The landscapes of Vanhankaupunginlahti are dominated by extensive beds of common reeds (Phragmites australis). The stems grow out of the plant’s perennial rootstock that spreads far and wide, as a result of which it is not uncommon for expansive reed beds to be composed of the same, genetically individual plant.
The reed stems form large amounts of plant waste, which eventually turns into peat. The eastern part of Vanhankaupunginlahti bay is also called Ryönälahti (literally ‘waste bay’) due to the drifting reed waste.
In the past, common reeds were used as animal fodder, and the City of Helsinki sold rights to harvest the reeds. A hundred years ago, the reed beds of Helsinki weren’t nearly as extensive and lush as they are now. The spread of the reeds has been aided by the eutrophication of the bay’s waters. They have been purposefully eradicated from the conservation area in connection with the restoration of the area’s coastal meadows.
The spread of the common reed has benefited the bird species that live in the reed beds, including the Eurasian reed warbler, the great reed warbler, the western marsh harrier and the bearded reedling, which are continuing to spread to new areas. The reed beds also provide shelter to roe deer and harvest mice, which climb up the reed stems.