I read about a fascinating new scientific study where Emmanuel Virot and colleagues at the Ecole Polytechnique and ESPCI ParisTech have concluded that there is a critical wind speed, of around 42 m/s (90 mph), at which almost all tree trunks break – regardless their size or species. Thus, under a simple scaling law, the critical wind speed is largely independent of the tree’s diameter, height or elastic properties.
That is so remarkably counterintuitive that it takes some effort to get one’s mind around it. The study does not look at tree loss due to uprooting. Rather, it focused on situations where the roots hold and there is a breakage. Some trees can break through torsion. However, most break through bending. The study looked at the bending breaks, which is referred to as “stem lodging”.
Looking at a 2009 storm called Klaus, the data showed the greatest damage to forests occurred in regions where the wind speed exceeded 42 m/s but also that it did not appear to vary on tree age and type. As an avid hiker, I find that incredibly surprising. I have seen a lot of bending breaks but always assumed that certain trees to more resistant to such loss.
In their modeling, the researchers doubled tree height but found that it increases the critical speed by only 9%. The elastic properties of the wood had a similarly small impact. That really puts serious question to the common expression that it is better to “bend than break.” It turns out that all trees break rather than bend at roughly the same rate. Go figure.