No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Modeling the capacity of riverscapes to support beaver dams
Abstract
Abstract The construction of beaver dams facilitates a suite of hydrologic, hydraulic, geomorphic, and ecological feedbacks that increase stream complexity and channel–floodplain connectivity that benefit aquatic and terrestrial biota. Depending on where beaver build dams within a drainage network, they impact lateral and longitudinal connectivity by introducing roughness elements that fundamentally change the timing, delivery, and storage of water, sediment, nutrients, and organic matter. While the local effects of beaver dams on streams are well understood, broader coverage network models that predict where beaver dams can be built and highlight their impacts on connectivity across diverse drainage networks are lacking. Here we present a capacity model to assess the limits of riverscapes to support dam-building activities by beaver across physiographically diverse landscapes. We estimated dam capacity with freely and nationally-available inputs to evaluate seven lines of evidence: (1) reliable water source, (2) riparian vegetation conducive to foraging and dam building, (3) vegetation within 100 m of edge of stream to support expansion of dam complexes and maintain large colonies, (4) likelihood that channel-spanning dams could be built during low flows, (5) the likelihood that a beaver dam is likely to withstand typical floods, (6) a suitable stream gradient that is neither too low to limit dam density nor too high to preclude the building or persistence of dams, and (7) a suitable river that is not too large to restrict dam building or persistence. Fuzzy inference systems were used to combine these controlling factors in a framework that explicitly also accounts for model uncertainty. The model was run for 40,561 km of streams in Utah, USA, and portions of surrounding states, predicting an overall network capacity of 356,294 dams at an average capacity of 8.8 dams/km. We validated model performance using 2852 observed dams across 1947 km of streams. The model showed excellent agreement with observed dam densities where beaver dams were present. Model performance was spatially coherent and logical, with electivity indices that effectively segregated capacity categories. That is, beaver dams were not found where the model predicted no dams could be supported, beaver avoided segments that were predicted to support rare or occasional densities, and beaver preferentially occupied and built dams in areas predicted to have pervasive dam densities. The resulting spatially explicit reach-scale (250 m long reaches) data identifies where dam-building activity is sustainable, and at what densities dams can occur across a landscape. As such, model outputs can be used to determine where channel–floodplain and wetland connectivity are likely to persist or expand by promoting increases in beaver dam densities.
Supplementary resource (1)
... In recent decades, the small rivers of Eastern Europe have been significantly affected by the beaver (predominantly the Eurasian beaver (Castor fiber L.)), and these affects manifest themself in the construction of dams and related ponds. This results in a decrease in the velocity of flow, a decrease in water runoff, and the accumulation of sediment and related pollutants along the channels and floodplains of these rivers, as well as the transformation of their floodplain landscapes [4][5][6][7][8][9][10][11][12]. It is (predominantly the Eurasian beaver (Castor fiber L.)), and these affects manifest themself in the construction of dams and related ponds. ...
... It is (predominantly the Eurasian beaver (Castor fiber L.)), and these affects manifest themself in the construction of dams and related ponds. This results in a decrease in the velocity of flow, a decrease in water runoff, and the accumulation of sediment and related pollutants along the channels and floodplains of these rivers, as well as the transformation of their floodplain landscapes [4][5][6][7][8][9][10][11][12]. It is important to note that this often occurs in conjunction with the negative anthropogenic impact on small watercourses. ...
... The density of beaver dams on the Morkváshinka and Morkváshka rivers reaches its peak in the sections of their channels with a relatively moderate (medium) gradient (1-3%). In general, the average density of beaver dams both for the entire length of the studied rivers and for their individual sections matches the data for the territory of North America at 7-10 units/km [7,41,42]. ...
