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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the authors used repeat photography, dendrochronological analysis, field observations along elevational transects and historical documents to study tree line dynamics in a sub-Arctic model area at different temporal and spatial scales.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 Methods We used repeat photography, dendrochronological analysis, field observations along elevational transects and historical documents to study tree line dynamics.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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Drought induced decline could portend widespread pine mortality at the xeric ecotone in managed mediterranean pine-oak woodlands

[...]

Guillermo Gea-Izquierdo1, Guillermo Gea-Izquierdo2, Bárbara Viguera2, Miguel L. Cabrera, Isabel Cañellas2 •
Aix-Marseille University1, Center for International Forestry Research2
15 May 2014-Forest Ecology and Management
TL;DR: The pervasive growth decline with enhanced water stress in pines from all health status at the species sampled xeric ecotone combined with the abundant crown decline symptoms observed, suggest pine vulnerability and could portend widespread mortality at its current low-elevation limit.

74 citations

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Modelling Tundra Vegetation Response to Recent Arctic Warming

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Paul A. Miller1, Benjamin Smith1•
Lund University1
03 Aug 2012-AMBIO: A Journal of the Human Environment
TL;DR: An individual-based dynamic vegetation model is applied over the Arctic forced by observed climate and atmospheric CO2 for 1980–2006, showing evidence that warming has led to increased productivity and stature of tundra vegetation and reduced albedo, effecting a positive feedback to climate warming.
Abstract: The Arctic land area has warmed by >1 °C in the last 30 years and there is evidence that this has led to increased productivity and stature of tundra vegetation and reduced albedo, effecting a positive (amplifying) feedback to climate warming. We applied an individual-based dynamic vegetation model over the Arctic forced by observed climate and atmospheric CO2 for 1980–2006. Averaged over the study area, the model simulated increases in primary production and leaf area index, and an increasing representation of shrubs and trees in vegetation. The main underlying mechanism was a warming-driven increase in growing season length, enhancing the production of shrubs and trees to the detriment of shaded ground-level vegetation. The simulated vegetation changes were estimated to correspond to a 1.75 % decline in snow-season albedo. Implications for modelling future climate impacts on Arctic ecosystems and for the incorporation of biogeophysical feedback mechanisms in Arctic system models are discussed. Electronic supplementary material The online version of this article (doi:10.1007/s13280-012-0306-1) contains supplementary material, which is available to authorized users.

71 citations

Cites background from "A century of tree line changes in s..."

  • ...Important lines of evidence include positive trends in surface greenness and photosynthetic activity inferred from satellite data (Tucker et al. 2001; Bunn and Goetz 2006; Bhatt et al. 2010; Beck and Goetz 2011), advancement of elevational and latitudinal treelines (Sonesson and Hoogesteger 1983; Kullman 2002; Harsch et al. 2009; Van Bogaert et al. 2010, 2011), and an increased cover, abundance and stature of shrubs in tundra areas (Kullman 2002; Jia et al. 2003; Tømmervik et al. 2004; Tape et al. 2006; Hedenås et al. 2011; Rundqvist et al. 2011)....

    [...]

  • ...…Beck and Goetz 2011), advancement of elevational and latitudinal treelines (Sonesson and Hoogesteger 1983; Kullman 2002; Harsch et al. 2009; Van Bogaert et al. 2010, 2011), and an increased cover, abundance and stature of shrubs in tundra areas (Kullman 2002; Jia et al. 2003; Tømmervik et al.…...

    [...]

Journal Article•DOI•
Site- and species-specific treeline responses to climatic variability in eastern Nepal Himalaya

[...]

Narayan Prasad Gaire1, Narayan Prasad Gaire2, Madan Koirala2, Dinesh Raj Bhuju1, Dinesh Raj Bhuju2, Marco Carrer3 •
Nepal Academy of Science and Technology1, Tribhuvan University2, University of Padua3
01 Jan 2017-Dendrochronologia
TL;DR: Alpine treelines act as bio-indicators and bio-monitors of environmental change impacts in high elevation forests and indicate that in addition to favorable climate, species-specific competitive abilities during the recruitment phase, recruitment suppression in the Krummholz and dwarf scrub belts, and grazing determine regeneration success and treeline position in the region.

