High nutrient loads hinder successful restoration of natural habitats in freshwater wetlands

Abstract

Restoration of natural processes in ecosystems is key to mitigate the biodiversity crisis. Here, we evaluate 20 Danish stream-valley restoration projects-mainly by rewetting-in terms of successful restoration of natural wetland habitats. We used quadratic discriminant analysis and generalized linear models to compare 80 vegetation plots from the restoration projects with >60,000 natural or semi-natural wetland reference plots. We modeled the influence of time since restoration, grazing, rewetting, and nutrient availability on (1) the probability that study plots belong to natural habitats and (2) their richness of high-quality-habitat indicator species. The probability of a restored wetland having developed into a natural wetland habitat-such as an alkaline fenwas generally below 10%. Also, we found only half as many indicator species in restored wetlands than in reference wetlands and we demonstrated that the number of characteristic alkaline fen species did not deviate from what could be expected under the prevailing nutrient conditions. We found a negative effect of soil nutrient availability on the number of high-quality-habitat indicator species and the lowest probability of plots being natural wetlands in the most nutrient rich plots. The effect of grazing was only positive in the first years after restoration and only in the most nutrient rich plots, while the effect of rewetting sites to historical hydrological conditions was generally negative. Our findings suggest that unnaturally high nutrient availability is probably the core limiting factor for successful restoration of natural wetlands and their associated plant diversity.

No lasting effects of a severe drought event on plant community composition in experimental grassland

“…The selection for relatively high Ellenberg N and low Grime S with increasing nitrogen availability was unsurprising and a natural outcome of how the indices are constructed. While grass species were more resilient to increasing nitrogen deposition than forb species in a study of acid grassland (Duprè et al 2010), dominance by tall-herb communities have been documented in studies of plant community responses to high nutrient content in restoration of wetland (Moeslund et al 2022). Furthermore, the dominant grasses at low and high nitrogen levels, respectively, are different.…”

Synthesis of special feature —Tailored Restoration Response: Predictions And Guidelines For Wetland Renewal

“…(P2): Restored hydrology alone is often insufficient to fully restore wetlands, as demonstrated in a research project led by Moeslund et al (2023). These findings suggest that the main barriers to restoration success of Danish wetland ecosystems are the high nutrient load and lack of herbivores (Fig.…”

“…Two plots with a relatively high number of high‐quality‐habitat indicator species (A) and (B); and two with a relatively low number of such species (C) and (D). Full and almost empty lab‐bottles indicate high and low soil nutrient availability (N) while ungrazed or grazed plots are indicated with a cow with or without a red cross, respectively (reproduced from Moeslund et al 2023). …”

Hungarian Grey cattle grazing outperforms mowing during wet meadow restoration following plantation forest clear-cut

“…The copyright holder for this preprint this version posted April 29, 2023. ; https://doi.org/10.1101/2023.04.28.538658 doi: bioRxiv preprint al., 2014), the complete regeneration of wet grasslands in terms of vegetation composition may take several decades (Moeslund et al, 2022).…”