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Rewilding is a developing concept in ecosystem stewardship that involves reorganizing and regenerating wildness in an ecologically degraded landscape, with present and future ecosystem function being of higher consideration than historical benchmark conditions. This approach differs from ecosystem restoration but the two concepts are often conflated because (a) they both rely on similar management actions (at least initially) and (b) it can be erroneously assumed that they both aim for similar states of wildness. Rewilding and restoring both influence biodiversity, and common management actions such as species reintroductions (e.g. beavers or wolves) can be integral to a rewilding project. However, in contrast with restoration, rewilding has lower fidelity to taxonomic precedent and promotes taxonomic substitutions for extinct native species that once underpinned the delivery of key ecological functions. We suggest the adaptive cycle as the appropriate conceptual framework in which to distinguish rewilding from ecosystem restoration. The focus of restoration ecology is to return an ecosystem to as close to its former state as is possible after a major disturbance, by directly reinstating it on the ‘foreloop’ of the adaptive cycle. In contrast, rewilding draws from the ‘backloop’ by promoting reorganization and redevelopment of the ecosystem under changing environmental conditions. If environmental conditions have changed so significantly that a regime shift is inevitable, then rewilding can facilitate the development of a novel ecosystem to sustain the provision of ecosystem services. Synthesis and applications. Rewilding and restoring both have their places in biodiversity conservation. In each case, their respective merits should be weighed in relation to stakeholder priorities, prevailing and predicted environmental conditions, the level of biological organization targeted for management, and existing and future management capacity. We provide simple schematic decision‐pathways to assist in exploring whether an ecologically degraded landscape might be a candidate for restoration, active rewilding, or passive rewilding. The adaptive cycle (Holling & Gunderson, Panarchy: Understanding transformations in human and natural systems, 2002, 25) provides a conceptual framework for differentiating between restoring and rewilding in ecology. Restoring shortcuts the backloop of the cycle to move the system from Ω directly back to K as quickly and predictably as possible after a disturbance. Rewilding draws from the backloop, facilitating reorganization and the transition from α to r phases so that the system maintains resilience while adapting to changed conditions. If environmental conditions have changed so significantly that a regime shift is inevitable then managers could opt for passive rewilding and allow a novel ecosystem to develop on its own. Alternatively, they could opt for active rewilding of a novel ecosystem to sustain the provision of ecosystem services under projected environmental conditions.

Aim To determine whether reintroduced beavers, as an example of native herbivorous megafauna, can increase freshwater biodiversity at the landscape scale and to compare effects on two contrasting taxonomic groups. Location South‐central Sweden. Methods We collected data on plant and water beetle composition and supporting environmental variables from 20 closely located wetlands, half created from the damming of streams by beavers—beaver ponds (BP), and half by other, mainly natural (e.g. topographic, river migration) means—other wetlands (OW). Differences in species composition and plant growth strategy (i.e. competitor, stress tolerator or ruderal) between wetland types were assessed using multivariate analyses. Results The species pool of both taxonomic groups was higher in BP than OW (plants + 17%; beetles + 15%). For both groups, the number of species unique to BP was 50% higher than those unique to OW. Plant and beetle compositions differed significantly between wetlands, most strongly for plants, while rarity scores showed no difference, and the incidence of invasive species was negligible. Plant composition was mostly influenced by open water, bare ground and woody debris in BP, and plant cover, height and leaf litter in OW. This was consistent with the characterization of BP vegetation by ruderal plants and OW by competitors and stress tolerators. A significant residual effect of wetland type on plant, but not beetle composition, suggests that beavers exert important direct effects on some biota (e.g. via herbivory) independent of the indirect effects they exert via environmental change. Main conclusions Beaver‐created ponds support novel biodiversity that is not merely a subset of that found elsewhere in the same landscape. As such, re‐establishing beaver populations where they are native should benefit freshwater biodiversity, but effects may be context and taxon specific. Beavers alone cannot solve the freshwater biodiversity crisis, but recognizing the widespread importance of herbivorous megafauna in maintaining heterogeneity and creating novel habitat will be a positive step.

