Beaver Sites Research Articles

Ecosystem engineers cause biodiversity spill-over: Beavers are associated with breeding bird assemblages on both wetlands and adjacent terrestrial habitats

The influence of ecosystem engineers on habitats and communities is commonly acknowledged in a site-bounded context, i.e. in places directly affected by the presence of the focal species. However, the spatial extent of the effects of such engineering is poorly understood, raising the question as to what impact they have on ecosystems situated beyond the species' direct influence. Beavers Castor spp., iconic ecosystem engineers, are capable of significantly transforming aquatic ecosystems. Their presence boosts biodiversity in adjacent aquatic and riparian habitats, but as a result of cascading processes, beavers may affect terrestrial habitats situated beyond the range of their immediate activity. Our study investigates the breeding bird assemblage along a spatial gradient from the water to the forest interior on central European watercourses modified and unmodified by beavers. The results show that beaver sites are characterized by a higher species richness and abundance of breeding birds than unmodified watercourses. Such sites also host a different species pool, as 27 % of the recorded bird species occurred exclusively on the beaver sites. The effect of the beaver's presence on the bird assemblage extended to adjacent terrestrial habitats located up to 100 m from the water's edge, where the species richness and abundance was higher and the species composition was substantially modified. We also found a positive correlation between the total area of beaver wetland and the numbers of bird species and individuals recorded. Our study adds to the general understanding of the spatial context of the ecosystem engineering concept, as the changes brought about by engineers have an influence beyond the area of their immediate occurrence. Our work also has implications for landscape planning and management, where existing beaver sites with terrestrial buffer zones may constitute a network of biodiversity hotspots.

Woody species response to altered herbivore pressure at Isle Royale National Park

AbstractHerbivores shape vegetative communities via numerous mechanisms, including browse. We used vegetation monitoring data from Isle Royale National Park to examine woody species change across a nine‐year interval, coinciding with herbivore escalation. Here, moose and snowshoe hare are the dominant herbivores, while the gray wolf is the apex predator. Our initial sampling period (2010) followed six years of low moose abundance, while our second sampling event (2019) followed a nine‐year escalation in moose density. We tested for change in both saplings and shrubs and compared diameter size distributions of common tree species in three island sections. We found a decline in large saplings of sugar maple, a species limited to the west section of the island. We also saw declines in small saplings of sugar maple, paper birch, and trembling aspen. For some species, including black spruce and white spruce, taxa that are unpalatable to moose, diameter distributions were proportionally larger (i.e., indicative of fewer small individuals) in 2019 than in 2010. In contrast, diameter distributions of black ash in the central section and trembling aspen in the central and east sections of the island were proportionally smaller (indicative of more small individuals) in 2019 than in 2010. We found that ~50% of common shrub taxa were more abundant during the second sampling event, while none declined. Our work here brings to light several unanticipated results. While we demonstrated partial recovery of trembling aspen, likely originating during the earlier period of low moose abundance, our results suggest further changes may be attributable to other island herbivores. The response of black ash, a hydric species, may be stemming from a sixfold increase in active beaver sites, while that of spruce may be attributable to a historic spike in snowshoe hare density. We currently have only a limited understanding of the impacts of the island's lesser studied herbivores on overstory regeneration. Further research on these linkages can inform decisions addressing controls on forest structure.

Beyond beaver wetlands: The engineering activities of a semi-aquatic mammal mediate the species richness and abundance of terrestrial birds wintering in a temperate forest

