Wetland restoration on Öland : a short-term evaluation of vascular plant community composition after topsoil removal and reinstated grazing

Abstract: Wetlands are recognized as important types of ecosystems, inhabiting rich biodiversity and performing multiple ecosystem services. However, many have been lost because of anthropogenic activities and a majority of the remaining wetland habitats are in bad conditions, displaying both loss of functionality and biodiversity. Despite large scale global incentives and extensive conservation programs, there are large gaps of knowledge in how to restore and maintain wetlands, where variable success rates have been reported. Here, a short term evaluation was conducted in Petgärdeträsk and Djustadträsk on Öland, after restorations had been initiated three years prior, focusing on the vascular plant community. Patches where vegetation had previously been completely removed were here compared to neighbouring untreated vegetation in order to study potential effects of restoration measures on biodiversity and plant community composition. As patches of different ages existed, these were further compared to evaluate the regeneration of vegetation and formation of community composition over time. In addition, two sites were evaluated in this study accordingly to the standardized national guidelines based on the European habitat protection directive. Studied either as an alkaline fen (EU-code 7230) or a potential Molinia meadow (EU-code 6410), the purpose was to evaluate if and what effect the restoration has had on the vegetation and the trajectory goal of reaching favourable conditions. As an alternative to functional groups, Ellenberg indicator values were applied to analyse the community composition and to study if the existing vegetation would indicate favourable ecological conditions. Results showed no clear pattern of regrowth or change in species composition over time after vegetation had been removed, although species unique to the scraped patches were observed. However, due to the short time since the initiation of the restoration, it remains unclear whether these species will persist and lead to a shift in community composition or are more opportunistic species that eventually will be outcompeted as the old vegetation establish further. For the Natura 2000-habitats, no evident improvement of the conditions were seen. The differences in the number of characteristic species and in vegetation height that were observed in the vegetation here, could be due to seasonal fluctuations and can therefore not be determined as effects of the restoration only. Three years is a relatively short time to evaluate effects of restorations, and despite inconclusive results hopefully this material can provide insight to the further development of the vegetative community if the same sites would to be revisited in the future. As discussed lastly, the need for thorough evaluations persists, where adopting wider perspectives and including analyses of functional diversity could improve our understanding of how vegetative communities function and hopefully facilitate the maintenance of valuable wetland habitats.