-Glacial and early Holocene
environments in the high mountains (cf. Anderson et al. 2009; Horáček et al. 2015). This view is
strongly substantiated by the present paper.
Further Details on Holocene Treeline, Glacier/Ice Patch and Climate History in Swedish Lapland
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This study was defrayed by a grant from the Göran Gustafsson Foundation. Dr. Lisa Öberg is thanked
for competent and constructive comments of an earlier version of the manuscript.
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Citation: Leif Kullman. " Further Details on Holocene Treeline, Glacier/Ice Patch and Climate History
in Swedish Lapland". International Journal of Research in Geography, vol 3, no. 4 2017, pp. 61-69.
Copyright: © 2017 Authors. This is an open-access article distributed under the terms of the Creative
Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any
medium, provided the original author and source are credited.
... Nevertheless, it has been evidenced by the megafossil approach that spruce grew on early deglaciated high-elevation nunataks already during the late-glacial and early Holocene epochs, about 13 000 and 11 200 years ago (14,17,18). This complies with newer data, indicating that the highest peaks were ice-free as early as about 20 000 years ago (3), in contrast to a more traditional view of early Holocene mountain deglaciation (40). ...
... The status of Picea abies as an early Holocene dweller in the Scandes is further enhanced by the present record is consistent with earlier evidence (cf. 14,17,18,21,35,31,34). Growth at this remarkable high elevation and at a particularly exposed site, close to a distinct high-mountain peak, argues for a climate strongly deviant from the present day. ...
... Specifically focusing on the history of Picea abies, the present result adheres to earlier studies, showing late-glacial and early Holocene presence of spruce on high early deglaciated nunataks, currently 600-700 m above present-day treelines (14,18). This circumstance provides some support to the hypothesis that spruce could have survived the Weichselian glaciation or parts of it in the Scandes, or, more likely, at coastal sites at the western margin of the ice sheet (13,18). ...
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A megafossil wood remnant of Norway spruce (Picea abies (L.) Karst.) was retrieved from a high-elevation nunatak in the southern Swedish Scandes. The site was nearly 600 m higher than the present-day treeline. These circumstances comply with analogous earlier recoveries, indicating presence of spruce at high elevations in the Scandes, several thousands of years prior to inferences made by pollen analysis. Radiocarbon-dating yielded a median age of 9300 cal a BP. This result adds firm detail and adheres to ongoing reappraisal of the structure and biodiversity of the late-glacial and early Holocene mountain landscape, in the light of growing megafossil and molecular genetic evidence.
... The Holocene arboreal and deglaciation histories in the mountain region are mainly based on megafossils, which is the approach that can most accurately decipher the broad course of change in space and time (Kullman 2017a(Kullman , 2018Paus & Haugland 2017). Novel and promising paleoenvironmental approaches, e.g. ...
... Composite of all radiocarbon dates (old and new) of mountain birch, relative to the altitude of the present birch tree line (2010). Source: Kullman (2013).Contrary to prior common pollen-based belief (e.g.Huntley & Birks 1983;Giesecke & Bennett 2004;Seppä et al. 2009), Norway spruce (Picea abies) and Scots pine (Pinus sylvestris) grew on early nunataks both in Sweden and Norway during the Late Glacial and early Holocene(Kullman 1996 b; 2002ba, 2017a,b, 2022Paus 2021;Paus et al. 2011). The highest recovery of spruce was close to the summit of Mt. ...
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... In the Pyrenees it was 400 m higher than the current treeline (Cunill et al. 2012). In the Swedish Scandes 600-700 m higher between 9.5-6.5 ka (Kullman 2017). In the British Columbia it was 235 m higher from 10.6 to 7.5 ka (Pisaric et al. 2003). ...