The engineering activities of the Eurasian beaver Castor fiber have far-reaching effects on the components of an environment and therefore modify the functioning of the ecosystem. The wetlands thereby created are the most conspicuous effect of beaver activity and attract water-related species. However, there is some evidence suggesting that beavers influence not only aquatic ecosystems but also the terrestrial habitats adjacent to these wetlands and the organisms occurring there. Because the impact of beavers on terrestrial birds is still poorly understood, this study evaluates the assemblage of birds wintering on beaver sites (N = 65) and paired reference sites (N = 65) in temperate forests of central Europe. We investigated the correlations between beaver presence, parameters of wetland areas, terrestrial vegetation characteristics, distance from the water’s edge and bird species richness and abundance. We found a greater species richness and abundance of wintering birds on beaver sites than on watercourses unmodified by this ecosystem engineer (by 38% and 61%, respectively). Species richness and abundance were higher in the terrestrial habitats near the edges of beaver ponds, but for some species this tendency also held in forests growing at some distance from beaver wetlands. Greater species richness was related to beaver presence, but also increased with a more open canopy and greater forest floor diversity, whereas bird abundance was correlated only with canopy openness. The beaver sites attracted primary cavity nesters, secondary cavity nesters and frugivorous species. This study provides evidence that the engineering activities of beavers during the growing season have a delayed cascading effect on the richness and abundance of the bird assemblage in terrestrial habitats in winter. This indicates that beaver ecosystem engineering should be seen as having a potential for carry-over effects, in which the consequences of beaver activity become apparent in subsequent seasons. Birds are considered to be ecological indicators, so our results highlight the importance of beavers for the distribution of terrestrial organisms at the local scale, and therefore the functioning of ecosystems beyond the immediate wetland area.

Eurasian beaver – A semi-aquatic ecosystem engineer rearranges the assemblage of terrestrial mammals in winter

There is increasing awareness of the ecosystem engineering services provided by recovering populations of Eurasian beaver. By modifying aquatic environments, this species has a significant, positive influence on biodiversity. Beaver activity affects not only aquatic ecosystems but also terrestrial habitats and organisms. Our study compares and evaluates the species richness and activity of terrestrial mammals in winter at beaver ponds (N = 65) and randomly-selected reference sites along nearby watercourses unmodified by beavers (N = 65) in Poland (central Europe). Mammal assemblages were investigated near pond/watercourse edges, and also at some distance from them. The species richness of mammal and numbers of their tracks were respectively 25% and 33% greater on the beaver than on the reference sites. The higher species richness on beaver sites extended to areas 40–60 m distant from ponds, devoid any signs of beaver activity. Twenty-three mammal species were recorded on beaver sites (mean species richness 3.8 ± 1.6 SD), and 20 on reference ones (3.0 ± 1.5 SD). The numbers of tracks of grey wolf, least weasel and European polecat were higher on beaver than reference sites. Mammal species richness and activity were related to the existence of beaver ponds, but were also correlated with the numbers of snags and coverage of grass, bramble and coniferous saplings in neighbouring terrestrial habitats. Large and small carnivores occurred more frequently and were more active on beaver sites. The frequencies of occurrence of mesocarnivores, mesoherbivores and small herbivores were correlated with habitat characteristics, regardless of whether beavers were present or not. Our results highlight the fact that both pond creation and the habitat changes resulting from the presence of beavers rearrange the occurrence and activity of the terrestrial mammal assemblage.

The impact of beaver dam removal on the chemical properties of water in drainage ditches in peatland forests

ABSTRACT Despite near-extinction in the nineteenth century, after efficient restoration measures the population of Eurasian beaver (Castor fiber L.) in Latvia currently is viable and growing. While the ecological effect of the species on water quality and biodiversity is generally positive, the high number of animals in production forests often creates challenges for management. Drainage ditches are among the most favoured habitats of beavers resulting in flooded stands, reduced tree growth and economical losses. The aim of the study was to evaluate the chemical properties of water in forest drainage ditches, affected by beaver activity, and their changes after the dam removal. Chemical composition of surface water in ditches was analysed in sampling points above dam, below dam and in the ditch itself after removal of the dam; results compared to pristine beaver site nearby on a small stream. Results did not show significant differences between concentrations above and below dams. After removal of the dams, significant increase in DOC, N-NO3 -, N-NH4 + and TSS concentrations and significant decrease in TP concentrations were observed in some of the sites. Observed concentrations of all measured parameters were significantly lower in pristine beaver site than in beaver sites on drainage ditches.

