Life-history traits controlling the survival of Tillaea aquatica: a threatened wetland plant species in intensively managed fishpond landscapes of the Czech Republic

Abstract

Tillaea aquatica (Crassulaceae) is considered as annual wetland species threatened by changes in land use and progressing eutrophication in large part of its European distribution range. We summarised the historical and recent data on this species, and analysed its distribution and associated habitat changes in the Czech Republic. We used permanent plots as well as seed bank and seed dispersal studies to obtain better insight into the plant’s survival strategy. During the second half of the twentieth century T. aquatica disappeared from most historical localities situated mainly in large fishponds. After 1999, altogether 18 new populations were found in small fry ponds and other fish-farming ponds. The largest populations of Tillaea were found in ponds with long-term bottom exposure where the vegetation of perennial herbs was eliminated by herbicides or grazing. Propagules easily dispersible by water, on gumboots or tyres of vehicles, and long-term soil seed bank also might contribute to persistence of the species in the habitats, diminishing the chance of extinction. As the fishpond management has changed, and so have done the original habitats of Tillaea, the species could survive in habitats different from those in the past. In this article, we suggest management measures aimed at promoting survival of Tillaea under new circumstances.