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... The tree line during the thermal maximum extended significantly higher than at present. While some estimate a 170-210 m higher treeline and 1 to 1.3͐ ͐ ºC higher summer temperatures (Paus and Haugeland 2016), megafossil finds at even higher altitudes implies treelines up to 600-700 m higher in altitude than in the early 2000s, suggesting up to 3.6 ºC higher summer temperatures (Kullman 2017a, Kullman 2017b. With cooling temperatures, pine increased in abundance, and spruce became common in pollen records towards the early Scandinavian iron age (around 2500 BP). ...
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... These tree trunks uncovered from retreating glaciers are irrefutable witnesses of extended preindustrial warm periods as they grew up well above the present-day tree lines [38]. from stalagmites in the Alps [39] and tree line investigations in Lapland [40] gave similar results, just as did ice core analyses from Greenland [41] and from the Antarctica [42]. ...
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Abstract It is very old wisdom that climate dictates farm management strategies. In recent years, however, we are increasingly confronted with claims that agriculture, livestock husbandry, and even food consumption habits are forcing the climate to change. We subjected this worrisome concern expressed by public institutions, the media, policy makers, and even scientists to a rigorous review, cross-checking critical coherence and (in)compatibilities within and between published scientific papers. Our key conclusion is there is no need for anthropogenic emissions of greenhouse gases (GHGs), and even less so for livestock-born emissions, to explain climate change. Climate has always been changing, and even the present warming is most likely driven by natural factors. The warming potential of anthropogenic GHG emissions has been exaggerated, and the beneficial impacts of manmade CO2 emissions for nature, agriculture, and global food security have been systematically suppressed, ignored, or at least downplayed by the IPCC (Intergovernmental Panel on Climate Change) and other UN (United Nations) agencies. Furthermore, we expose important methodological deficiencies in IPCC and FAO (Food Agriculture Organization) instructions and applications for the quantification of the manmade part of non-CO2-GHG emissions from agro-ecosystems. However, so far, these fatal errors inexorably propagated through scientific literature. Finally, we could not find a clear domestic livestock fingerprint, neither in the geographical methane distribution nor in the historical evolution of mean atmospheric methane concentration. In conclusion, everybody is free to choose a vegetarian or vegan lifestyle, but there is no scientific basis, whatsoever, for claiming this decision could contribute to save the planet’s climate. Keywords: greenhouse gas emissions, carbon dioxide, methane, nitrous oxide, agroecosystems, deforestation, climate change
Rocky Mountain National Park contains a dense record of prehistoric Native American archaeological locales and biological resources, but questions remain about the past use of the Park’s ice patches by ancient humans and animals. Our survey of 30 locations in the Park revealed that the majority of ice patches are small in size and contain limited evidence of past visitation by mobile peoples, but moderate use by game. In this paper, we present new radiocarbon dates for materials documented in the recently melted forefield of the ROMO 9 ice patch, a mid-sized ice body located in alpine tundra along the Continental Divide. Dated materials include timber-sized pine trees, keratin and bone collagen from large game (bighorn sheep, elk), and a possible wooden artifact made from Mountain mahogany. Results suggest most finds date to several periods of known neoglaciation, during the mid-Holocene (c. 4150 cal BP) and the Little Ice Age (c. 115 cal BP). Our results corroborate past findings on mid-Holocene timberline in the Colorado Front Range, as well as the paucity of archaeological evidence from small ice patches in Colorado.
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Adds detail to early Holocene tree exclaves in ice-empty glacier niches
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Peripheral populations of cold-marginal tree species are often supposed to serve as dispersal nodes in relation to rapid climate warming. The history and evolution of a discrete outlying subarctic stand of Norway spruce (Picea abies (L.) Karst.), growing in northern Swedish Lapland, was investigated. Accordingly, it was hypothesized that climate change and variability over the past century have evoked substantial population growth and spread in the surrounding subarctic landscape. Radiocarbon-dating of megafossil spruce tree remnants preserved in the soil revealed that spruce was present at the study site by 7125 cal. yr B.P., contrasting with orthodox pollen-based interpretations of late-Holocene first spruce immigration to northern Sweden. Subsequently, the stand history is unknown until the mid-17th century AD, when the first specimen of the extant population emerged. Continuous presence and build-up of the spruce stand was initiated by the early 18th century. All-time-high initiation of new stems occurred by the 1920s, i.e. shortly prior to the first warming peak of the 20th century. This process shows no positive correlation with summer or winter temperature rise. Overall, the existence of the spruce population, as we see it today, may relate to the general post-Little Ice Age warming of all seasons and release from permafrost and severe seasonal ground frost. In perspective of these results, no broad-scale expansion of spruce forest is likely to take place in the case of hypothetical future summer climate warming.
