Wood quality and storm damage risk
On December 26 in 1999, the windstorm «Lothar» stroke large parts of western and central Europe. In Switzerland, the resulting damages amounted to 12.7 Mio m³ of timber, corresponding to 2.8 times the annual national timber harvest. Although the main reason for these exceptional windthrow damages were the extreme peak velocities in the Swiss Plateau, nutritional changes may have increased the risk of wind damage. Results of simulation experiments revealed that wood density tends to increase in elevated CO₂, and to decrease when N availability is enhanced (e.g. by soluble N deposition). Such damages in wood quality could theoretically influence the risk of damage.
We used the «Lothar» catastrophe as a natural experiment to test whether there are links between damage and wood properties. Lower wood density as a response to high N-input reduces wood stiffness and increases the risk of wood fracture. In this project we investigate whether we can find damage patterns among the trees thrown by «Lothar» which correspond to the experimental findings. Increased radial growth and reduced wood density seems likely because atmospheric N deposition strongly increased since 1950. In 104 windthrow sites across the Swiss Plateau, more than 1600 wood cores from broken uprooted and still standing, not damaged spruce trees were collected in February and March 2000. Wood properties and chemistry of the wood samples are analysed. We find same characteristic correlations between physical and chemical wood properties and damage type.
This project is part of the «Lothar» research program of the Federal Office of Environment, Forest and Landscape FOEFL, Bern (BUWAL).