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Journal Article•DOI•

A century of tree line changes in sub-Arctic Sweden shows local and regional variability and only a minor influence of 20th century climate warming

Rik Van Bogaert1, Kristof Haneca1, Jan Hoogesteger2, Christer Jonasson3, Christer Jonasson4, Morgan De Dapper1, Terry V. Callaghan5, Terry V. Callaghan4 •
Ghent University1, University of Helsinki2, Uppsala University3, Royal Swedish Academy of Sciences4, University of Sheffield5
01 May 2011-Journal of Biogeography (Blackwell Publishing Ltd)-Vol. 38, Iss: 5, pp 907-921
TL;DR: In this article, the authors used repeat photography, dendrochronological analysis, field observations along elevational transects and historical documents to study tree line dynamics in a sub-Arctic model area at different temporal and spatial scales.
Abstract: Aim Models project that climate warming will cause the tree line to move to higher elevations in alpine areas and more northerly latitudes in Arctic environments. We aimed to document changes or stability of the tree line in a sub-Arctic model area at different temporal and spatial scales, and particularly to clarify the ambiguity that currently exists about tree line dynamics and their causes. Location The study was conducted in the Tornetrask area in northern Sweden where climate warmed by 2.5 degrees C between 1913 and 2006. Mountain birch (Betula pubescens ssp. czerepanovii) sets the alpine tree line. Methods We used repeat photography, dendrochronological analysis, field observations along elevational transects and historical documents to study tree line dynamics. Results Since 1912, only four out of eight tree line sites had advanced: on average the tree line had shifted 24 m upslope (+0.2 m year-1 assuming linear shifts). Maximum tree line advance was +145 m (+1.5 m year-1 in elevation and +2.7 m year-1 in actual distance), whereas maximum retreat was 120 m downslope. Counter-intuitively, tree line advance was most pronounced during the cooler late 1960s and 1970s. Tree establishment and tree line advance were significantly correlated with periods of low reindeer (Rangifer tarandus) population numbers. A decreased anthropozoogenic impact since the early 20th century was found to be the main factor shaping the current tree line ecotone and its dynamics. In addition, episodic disturbances by moth outbreaks and geomorphological processes resulted in descent and long-term stability of the tree line position, respectively. Main conclusions In contrast to what is generally stated in the literature, this study shows that in a period of climate warming, disturbance may not only determine when tree line advance will occur but if tree line advance will occur at all. In the case of non-climatic climax tree lines, such as those in our study area, both climate-driven model projections of future tree line positions and the use of the tree line position for bioclimatic monitoring should be used with caution.

Summary (1 min read)

Jump to: [A century of tree line changes in sub-Arctic Sweden shows local and regional] – [Tables] – [Figure legends] and [Figures]

A century of tree line changes in sub-Arctic Sweden shows local and regional

  • Twentieth century tree line changes in Swedish sub-Arctic Abstract 1 Models project that climate warming will cause the treeline to move to higher 2 elevations in alpine areas and more northerly latitudes in Arctic environments, also known as Running head.
  • The lack of 446 recent tree (>2 m) establishment and the browsing scars documented in the tree rings 447 indicated that, in addition to moth herbivory, reindeer browsing is still a controlling 448 factor at these sites (Fig. 5, Table 4).

Tables

  • Previous field studies on observed treeline shifts and their presumed causes in the Torneträsk area of sub-Arctic Sweden.
  • Browsing damage was classified visually and for five sites also by dendrochronological analysis (the values listed in brackets).
  • So as not to bias the results, Mount Nuolja (site S3), for which the two treeline sites were not randomly selected, was not included in the calculation of the mean elevational shift of the treeline in the Torneträsk area.
  • Pearson correlation coefficients and R2-values (the proportion of explained variance in documented treeline shifts) obtained by forward selection of the different variables are listed at the bottom of the table.