Small mammal assemblage in beaver-modified habitats

One of the less studied positive interactions among organisms is facilitation. Facilitation may have significant impact on diversity of species especially in low productive environments. We studied the effects of well-known facilitator and ecosystem engineer, the North American beaver (Castor canadensis), on small mammal assemblages in the boreal zone. The small mammals, namely voles, mice, and shrews, were trapped over 2 years in ten beaver-modified habitats and in ten control sites. Contrary to our expectations, we did not observe any differences between species or individual numbers between beaver-modified and control sites. However, there were differences in species composition between sites; grass-eating field voles (Microtus agrestis) and invertebrate-eating shrews (Sorex araneus, Neomys fodiens) tended to be more common in beaver sites while forest-dwelling wood lemmings (Myopus schisticolor) and yellow-necked mice (Apodemus flavicollis) were only captured in control sites. The most common species in both habitats was the bank vole (Myodes glareolus), which is a generalist in its habitat requirements. The bank vole’s population structures were similar between the two habitat types. The actions of beavers in water bodies within boreal forests seem to have no effect on the small mammal diversity and their numbers at the regional scale but may have positive effect on them at the larger landscape level as beavers are increasing the overall habitat diversity in the landscape.

Beaver-induced spatiotemporal patch dynamics affect landscape-level environmental heterogeneity

Beavers (Castor sp.) are ecosystem engineers that cause significant changes to their physical environment and alter the availability of resources to other species. We studied flood dynamics created by American beaver (C. canadensis K.) in a southern boreal landscape in Finland in 1970–2018. We present for the first time, to our knowledge, a temporally continuous long-term study of beaver-induced flood disturbances starting from the appearance of beaver in the area. During the 49 years, the emergence of new sites flooded by beaver and repeated floods (61% of the sites) formed a dynamic mosaic characterized by clustered patterns of beaver sites. As beaver dispersal proceeded, connectivity of beaver sites increased significantly. The mean flood duration was approximately three years, which highlights the importance of datasets with high-temporal resolution in detecting beaver-induced disturbances. An individual site was often part of the active flood mosaic over several decades, although the duration and the number of repeated floods at different sites varied considerably. Variation of flood-inundated and post-flood phases at individual sites resulted in a cumulative number of unique patches that contribute to environmental heterogeneity in space and time. A disturbance mosaic consisting of patches differing by successional age and flood history is likely to support species richness and abundance of different taxa and facilitate whole species communities. Beavers are thus a suitable means to be used in restoration of riparian habitat due to their strong and dynamic influence on abiotic environment and its biotic consequences.

The beaver facilitates species richness and abundance of terrestrial and semi-aquatic mammals

Beavers are ecosystem engineers which are capable to facilitate many groups of organisms. However, their facilitation of mammals has been little studied. We applied two methods, camera trapping and snow track survey to investigate the facilitation of a mammalian community by the ecosystem engineering of the American beaver (Castor canadensis) in a boreal setting. We found that both mammalian species richness (83% increase) and occurrence (12% increase) were significantly higher in beaver patches than in the controls. Of individual species, the moose (Alces alces) used beaver patches more during both the ice-free season and winter. The Eurasian otter (Lutra lutra), the pine marten (Martes martes) and the least weasel (Mustela nivalis) made more use of beaver sites during the winter. Our study highlights the role of ecosystem engineers in promoting species richness and abundance, especially in areas of relatively low productivity. Wetlands and their species have been in drastic decline during the past century, and promoting facilitative ecosystem engineering by beaver is feasible in habitat conservation or restoration. Beaver engineering may be especially valuable in landscapes artificially deficient in wetlands.

