Understanding restoration effectiveness is often impaired by a lack of high-quality, long-term monitoring data and, to date, few researchers have used species' trait information to gain insight into the processes that drive the reaction of fish communities to restoration. We examined fish-community responses with a highly resolved data set from 21 consecutive years of electrofishing (4 years prerestoration and 17 years postrestoration) at multiple restored and unrestored reaches from a river restoration project on the Lippe River, Germany. Fish abundance peaked in the third year after the restoration; abundance was 6 times higher than before the restoration. After 5-7 years, species richness and abundance stabilized at 2 and 3.5 times higher levels relative to the prerestoration level, respectively. However, interannual variability of species richness and abundance remained considerable, illustrating the challenge of reliably assessing restoration outcomes based on data from individual samplings, especially in the first years following restoration. Life-history and reproduction-related traits best explained differences in species' responses to restoration. Opportunistic short-lived species with early female maturity and multiple spawning runs per year exhibited the strongest increase in abundance, which reflected their ability to rapidly colonize new habitats. These often small-bodied and fusiform fishes typically live in dynamic and ephemeral instream and floodplain areas that river-habitat restorations often aim to create, and in this case their increases in abundance indicated successful restoration. Our results suggest that a greater consideration of species' traits may enhance the causal understanding of community processes and the coupling of restoration to functional ecology. Trait-based assessments of restoration outcomes would furthermore allow for easier transfer of knowledge across biogeographic borders than studies based on taxonomy.
Many European lake ecosystems, including their respective catchment areas, underwent anthropogenic environmental changes over the last centuries. This has resulted in changes in the aquatic and terrestrial vegetation, but historical records on the composition of the past vegetation on centennial scale are scarce. In this study, we examined changes in the terrestrial and aquatic plant communities in and around Lower Lake Constance using metabarcoding of sedimentary DNA (sedDNA) of three cores from different sub‐basins covering the past, up to 300 years. We successfully identified an average of c. 3000 sequence variants (molecular operational taxonomic units ‐ MOTUs) and obtained a taxonomically annotated dataset of 127 species, 104 genera, and 72 families. We could detect major changes in the terrestrial and aquatic vegetation of the Lower Lake Constance region by examining the cores. For example, alpha diversity decreased in the last c. 100 years, and this decrease was more pronounced in the terrestrial than in the aquatic plant community. Unlike the terrestrial plant community, the current aquatic plant‐community composition partially resembles the community from before the 20th‐century eutrophication phase of the lake. In addition to changes that can be attributed to anthropogenic impacts, we also captured the effect of DNA sedimentation on the terrestrial DNA diversity representation in sediments during periods of extensive flooding and potentially as a consequence of extremely cold winters. With sedDNA from Lower Lake Constance, we provide a new local dataset to investigate and extend the historical changes of different shoreline habitats and to identify characteristic and invasive plant species. Such highly resolved datasets spanning the past centuries can provide detailed information on human environmental history in densely populated regions that have undergone severe changes in the recent past.
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Species are known to respond differently to restoration efforts, but we still lack a clear conceptual understanding of these differences. We analyzed the development of an entire fish community as well as the relationship between multi-metric response patterns of fish species and their ecological species traits at a comprehensively monitored river restoration project, the Lippe River in Germany. Using electrofishing data from 21 consecutive years (4 years pre- and 17 years post-restoration) from multiple restored and unrestored control reaches, we demonstrated that this restoration fully reached its targets, approximately doubling both species richness and abundance. Species richness continuously increased while fish density exhibited an overshooting response in the first years post restoration. Both richness and abundances stabilized approximately seven years after the restoration, although interannual variability remained considerable. The response of each species to the restoration was characterized using a set of six parameters. Relating the dissimilarity in species response to their ecological dissimilarity, based on 13 species traits, we found life-history and reproduction-related traits were the most important for species’ responses to restoration. Short-lived species with early female maturity and multiple spawning runs per year exhibited the strongest response, reflecting the ability of fast reproducers to rapidly colonize new habitats. Fusiform-bodied species also responded more positively than deep-bodied species, reflecting the success of this restoration to reform appropriate hydromorphological conditions (riffles and shallow bays), for which these species depend. Our results demonstrate that repeated sampling over periods longer than seven years are necessary to reliably assess river restoration outcomes. Furthermore, this study emphasizes the utility of species traits for examining restoration outcomes, particularly the metapopulation and metacommunity processes driving recovery dynamics. Focusing on species traits instead of species identity also allows for easier transfer of knowledge to other biogeographic areas and promotes coupling to functional ecology.
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