, Volume 9, Issue 3, pp 330–343 | Cite as

Drought as an Inciting Mortality Factor in Scots Pine Stands of the Valais, Switzerland

  • Christof BiglerEmail author
  • Otto Ulrich Bräker
  • Harald Bugmann
  • Matthias Dobbertin
  • Andreas Rigling


During the 20th century, high mortality rates of Scots pine (Pinus silvestris L.) have been observed over large areas in the Rhône valley (Valais, Switzerland) and in other dry valleys of the European Alps. In this study, we evaluated drought as a possible inciting factor of Scots pine decline in the Valais. Averaged tree-ring widths, standardized tree-ring series, and estimated annual mortality risks were related to a drought index. Correlations between drought indices and standardized tree-ring series from 11 sites showed a moderate association. Several drought years and drought periods could be detected since 1864 that coincided with decreased growth. Although single, extreme drought years had generally a short-term, reversible effect on tree growth, multi-year drought initiated prolonged growth decreases that increased a tree’s long-term risk of death. Tree death occurred generally several years or even decades after the drought. In conclusion, drought has a limiting effect on tree growth and acts as a bottleneck event in triggering Scots pine decline in the Valais.


drought tree mortality Scots pine (Pinus silvestris L.) air pollution mortality risk statistical models tree rings climate competition 



We would like to thank Bärbel Zierl (Forest Ecology, Zürich, Switzerland) and Esther Hegglin (Zug, Switzerland) for their support in the field. We are also indebted to Felix Kienast and Fritz Schweingruber (both WSL, Birmensdorf, Switzerland) for use of their tree-ring data. Thanks are due to Ludger Wenzelides (Forest Ecology, Zürich, Switzerland) for creating the GIS map, to Thomas Wohlgemuth (WSL, Birmensdorf, Switzerland) for his helpful comments on an earlier version of the manuscript, and to Rosemary Sherriff (University of Colorado, Boulder, USA) for improving the language of the manuscript. We would also like to thank the Seminar for Statistics (ETH, Zürich, Switzerland) for statistical advice. We appreciate helpful comments from two anonymous reviewers and the editor. Finally, we are grateful to the Forest Service of the canton of Valais for their generous support.


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Copyright information

© Springer Science+Business Media, Inc. 2006

Authors and Affiliations

  • Christof Bigler
    • 1
    • 2
    Email author
  • Otto Ulrich Bräker
    • 3
  • Harald Bugmann
    • 1
  • Matthias Dobbertin
    • 3
    • 4
  • Andreas Rigling
    • 3
  1. 1.Forest Ecology, Department of Environmental SciencesSwiss Federal Institute of Technology (ETH)ZürichSwitzerland
  2. 2.Department of GeographyUniversity of ColoradoBoulderUSA
  3. 3.Swiss Federal Institute for ForestSnow and Landscape Research WSLBirmensdorfSwitzerland
  4. 4.Department of Environmental Science, Policy and ManagementUniversity of CaliforniaBerkeleyUSA

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