The importance of spatial scale in habitat selection by European beaver

We evaluated habitat selection by European beaver Castor fiber L. across a spatial gradient from local (within the family territory) to a broad, ecoregional scale. Based on aerial photography, we assessed the habitat composition of 150 beaver territories along the main water bodies of the Vistula River delta (northern Poland) and compared these data with 183 randomly selected sites not occupied by the species. The beavers preferred habitats with high availability of woody plants, including shrubs, and avoided anthropogenically modified habitats, such as arable lands. Within a single family territory, we observed decreasing woody plant cover with increasing distance from a colony centre, which suggests that beaver habitat preferences depend on the assessment of both the abundance and spatial distribution of preferred habitat elements. We tested the importance of spatial scale in beaver habitat selection with principal coordinates of neighbour matrices analysis, which showed that the geographical scale explained 46.7% of the variation in habitat composition, while the local beaver density explained only 10.3% of this variability. We found two main spatial gradients that were related to the broad spatial scale: first, the most important gradient was related to the largest distances between beaver sites and was independent of woody plant cover and the local beaver site density. The second most important gradient appeared more locally and was associated with these variables. Our results indicate that European beaver habitat selection was affected by different scale‐related phenomena related 1) to central place foraging behaviour, which resulted in the clumped distribution of woody plants within the territory, and 2) local population density and woody plant cover. Finally, 3) habitat selection occurs independently across the largest spatial scale studied (e.g. between watersheds), which was probably due to the limited natal dispersal range of the animals.

Beavers promote calicioid diversity in boreal forest landscapes

Beavers are ecosystem engineers that modify and maintain a range of special habitat types in boreal forests. They also produce large quantities of deadwood that provide substrate for many lignicolous organisms such as calicioid fungi (Ascomycota). We studied how calicioid diversity differed between boreal riparian forests with and without beaver activity. The results show that calicioid diversity were significantly higher at beaver sites compared to the other two forest site types studied. The large quantity and diverse forms of deadwood produced by beavers clearly promotes calicioid diversity in the boreal landscape. The specific lighting and humidity conditions within beaver wetlands could be the reason why they promote the success of certain calicioid species.

Beaver activity increases aquatic subsidies to terrestrial consumers

Summary The occurrence and importance of fluxes of nutrients and organic matter between aquatic and terrestrial habitats is well established, but how catchment characteristics influence these fluxes remains unclear. Beaver (Castor canadensis) alter freshwater ecosystems and increase aquatic production, but it is unknown how these changes influence the magnitude and lateral dispersal of aquatic nutrients into terrestrial ecosystems. We examined differences in abundances of dominant aquatic invertebrates, wolf spiders (Lycosidae), and deer mice (Peromyscus maniculatus), at beaver and non‐beaver sites. We used stable isotopes to track aquatic‐derived carbon in terrestrial consumers and linear mixed‐effects models to examine the importance of beaver presence and distance from stream channel on the percentage of aquatic‐derived carbon in terrestrial consumers. Sites with beaver activity had >200% higher aquatic invertebrate emergence rates as well as 60% and 75% higher abundances of spiders and deer mice, respectively, relative to non‐beaver sites. The tissues of both spiders and deer mice exhibited a greater percentage of aquatic‐derived carbon at sites with beaver activity than at non‐beaver sites. Aquatic‐derived carbon in deer mice declined linearly with distance from the stream edge at both beaver and non‐beaver sites. The contribution of aquatic‐derived carbon in mice extended farther from the stream edge in beaver‐modified catchments. Aquatic‐derived carbon in spiders also declined linearly with distance from the stream at beaver sites but not at non‐beaver sites. We documented a novel example of increased aquatic subsidy to riparian areas with beaver activity, leading to changes in the magnitude of the lateral dispersal of aquatic nutrient subsidies to the terrestrial environment in small stream systems. Understanding the effects of natural disturbance regimes, such as beaver modification, will be important for management and, where appropriate, restoration of natural catchment processes.

Aspen and Willow Restoration Using Beaver on the Northern Yellowstone Winter Range

Aspen (Populus tremuloides) on the northern Yellowstone winter range has declined over the last half‐century. Beaver (Castor canadensis) were reintroduced in Eagle Creek in 1991 in an attempt to reverse this trend. In 2005, we assessed the efficacy of this project by quantifying the long‐term effects of beaver on aspen stands and the riparian area in this drainage. Between 1990 and 2005, the canopy cover of mature aspen decreased more than 62%, whereas immature aspen cover more than tripled, resulting in a total aspen canopy cover decrease (p< 0.05) from 43 to 25% (a loss of 7.25 ha). Willow canopy cover increased from 10 to 14% during the same period. The impacts of beaver on aspen stands were estimated by comparing vegetative changes among control sites with less than 10% beaver use (n= 5), active beaver sites (n= 6), sites inactive for 1–3 years (n= 7), sites inactive for 4–6 years (n= 4), and sites inactive for 7–11 years (n= 5). Aspen sprout and sapling densities were greater (p= 0.01) on sites which were active and inactive for 1–3 years compared to the other sites. Aspen ramets were not able to grow taller than 2 m on sites without beaver activity for 4–11 years due to ungulate herbivory. Although beaver stimulated the growth of aspen sprouts and saplings, ungulate herbivory prevented successful aspen recovery in the Eagle Creek drainage of the northern Yellowstone winter range 14 years after beaver reintroduction.

