The European aspen
The European aspen is the only Scandinavian representative of the aspens in the poplar family. The European aspen is called bævreaspen in Danish (bævre means “tremble”) because its leaves move with the slightest wind.
If you are standing by a group of European aspens on a dead calm day, the leaves will often make a “rattling” sound. This is because of the long compressed leaf stems and the slightly spoon-shaped leaves. The shape of the leaf means that there is a negative pressure on the upper surface when the wind passes through the tree’s crown. The leaf turns to equalise the pressure between the top and the bottom. This is possible because of the long soft compressed stalk, which acts as a sort of flat spring which can both turn and bend without breaking, so when the leaves can bend with the wind, neither are they broken by strong winds. See if you can roll a stalk between two fingers – hold the stalk close to the leaf blade.
The European aspen was one of the first trees to immigrate to Denmark over 12,000 years ago. The seeds are very small and easily spread by the wind, but they don’t sprout well in Denmark. Perhaps this little aspen grove is an exception to the rule, or there may also have been a root fragment in the soil used to make the dam in the 1950s. The grove has then grown from the root suckers, so all the . trees would thus be the same plant.