A very noticeable increase in the beaver population (mainly the Eurasian beaver (Castor fiber L.)) in the East European Plain since the end of the 20th century through reintroduction contributed to the emergence of a large number of beaver dams and ponds, which resulted in the transformation of the channels and the hydrological regime of small rivers. In this paper, for the first time in the Middle Volga region, regularities in the distribution of beaver dams and ponds on small rivers were revealed based on a topographic survey of the river channel, regulated by beaver activity in recent decades. The materials of the paper were obtained during field (geodetic) work in August and September of 2022 in the valleys of two small rivers typical for the north of the Volga Upland, Morkváshinka River (16.6 km) and Morkváshka River (7.8 km), with subsequent statistical processing. According to the results obtained, all the dams we encountered were located in the sections of their channels with relatively small (up to 1%) and medium (1–3%) average gradients. In the upper reaches of the rivers, the expansion of beaver activity is limited to the large gradients of their channels. Along the entire length, there is an alternation of sectors with a “natural” (not regulated by beavers) channel and a cascade of beaver ponds. Drained (at the time of the survey) sectors without dams, as well as those with preserved and destroyed dams, were also identified on the Morkváshinka River. On the whole, 26–48% of the length of the studied rivers has been transformed by beaver activity. The average number of dams per kilometer of the watercourse is 3.7–5.1. The most favorable channel gradients for beaver activity are 3.6–16.6 m/km, or 0.36–1.66%. The average gradient of the channel, above which no beaver dams and related ponds were found in these rivers, is 30 m/km, or 3%. An increase in the channel gradient upstream of the rivers is reflected in the size of beaver dams and ponds. The beaver dams and ponds are slightly larger in the sections of the rivers with a relatively small average gradient than in the sections with a medium average gradient of the channel.
... This is due in part to the wide variety of shapes and sizes of beaver dams, and the broad distribution of them across topographic, climatic, and ecological settings (Figure 1). While sophisticated habitat suitability models can estimate how many beaver dams a given stream or river can theoretically support based on its physical and ecological setting (Dittbrenner et al., 2018;Macfarlane et al., 2015), there are no models that can identify where beavers have already built their dams and created wetland habitat. ...
... The DEMs were collected with LIDAR and photogrammetric methods. We allowed the model to determine its own slope thresholds for beaver dam building activity, though it is generally accepted within the environmental science community that beavers typically prefer low-grade slopes (Macfarlane et al., 2015;Naiman et al., 1988). A 256 × 256 pixel patch was extracted over the center of each training data point. ...
... Additionally, our model framework can be used in parallel with capacity models like the Beaver Restoration Assessment Tool (BRAT) to fine-tune beaver-based river restoration practices (Macfarlane et al., 2015). Knowing the actual locations of beaver dams can be used to calibrate, verify, and validate beaver dam capacity estimates. ...
Beavers are ecosystem engineers that create and maintain riparian wetland ecosystems in a variety of ecologic, climatic, and physical settings. Despite the large‐scale implications of ongoing beaver conservation and range expansion, relatively few landscape‐scale studies have been conducted, due in part to the significant time required to manually locate beaver dams at scale. To address this need, we developed EEAGER—an image recognition machine learning model that detects beaver complexes in aerial and satellite imagery. We developed the model in the western United States using 13,344 known beaver dam locations and 56,728 nearby locations without beaver dams. Performance assessment was performed in twelve held out evaluation polygons of known beaver occupancy but previously unmapped dam locations. These polygons represented regions similar to the training data as well as more novel landscape settings. Our model performed well overall (accuracy = 98.5%, recall = 63.03%, precision = 25.83%) in these areas, with stronger performance in regions similar to where the model had been trained. We favored recall over precision, which results in a more complete catalog of beaver dams found but also a higher incidence of false positives to be manually removed during quality control. These results have far‐reaching implications for monitoring of beaver‐based river restoration, as well as potential applications detecting other complex landforms.
... Beavers primarily inhabit and dam smallto mid-sized streams (2-15 m wide) with perennial flows, woody vegetation in the riparian zones, and reasonable levels of stream energy (Macfarlane et al. 2017). The stream lengths affected by beavers overlap many other taxa, so beaver expansion may affect the population dynamics of salmonids (Oncorhynchus and Salvelinus; Rosenfeld et al. 2002, Burnett et al. 2007, amphibians (Stevens et al. 2007, Hossack et al. 2015, birds (Nummi and Holopainen 2014), and other species (Wright et al. 2002, Wright 2009). ...
... The stream lengths affected by beavers overlap many other taxa, so beaver expansion may affect the population dynamics of salmonids (Oncorhynchus and Salvelinus; Rosenfeld et al. 2002, Burnett et al. 2007, amphibians (Stevens et al. 2007, Hossack et al. 2015, birds (Nummi and Holopainen 2014), and other species (Wright et al. 2002, Wright 2009). The longterm consequences of stream modification by beavers on other taxa will be a function of what stream and riparian conditions are changed (Collen and Gibson 2000), the magnitude of those changes (Kemp et al. 2012, Weber et al. 2017, Majerova et al. 2019, the portion of the river modified (Remillard et al 1987, Demmer and Beschta 2008, Macfarlane et al. 2017, and the durability of the constructed dams (Demmer andBeschta 2008, Andersen andShafroth 2010). ...