Poor condition of many streams and concerns about future droughts in the arid and semi-arid western USA have motivated novel restoration strategies aimed at accelerating recovery and increasing water resources. Translocation of beavers into formerly occupied habitats, restoration activities encouraging beaver recolonization, and instream structures mimicking the effects of beaver dams are restoration alternatives that have recently gained popularity because of their potential socioeconomic and ecological benefits. However, beaver dams and dam-like structures also harbor a history of social conflict. Hence, we identified a need to assess the use of beaver-related restoration projects in western rangelands to increase awareness and accountability, and identify gaps in scientific knowledge. We inventoried 97 projects implemented by 32 organizations, most in the last 10 years. We found that beaver-related stream restoration projects undertaken mostly involved the relocation of nuisance beavers. The most common goal was to store water, either with beaver dams or artificial structures. Beavers were often moved without regard to genetics, disease, or potential conflicts with nearby landowners. Few projects included post-implementation monitoring or planned for longer term issues, such as what happens when beavers abandon a site or when beaver dams or structures breach. Human dimensions were rarely considered and water rights and other issues were mostly unresolved or addressed through ad-hoc agreements. We conclude that the practice and implementation of beaver-related restoration has outpaced research on its efficacy and best practices. Further scientific research is necessary, especially research that informs the establishment of clear guidelines for best practices.

While large herbivores can have strong impacts on terrestrial ecosystems, much less is known of their role in aquatic systems. We reviewed the literature to determine: 1) which large herbivores (> 10 kg) have a (semi‐)aquatic lifestyle and are important consumers of submerged vascular plants, 2) their impact on submerged plant abundance and species composition, and 3) their ecosystem functions. We grouped herbivores according to diet, habitat selection and movement ecology: 1) Fully aquatic species, either resident or migratory (manatees, dugongs, turtles), 2) Semi‐aquatic species that live both in water and on land, either resident or migratory (swans), 3) Resident semi‐aquatic species that live in water and forage mainly on land (hippopotamuses, beavers, capybara), 4) Resident terrestrial species with relatively large home ranges that frequent aquatic habitats (cervids, water buffalo, lowland tapir). Fully aquatic species and swans have the strongest impact on submerged plant abundance and species composition. They may maintain grazing lawns. Because they sometimes target belowground parts, their activity can result in local collapse of plant beds. Semi‐aquatic species and turtles serve as important aquatic–terrestrial linkages, by transporting nutrients across ecosystem boundaries. Hippopotamuses and beavers are important geomorphological engineers, capable of altering the land and hydrology at landscape scales. Migratory species and terrestrial species with large home ranges are potentially important dispersal vectors of plant propagules and nutrients. Clearly, large aquatic herbivores have strong impacts on associated species and can be critical ecosystem engineers of aquatic systems, with the ability to modify direct and indirect functional pathways in ecosystems. While global populations of large aquatic herbivores are declining, some show remarkable local recoveries with dramatic consequences for the systems they inhabit. A better understanding of these functional roles will help set priorities for the effective management of large aquatic herbivores along with the plant habitats they rely on.

Recent technological innovations have led to the development of miniature, accelerometercontaining electronic loggers which can be attached to free-living animals. Accelerometers provide information on both body posture and dynamism which can be used as descriptors to define behaviour. We deployed tri-axial accelerometer loggers on 12 free-ranging Eurasian beavers Castor fiber in the county of Telemark, Norway, and on four captive beavers (two Eurasian beavers and two North American beavers C. canadensis) to corroborate acceleration signals with observed behaviours. By using random forests for classifying behavioural patterns of beavers from accelerometry data, we were able to distinguish seven behaviours; standing, walking, swimming, feeding, grooming, diving and sleeping. We show how to apply the use of acceleration to determine behaviour, and emphasise the ease with which this non-invasive method can be implemented. Furthermore, we discuss the strengths and weaknesses of this, and the implementation of accelerometry on animals, illustrating limitations, suggestions and solutions. Ultimately, this approach may also serve as a template facilitating studies on other animals with similar locomotor modes and deliver new insights into hitherto unknown aspects of behavioural ecology

