Plant species dynamics during restoration of heath ponds in northwestern Germany
Urban, Katharina E.
This study aimed at testing different restoration measures in oligotrophic heath ponds inhabited by amphibious, oligo- or mesotraphent plant species, many of which belong to the Littorelletea communities, to better understand the underlying processes of vegetation dynamics and to improve restoration techniques. Colonisation processes after vegetation removal and other measures were studied up to nine years in two heath ponds in northwestern Germany. On bare sandy soils where vegetation had been removed, initially environmental conditions were unstable. Most species expanded (but slowly) interspecific competition played a minor role. Where only Sphagnum mosses had been removed, the remaining vegetation expanded rapidly into free spaces and, furthermore, promoted germination and seedling growth. However, later Sphagnum mosses reappeared and hampered the growth and expansion of many vascular plant species.Morphogenetic plasticity, the ability of re-structuring the local distribution of the population and the possibility to form a long-term persistent seed bank (≈ 30 years), were identified as important features of pioneer plants in dynamic environments. Water table variation effected germination. For seedling survival even slight differences were relevant. In one pond studied, acidification caused a decline of characteristic soft water species (Littorelletea) 10 13 years after vegetation removal. In the other pond, a vegetation removal experiment was assumed to result in a long-lasting benefit for Scheuchzerio-Caricetea species. However, during the up to 9-year long study period, species turnovers were high and fairly unpredictable due to considerable fluctuations of the water table.