69 citations

Journal Article•DOI•
Temporal context affects the observed rate of climate‐driven range shifts in tree species

[...]

Katherine M. Renwick1, Monique E. Rocca1•
Colorado State University1
01 Jan 2015-Global Ecology and Biogeography
TL;DR: In this paper, the authors present a conceptual framework for understanding how migration timing affects the observed rate of change in global forest ecosystems, and synthesize evidence from present-day tree species migrations to determine how different migration constraints can delay tree species range shifts.
Abstract: Aim Range shifts associated with 20th-century warming have been documented for a wide range of taxa, but many species are not migrating fast enough to keep pace with the rapidly changing climate. Tree species can experience particularly long time lags in their migration response, resulting in altered forest composition and potentially delaying the migration of other obligate species. Here we review potential causes of these time lags and develop a conceptual framework for understanding how migration timing affects the observed rate of change. Location Global forest ecosystems. Methods We synthesize evidence from present-day tree species migrations to determine how different migration constraints can delay tree species range shifts. Results The rate of present-day tree migrations is frequently slower than expected, and many factors may contribute to observed migration lags. Migration constraints can be overcome given the right combination of circumstances, resulting in episodic range shifts that create temporal variability in migration rates. Given projected increases in forest disturbances and extreme climatic events, episodic range shifts are likely. Main conclusions Recent efforts to explain the slow rate of tree migration have primarily focused on dispersal limitation and niche-based constraints such as competition and other biotic interactions. We argue that these constraints cannot be fully understood without considering the temporal context of tree migration. Attempts to forecast and manage future distribution shifts must consequently consider how migration timing may affect observed patterns of change.

69 citations

Journal Article•DOI•
Aspect and slope influence plant community composition more than elevation across forest-tundra ecotones in subarctic Canada

[...]

Katherine D. Dearborn1, Ryan K. Danby1•
Queen's University1
01 May 2017-Journal of Vegetation Science
TL;DR: In this article, the authors surveyed plant communities and measured key abiotic variables across forest-tundra ecotones in six alpine valleys, each with a north and a south-facing slope, in two mountain ranges of southwest Yukon.
Abstract: Questions How does treeline community composition vary between elevations, aspects and slope angles in the alpine subarctic and what are the specific abiotic factors governing this variability? How do species richness and rates of community turnover vary from low to high elevation across the forest-tundra ecotone? What do the results indicate about future vegetation change? Location: Kluane Region, southwest Yukon, Canada. Methods We surveyed plant communities and measured key abiotic variables across forest-tundra ecotones in six alpine valleys, each with a north and a south-facing slope, in two mountain ranges of southwest Yukon. We used non-metric multidimensional scaling to identify patterns in plant community composition and infer which abiotic variables drive these patterns. We calculated species richness and community dissimilarity at regular elevational intervals to assess trends in richness and rates of community turnover within the ecotone. Results Plant communities varied more with aspect and slope angle than they did with elevation. Aspect-related differences were driven by warmer soil temperatures and deeper active layers on south compared to north-facing slopes, while differences related to slope angle occurred only on north-facing slopes and were driven by soil moisture. Species richness increased with elevation on north-facing slopes and showed no trend with elevation on south-facing slopes. Rates of community turnover were higher on south-facing than north-facing slopes. Conclusions Plant community composition within the forest-tundra ecotone is driven primarily by soil temperature and, to a lesser extent, soil moisture, both of which vary more in relation to aspect and slope angle than they do between forest and tundra elevations. We recommend that models of vegetation change in subarctic alpine regions address the possibility of change occurring at different rates and in different directions depending on the topographic characteristics of each slope. This article is protected by copyright. All rights reserved.

67 citations

Cites background from "A century of tree line changes in s..."

  • ...Forest line, defined here as the upper limit of 30% canopy cover of trees at least 5 m in height (see Van Bogaert et al. 2011) occurs approximately 100 m a.s.l. below tree line....

    [...]

  • ...Species richness is generally expected to be higher in ecotones than in adjacent communities (Lomolino 2001; but see Van der Maarel 1976)....

