The magic number is 42 m/s (94 mph). Using mathematical data and physical experiments, scientists say they have found the law that governs the resistance of wooden beams under stress. According to the study (
link), researchers hung weights from wooden rods and pieces of pencil lead to record the amount of force needed to snap the cylinder. As one might sense, they found that for a fixed length, increasing the diameter made the rods stronger: They could bend more before breaking. This would make tall skinny trees most vulnerable, but, as the team points out, trees don’t grow taller without getting disproportionately thicker as well. By incorporating established laws of tree allometry - which explain the relationship of tree size parameters such as diameter and height - the team was able to mathematically explain why the trees break once the wind speeds reached 42 m/s. The equations show that changing the characteristics of the trees had meager effects: Doubling the size of a tree only increases the required wind speed by 9%; likewise, using wood more resistant to fracturing (oak versus pine) increased the critical wind speed by less than 10%. The scientists point out that their finding may reflect an optimization over evolutionary time, as wind speeds on Earth rarely exceed 50 m/s.
Source: http://www.sciencemag.org/news/2016/02/trees-regardless-size-all-break-same-wind-speed-here-s-why