Habitat use and selectivity by beavers (Castor fiber) in anthropogenic landscape

The aim of this article was to reveal utilization peculiarities of various habitats by beavers in a relatively highly anthropogenic landscape of Lithuania. Particular attention was paid to habitat distribution and selectivity by beavers under conditions of dense population. At present, based on expert estimations, the total numbers of beaver population reach about 100 000 of individuals, with the average beaver site density of 0.41 site/km2. The greatest part of beaver sites (36%) was situated in canals of land reclamation in 2008. Beaver sites in natural rivers have comprised about 18%, in brooks – 12%, in lakes – 17%, in swamps and peat bogs – 15%. Habitat distribution of beaver sites was found to be related to landscape type. The most attractive habitats were the forest drainage canals (indicator of selectivity, HS = 3.5 ± 3.97 (SD)), followed by rivers (HS = 2.2 ± 1.78), lakes (HS = 1.2 ± 2.49). The least attractive habitats were the field drainage canals (HS = 0.3 ± 0.35). Utilization of habitats by beavers was found to be influenced by the structure of habitats. An increase of proportion of a habitat in the habitat structure, usually leads to an increase of the beaver site proportion in this habitat. This was found to be true for all habitat types, except the field canals due to a certain avoidance of this habitat by beavers. The increase of the proportion of a habitat in the habitat structure was found negatively influencing the usage of other habitats by beavers. In this respect, rivers, brooks, forest canals, and lakes were most antagonistic to the remaining habitats. Keywords: Castor fiber, habitat distribution, habitat selectivity, anthropogenic landscape, Lithuania

Beaver impact on canals of land reclamation in two different landscapes

We tested the assumption that beavers can differently impact land reclamation canals (open drains) in two types of landscapes – hilly moraine uplands (uplands) and clayey plains (plains). The two types of landscapes differ in physical peculiarities as well as in the level of agricultural use, which influence beaver impact and capabilities of this ecosystem engineer to renaturalize open drains. Generally, beavers had a greater impact on open drains in uplands. It was expressed in a higher proportion of beaver sites with beaver-made channels and beaver-formed wetlands and in wider beaver impoundments, compared with plains. Beaver sites in land reclamation canals in plains had longer impoundments; however, the mean number of beaver dams per site did not reliably differ between the two landscape types. We found beaver sites being more expressed in outskirt and forest canals than in field canals in both landscapes. The longevity of beaver sites (many of which persist for decades due to interchanging recoloniza...

Beaver (Castor canadensis) Impacts on Herbaceous and Woody Vegetation in Southeastern Georgia

North American beavers alter habitat properties such as stream flow, faunal composition and plant community structure. In North America, the majority of studies on impacts by beavers have occurred in the northeast or western regions. This study examined the effect of wood-cutting and foraging by beaver on the surrounding plant community in Southeastern Georgia. To determine their impact, beaver modified habitat and nearby, but non-impacted riparian habitat, were sampled in a matched pair design. Vegetation surveys were performed, and species richness, density, relative abundance and canopy cover were calculated for every site. Richness of herbaceous vegetation was higher at distances closer to shore while richness of large woody vegetation increased with distance from shore with no difference found between beaver and control sites. The composition of herbaceous or woody vegetation did not differ significantly between beaver and control sites; species had an equal chance of occurring in either site. Canopy cover was similar at the two site types. Non-native species were rare and did not differ by site type. Beavers were in low density and had a relatively benign impact on the plant community. Density of woody plants was higher at beaver sites, suggesting that beavers may favor areas of abundant woody vegetation. Beaver impact may be less in southern regions than in northern ones. This may reflect the lower density of beavers, but impact also could be due to the year round availability of and access to vegetation.

