Nigel. J. Willby

Reintroduction of keystone species is considered part of the solution to the current biodiversity crisis. The Eurasian beaver ( Castor fiber ) is one such species, shaping its habitat by felling trees, building dams and creating wetlands. However, whilst the potential benefits to aquatic biodiversity and ecological functioning have been studied on a local scale, the impacts of beavers on catchment‐scale processes such as fish migration remain understudied. Sequencing of environmental DNA (eDNA metabarcoding) from water samples is a cost‐effective method to study species distributions across large geographical scales. Here, eDNA samples ( n = 426) were collected from 142 sites across Britain's oldest and largest established wild beaver population, located on Tayside, East Scotland and analysed using a vertebrate‐specific metabarcoding assay. We combined detection/non‐detection data from eDNA results with other environmental and anthropogenic variables to model the effects of beaver eDNA detections on the distribution of three migratory fish species. Using generalised linear models, we found no effects of the current beaver eDNA detections on the distribution of Atlantic salmon or lamprey, but a positive co‐occurrence with European eel at the catchment scale. Model outputs also reinforced previous findings on the impact of barriers to migration and other abiotic and biotic factors on fish species, demonstrating the effectiveness of eDNA sampling in rivers for understanding species distributions at a catchment scale. Synthesis and applications . This study provides novel insights into the catchment‐scale co‐distribution of beavers and migratory fish, and there was no evidence of negative effects on the catchment‐scale distribution of migratory fish species. More generally, this study highlights how catchment‐wide eDNA monitoring can be applied by environmental managers to aid decision‐making and impact assessment of multiple priority species at the catchment scale.

Forests are critical to the provision of goods and services. They experience many threats including the presence of invasive alien plants (IAPs) which can impact native biodiversity and ecosystem functioning. However, there is a lack of synthesis around outcomes and costs of managing IAPs in forests. We conducted a systematic review to identify (i) where IAP management is reported globally, (ii) which IAP species are being managed, (iii) which methods are being used and (iv) which are the most effective, relative to a control or baseline condition, at managing IAPs in forests. Studies assessing outcomes of IAP management in forests were conducted in 26 countries. The United States dominated the evidence base, accounting for 61% of included studies, covering the widest range of IAP species. This likely reflects a combination of extensive forest cover, high IAP prevalence, and research infrastructure and investment. Across 192 studies, 623 combinations of species and management treatments were studied. Chemical application was most popular (41% of methods) and generally had a high success rate. Most methods had mixed outcomes, with the use of animals for grazing being the most varied. Low replication across treatments made it difficult to draw firm conclusions about management effectiveness. Only 15% of included studies evaluated the effect of seasonal timing on management outcomes, despite evidence from these studies that seasonality can influence success. Furthermore, only 6% of studies reported management costs, and reporting was inconsistent among those that did. Synthesis and applications . This review exposes urgent and critical knowledge gaps in forest IAP management, which need addressing to meet global targets for biodiversity and forest health. These gaps include highly uneven global research effort, narrow species focus, limited method replication, overlooked seasonal effects, and inconsistent cost reporting. A strong legacy of using chemical methods may also be deterring efforts to develop non‐chemical approaches. Immediate action is needed to develop standardised methodologies and reporting channels to close these gaps and thus aid informed choice of management options by practitioners.

SCIEPublish is an international open-access journal publishing service provider run by SCIE Publishing Limited, dedicated to supporting and inspiring scientists or institutions/societies who aspire to publish high-quality journals.