    [...]

  • ...Van Bogaert, R., Haneca, K., Hoogesteger, J., Jonasson, C., De Dapper, M. & Callaghan, T.V. 2011....

    [...]

  • ...Van der Maarel, E. 1976....

    [...]

References
More filters
Book•
Arctic climate impact assessment

[...]

Carolyn Symon, Lelani Arris, Bill Heal, Assesment Intergration Team
01 Jan 2005
TL;DR: The Arctic Climate Impact Assessment (ACIA) as mentioned in this paper is an assessment of the effects of climate change on the Arctic environment and its impacts on the local communities and their livelihoods.
Abstract: 1. An introduction to the Arctic Climate Impact Assessment 2. Arctic climate: past and present 3. The changing Arctic: indigenous perspectives 4. Future climate change: modeling and scenarios for the Arctic 5. Ozone and ultraviolet radiation 6. Cryosphere and hydrology 7. Arctic tundra and polar fesert ecosystems 8. Freshwater ecosystems and Fisheries 9. Marine Systems 10. Principles of conserving the Arctic's Biodiversity 11. Management and conservation of wildlife in a changing Arctic environment 12. Hunting, herding, fishing, and gathering: indigenous peoples and renewable resource use in the Arctic 13. Fisheries and aquaculture 14. Forests, land management, and agriculture 15. Human health 16. Infrastructure: buildings, support systems, and industrial facilities 17. Climate change in the context of multiple stressors and resilience 18. Summary and synthesis of the ACIA Appendix A. Chapter authors Appendix B. Biographies Appendix C. Reviewers Appendix D. Species names Appendix E. Acronyms Appendix F. Glossary.

1,775 citations

Journal Article•DOI•
Vegetation Ecology of Central Europe.

[...]

J. R. Etherington, Heinz Ellenberg, G. K. Strutt
01 Sep 1989-Journal of Ecology

1,311 citations

Journal Article•DOI•
Are treelines advancing? A global meta‐analysis of treeline response to climate warming

[...]

Melanie A. Harsch1, Philip E. Hulme1, Matt S. McGlone2, Richard P. Duncan1, Richard P. Duncan2 •
Lincoln University (New Zealand)1, Landcare Research2
01 Oct 2009-Ecology Letters
TL;DR: Diffuse treelines may be more responsive to warming because they are more strongly growth limited, whereas other treeline forms may be subject to additional constraints.
Abstract: Treelines are temperature sensitive transition zones that are expected to respond to climate warming by advancing beyond their current position. Response to climate warming over the last century, however, has been mixed, with some treelines showing evidence of recruitment at higher altitudes and/or latitudes (advance) whereas others reveal no marked change in the upper limit of tree establishment. To explore this variation, we analysed a global dataset of 166 sites for which treeline dynamics had been recorded since 1900 AD. Advance was recorded at 52% of sites with only 1% reporting treeline recession. Treelines that experienced strong winter warming were more likely to have advanced, and treelines with a diffuse form were more likely to have advanced than those with an abrupt or krummholz form. Diffuse treelines may be more responsive to warming because they are more strongly growth limited, whereas other treeline forms may be subject to additional constraints.

1,003 citations

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

  • ...In contrast to Harsch et al. (2009) who concluded that the role of disturbance during recent climate warming is restricted to determining when tree line advance will occur, this study shows that disturbance and its after-effects may equally well determine ı́f tree line advance will occur at all....

    [...]

  • ...As the location of elevational and polar tree lines is mainly caused by heat deficiency, in the Northern Hemisphere climate warming is expected to cause tree lines to advance to higher elevations and more northerly latitudes (Harsch et al., 2009)....

    [...]

  • ...…widely held expectations of vegetation responses to warming, i.e. that Arctic tree lines will move northwards and elevational tree lines upslope (Harsch et al., 2009), this study documented highly varying tree line dynamics for the Torneträsk area in sub-Arctic Sweden during a period of…...

    [...]

  • ...A global study by Harsch et al. (2009) showed that only 52% of all 166 global tree line sites had advanced over the past 100 years despite documented amplified climate warming at high-elevation areas and northern latitudes (ACIA, 2005)....

