How do alder catkins release their mature fruits?

Alders (genus Alnus) produce small, winged nutlets that are dispersed by wind. These fruits develop within conelike structures, which are modified female catkins.123

Unlike some other plants that shed their entire catkin or release seeds through active mechanical mechanisms, the conelike structures of the alder remain on the branches after the mature fruits have been released. The small, winged nutlets are shed from these persistent, woody, conelike structures, allowing them to be carried away by the wind.12