Beavers modify riverine systems by building dams that alter downstream fluxes of water and sediment. Where beavers have been lost and stream channels degraded, beaver dam analogs (BDAs) are being used to mimic the effects of beaver engineering. Central to the success of these structures in accelerating stream recovery is creating similar ecosystem responses as beaver dams including sediment retention. Unknown is the relative importance of beaver actions versus erosion in the catchment in generating the retained sediment. This study tested the viability of sediment fingerprinting to determine the source of sediment retained by beaver dams and BDAs in a watershed in Alberta, Canada. Concentrations of 29 elements were measured as potential tracers from known sediment sources: upland, terrace, stream bank, and beaver canal. Virtual mixture tests, used to compare the computed source estimates with known source mixtures, revealed that sediment fingerprinting is a robust method for identifying sources of sediment retained by beaver ponds and BDAs. The un‐mixing model results indicate that on average 56% of the sediment retained by the beaver dams originated from terraces, 23% from uplands, and 13% from beaver canals. About 89% of sediment retained by the BDAs originated from eroding stream banks. We conclude that the geomorphic effects of beavers and their dams are more diverse, resulting in more diverse sources of sediment retained by their dams. This differentiates beaver dams from BDAs. The study has implications for informing management practices that involve beavers and beaver mimicry. Plain Language Summary Growing recognition of the importance of beaver dams in maintaining naturally functioning streams and floodplains has spurred the use of beaver mimicry structures to accelerate stream recovery where stream channels have cut downward because beavers are absent. Despite the importance of sediment trapping in determining the success of beaver mimicry structures in raising the stream bed, the source of the trapped sediment is poorly known and seldom analyzed. This study investigated whether sediment fingerprinting, a well‐known method for assessing sources of lake, estuary and floodplain sediment deposits, could reliably establish the sources of sediment retained by beaver dams and beaver mimicry structures. We tested this method in a watershed in the Canadian Rocky Mountains and found that it effectively differentiated between the sources of sediment trapped by beaver dams and beaver mimicry structures. Sediment trapped by the mimicry structures originated mainly from stream banks flooded by the structures, whereas beaver dams trapped sediment originating from a combination of riparian areas, canals dug by beavers and hillslopes. Beaver mimicry structures did not replicate the sediment trapping processes of beaver dams because the beavers were important in actively mobilizing the sediment that became trapped by their dams. Key Points Sediment fingerprinting can effectively establish the source of sediment retained by beaver dams and beaver dam analogs (BDAs) Sediment retained by beaver dams originates from different and more diverse sources than sediment retained by BDAs BDA sediment composition does not replicate that of beaver dams as beavers contribute sediment via canal building and terrace inundation

Beavers and the dams they build are not always embraced in the areas where they do their work. But there's a growing recognition that they also are building a kind of natural infrastructure that helps with water management and the climate. Science correspondent Miles O'Brien went to see the beavers at work during their busy season and has the story for our ongoing coverage of Tipping Points.

Beavers are starting to colonize low arctic tundra regions in Alaska and Canada, which has implications for surface water changes and ice-rich permafrost degradation. In this study, we assessed the spatial and temporal dynamics of beaver dam building in relation to surface water dynamics and thermokarst landforms using sub-meter resolution satellite imagery acquired between 2002 and 2019 for two tundra areas in northwestern Alaska. In a 100 km2 study area near Kotzebue, the number of dams increased markedly from 2 to 98 between 2002 and 2019. In a 430 km2 study area encompassing the entire northern Baldwin Peninsula, the number of dams increased from 94 to 409 between 2010 and 2019, indicating a regional trend. Correlating data on beaver dam numbers with surface water area mapped for 12 individual years between 2002 and 2019 for the Kotzebue study area showed a significant positive correlation (R2 = 0.61; p < .003). Beaver-influenced waterbodies accounted for two-thirds of the 8.3% increase in total surface water area in the Kotzebue study area during the 17 year period. Beavers specifically targeted thermokarst landforms in their dam building activities. Flooding of drained thermokarst lake basins accounted for 68% of beaver-influenced surface water increases, damming of lake outlets accounted for 26%, and damming of beaded streams accounted for 6%. Surface water increases resulting from beaver dam building likely exacerbated permafrost degradation in the region, but dam failure also factored into the drainage of several thermokarst lakes in the northern Baldwin Peninsula study region, which could promote local permafrost aggradation in freshly exposed lake sediments. Our findings highlight that beaver-driven ecosystem engineering must be carefully considered when accounting for changes occurring in some permafrost regions, and in particular, regional surface water dynamics in low Arctic and Boreal landscapes.

