In most cases, these pegs are made of (steamed) beech or maple wood. The shape and material make them ideally suited for use on the beach, in the dunes and (especially) on swampy soil such as along rivers. If you want to leave this type of peg in the ground for a long time, you can paint it with red lead or primer (preferably water-based with a view to the environment!), which will significantly extend its lifespan.