... In documenting how stream and riparian conditions change, it is important to understand how many and how quickly stream reaches are being occupied by beavers. Modeling efforts indicate that beavers could occupy a large number of stream reaches in the western United States (Macfarlane et al. 2017, Dittbrenner et al. 2018, Touihri et al. 2018), but potential dam sites are not the same as estimates of current occupancy rates, given the existing beaver populations and land management strategies. Demmer and Beschta (2008) found nearly 70 dams built along 25.4 km of a stream in a 5-year time span, following changes in land management practices that fostered improvements of riparian conditions. ...
A before-after control-impact (BACI) design was used to simultaneously evaluate how stream habitat, macroinvertebrate communities, stream temperatures, and riparian conditions responded to beavers building damswithin a stream reach. Summarized conditions describing beaver-dammed and undammed stream reaches suggested that 13 of the 18 evaluated metrics differed. After accounting for beavers’ selection of lower-gradient stream reaches with less forested cover, the number of stream and riparian metrics that differed significantly dropped to 5. Beaver dams
increased pool area and depth, despite failing to increase the frequency of wood >10 cm in diameter. This suggests that beavers build dams utilizing pieces of wood smaller than most monitoring programs count. Changes in stream and riparian conditions due to beavers were insufficient to alter macroinvertebrate metrics commonly used to assess water quality. The presence of beaver dams in a reach was associated with less vegetative and woody cover along the stream’s
edge. The reduction of shrub cover and the presence of upstream beaver dams likely played a role in the small increases observed in water temperatures. The fact that beavers tended to build dams in reaches with elevated water tables may
have minimized water temperature increases. Based on the beaver occupancy rate found in this study, changes in stream and riparian conditions due to new beaver dams should be expected in 5% to 15% of the stream reaches similar
to those in this study over the next 2 decades. An increasing number of beavers occupying stream reaches represents animportant passive restoration approach that will improve the quality of aquatic systems on public lands.
... Typically, dams are constructed in small rivers <6 m wide and <0.7 m deep (Hartman & Tornlov, 2006). Other factors that influence dam construction and density are building material availability, stream power, stream gradient and stream width (Dittbrenner et al., 2018;Graham et al., 2020;Macfarlane et al., 2017). It is typical for dams to be constructed in low-medium gradient headwater streams ≤5th order Gurnell, 1998;Rosell et al., 2005;Stevens et al., 2007). ...
... where the structures are more likely to persist Green & Westbrook, 2009;Macfarlane et al., 2017;Westbrook et al., 2020) and they can activate the floodplain rapidly and over larger areas enhancing transient storage and reducing overland velocities. The effect of beaver dams on high flows, therefore, varies F I G U R E 8 Conceptual model describing the mechanisms of flow attenuation within a beaver wetland with an unconfined floodplain. ...
... These factors will need to be considered, alongside other potential impacts of dams, on biodiversity and economically valuable land/infrastructure. Beavers preferentially dam streams with wider floodplain extents (Dittbrenner et al., 2018) and with lower stream gradients (Dittbrenner et al., 2018;Graham et al., 2020;Hartman & Tornlov, 2006;Macfarlane et al., 2017) where available, often at locations immediately downstream of tributary confluences (Baskin et al., 2011). Therefore, it is possible that the greatest attenuation benefit will accrue during the initial stage of beaver population expansion as these preferred locations are occupied. ...
Beavers influence hydrology by constructing woody dams. Using a Before After Control Impact experimental design, we quantified the effects of a beaver dam sequence on the flow regime of a stream in SW England and consider the mechanisms that underpin flow attenuation in beaver wetlands. Rainfall‐driven hydrological events were extracted between 2009 and 2020, for the impacted (n=612) and control (n=634) catchments, capturing events seven years before and three years after beaver occupancy, at the impacted site. General additive models were used to describe average hydrograph geometry across all events. After beaver occupancy, Lag times increased by 55.9% in the impacted site and declined by 17.5% in the control catchment. Flow duration curve analysis showed a larger reduction in frequency of high flows, following beaver dam construction, with declines of Q5 exceedance levels of 33% for the impacted catchment and 15% for the control catchment. Using event total rainfall to predict peak flow, five generalised linear models were fitted to test the hypothesis that beaver dams attenuate flow, to a greater degree, with larger storm magnitude. The best performing model showed, with high confidence, that beaver dams attenuated peak flows, with increasing magnitude, up to between 0.5‐2.5 m3 s‐1 for the 94th percentile of event total rainfall; but attenuation beyond the 97th percentile cannot be confidently detected. Increasing flow attenuation, with event magnitude, is attributed to transient floodplain storage in low gradient/profile floodplain valleys that results from an increase in active area of the floodplain. These findings support the assertion that beaver dams attenuate flows. However, with long‐term datasets of extreme hydrological events lacking, it is challenging to predict the effect of beaver dams during extreme events with high precision. Beaver dams will have spatially variable impacts on hydrological processes, requiring further investigation to quantify responses to dams across differing landscapes and scales. This article is protected by copyright. All rights reserved.