Figure legends

  • The Torneträsk study area in sub-Arctic Sweden.
  • The locations of the historical transects and photo points that have been revisited to study changes in the tree line ecotone are indicated.
  • The statistically-determined 30%-tree cover isoline is plotted in yellow.
  • Upper photo on the left: E. Persson, bottom left: B. Mesch; upper and bottom right: R. Van Bogaert.
  • Fig. 8. Tree (>2 m) establishment at the Torneträsk tree line versus summer (June- August) temperature and reindeer population numbers for the period 1800-2000.

Figures

  • Historical transects and photo points that have been revisited to study changes in the tree line ecotone are indicated.
  • The statistically-determined 30% tree-cover isoline is plotted in yellow.
  • Upper photo: E. Persson, lower photo: S. Johnsson.
  • Upper photo on the left: E. Persson, bottom left: B. Mesch; upper and bottom right: R. Van Bogaert. relation to disturbance (b) and summer temperature (c) for the period 1964-2006.
  • August) temperature and reindeer population numbers for the period 1800-2000.

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This item is the archived peer-reviewed author-version of:
A century of tree line changes in sub-Arctic Sweden shows local and regional variability and only a
minor influence of 20th century climate warming
Van Bogaert, R.; Haneca, K.; Hoogesteger, J.; Jonasson, C.; De Dapper, M.; Callaghan, T.V.
In: Journal of Biogeography, 38 (5), 907-921, 2011.
doi: 10.1111/j.1365-2699.2010.02453.x
To refer to or to cite this work, please use the citation to the published version:
Van Bogaert, R.; Haneca, K.; Hoogesteger, J.; Jonasson, C.; De Dapper, M.; Callaghan, T.V.
(2011). A century of tree line changes in sub-Arctic Sweden shows local and regional
variability and only a minor influence of 20th century climate warming. Journal of
Biogeography 38 (5), 907-921. doi: 10.1111/j.1365-2699.2010.02453.x
1
A century of tree line changes in sub-Arctic Sweden shows local and regional
variability and only a minor influence of 20
th
century climate warming
Rik Van Bogaert
1,2*
, Kristof Haneca
3
, Jan Hoogesteger
4
, Christer Jonasson
5,6
, Morgan
De Dapper
2
and Terry V Callaghan
5,7
1
Flanders Research Foundation (FWO); Egmontstraat 5, B-1000 Brussels, Belgium
2
Department of Geography, Ghent University, Krijgslaan 281 S8, B-9000 Ghent, Belgium
3
Flemish Heritage Institute, Koning Albert II-laan 19 bus 5, B-1210 Brussels, Belgium,
formerly Laboratory of Wood Technology, Ghent University Coupure Links 653, 9000
Ghent, Belgium
4
Department of Forest Sciences, University of Helsinki, PO Box 27, FI-00014 Helsinki,
Finland
5
Abisko Scientific Research Station, Royal Swedish Academy of Sciences, SE-98107
Abisko, Sweden
6
Department of Physical Geography, Uppsala University, S-75122 Uppsala, Sweden
7
Department of Animal and Plant Sciences, University of Sheffield, Western Bank, Sheffield
S10 2TN, UK
*Corresponding author: Address: Yzerhand 85, B-9120 Beveren, Belgium.
rikvanbogaert@gmail.com
Running head: Twentieth century tree line changes in Swedish sub-Arctic
2
Abstract 1
Models project that climate warming will cause the treeline to move to higher 2
elevations in alpine areas and more northerly latitudes in Arctic environments. We 3
aimed to document changes or stability of the treeline in a sub-Arctic model area at 4
different temporal and spatial scales, and particularly to clarify the ambiguity that 5
currently exists about treeline dynamics and their causes. The study was conducted in 6
the Torneträsk area in northern Sweden where climate warmed by 2.5 ˚C between 7
1913 and 2006. Mountain birch (Betula pubescens ssp. czerepanovii) sets the alpine 8
treeline. We used repeat photography, dendrochronological analysis, field 9
observations along elevational transects and historical documents to study treeline 10
dynamics. Since 1912, only four out of eight treeline sites had advanced: on average 11
the treeline had shifted 24 m upslope (+0.2 m year
-1
assuming linear shifts). 12
Maximum treeline advance was +145 m (+1.5 m year
-1
in elevation and +2.7 m year
-1
13
in actual distance), whereas maximum retreat was 120 m downslope. Counter-14
intuitively, treeline advance was most pronounced during the cooler late 1960s and 15
1970s. Tree establishment and treeline advance were significantly correlated with 16
periods of low reindeer (Rangifer tarandus) population numbers. A decreased 17
anthropozoogenic impact since the early 20
th
century was found to be the main factor 18
shaping the current treeline ecotone and its dynamics. In addition, episodic 19
disturbances by moth outbreaks and geomorphological processes resulted in descent 20
and long-term stability of the treeline position, respectively. In contrast to what is 21
generally stated in the literature, this study shows that in a period of climate warming, 22
disturbance may not only determine when treeline advance will occur but if treeline 23
advance will occur at all. In the case of non-climatic climax treelines, such as those in 24
our study area, both climate-driven model projections of future treeline positions and 25
3
the use of the treeline position for bioclimatic monitoring should be used with caution.26
27
28
Key words: climate warming, dendrochronology, herbivory, human impact, mountain 29
birch, reindeer, sub-Arctic, Sweden, tree line, tree line causes 30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
4
Introduction 47
Mean annual temperatures have risen globally over the past century, with the most
48
pronounced and rapid changes at high elevations and latitudes (ACIA, 2005). As the
49
location of elevational and polar treelines is mainly caused by heat deficiency, in the
50
Northern Hemisphere climate warming is expected to cause treelines to advance to
51
higher elevations and more northerly latitudes (Harsch et al., 2009). Indeed, modern
52
evidence for such relocations exists and these have been explicitly or implicitly
53
related to recent climate warming (Shiyatov et al., 2007; Kullman and Öberg, 2009).
54
However, in many circumpolar and high-elevational areas the position of the treeline
55
has not changed (Masek, 2001; Holtmeier et al., 2003; Payette, 2007; Van Bogaert et
56
al., 2007) or has even retreated (Vlassova, 2002; Dalen and Hofgaard, 2005; Kullman,
57
2005; Cherosov et al., 2010).
58
Treeline heterogeneity increases from global to regional, to landscape and to local
59
scales of analysis (Callaghan et al., 2002). Moreover, the factors controlling the
60
position and structure of the treeline are highly scale-dependent and vary from place
61
to place (Sveinbjörnsson et al., 2002). Individual trees and the forest system may
62
respond differently to change; warming may increase tree growth, while at the same
63
time seedling survival may be reduced because of water stress brought about by
64
greater evapotranspiration and drying of the uppermost soil. Furthermore, the time-
65
scale of a study influences outcomes because it determines the processes and
66
responses that can be studied. There are short-term responses (defined as a year or
67
less and reflected in individual tree growth), medium-term responses (some years to a
68
few decades and reflected in changing survival rates of seedlings and altered tree
69
physiognomy) and long-term responses (several decades to centuries and reflected in
70
a general treeline advance or retreat) (Holtmeier and Broll, 2005).
71
Citations
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Journal Article•DOI•
Failure to migrate: lack of tree range expansion in response to climate change