    [...]

Journal Article•DOI•
Sensitivity and response of northern hemisphere altitudinal and polar treelines to environmental change at landscape and local scales

[...]

Friedrich-Karl Holtmeier1, Gabriele Broll2•
University of Münster1, University of Vechta2
01 Sep 2005-Global Ecology and Biogeography
TL;DR: The sensitivity and response of northern hemisphere altitudinal and polar treelines to environmental change are increasingly discussed in terms of climate change, often forgetting that climate is only one aspect of environmental variation as mentioned in this paper.
Abstract: The sensitivity and response of northern hemisphere altitudinal and polar treelines to environmental change are increasingly discussed in terms of climate change, often forgetting that climate is only one aspect of environmental variation. As treeline heterogeneity increases from global to regional and smaller scales, assessment of treeline sensitivity at the landscape and local scales requires a more complex approach than at the global scale. The time scale (short-, medium-, long-term) also plays an important role when considering treeline sensitivity. The sensitivity of the treeline to a changing environment varies among different types of treeline. Treelines controlled mainly by orographic influences are not very susceptible to the effects of warming climates. Greatest sensitivity can be expected in anthropogenic treelines after the cessation of human activity. However, tree invasion into former forested areas above the anthropogenic forest limit is controlled by site conditions, and in particular, by microclimates and soils. Apart from changes in tree physiognomy, the spontaneous advance of young growth of forest-forming tree species into present treeless areas within the treeline ecotone and beyond the tree limit is considered to be the best indicator of treeline sensitivity to environmental change. The sensitivity of climatic treelines to climate warming varies both in the local and regional topographical conditions. Furthermore, treeline history and its after-effects also play an important role. The sensitivity of treelines to changes in given factors (e.g. winter snow pack, soil moisture, temperature, evaporation, etc.) may vary among areas with differing climatic characteristics. In general, forest will not advance in a closed front but will follow sites that became more favourable to tree establishment under the changed climatic conditions.

518 citations

Journal Article•DOI•
Variability, contingency and rapid change in recent subarctic alpine tree line dynamics

[...]

Ryan K. Danby1, David S. Hik1•
University of Alberta1
01 Mar 2007-Journal of Ecology
TL;DR: In this article, the authors examined recent tree line dynamics at six topographically different, but climatically similar, sites in south-west Yukon, Canada and found that tree line elevation and stand density increased significantly during the early to mid 20th century.
Abstract: Summary 1 Boundaries between forest and tundra ecosystems, tree lines, are expected to advance in altitude and latitude in response to climate warming. However, varied responses to 20th century warming suggest that in addition to temperature, tree line dynamics are mediated by species-specific traits and environmental conditions at landscape and local scales. 2 We examined recent tree line dynamics at six topographically different, but climatically similar, sites in south-west Yukon, Canada. Dendroecological techniques were used to reconstruct changes in density of the dominant tree species, white spruce (Picea glauca), and to construct static age distributions of willow (Salix spp.), one of two dominant shrub genera. Data were analysed to identify periods and rates of establishment and mortality and to relate these to past climate. 3 Tree line elevation and stand density increased significantly during the early to mid 20th century. However, this change was not uniform across sites. Spruce advanced rapidly on south-facing slopes and tree line rose 65–85 m in elevation. Tree line did not advance on north-facing slopes, but stand density increased 40–65%. Differences observed between aspects were due primarily to the differential presence of permafrost. Additional variability among sites was related to slope and vegetation type. Results were less conclusive for willow, but evidence for an advance was found at two sites. 4 Increases in stand density were strongly correlated with summer temperatures. The period of rapid change coincided with a 30-year period of above average temperatures, beginning in 1920. The highest correlations were obtained using a forward average of 30–50 years, supporting the hypothesis that tree line dynamics are controlled more by conditions influencing recruitment than by establishment alone. 5 The changes observed at several sites are suggestive of a threshold response and challenge the notion that tree lines respond gradually to climate warming. Overall, the results provide further evidence to support the idea that the pattern and timing of change is contingent on local, landscape, and regional-scale factors, as well as species’ biology.

334 citations

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

  • ...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....

    [...]

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