... Examples of beaver-related alterations include increased ecosystem metabolisms (Wegener et al., 2017), shifts in riparian vegetation (Hayes et al., 2014;Pollock et al., 2007) and increased surface water exposure (Hood & Bayley, 2008). These open water resources provide vital habitats for fish (Schlosser, 1995;Schlosser & Kallemeyn, 2000), birds (Brown et al., 1996;Macfarlane et al., 2017) and herptiles (Russell et al., 1999;Stevens et al., 2007), leading to enhanced biological diversity (Hood & Bayley, 2008;McKinstry et al., 2001). Watersheds with impoundment structures delay streamflow concentration times compared to those without (Pollock et al., 2003) and exhibit a decrease in peak flow (Nyssen et al., 2011) as well as an overall reduction of suspended sediment export (Maret et al., 1987;Pollock et al., 2003;Stout et al., 2017). ...
... In general, beaver select smaller low gradient streams with ample vegetation for food and dam building (Pollock et al., 2003), but will move to higher gradient or larger streams to accommodate large populations (Müller-Schwarze & Schulte, 1999). To better understand what attracts beaver, several studies have used physical and biological metrics to estimate the capacity of a landscape to support these impoundments, condensed into habitat suitability indices (HSI) (Allen, 1982;Anderson & Bonner, 2013;Macfarlane et al., 2017;Retzer et al., 1956). While many studies have created suitability metrics to guide management efforts, there is disagreement on which parameters can best predict beaver activity (Anderson & Bonner, 2013;Macfarlane et al., 2017;Retzer et al., 1956). ...
... To better understand what attracts beaver, several studies have used physical and biological metrics to estimate the capacity of a landscape to support these impoundments, condensed into habitat suitability indices (HSI) (Allen, 1982;Anderson & Bonner, 2013;Macfarlane et al., 2017;Retzer et al., 1956). While many studies have created suitability metrics to guide management efforts, there is disagreement on which parameters can best predict beaver activity (Anderson & Bonner, 2013;Macfarlane et al., 2017;Retzer et al., 1956). As a result, reintroduction efforts guided by suitability indices can experience beaver relocations without desired restoration results (Babik & Meyer, 2015;Brick & Woodruff, 2019;Castro et al., 2017). ...
Beavers are of increasing interest as a mechanism for ecosystem restoration. However, the physical watershed characteristics that allow for successful beaver re‐establishment are not consistent across habitat suitability models. We delineated the extent of beaver impounded surface water in the Pole Mountain Area (PMA) of Southeastern Wyoming with six National Agricultural Imagery Program acquisitions over an 18‐year time period via a random forest classification algorithm. We computed beaver pond area for first and second‐order watersheds within the PMA and related the impounded pond area to climatic metrics such as maximum annual snow water equivalent and snow melt and rain input into the ground. There was no apparent relationship between annual climate metrics and beaver pond area. Further, we developed a random forest regression model to correlate beaver pond area with topographically derived watershed characteristics (e.g., hillslope size, riparian area size) to explore physical controls on impounded area at the watershed scale. Controls differed for first and second‐order watersheds, with pond area in smaller watersheds largely being controlled by lateral water contributions from the hillslopes, and in the larger watersheds by water from upstream and available space in the riparian areas. Interestingly, vegetation height did not emerge as an important predictor for pond area, likely because of generally good availability of forage material in all watersheds. This study improves our understanding of watershed characteristics that contribute to beaver habitat suitability and can be used to guide beaver re‐introduction efforts through analysis targeted at identifying watersheds most appropriate to beaver pond construction.
... BRAT was used to estimate current and historical beaver dam capacity for the study area (MacFarlane et al., 2017). BRAT calculates the capacity of dams for each stream based on four main variables: hydrology, topography, vegetation, and land use. ...
... LF rasters were edited to include a vegetation suitability code category. Vegetation codes were assigned by hand to individual vegetation types included in each raster and largely followed guidelines provided in MacFarlane et al. (2017). Generally, riparian vegetation such as willows, cottonwoods, and aspen was assigned high vegetation codes for being most suitable, while barren land, agricultural fields, and urbanized settings were assigned low vegetation codes for being unsuitable. ...