Across Eurasia and North America, beaver ( Castor spp), their dams and their human-built analogues are becoming increasingly common restoration tools to facilitate recovery of streams and wetlands, providing a natural and cost-effective means of restoring dynamic fluvial ecosystems. Although the use of beaver ponds by numerous fish and wildlife species is well documented, debate continues as to the benefits of beaver dams, primarily because dams are perceived as barriers to fish movement, particularly migratory species such as salmonids. In this study, through a series of field experiments, we tested the ability of juvenile salmonids to cross constructed beaver dams (aka beaver dam analogues). Two species, coho salmon ( Oncorhynchus kisutch ) and steelhead trout ( O . mykiss ), were tracked using passive integrated transponder tags (PIT tags) as they crossed constructed beaver dam analogues. We found that when we tagged and moved these fishes from immediately upstream of the dams to immediately downstream of them, most were detected upstream within 36 hours of displacement. By the end of a 21-day field experiment, 91% of the displaced juvenile coho and 54% of the juvenile steelhead trout were detected on antennas upstream of the dams. In contrast, during the final week of the 21-day experiment, just 1 of 158 coho salmon and 6 of 40 (15%) of the steelhead trout were still detected on antennas in the release pool below the dams. A similar but shorter 4-day pilot experiment with only steelhead trout produced similar results. In contrast, in a non-displacement experiment, juveniles of both species that were captured, tagged and released in a pool 50 m below the dams showed little inclination to move upstream. Further, by measuring hydraulic conditions at the major flowpaths over and around the dams, we provide insight into low-flow conditions under which juvenile salmonids are able to cross these constructed beaver dams, and that multiple types of flowpaths may be beneficial towards assisting fish movement past instream restoration structures. Finally, we compared estimates of the number of juvenile salmonids using the pond habitat upstream of the dam relative to the number that the dam may have prevented from moving upstream. Upstream of the dams we found an abundance of juvenile salmonids and a several orders of magnitude difference in favor of the number of juveniles using the pond habitat upstream of the dam. In sum, our study suggests beaver dams, BDAs, and other channel spanning habitat features should be preserved and restored rather than removed as perceived obstructions to fish passage.

Territorial animals carry out extra-territorial movements (forays) to obtain pre-dispersal information or to increase reproductive success via extra-pair copulation. However, little is known about other purposes and spatial movement patterns of forays. In this study, we GPS-tagged 54 Eurasian beavers (Castor fber), a year-round territorial, monogamous mammal, during the non-mating season. We investigated forays in territory-holding breeders (dominants) and non-breeding (subordinate) family members. Twenty of 46 dominant individuals (44%), and 6 of 10 subordinates (60%) conducted forays. Generally, beavers spent between 0 and 11% of their active time on forays, travelled faster and spend more time in water when on forays compared to intra-territorial movements, suggesting that forays are energetically costly. Further, beavers in smaller territories conducted more forays. Possibly, smaller territories might not have sufcient resources and thus dominant individuals might conduct forays to assess possibilities for territory expansion, and potentially for foraging. Generally, besides territory advertisement (e.g. via scent-marking), forays might serve as an additional mechanism for territory owners to assess neighbours. Subordinates spent more time on forays, moved greater distances and intruded into more territories than dominant individuals did, suggesting that they prospected to gain information on the population density and available mates before dispersal.