The response of ash-alder swamp forest to increasing stream water level caused by damming by the European beaver (Castor fiber L.)

The response of an ash-alder swamp forest to water damming was studied in the Łutownia stream running in Bialowieza Forest. The Łutownia stream with artificial dam existing from 2001 for small water retention purposes was the test object. The first observation of vegetation was done in 2004, when small retention construction started to influence surrounding forest, but beavers had not built their dam yet. After one year of experiments (2005) the beaver dam was constructed close to man-made dam and its influence was most significant for further studies. So, the first observation refers to the status of ash-alder swamp forest before beaver damming. Water table level was measured from the beginning of 2004. The main goal of presented studies was to determine changes of terrestrial vegetation and its habitat after increasing of the water level in the stream. One square metre plots in a frame 5 x 5m were localized in a transect close to the stream upstream and downstream artificial dam. Within 104 such plots ground vegetation (growing up to 0.5 m above ground) was described using Braun-Blanquet scale of abundance. The vegetation studies were conducted twice in 2004 and repeated in 2007. The list of species and their abundance were determined twice: in spring and in summer. Changes of species richness and coverage by species characteristic for floodplain and swamp forest site were evaluated. Ecological indices of soil moisture and fertility determined as the means weighed by percent cover by plant species were calculated for two periods of observation. Calculated indicator values showed that water retention increased the number of swamp forest species by 8 times, but the area of swamp habitat increased 16 times compared with 2004. The mean number of species per sample plot was the same before and after water damming by beavers. The plant association (ash-alder riparian forest) changed its floristic composition to swampier variant. Obtained results showed real impact of beavers’ activity on ground vegetation and its habitat in ashalder swamp forest. Observed increased number of swamp species close to the beaver dam is positive from ecological point of view. Presented results indicate also, that species richness is strongly controlled by beaver damming. The population dynamics of beavers could also potentially affect species richness by altering the age distribution of beaver dams and abandoned ponds across the river valley landscape. Generally, this point of view could have adverse social effects because beavers’ activity brings losses to forestry and agriculture. Therefore, we should try to find a balance between economy and wildlife management. Monitoring of the beaver sites should be continued to evaluate ecological consequences and to find best solution of these problems. DOI: 10.2478/v10025-010-0032-7 Unauthenticated Download Date | 6/13/16 9:14 AM 250 J. CZEREPKO et al.

SEXUAL DIMORPHISM IN THE DEVELOPMENT OF SCENT STRUCTURES FOR THE OBLIGATE MONOGAMOUS EURASIAN BEAVER (CASTOR FIBER)

Scent marking is a common form of territorial demarcation in mammals and differential marking by the sexes may select for differences in scent gland developmental rates or size. Rates of marking reflect level of defense and so behavioral dimorphism in marking by the sexes may select for dimorphism in scent structures. Eurasian beavers (Castor fiber) are monogamous, territorial mammals that show some behavioral dimorphism in territoriality. Beavers have 2 primary scent structures, anal glands and castor sacs. Anal gland secretion appears to serve as a family or individual identifier. Castor fluid is the main source of chemical signals used for marking territories. We examined beavers collected from 3 different habitats, namely streams, creeks and tarns (small lakes), which varied in the density of beaver sites. The objectives of this study were to examine if morphological attributes of Eurasian beaver scent structures reflected differences in adult beaver territorial function or in the ontogeny of the sexes. We hypothesized that male beavers would have larger castor sacs and anal glands, and that beavers from sites of greater density, and thus greater rates of intrusion, would have larger castor sacs and anal glands. Our results showed that investment did not differ by habitat type. Although the combined weight of the scent structures did not differ between the sexes, males developed significantly larger anal glands but somewhat smaller castor sacs than females. Total investment to scent structures may be limited but allocation is flexible. Males patrol the territory more extensively and may benefit by releasing anal gland secretion to signal their identity to potential intruders. Higher rates of marking may decrease castor sac size by reducing the amount of stored scent material. Hence, even in monogamous mammals, sexual dimorphism can arise from behavioral dimorphism.