... Analysis of factors limiting beaver dam capacity A simple analysis was performed to investigate potential factors limiting current beaver dam capacity, in order to identify potential barriers to beaver populations or restoration. First, physical and hydrological constraints of slope and discharge were considered; reaches with a slope greater than 17% (0.17 m/m) were considered slope-limited, reaches with a baseflow discharge stream power greater than 190 W/m were considered to have baseflows too high to construct dams (baseflow limited), and reaches with a Q 2 discharge stream power greater than 2400 W/m were considered to have peak flows high enough to consistently blowout dams (high flow limited) (MacFarlane et al., 2017). Drainage area influences were then considered such that reaches with drainage areas greater than the predefined threshold were considered drainage area-limited. ...
The loss of beaver populations has commonly been accompanied by the failure of beaver dams, leading to stream incision, water table lowering, and the eventual transition from a beaver meadow to a drier riparian corridor. Widespread decline in North American beaver populations (Castor canadensis) has been documented from pre‐European settlement to the current day, representing an estimated 80% to 98% loss of historical populations. While individual case studies have investigated the ecosystem impacts of local beaver population loss, few studies have quantified large‐scale changes associated with widespread population decline. Here, we use the Beaver Restoration Assessment Tool to model landscape‐scale habitat suitability and beaver dam capacity in Colorado, USA, in order to determine whether a widespread loss in beaver population corresponds to a similar scale decline in the capacity to sustain beaver on the landscape and declines in physical benefits associated with beaver, such as surface water and sediment storage. Currently, the statewide stream network (298,119 stream kilometers) can support approximately 1.36 million beaver dams, compared with 2.39 million dams historically. All regions of Colorado have seen a decline in beaver dam capacity from historical conditions, likely due to agriculture, urbanization, and loss of vegetation necessary to beaver. Beaver dam capacity loss is accompanied by an approximate 40% decline in beaver‐mediated surface water and sediment storage potential across the state. Regions with high percent loss in storage potentials also had a high percentage of drainage network that had experienced beaver dam capacity losses of 15 or more dams per kilometer, which highlights the disproportionate impacts of losing high dam density reaches (i.e., beaver meadows). Extreme dam density declines were rare, and instead, most reaches have undergone a shift from high to moderate capacity. Statewide shifts in beaver dam capacity highlight the opportunity for using beaver‐related restoration in Colorado and across the American West.
... Beavers are ecosystem engineers that build dams across and alongside rivers (Brazier et al., 2020;Larsen et al., 2020). These wood accumulations increase the storage of water, sediment, organic matter and nutrients on floodplains, and thus have several ecological benefits (Bouwes et al., 2016;Macfarlane et al., 2017;Wohl, 2013). As beaver dams impound water upstream, they also raise the possibility of beaver dam outburst floods. ...
... Beavers require sufficient stream flow as a reliable water source. Yet, rivers should neither be too wide nor too deep to inhibit building and persistence of dams (Collen and Gibson, 2000;Gurnell, 1998;Macfarlane et al., 2017). ...
... The available data and the representation of the flow network by D8 flow directions do not permit us to represent these factors. In addition, beaver dams entail hydrologic (creating wetlands), hydraulic (slow down runoff), geomorphic (sediment trapping), and ecological feedbacks (subirrigation of downstream valley bottoms that promotes establishment and expansion of riparian vegetation); all of which tend to increase stream complexity and channel-floodplain connectivity (Macfarlane et al., 2017). These feedbacks may lead to spatial clustering, as beaverengineered river reaches may increase local beaver populations. ...
Many geomorphic phenomena such as bank failures, landslide dams, riffle‐pool sequences and knickpoints can be modelled as spatial point processes. However, as the locations of these phenomena are constrained to lie on or alongside rivers, their analysis must account for the geometry and topology of river networks. Here, we introduce a new numeric class in TopoToolbox called Point Pattern on Stream networks (PPS), which supports exploratory analysis, statistical modelling, simulation and visualization of point processes. We present three case studies that aim at inferring processes and factors that control the spatial density of geomorphic phenomena along river networks: analysis of a synthetic dataset of points on a stream network, the analysis of knickpoints in river profiles, and modelling spatial locations of beaver dams based on topographic metrics. The case studies rely on exploratory analysis and statistical inference using inhomogeneous Poisson point processes. Thereby, statistical and probabilistic procedures implemented in PPS provide a systematic approach for treating and quantifying uncertainties. PPS provides a consistent numeric framework for modelling point processes on river networks with a wide range of applications in fluvial geomorphology, but also other disciplines such as ecology.