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Kai Zhu1, Christopher W. Woodall2, James S. Clark1•
Duke University1, United States Forest Service2
01 Mar 2012-Global Change Biology
TL;DR: In this paper, the authors compare the present latitudes of seedlings and adult trees at their range limits using large-scale forest inventory data and find no consistent evidence that population spread is greatest in areas where climate has changed most; nor are patterns related to seed size or dispersal characteristics.
Abstract: Tree species are expected to track warming climate by shifting their ranges to higher latitudes or elevations, but current evidence of latitudinal range shifts for suites of species is largely indirect. In response to global warming, offspring of trees are predicted to have ranges extend beyond adults at leading edges and the opposite relationship at trailing edges. Large-scale forest inventory data provide an opportunity to compare present latitudes of seedlings and adult trees at their range limits. Using the USDA Forest Service’s Forest Inventory and Analysis data, we directly compared seedling and tree 5th and 95th percentile latitudes for 92 species in 30 longitudinal bands for 43 334 plots across the eastern United States. We further compared these latitudes with 20th century temperature and precipitation change and functional traits, including seed size and seed spread rate. Results suggest that 58.7% of the tree species examined show the pattern expected for a population undergoing range contraction, rather than expansion, at both northern and southern boundaries. Fewer species show a pattern consistent with a northward shift (20.7%) and fewer still with a southward shift (16.3%). Only 4.3% are consistent with expansion at both range limits. When compared with the 20th century climate changes that have occurred at the range boundaries themselves, there is no consistent evidence that population spread is greatest in areas where climate has changed most; nor are patterns related to seed size or dispersal characteristics. The fact that the majority of seedling extreme latitudes are less than those for adult trees may emphasize the lack of evidence for climate-mediated migration, and should increase concerns for the risks posed by climate change.