Beavers are second only to humans in their capacity to transform landscapes. Biodiversity responses to their habitat engineering activities are well studied but rarely so ‘beyond the pond’ despite habitat alteration commonly extending into more terrestrial environments. Potentially profound spillover effects on, for example, pollinator communities, may therefore be overlooked. In this study, we compared plant communities, pollinator communities and plant–pollinator networks around beaver wetlands and human‐created ponds. Specifically, we tested if these wetland types differ in terms of (1) plant species richness and community composition, (2) pollinator species richness and abundance, and the floral characteristics (number of species in flower and maximum flower coverage) to which pollinators respond and (3) specialisation of their plant‐pollinator networks. Plant composition but not species richness differed between the two wetland types. Beaver wetlands supported more ruderal and competitor indicator species, whereas human‐created ponds had more stress tolerators. Hoverfly richness (+29%), hoverfly abundance (+119%) and butterfly abundance (+45%) were higher in beaver wetlands, the former two being positively associated with number of species in flower and maximum flower coverage, and the latter with open habitats. Butterfly richness and both the richness and abundance of bees and moths showed no difference between wetland types. Hoverflies were the dominant flower visitor in beaver wetlands and bees in human‐created ponds, but network level specialisation did not differ significantly between the two wetland types. Synthesis and applications . Our results show that beaver wetlands boost hoverfly richness/abundance and butterfly abundance and diversify foraging resources for pollinators while comparing favourably with human‐created ponds for other pollinators. Support for beaver wetlands, in tandem with riparian buffers and pond margins, should therefore be advocated in agri‐environment schemes to recognise the pollinator services they provide.

Reintroduction of keystone species is considered part of the solution to the current biodiversity crisis. The Eurasian beaver ( Castor fiber ) is one such species, shaping its habitat by felling trees, building dams and creating wetlands. However, while the potential benefits to aquatic biodiversity and ecological functioning have been studied on a local scale, the impacts of beavers on catchment-scale processes such as fish migration remain understudied. Sequencing of environmental DNA (eDNA metabarcoding) from water samples is a cost-effective method to study species distributions across large geographical scales. Here, eDNA samples ( n =426) were collected from 142 sites across the UK’s oldest and largest established wild beaver population, located on Tayside, East Scotland, and analysed using a vertebrate specific metabarcoding assay. We combined presence/absence data from eDNA results with other environmental and anthropogenic variables to model the effects of beaver presence on the distribution of three migratory fish species. Using generalised linear models, we found no effects of the current beaver presence on the distribution of Atlantic salmon or lamprey, but a positive co-occurrence with European eel at the catchment scale. Model outputs also reinforced previous findings on the impact of barriers to migration and other abiotic and biotic factors on fish species, demonstrating the effectiveness of eDNA sampling in rivers for understanding species distributions at a catchment scale. This case study provides novel insights into the co-distribution of beavers and migratory fish, and highlights how catchment-wide eDNA monitoring can be applied by environmental managers to aid decision-making and impact assessment more generally.

Global water security is critical for human health, well-being, and economic stability. However, freshwater environments are under increasing anthropogenic pressure and now, more than ever, there is an urgent need for integrated approaches that couple issues of water security and the remediation of degraded aquatic environments. One such strategy is the use of floating treatment wetlands (FTW), which are artificial floating mats that sustain and support the growth of macrophytes capable of removing nutrients from over-enriched waterbodies. In this study, we quantify a range of indicators associated with FTWs, planted with different vegetation community types (i.e., monocultures and polycultures) over the course of a three-year field-scale study. The composition of the two different types of FTWs changed significantly with a convergence in diversity and community composition between the two types of FTWs. Phytoremediation potential of the two FTW communities, in terms of nutrient standing stocks, were also similar but did compare favourably to comparable wild-growing plant communities. There were few substantial differences in invertebrate habitat provision under the FTWs, although the high incidence of predators demonstrated that FTWs can support diverse macroinvertebrate communities. This field-scale study provides important practical insights for environmental managers and demonstrates the potential for enhanced ecosystem service provision from employing nature-based solutions, such as FTWs, in freshwater restoration projects.

