Early vegetation succession on gravel bars of Czech Carpathian streams

Abstract

Rivers with a natural flooding regime and gravel accumulations are an important natural habitat endangered by regulations and other types of human impact. Succession after disturbances by floods creates a mosaic of different vegetation types, some of them containing rare specialist species. We studied vegetation succession and changes in plant diversity on river gravel bars of four streams in the Western Carpathians and their foothills in the eastern Czech Republic. This area experienced extreme 50-year flood event in May 2010. Gravel bar vegetation was destroyed, some of the former bars were covered by sediments, and some new bars arose. We sampled gravel bar vegetation two months after the floods and repeated the sampling on each site during the next three years. Initial vegetation has developed through a sparse and species-rich stage into denser stands with more shade-tolerant species. In the fourth year, tall herbs, such as Urtica dioica, Phalaris arundinacea and the alien Impatiens glandulifera, dominated the communities, but shrub vegetation started to develop only in a few places. Species capable of vegetative dispersal prevailed over species dispersed by seeds only. Altitude and size of gravel/stone particles were identified as important factors affecting vegetation succession. The succession ran faster on gravelly substrates at lower altitudes than on stony substrates at higher altitudes. Although the studied streams are partly influenced by human interventions and host only few gravel bar specialists, they are of considerable conservation importance.