567 citations

Journal Article•DOI•
Plants and climate change: complexities and surprises.

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Camille Parmesan1, Mick E. Hanley1•
University of Plymouth1
01 Nov 2015-Annals of Botany
TL;DR: It is argued that inconclusive, unexpected, or counter-intuitive results should be embraced in order to understand apparent disconnects between theory, prediction, and observation, and that the need for ecologists to conduct community-level experiments in systems that replicate multiple aspects of ACC is highlighted.

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Species better track climate warming in the oceans than on land

[...]

Jonathan Lenoir1, Romain Bertrand2, Lise Comte3, Lise Comte4, Luana Bourgeaud2, Tarek Hattab5, Jérôme Murienne2, Gaël Grenouillet2, Gaël Grenouillet6 •
University of Picardie Jules Verne1, University of Toulouse2, University of Washington3, University of Tennessee4, IFREMER5, Institut Universitaire de France6
25 May 2020-Nature Ecology and Evolution
TL;DR: Compiling a global geo-database of >30,000 range shifts, the authors show that marine species closely track shifting isotherms, whereas terrestrial species lag behind, probably due to wider thermal safety margins and movement constraints imposed by human activities.
Abstract: There is mounting evidence of species redistribution as climate warms. Yet, our knowledge of the coupling between species range shifts and isotherm shifts remains limited. Here, we introduce BioShifts—a global geo-database of 30,534 range shifts. Despite a spatial imbalance towards the most developed regions of the Northern Hemisphere and a taxonomic bias towards the most charismatic animals and plants of the planet, data show that marine species are better at tracking isotherm shifts, and move towards the pole six times faster than terrestrial species. More specifically, we find that marine species closely track shifting isotherms in warm and relatively undisturbed waters (for example, the Central Pacific Basin) or in cold waters subject to high human pressures (for example, the North Sea). On land, human activities impede the capacity of terrestrial species to track isotherm shifts in latitude, with some species shifting in the opposite direction to isotherms. Along elevational gradients, species follow the direction of isotherm shifts but at a pace that is much slower than expected, especially in areas with warm climates. Our results suggest that terrestrial species are lagging behind shifting isotherms more than marine species, which is probably related to the interplay between the wider thermal safety margin of terrestrial versus marine species and the more constrained physical environment for dispersal in terrestrial versus marine habitats. Compiling a global geo-database of >30,000 range shifts, the authors show that marine species closely track shifting isotherms, whereas terrestrial species lag behind, probably due to wider thermal safety margins and movement constraints imposed by human activities.

292 citations

Book Chapter•DOI•
Detection and attribution of observed impacts

[...]