... This report presents an application of the Beaver Restoration Assessment Tool 3.0.20 (BRAT; http://brat.riverscapes.xyz/) a tool for building realistic expectations for partnering with beaver in conservation and restoration (Macfarlane et al., 2017). In this application, we analyzed all the perennial rivers and streams of the Greater Yellowstone Area (GYA) outside of Montana. ...
... With the development of the Beaver Restoration Assessment Tool (BRAT) (Macfarlane et al., 2017), predictive spatial models resolving where beaver dams within a drainage network can be built and sustained have been realized. In summary, dam building beaver need water and wood. ...
... Specifically, BRAT is a spatially explicit network tool that predicts where along streams and rivers beaver may be useful as a restoration tool and where they may be a nuisance, in which case their impacts can be mitigated or the nuisance beaver can serve as a source population for live-trapping and relocation to areas where they can help achieve restoration and conservation objectives. The BRAT model has been run for the entire state of Utah (Macfarlane et al. 2017), the entire state of Idaho (Macfarlane et al. 2019), and large portions of California. Additionally, BRAT has been run for smaller portions of New York, Washington and the United Kingdom. ...
This report presents an application of the Beaver Restoration Assessment Tool 3.0.20 (BRAT; http://brat.riverscapes.xyz/) a tool for building realistic expectations for partnering with beaver in conservation and restoration (Macfarlane et al., 2017). In this application, we analyzed all the perennial rivers and streams of the Greater Yellowstone Area (GYA) outside of Montana. Montana Natural Heritage Program is currently running the Montana portion with Bureau of Land Management funding.
... On streams, what is suitable is perennial flow without large floods happening too often such that dams regularly fail 37 . The BRAT model uses the stream power associated with the two-year recurrence interval peak flood (Q2) to infer the likelihood that a beaver dam will persist once built 34 . Knowing that climate changes are already leading to wetter conditions in this part of Canada 38 and are likely to continue into the future 19 , we ran scenarios in the BRAT model across the park wherein only Q2 was modified to assess how climatic-induced changes to streamflow might influence beaver dam capacity (see "Methods"). ...
... The modelling results indicate that a doubling of the size of the 2-year flood will reduce beaver dam capacity in RMNP by 21%. The BRAT model classifies a stream reach as not capable of supporting beaver dams where stream power exceeds 2000 W/m; a threshold above which McFarlane et al. 34 indicate beaver dams commonly fail. However, there is significant uncertainty around dam failure threshold. ...
... The requisite inputs to the beaver dam capacity model include a drainage network layer, vegetation type raster data of historic and existing conditions, a digital elevation model (DEM) raster, and streamflow (baseflow and peak flow) information throughout the drainage network. Methods by Macfarlane et al. 34 were followed using ESRI ArcMap 10.5 with minor customizations including the preprocessing of BRAT vegetation and stream power data to customize the tool to the boreal forest generally and Riding Mountain National Park specifically. www.nature.com/scientificreports/ ...
Environmental changes are altering the water cycle of Canada’s boreal plain. Beaver dams are well known for increasing water storage and slowing flow through stream networks. For these reasons beavers are increasingly being included in climate change adaptation strategies. But, little work focuses on how environmental changes will affect dam building capacity along stream networks. Here we estimate the capacity of the stream network in Riding Mountain National Park, Manitoba, Canada to support beaver dams under changing environmental conditions using a modelling approach. We show that at capacity, the park’s stream network can support 24,690 beaver dams and hold between 8.2 and 12.8 million m³ of water in beaver ponds. Between 1991 and 2016 the park’s vegetation composition shifted to less preferred beaver forage, which led to a 13% decrease in maximum dam capacity. We also found that dam capacity is sensitive to the size of regularly-occurring floods—doubling the 2-year flood reduces the park’s dam capacity by 21%. The results show that the potential for beaver to offset some expected climatic-induced changes to the boreal water cycle is more complex than previously thought, as there is a feedback wherein dam capacity can be reduced by changing environmental conditions.
... Unfortunately, there is no information available on pre-settlement conditions and desired future conditions, limiting directions for management activities. MacFarlane et al. (2015) proposed a model that results in spatially explicit reach-information for streams where beaver dam-building is sustainable and density of dams that are expected to occur across a landscape. A recent (2015) geomorphological survey of Daly Creek combined with 10 year of stream flow data, a vegetation cover type map (Holthuijzen 2016b), and riparian monitoring data (Holthuijzen 2015a(Holthuijzen , 2017a can provide the basis to use the model developed by MacFarlane et al. (2015) to spatially explicitly determine where and how many beaver dams (dams/km) can be expected. ...