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This paper elaborates and visualizes processes recorded in a recent regional and multi-site study of elevational treeline dynamics during the period 1915 to 2007 in the Swedish Scandes. The purpose is to give a concrete face of the landscape transformation which is associated with the recorded treeline shifts. The main focus is on stand-level structure of past and present treelines and the advance zones, where climate change elicited responses by Betula pubescens ssp. czerepanovii, Picea abies and Pinus sylvestris. All species shifted their treelines upslope by a maximum of c. 200 m in elevation. Most sites, however, manifested changes of smaller magnitudes. This relates to topoclimatic constraints which decouple treeline performance from the macroclimate. The general character of sites which support large and small treeline shifts, respectively, are outlined. The spacing, age structure, growth rates of the tree advance zones are accounted for each of the concerned species. In temporal and spatial detail, the different tree species responded individualistically according to their specific ecologies. Current spread of young seedlings and saplings to increasingly higher elevations in the alpine tundra is particularly highlighted as it may represent the forefront of future treeline advance. It is argued that the current evolution of the treeline ecotone represents a fundamental, although not necessarily entirely unique, reversal of the long-term (Holocene) trend of neoglacial treeline descent.
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Most alpine glaciers in the Northern Hemisphere reached their maximum extents of the Holocene between ad 1600 and 1850. Since the late 1800s, however, glaciers have thinned and retreated, mainly because of atmospheric warming. Glacier retreat in western Canada and other regions is exposing subfossil tree stumps, soils and plant detritus that, until recently, were beneath tens to hundreds of metres of ice. In addition, human artefacts and caribou dung are emerging from permanent snow patches many thousands of years after they were entombed. Dating of these materials indicates that many of these glaciers and snow patches are smaller today than at any time in the past several thousand years. This evidence, in turn, suggests that glacier recession in the 20th century is unprecedented during the past several millennia and that glaciers in western Canada have reached minimum extents only 150–300 years after they achieved their maximum Holocene extents.
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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 floor 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.
Transition zones between mountain forests and treeless tundra, i.e. treeline ecotones, are characterized by great regional variety. In this paper, we discuss the biodiversity in various trophic levels in treeline ecotones throughout Europe, with particular focus on recent changes in land use and climate in northern and central mountains. In northernmost Europe, mountain birch prevails, while conifers (spruce, pine, larch) are the dominating species further south. While at continent-wide to global scales, the ecotone position is largely controlled by heat deficiency, it depends on a multitude of partly interacting abiotic and biotic factors other than climate at smaller scales. Climate change is a driving factor in treeline ecotone change, including physiognomic structure and biodiversity, although the effects of climate and other factors often overlap. Historical legacy plays an important role in this respect, and human impacts are particularly important. The recent decline in pastoral use of many European treeline areas often strongly influences plant diversity and re-growth of trees and other woody species. Climate change together with changing tree cover may influence snow cover, moisture regime, and nutrient conditions. Subsequently changed site conditions influence plant-plant interactions, favoring some species and disfavoring others, and plant-animal interactions. Native animals may cause widespread or local disturbances in treeline ecotone areas. Mass outbreaks of leaf-eating insects, for example, usually affect comparatively large forested areas whereas mammalian herbivores and birds have more local impact. However, high numbers of wild or domestic mammalian herbivores may challenge the carrying capacity of treeline ecotone areas at the same time as they preserve an open pasture character. This calls for cross-disciplinary study approaches, addressing the complexity of the ecotone regarding both causal background and biogeographic diversity.