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CR 53:63-76 (2012)  -  DOI:

Legacies of pre-industrial land use can bias modern tree-ring climate calibrations

Björn E. Gunnarson1,2,*, Torbjörn Josefsson3, Hans W. Linderholm4, Lars Östlund1

1Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, 901 83 Umeå, Sweden
2Department of Physical Geography and Quaternary Geology, Stockholm University, 106 91 Stockholm, Sweden
3Landscape Ecology Group, Department of Ecology and Environmental Science, Umeå University, 901 87 Umeå, Sweden
4Regional Climate Group, Department of Earth Sciences, University of Gothenburg, 405 30 Gothenburg, Sweden

ABSTRACT: In Scandinavia, dendrochronological reconstructions of past climate have mostly been based on tree-ring data from forests in which there has been, supposedly, very little or no human impact. However, human land use in sub-alpine forests has a substantially longer history and more profound effects on the forest ecosystems than previously acknowledged. Therefore, to assess human influence on tree-ring patterns over the last 500 yr, we have analyzed tree-ring patterns using trees from 2 abandoned Sami settlements and a reference site with no human impact—all situated in the Tjeggelvas Nature Reserve in north-west Sweden. The hypothesis was that land-use legacies have affected tree-ring patterns, and in turn, the resulting palaeoclimate inferences that have been made from these patterns. Our results show that climate signals are strongest at the reference site and weakest at one of the settlement sites. From the 1940s to the present, tree growth at this settlement site has been significantly lower than at the reference site. Lower tree growth at old settlements may have resulted from rapid changes in the traditional land use, or following the abrupt change when the settlements were abandoned. Without site-specific knowledge of past land use, there is a high risk of accidently sampling trees that have been affected by human-induced disturbances in the past. This may create bias in the climate signals inferred from such trees, and hence bias the outcome of climate reconstructions. We therefore recommend sampling several separate sites in study areas to improve the robustness of inferences.

KEY WORDS: Scots pine · Tree-rings · Maximum latewood density · Climate reconstruction · Human land use · Vegetation history

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Cite this article as: Gunnarson BE, Josefsson T, Linderholm HW, Östlund L (2012) Legacies of pre-industrial land use can bias modern tree-ring climate calibrations. Clim Res 53:63-76.

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