Wolfgang Cramer, Gary W. Yohe, Maximilian Auffhammer, Christian Huggel, Ulf Molau, M.A.F.S. Dias, Rik Leemans 
01 Jan 2014
TL;DR: Cramer et al. as discussed by the authors synthesize the scientific literature on the detection and attribution of observed changes in natural and human systems in response to observed recent climate change, and assesses the degree to which detected changes in such systems can be attributed to all aspects of recent climate changes.
Abstract: Author(s): Cramer, W; Yohe, GW; Auffhammer, M; Huggel, C; Molau, U; Da Silva Dias, MAF; Solow, A; Stone, DA; Tibig, L; Leemans, R; Seguin, B; Smith, N; Hansen, G | Abstract: Introduction This chapter synthesizes the scientific literature on the detection and attribution of observed changes in natural and human systems in response to observed recent climate change. For policy makers and the public, detection and attribution of observed impacts will be a key element to determine the necessity and degree of mitigation and adaptation efforts. For most natural and essentially all human systems, climate is only one of many drivers that cause change-other factors such as technological innovation, social and demographic changes, and environmental degradation frequently play an important role as well. Careful accounting of the importance of these and other confounding factors is therefore an important part of the analysis. At any given location, observed recent climate change has happened as a result of a combination of natural, longer term fluctuations and anthropogenic alteration of forcings. To inform about the sensitivity of natural and human systems to ongoing climate change, the chapter assesses the degree to which detected changes in such systems can be attributed to all aspects of recent climate change. For the development of adaptation policies, it is less important whether the observed changes have been caused by anthropogenic climate change or by natural climate fluctuations. Where possible, the relative importance of anthropogenic drivers of climate change is assessed as well. 18.1.1. Scope and Goals of the Chapter Previous assessments, notably in the IPCC Fourth Assessment Report (AR4; Rosenzweig et al., 2007), indicated that numerous physical and biological systems are affected by recent climate change. Owing to a limited number of published studies, human systems received comparatively little attention in these assessments, with the exception of the food system, which is a coupled human-natural system. This knowledge base is growing rapidly, for all types of impacted systems, but the disequilibrium remains (see also Section 1.1.1, Figure 1-1). The great majority of published studies attribute local to regional changes in affected systems to local to regional climate change.

147 citations

Journal Article•DOI•
Ecosystem change and stability over multiple decades in the Swedish subarctic: complex processes and multiple drivers.

[...]

Terry V. Callaghan1, Terry V. Callaghan2, Christer Jonasson2, Tomas Thierfelder3, Zhenlin Yang1, Zhenlin Yang2, Henrik Hedenås3, Margareta Johansson4, Margareta Johansson2, Ulf Molau5, Ulf Molau6, Rik Van Bogaert7, Anders Michelsen8, Johan Olofsson9, Dylan Gwynn-Jones10, Stef Bokhorst3, Gareth K. Phoenix1, Jarle W. Bjerke11, Hans Tømmervik11, Torben R. Christensen4, Edward Hanna1, Eva K. Koller12, Eva K. Koller1, Victoria L. Sloan1, Victoria L. Sloan13 •
University of Sheffield1, Royal Swedish Academy of Sciences2, Swedish University of Agricultural Sciences3, Lund University4, Stockholm University5, University of Gothenburg6, Natural Resources Canada7, University of Copenhagen8, Umeå University9, Aberystwyth University10, Norwegian Institute for Air Research11, Bangor University12, Oak Ridge National Laboratory13
19 Aug 2013-Philosophical Transactions of the Royal Society B
TL;DR: A unique geo-referenced record of environmental and ecosystem observations from the area since 1913 is presented, which is of immediate relevance to local stakeholders who need to adapt to new opportunities and to respond to challenges.
Abstract: The subarctic environment of northernmost Sweden has changed over the past century, particularly elements of climate and cryosphere. This paper presents a unique geo-referenced record of environmental and ecosystem observations from the area since 1913. Abiotic changes have been substantial. Vegetation changes include not only increases in growth and range extension but also counterintuitive decreases, and stability: all three possible responses. Changes in species composition within the major plant communities have ranged between almost no changes to almost a 50 per cent increase in the number of species. Changes in plant species abundance also vary with particularly large increases in trees and shrubs (up to 600%). There has been an increase in abundance of aspen and large changes in other plant communities responding to wetland area increases resulting from permafrost thaw. Populations of herbivores have responded to varying management practices and climate regimes, particularly changing snow conditions. While it is difficult to generalize and scale-up the site-specific changes in ecosystems, this very site-specificity, combined with projections of change, is of immediate relevance to local stakeholders who need to adapt to new opportunities and to respond to challenges. Furthermore, the relatively small area and its unique datasets are a microcosm of the complexity of Arctic landscapes in transition that remains to be documented.

