Article

Ecosystems

, Volume 9, Issue 3, pp 330-343

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

  • Christof BiglerAffiliated withForest Ecology, Department of Environmental Sciences, Swiss Federal Institute of Technology (ETH)Department of Geography, University of Colorado Email author 
  • , Otto Ulrich BräkerAffiliated withSwiss Federal Institute for Forest, Snow and Landscape Research WSL
  • , Harald BugmannAffiliated withForest Ecology, Department of Environmental Sciences, Swiss Federal Institute of Technology (ETH)
  • , Matthias DobbertinAffiliated withSwiss Federal Institute for Forest, Snow and Landscape Research WSLDepartment of Environmental Science, Policy and Management, University of California
  • , Andreas RiglingAffiliated withSwiss Federal Institute for Forest, Snow and Landscape Research WSL

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Abstract

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.

Keywords

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