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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the authors used repeat photography, dendrochronological analysis, field observations along elevational transects and historical documents to study tree line dynamics in a sub-Arctic model area at different temporal and spatial scales.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 Methods We used repeat photography, dendrochronological analysis, field observations along elevational transects and historical documents to study tree line dynamics.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.

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Plants and climate change: complexities and surprises.

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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

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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.

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Book Chapter•DOI•
Detection and attribution of observed impacts

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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.

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

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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•
How can the dynamics of the tundra-taiga boundary be remotely monitored?

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Gareth Rees1, Ian A. Brown, Kari Mikkola, Tarmo Virtanen, Ben R. Werkman •
Scott Polar Research Institute1
01 Aug 2002-AMBIO: A Journal of the Human Environment
TL;DR: Most remote-sensing observations that are suited to the measurement of the distribution of vegetation, and identification of its type, are based on the visible and near-infrared parts of the electromagnetic spectrum, although there is increasing interest in the use of active microwave (radar) techniques.
Abstract: This paper discusses some of the difficulties in establishing the location of the Arctic treeline and forest line on a circumpolar basis, and the contribution that remote sensing, particularly from spaceborne platforms, can make in resolving them. Spaceborne techniques can provide spatial resolutions as fine as a few meters, although the requirements for regional or global coverage are likely to limit the resolution to 30 to 100 m. Since this will preclude the identification of individual trees, the definition of the treeline will be based on statistical parameters estimated from satellite images. The optimum criteria for these parameters remain to be determined. Most remote-sensing observations that are suited to the measurement of the distribution of vegetation, and identification of its type, are based on the visible and near-infrared (VIR) parts of the electromagnetic spectrum, although there is increasing interest in the use of active microwave (radar) techniques. We discuss the basis of both types of approach and the techniques that follow from them, and present 3 case studies from the Russian Arctic.

59 citations

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

  • ...This boundary was set to 30% tree-cover in a convention used by most other tree line studies (Rees et al., 2002)....

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Journal Article•
Human impacts on the tundra-taiga zone dynamics: the case of the Russian lesotundra.

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T K Vlassova
01 Aug 2002-AMBIO: A Journal of the Human Environment
TL;DR: The human impacts discussed in this article, which may actually lead to a southward movement of the lesotundra zone, are considered.
Abstract: The tundra-taiga zone is considered not only as a natural ecotone, but as a unique fringe zone with socioeconomic peculiarities This holistic approach enables us to analyze several significant types of human impacts (industrial impacts and those associated with renewable resources development, including traditional reindeer herding and human settlements) and their role in the displacement of the lesotundra zone In Russia, there is much evidence of deforestation and ecosystem degradation in different regions of the lesotundra zone and the northern taiga which borders the lesotundra zone One indicator of this is that in the Archangelsk region and the Komi Republic, the observed current southern border of the lesotundra zone lies 40-100 km to the south of the southern boundary of the Protection Belt of Pretundra Forests, established in 1959 Human impacts also displace the northern boundary of the lesotundra zone (the boundary with the tundra zone) to the south As a result, according to published estimations, the total area of human-made tundra and lesotundra stretching from the Kola Peninsula to Chukotka, is c 470-500,000 km2 The increases in man-made tundra lead to negative consequences for the sociocultural sustainability of the lesotundra zone, a decrease in the quality of life (notably for permanent residents and native people and increases in mortality and depopulation It cannot be predicted with any certainty that climate warming in the tundra-taiga zone will lead to a northward movement of the boreal forest treeline We need also to consider the human impacts discussed in this article, which may actually lead to a southward movement of the lesotundra zone

55 citations

Journal Article•DOI•
Factors structuring the treeline ecotone in Fennoscandia

[...]

Jon Moen1, David M. Cairns2, Charles W. Lafon2•
Umeå University1, Texas A&M University2
13 Aug 2008-Plant Ecology & Diversity
TL;DR: Many hypotheses have been put forward to explain the structure and position of alpine treelines as discussed by the authors, ranging from sharp boundaries to networks of tree patches with varying degrees of complexity, and the spatial complexity of the ecotone.
Abstract: Many hypotheses have been put forward to explain the structure and position of alpine treelines. The spatial complexity of the ecotone, ranging from sharp boundaries to networks of tree patches wit ...

55 citations

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

  • ...Unfortunately, this information is often not available (Moen et al., 2008) and is a major weakness in studies dealing with range migrations of plant species....

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Journal Article•DOI•
Wind-Conditioned 20th Century Decline of Birch Treeline Vegetation in the Swedish Scandes

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Leif Kullman
29 Jan 2010-Arctic
TL;DR: In this article, the authors focused on a frequent, although not dominant, mode of treeline change in the Swedish Scandes over the past century, and inferred that the extant and extinct birch populations represent different phases in an unbroken process of stand-level demise, hypothetically initiated in response to reindeer disturbance during the final phase of the Little Ice Age.
Abstract: The study focused on a frequent, although not dominant, mode of treeline change in the Swedish Scandes over the past century. Monitoring of stand density decline in a wind-exposed subalpine birch ( Betula pubescens ssp. tortuosa ) population was carried out over the past 30 years. The overall result included substantial and unbalanced individual mortality and a drastic reduction in stature of surviving birches. Radiocarbon dating of in situ subfossil birch-tree remains in an adjoining but windier site revealed complete stand demise over the past century or so. It is inferred that the extant and extinct birch populations represent different phases in an unbroken process of stand-level demise, hypothetically initiated in response to reindeer disturbance during the final phase of the Little Ice Age. This process was subsequently communicated more or less autogenically in a leeward direction as a consequence of the exposed and drought-prone nature of the site. Increasing westerly wind circulation and decreasing soil moisture (earlier snowmelt) during the past century may have contributed in this respect, although these aspects require further study. Within strongly wind-exposed terrain, a century of substantial warming has not sufficed to offset the birch decline. The results highlight the conclusion that under certain circumstances, wind and associated ecological and physiological effects are the overriding determinants of treeline position and structure. These are fundamental insights for generating realistic landscape-scale models of treeline change in a hypothetically warmer future.

47 citations

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

  • ...However, in many circumpolar and high-elevational areas the position of the tree line has not changed (Masek, 2001; Holtmeier et al., 2003; Payette, 2007; Van Bogaert et al., 2007) or has even retreated (Vlassova, 2002; Dalen & Hofgaard, 2005; Kullman, 2005; Cherosov et al., 2010)....

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T. Helle, F. E. Wielgolaski
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40 citations

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

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