Environmental DNA (eDNA) metabarcoding is transforming biodiversity monitoring in aquatic environments where the method has repeatedly shown comparable or better performance than conventional approaches to fish monitoring. This method has been developed and deployed, primarily using shoreline sampling during the winter months, across 101 lakes in Great Britain alone, covering a wide spectrum of lake types and ecological quality. Previous analyses on a subset of these lakes indicated that 20 water samples per lake are sufficient to reliably estimate fish species richness, but it is unclear how reduced eDNA sampling effort affects richness, or other biodiversity estimates and metrics. As the number of samples strongly influences the cost of monitoring programmes, it is essential that sampling effort is optimised for a specific monitoring objective. The aim of this project was to explore the effect of reduced eDNA sampling effort on biodiversity metrics (namely species richness and community composition) using algorithmic and statistical resampling techniques. The results showed that reliable estimation of lake fish species richness could in fact usually be achieved with a much lower number of samples. For example, in almost 90% of lakes, 95% of complete fish richness could be detected with only 10 water samples, regardless of lake area. Similarly other measures of alpha and beta-diversity were not greatly affected by a reduction in sample size from 20 to 10 samples. We also found that there is no significant difference in detected species richness between shoreline and offshore sampling transects, allowing for simplified field logistics. This could potentially allow the effective sampling of a larger number of lakes within a given monitoring budget. However, rare species were more often missed with fewer samples, with potential implications for monitoring of invasive or endangered species. These results should inform the design of eDNA sampling strategies, so that these can be optimised to achieve specific monitoring goals.

Flow regulation is a prolific and growing influence on rivers world‐wide. Nine cascade hydropower dams were constructed along the 1,150‐km Wujiang River in China over the past 30 years, disrupting longitudinal continuity. Water level fluctuations in the associated reservoirs range between daily, weekly, seasonal, and annual, depending on the type of regulation, but the comparative impacts of these regimes on plant growth strategies, or the extent of their downstream influence, is unknown. Competitor, stress‐tolerator, and ruderal (CSR) plant strategies were used to assess the impact of reservoir regulation type on the riparian herbaceous plant community based on sampling the inundation zone of nine reservoirs and their downstream river reaches during 2017 and 2018. Our results revealed profound differences in CSR plant strategies of the dominant vegetation with respect to water level regime. While ruderal plants dominated (45%–60% of species), irrespective of regulation type, vegetation in reservoirs exhibited a strong shift from stress‐tolerators (e.g., Cynodon dactylon, C‐11.9:S‐41.5:R‐46.5%) to competitors (e.g., Reynoutria japonica, C‐77.9:S‐0:R‐22.0%) with increasing intensity of water level fluctuation, reflecting the shift from annual to daily regulation. The width of the inundation zone was the best overall variable in explaining the CSR strategies of riparian vegetation, both in the reservoir inundation zone (r²‐adj = 15.4%) and the downstream river (r²‐adj = 7.3%). Retention time significantly explained variation in CSR plant strategies in the reservoir inundation zone (r²‐adj = 3.7%, p = 0.002) but not downstream (p > 0.01). There was also a clear scale dependency of CSR plant strategies, with an increase in stress tolerators (average slope = 0.7%/km) and decline of competitor (average slope = −0.3%/km) and ruderal plants (average slope = −0.9%/km) with increasing distance downstream from dams. The growth strategies of the dominant riparian vegetation changed with the magnitude and frequency of water level fluctuations caused by differences in regulation type, and local environmental conditions. Clear scale dependency in the CSR plant strategies was observed with distance from the dam, with ruderals dominating closest to the reservoirs and declining gradually downstream as stress tolerators increased. Our study helps to evaluate the impact of river damming on the functional traits of riparian vegetation and to predict the resilience and restoration potential of riparian vegetation under different forms of human disturbance.

Successful plant invasions are hypothesised to be associated with close environmental matching or species poor communities. However, positive correlations between non-native abundance and native plant richness can also arise due to habitat heterogeneity (defined here as variation in abiotic and biotic conditions over space and time). We analysed survey and palaeoecological data for macrophytes in lakes covering a gradient of eutrophication and connectivity to partition the roles of environmental matching, macrophyte diversity and habitat heterogeneity in explaining abundance and invasibility of Elodea canadensis, a widely distributed non-native macrophyte in Europe. There was no association between invasibility and macrophyte species richness. Instead habitat heterogeneity variously enabled the coexistence of native macrophytes and E. canadensis in lake metacommunities over time. Invasion resistance was associated with high native macrophyte cover and unfavourable environmental conditions. We show how spatial and temporal scales can determine the relationship between habitat heterogeneity and invasibility in lake systems.