138 citations

References
More filters
Journal Article•DOI•
Treeline advance - driving processes and adverse factors

[...]

Friedrich Karl Holtmeier1, Gabriele Broll2•
University of Münster1, University of Vechta2
29 Jun 2007-Landscape Online
TL;DR: In this article, the effects of varying topography on site conditions and the after-effects of historical disturbances by natural and anthropogenic factors may override the effect of slightly higher average temperatures.
Abstract: The general trend of climatically-driven treeline advance is modified by regional, local and temporal variations. Treelines will not advance in a closed front parallel to the shift of any isotherm to higher elevations and more northern latitudes. The effects of varying topography on site conditions and the after-effects of historical disturbances by natural and anthropogenic factors may override the effects of slightly higher average temperatures. Moreover, the varying treeline-forming species respond in different ways to a changing climate. Forest advance upwards and northwards primarily depends on successful regeneration and survival of young growth rather than on increasing growth rates of mature trees. Every assessment of treeline response to future climate change must consider the effects of local site conditions and feedbacks of increasing tree population in modulating the climatically-driven change. Treeline-shift will influence regional and local climates, pedogenesis, plant communities, animal populations and biodiversity as well as having a considerable effect on economic changes in primary production. A better understanding of the functional relationships between the many treeline-relevant factors and treeline dynamics can be achieved only by extensive research at different scales within different climatic regions supported by as many as possible experimental studies in the field together with laboratory and remote sensing techniques.

270 citations

"A century of tree line changes in s..." refers background in this paper

  • ...At present, one of the most important gaps and uncertainties in tree line research appears on intermediate (10–10,000 km2) spatial scales (Holtmeier & Broll, 2007; Kullman & Öberg, 2009) at which feedbacks to the climate system are significant (Harding et al., 2002), yet studies on the causes of…...

    [...]

  • ...On a global scale, heat deficiency may be the dominant factor controlling tree line dynamics, but regional studies have shown that tree line position rarely changes in parallel with the shift of any isotherm (Holtmeier & Broll, 2007)....

    [...]

  • ...Projecting future tree line dynamics The extreme discrepancy that exists between model projections of the tree line position and in situ observations is a world-wide phenomenon (Holtmeier & Broll, 2007; Van Bogaert et al., 2007)....

    [...]

Journal Article•DOI•
Herbivory influences tree lines.

[...]

David M. Cairns1, Jon Moen2•
Texas A&M University1, Umeå University2
01 Dec 2004-Journal of Ecology
TL;DR: A conceptual model in which differing relative impacts of foliage consumption, availability of establishment sites, trampling, dispersal and seed predation can lead to very different tree-line responses is proposed, suggesting range expansion is occurring much more slowly, if at all.
Abstract: Summary 1 Transitions between major vegetation types, such as the tree line, are useful systems for monitoring the response of vegetation to climate change. Tree lines have, however, shown equivocal responses to such change. 2 Tree lines are considered to be primarily thermally controlled, although recent work has highlighted the importance of biotic factors. Dispersal limitation and the invasibility of the tundra matrix have been implicated and here we propose herbivory as an additional control at some tree lines. 3 We propose a conceptual model in which differing relative impacts of foliage consumption, availability of establishment sites, trampling, dispersal and seed predation can lead to very different tree-line responses. 4 The presence of large numbers of small trees above the current tree line at a site in northern Sweden that experiences limited reindeer (Rangifer tarandus) herbivory suggests range expansion. Other locations in the same region with higher reindeer populations have considerably fewer small trees, suggesting that range expansion is occurring much more slowly, if at all. 5 The use of tree lines as indicators of climate change is confounded by the activity of herbivores, which may either strengthen or nullify the impacts of a changed climate. Similar arguments are likely to be applicable to other ecotones.

242 citations

"A century of tree line changes in s..." refers background in this paper

  • ...At the tree line, disturbance by reindeer (Rangifer tarandus L.) may be significant (Cairns & Moen, 2004)....

    [...]