Hydrogeomorphic effects of beaver dams on floodplain morphology: avulsion processes and sediment fluxes in upland valley floors (Spessart, Germany) [ Les effets hydro-géomorphologiques des barrages de castors sur la morphologie de la plaine alluviale : processus d'avulsions et flux sédimentaires des vallées intra-montagnardes (Spessart, Allemagne).

In a two years study, several methods were used to visualise and analyse beaver-induced hydrogeomorphic changes of channel pattern, sediment fluxes and erosion processes on the upland valley floor of the 3rd order river Jossa (Spessart/Germany). There, the re-introduced population of Castor fiber albicus shows intensive dam-building activity Using GIS and aenal photography, different stages of river and floodplain morphology (1998-2001) were mapped In addition, length of water courses, areal extent of ponds and wetlands, sediment depths, volumes and sedimentation rates, as well as erosion rates and amounts of eroded matenal were calculated. The results revealed that beaver dams create large wetlands and greatly increase the area of open water surface and quiet reaches by damming-up ponds. Moreover, they enhance the total water flow length by diverting water onto the floodplain, resulting in a multi-channeled (anastomosing) drainage network Where pond drainage was concentrated on a few relative stable channels, headcut erosion led to the development of one single dominant channel. Five stages of this development to a channel relocation were observed, resembling stages of a gradual avulsion. This implies that beaver dams should be recognised as possible - or even as important - avulsion triggers Intensified deposition of predominantly sands and organic silts occurred within the beaver ponds. Moreover, extended avulsion deposits caused by permanent overbank flow revealed the multi-channeled drainage network to be an important depositional environment of beaver sites. The highest amounts of sediments were deposited within the channel-bed and adjacent anthropogenic ditches, smaller amounts were accumulated on the inundated floodplain. The results may provide a rationale for attributing beaver activities a high significance as a forcing factor of Quaternary floodplain development along low order rivers in Central Europe.

Beaver Abundance and Beaver Site Use in a Hilly Landscape (Eastern Lithuania)

To study the peculiarities of a local beaver population abundance and dynamics of beaver site use in a hilly landscape, there were beaver sites registered yearly, with their use, habitat and type of the main shelter established on the territory (Eastern Lithuania) covering an area of 2.4 thousand ha during the period of 1983–1994 and the year 2001. The population density having increased, abandoned beaver sites made up 44–58% of their total number. The number of active beaver sites in swamps, small and shallow rivulets and ditches, with a lodge being the main type of the main shelter, increased respectively (up to 74%). The use of beaver sites proved to be very dynamic, the mean duration of their continuous use amounting to 2.61 ± 0.23 (±SE) years. A great part (≥43%) of abandoned beaver sites were after a short period of time (2.72 ± 0.29 years on the average) recolonized by beavers again.

Colonization, riparian habitat selection and home range size in a reintroduced population of European beavers in the Loire

1. Colonization in a reintroduced population of European beavers in the Loire Valley was studied between 1974 and 1999. It followed a discontinuous remoteness model and a scattered distribution, beavers occupying only 25% of the river system over the 2800 km explored.2. After 5 years, the colonization rate reached 104.2% year–1 of new sites occupied (SD 75% year–1), before dropping over the next 20 years. Nevertheless, the number of new colonies per km (0.125) remained stable throughout the years.3. Populus nigra, Salix alba and Fraxinus angustifolia were the dominant woody species in beaver sites, often associated with some herbaceous species.4. The length of willow grove dominated by S. alba and P. nigra (x) was the best predictor of beaver home range (y), fitting the equation y=−0.742x + 5.9. Long‐term maintenance of the population requires a minimum of 1.79‐km of willows per colony.5. In cutting tree trunks, beavers stimulate shoot development from the remaining stumps. They rejuvenate riparian forests, increase the number of tree stems and help stabilize the banks. Their effect on woody plant morphogenesis may have consequences for the helophyte communities used as food or habitat by other aquatic species.