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

• Published in: Ecosystems (New York) 2006-04, Vol.9 (3), p.330-343
• Main Authors: Bigler, C, Braker, O.U, Bugmann, H, Dobbertin, M, Rigling, A
• Format: Article
• Language: English
• Subjects: air pollution; Animal and plant ecology; Animal, plant and microbial ecology; Biological and medical sciences; Coniferous forests; Datasets; Dead wood; Death; Drought; Drought index; Evergreen trees; Extreme drought; Forest ecology; Forestry; Fundamental and applied biological sciences. Psychology; General aspects; Growth rings; Health risks; Mortality; Mortality risk; Pine trees; Pinus sylvestris; risk assessment; statistical models; Synecology; Terrestrial ecosystems; Tree growth; tree mortality; Trees
• ISSN: 1432-9840; 1435-0629
• DOI: 10.1007/s10021-005-0126-2

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.