  • ...We confirmed the hypothesis of Emanuelsson (1987) and Cairns & Moen (2004) that the impacts of humans and semidomesticated herbivores have significantly determined the elevational shifts of the tree line boundary (Table 1)....

    [...]

Journal Article•DOI•
Post-Little Ice Age tree line rise and climate warming in the Swedish Scandes: a landscape ecological perspective

[...]

Leif Kullman1, Lisa Öberg2•
Umeå University1, Mid Sweden University2
01 May 2009-Journal of Ecology
TL;DR: In this article, the authors quantified the elevation tree line change in the southern Swedish Scandes for the period 1915-2007 and for two sub-periods 1915-1975 and 1975-2007.
Abstract: Elevational tree line change in the southern Swedish Scandes was quantified for the period 1915-2007 and for two sub-periods 1915-1975 and 1975-2007. The study focused on Betula pubescens ssp. czer ...

229 citations

"A century of tree line changes in s..." refers background or result in this paper

  • ...The importance of an ample snow cover for mountain birch, providing insulation in winter and moisture in spring, has been elucidated in previous tree line studies (Dalen & Hofgaard, 2005; Kullman & Öberg, 2009)....

    [...]

  • ...In contrast to other studies (Danby & Hik, 2007; Kullman & Öberg, 2009), slope aspect and inclination were not correlated with elevational shifts of the tree line ecotone....

    [...]

  • ...Indeed, modern evidence for such relocations exists and these have been explicitly or implicitly related to recent climate warming (Shiyatov et al., 2007; Kullman & Öberg, 2009)....

    [...]

  • ...…of the most important gaps and uncertainties in tree line research appears on intermediate (10–10,000 km2) spatial scales (Holtmeier & Broll, 2007; Kullman & Öberg, 2009) at which feedbacks to the climate system are significant (Harding et al., 2002), yet studies on the causes of tree line…...

    [...]

  • ...However, the fastest upslope shifts of tree lines recorded during 20th century warming are in the range of 1 to 2 m year)1 (Shiyatov et al., 2007; Kullman & Öberg, 2009)....

    [...]

Journal Article•DOI•
A new climate era in the sub-Arctic: Accelerating climate changes and multiple impacts

[...]

Terry V. Callaghan1, Terry V. Callaghan2, Fredrik Bergholm3, Torben R. Christensen4, Christer Jonasson2, Ulla Kokfelt4, Margareta Johansson2, Margareta Johansson4 •
University of Sheffield1, Royal Swedish Academy of Sciences2, Royal Institute of Technology3, Lund University4
01 Jul 2010-Geophysical Research Letters
TL;DR: Callaghan et al. as discussed by the authors showed that the Swedish sub-Arctic has reached a level at which statistical analysis shows for the first time that current warming has exceeded that in the late 1930' s and early 1940' s, and has significantly crossed the 0 degrees C mean annual temperature threshold which causes many cryospheric and ecological impacts.
Abstract: Climate warming in the Swedish sub-Arctic since 2000 has reached a level at which statistical analysis shows for the first time that current warming has exceeded that in the late 1930' s and early 1940' s, and has significantly crossed the 0 degrees C mean annual temperature threshold which causes many cryospheric and ecological impacts. The accelerating temperature increase trend has driven similar trends in the century-long increase in snow thickness, loss of lake ice, increases in active layer thickness, lake water TOC (total organic carbon) concentrations and the assemblages of diatoms, and changes in tree-line location and plant community structure. Some of these impacts were not evident in the first warm period of the 20th Century. Changes in climate are associated with reduced temperature variability, particularly loss of cold winters and cool summers, and an increase in extreme precipitation events that cause mountain slope instability and infrastructure failure. The long term records of multiple, local environmental factors compiled here for the first time provide detailed information for adaptation strategy development while dramatic changes in an environment particularly vulnerable to climate change highlight the need to adopt global mitigation strategies. Citation: Callaghan, T. V., F. Bergholm, T. R. Christensen, C. Jonasson, U. Kokfelt, and M. Johansson (2010), A new climate era in the sub-Arctic: Accelerating climate changes and multiple impacts, Geophys. Res. Lett., 37, L14705, doi:10.1029/2009GL042064.