... MacFarlane et al. (2015) proposed a model that results in spatially explicit reach-information for streams where beaver dam-building is sustainable and density of dams that are expected to occur across a landscape. A recent (2015) geomorphological survey of Daly Creek combined with 10 year of stream flow data, a vegetation cover type map (Holthuijzen 2016b), and riparian monitoring data (Holthuijzen 2015a(Holthuijzen , 2017a can provide the basis to use the model developed by MacFarlane et al. (2015) to spatially explicitly determine where and how many beaver dams (dams/km) can be expected. Ongoing annual spatial explicit surveys of beaver dams and ponds along Daly Creek could be used to verify this model. ...
Starting in 2007, riparian woody vegetation along the main Daly Creek drainage continues to recover after restriction of livestock grazing and aided by rapidly expanding beaver activity. At the Eagle Creek MU, an improved and upgraded irrigation water distribution system has resulted in wet meadow complexes and expanding native herbaceous plant populations. Increasing complexity in the vertical structure of vegetation along the Daly Creek drainage and an expanding, connected riparian corridor is expected to positively influence the abundance and diversity of avian communities. Improved wetland conditions at the Eagle Creek MU are hypothesized to lead to more diverse plant communities and associated avian community. The general objective of this study is to document changes in avian abundance and composition at the Daly Creek drainage and Eagle Creek MU during 2012-2018. Specific objectives are to determine: 1) the abundance, diversity and composition of avian communities during the nesting season (middle of June through the middle of July) and 2) changes in avian community composition and abundance in relation to shifting riparian habitat conditions. Daly Creek drainage are referred to as “Daly Creek” and the Eagle Creek MU as “Eagle Creek”. Annually, up to 20 sites were surveyed at Daly Creek and 11 sites at Eagle Creek. Fixed, permanent
circular point counts were used that were monitored for 8-min each during each survey. Monitoring started in spring 2012 and 2013 at Daly- and Eagle Creek, respectively and continued annually through 2017. Surveys were conducted in spring and summer, except in 2015 when sites were only monitored in summer. I monitored Forested Wetland, Scrub-Shrub Wetland cover types at Daly Creek and Grassland (wet meadows) and Scrub-Shrub Wetland and Forested Wetland at Eagle Creek. Bird abundances and composition along Daly Creek showed limited change over time. No differences were found between summer and spring bird abundances for Forested Wetland and Scrub-Shrub Wetland vegetation cover types. At Eagle Creek, Scrub-Shrub Wetland and Forested Wetland showed the highest bird densities compared to Grassland. Summer bird densities in Forested Wetland were significantly higher in 2015 than in other years, but not for spring surveys. Species diversity was higher for Scrub-Shrub Wetland compared to Forested Wetland at Daly Creek, but no differences were found between summer and spring for
each of the vegetation cover types over the monitoring period. At Eagle Creek, summer bird diversity was highest in 2015 compared to other years. No other differences were found among cover types, among years for each cover type, or seasons. Shannon diversity indices were remarkably similar between the 2 vegetation cover types for each of the areas monitored, paralleled by evenness, without a clear temporal trend. Generally, community analyses did not
show strong unidirectional trends of avian communities for the vegetation cover types monitored. Avian communities for vegetation cover types at both Daly Creek and Eagle Creek became more similar during 2012 through 2018, but showed a modest difference between monitoring sites at Daly Creek and Eagle Creek. In conclusion, changes to the avian abundance and diversity at Daly Creek and Eagle Creek were at most weak and changes in avian community composition modest. At Daly Creek the riparian (woody) vegetation is narrow, fragmented, and lacks large, mature trees that provide spatial and structural habitat diversity to multiple avian
guilds. This may provide an explanation for similar avian abundances and diversity over the monitoring period. Changes in management at Eagle Creek have been recent (2014 and 2015) and have only modestly influenced avian abundance and diversity
... While remote sensing and new analytical techniques have allowed more rapid mapping and assessment of floodplain, riparian, and riverine habitat (Beechie and Imaki 2014;Macfarlane et al. 2017bMacfarlane et al. , 2017aBond et al. 2018), reliable methods to adequately quantify historic, current, and potential salmonid abundance at the reach, tributary, and watershed scale have proven more challenging. The scale of watershed restoration and the cost and logistical constraints of measuring fish habitat capacity, current abundance, or survival at both a reach and watershed scale have hampered these efforts. ...
