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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

(2011) JOURNAL OF BIOGEOGRAPHY. 38(5). p.907-921
Author
Organization
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 Methods We used repeat photography, dendrochronological analysis, field observations along elevational transects and historical documents to study tree line dynamics.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.
Keywords
Sweden, tree line dynamics, TUNDRA-TAIGA INTERFACE, sub-Arctic, reindeer, mountain birch, human impact, herbivory, dendrochronology, Climate warming, PUBESCENS SSP TORTUOSA, MOUNTAIN BIRCH, SCANDES MOUNTAINS, SWEDISH SCANDES, DYNAMICS, VEGETATION, LANDSCAPE, TREELINES, FORESTS

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Citation

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Chicago
Van Bogaert, Rik, Kristof Haneca, Jan Hoogesteger, Christer Jonasson, Morgan De Dapper, and Terry V Callaghan. 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.
APA
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.
Vancouver
1.
Van Bogaert R, Haneca K, Hoogesteger J, Jonasson C, De Dapper M, Callaghan TV. 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. 2011;38(5):907–21.
MLA
Van Bogaert, Rik, Kristof Haneca, Jan Hoogesteger, et al. “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 (2011): 907–921. Print.
@article{1221992,
  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.},
  author       = {Van Bogaert, Rik and Haneca, Kristof and Hoogesteger, Jan and Jonasson, Christer and De Dapper, Morgan and Callaghan, Terry V},
  issn         = {0305-0270},
  journal      = {JOURNAL OF BIOGEOGRAPHY},
  keyword      = {Sweden,tree line dynamics,TUNDRA-TAIGA INTERFACE,sub-Arctic,reindeer,mountain birch,human impact,herbivory,dendrochronology,Climate warming,PUBESCENS SSP TORTUOSA,MOUNTAIN BIRCH,SCANDES MOUNTAINS,SWEDISH SCANDES,DYNAMICS,VEGETATION,LANDSCAPE,TREELINES,FORESTS},
  language     = {eng},
  number       = {5},
  pages        = {907--921},
  title        = {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},
  url          = {http://dx.doi.org/10.1111/j.1365-2699.2010.02453.x},
  volume       = {38},
  year         = {2011},
}

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