212 citations

"A century of tree line changes in s..." refers background in this paper

  • ...Daily temperature and precipitation measurements are available since 1913 (Callaghan et al., 2010), human impact has been described in detail since 1600 (Emanuelsson, 1987), reindeer population numbers since 1750 (Emanuelsson, 1987) and moth outbreaks on birch have been reported since 1862 (Tenow,…...

    [...]

  • ...Daily temperature and precipitation measurements are available since 1913 (Callaghan et al., 2010), human impact has been described in detail since 1600 (Emanuelsson, 1987), reindeer population numbers since 1750 (Emanuelsson, 1987) and moth outbreaks on birch have been reported since 1862 (Tenow, 1972)....

    [...]

  • ...The Torneträsk area has an exceptionally long-term record of climatic and other environmental data offering a powerful instrument for validation of measurements (Callaghan et al., 2010)....

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  • ...The Torneträsk area has an exceptionally long-term record of climatic and other environmental data offering a powerful instrument for validation of measurements (Callaghan et al., 2010)....

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  • ...5 C increase in temperature over the period 1913– 2006 (Callaghan et al., 2010)....

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Jed O. Kaplan1, Mark New2•
University of Bern1, University of Oxford2
20 Oct 2006-Climatic Change
TL;DR: In this article, the authors used data from six Global Climate Models (GCMs) forced by four greenhouse gas emissions scenarios, the BIOME4 biogeochemistry-biogeography model, and remote sensing data to investigate the potential impact of stabilization of global temperature at 2 ∘C.
Abstract: The signatories to United Nations Framework Convention on Climate Change are charged with stabilizing the concentrations of greenhouse gases in the atmosphere at a level that prevents dangerous interference with the climate system. A number of nations, organizations and scientists have suggested that global mean temperature should not rise over 2 ∘C above preindustrial levels. However, even a relatively moderate target of 2 ∘C has serious implications for the Arctic, where temperatures are predicted to increase at least 1.5 to 2 times as fast as global temperatures. High latitude vegetation plays a significant role in the lives of humans and animals, and in the global energy balance and carbon budget. These ecosystems are expected to be among the most strongly impacted by climate change over the next century. To investigate the potential impact of stabilization of global temperature at 2 ∘C, we performed a study using data from six Global Climate Models (GCMs) forced by four greenhouse gas emissions scenarios, the BIOME4 biogeochemistry-biogeography model, and remote sensing data. GCM data were used to predict the timing and patterns of Arctic climate change under a global mean warming of 2 ∘C. A unified circumpolar classification recognizing five types of tundra and six forest biomes was used to develop a map of observed Arctic vegetation. BIOME4 was used to simulate the vegetation distributions over the Arctic at the present and for a range of 2 ∘C global warming scenarios. The GCMs simulations indicate that the earth will have warmed by 2 ∘C relative to preindustrial temperatures by between 2026 and 2060, by which stage the area-mean annual temperature over the Arctic (60–90∘N) will have increased by between 3.2 and 6.6 ∘C. Forest extent is predicted by BIOME4 to increase in the Arctic on the order of 3 × 106 km2 or 55% with a corresponding 42% reduction in tundra area. Tundra types generally also shift north with the largest reductions in the prostrate dwarf-shrub tundra, where nearly 60% of habitat is lost. Modeled shifts in the potential northern limit of trees reach up to 400 km from the present tree line, which may be limited by dispersion rates. Simulated physiological effects of the CO2 increase (to ca. 475 ppm) at high latitudes were small compared with the effects of the change in climate. The increase in forest area of the Arctic could sequester 600 Pg of additional carbon, though this effect is unlikely to be realized over next century.

163 citations

"A century of tree line changes in s..." refers background in this paper

  • ...In the next 100 years, alpine and polar tree lines are projected to shift upslope by 2 to 6 m year)1 (Moen et al., 2004) and northwards by 7.4–20 km year)1 (Kaplan & New, 2006) if climate warming continues....

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