... A further modification of this approach, the unit characteristic method (UCM), estimates capacity of a stream using standard habitat survey data and known species preferences for depth, velocity, cover and other factors (Cramer and Ackerman 2009). Subsequent efforts have applied models to explain losses in habitat capacity because of reductions of beaver ponds and floodplain habitat (Pollock et al. 2004;Roni et al. 2016;Macfarlane et al. 2017b;Bond et al. 2018). ...
Objective
A variety of analytical approaches have been developed in recent years to estimate salmon Oncorhynchus spp. freshwater habitat capacity to assist with planning and evaluating habitat restoration. We compared and contrasted seven different methods for estimating juvenile Chinook Salmon O. tshawytscha habitat rearing capacity (total number of fish that a given area of habitat can support), abundance, and habitat suitability in a 3.2‐km reach of the Grande Ronde River, Oregon.
Methods
This included approaches that used statistical methodologies applied to existing empirical data sets, including quantile random forests (QRFs) and spatial stream networks (i.e., Fish Data Analysis Tool [FDAT]), and deterministic models that included the habitat suitability index, the unit characteristic method (UCM), and three habitat expansion methods.
Result
We hypothesized that the methods would provide comparable estimates. However, the approaches provided very divergent estimates for the same stream reach, ranging from 1048 to 24,530 juvenile Chinook Salmon. The simple habitat expansion methods appeared to be the most similar to the actual parr (juvenile) abundance obtained from recent snorkel surveys (4179 juveniles). The fish density data (fish/m ² ) and habitat data used in the models were likely the main drivers of the differences between the UCM and habitat expansion methods.
Conclusion
The habitat expansion approaches, which are based on detailed habitat surveys, appear to be particularly suitable for estimating capacity within a reach; thus, they may be suitable for evaluating changes due to habitat restoration. The model‐based approaches (QRF and FDAT) appear to yield coarser estimates, in part because they use various inputs at the reach and landscape scales. As such, they are more useful for relative comparisons among reaches in watersheds to assist with watershed‐scale restoration planning and prioritization. Because all of the methods rely on fish density in different types of habitats, regional or local data on fish densities would improve their accuracy.
... ii. Beaver Dam Capacity (BDC) (Macfarlane et al., 2017;Stoll & Westbrook, 2020) which describes the density of dams that could be For every reach within the river network, an attempt was made to generate a theoretical territory: a target reach length was randomly drawn from a uniform distribution between 1337 and 1923 m which equates to one standard deviation around mean territory lengths reported by Campbell et al. (2005), Graf, Mayer, et al. (2016), John and Kostkan (2009), Mayer et al. (2017) and Vorel et al. (2008). The stream reach was then buffered by half the target length value. ...
... Panel a is derived using the higher minimum Beaver Forage Index (BFI) threshold of 3.0; panel b uses a minimum BFI threshold of 1.3. We can interpret these limits as the upper and lower estimates of the minimum forage quality required to sustain a territory prohibitive issue because it is widely accepted that woody habitat is extremely important for beavers and they will preferentially seek out these locations Macfarlane et al., 2017;Vorel et al., 2015;Zwolicki et al., 2019). As beaver populations grow, the density of woody feeding signs increases dramatically, as demonstrated in Figure 4; therefore, it becomes more challenging to differentiate between neighbouring territories as they begin to border each other (Campbell et al., 2005;Graf, Mayer, et al., 2016). ...
Eurasian beaver (Castor fiber) were nearly hunted to extinction but have recovered to occupy much of their former range. Beaver were extirpated from Great Britain c. 400 years ago but have recently been reintroduced. The River Otter catchment, Devon was the site of the first licensed wild release of beavers in England. With further releases being considered, there is a need to better understand population dynamics of this native, keystone species to inform conservation and management.
Field signs were surveyed from 2015 to 2021. A semi‐automated territory detection method was adopted to estimate territory counts. A spatially explicit model was developed to estimate the ecological territory capacity of the catchment. Future territory expansion was modelled using logistic growth curves; initial growth rate was estimated from observed territory counts and the estimated territory capacity range was used to define the limiting value of the growth curve. Beaver territory removal was simulated, across a range of management intensities and start times, to determine potential impacts of translocation or lethal control upon population dynamics.
Territory numbers increased from four to 18, inclusive of four additionally released individuals, during study period. In the absence of population management, the territory capacity of the catchment was estimated to range between 120 and 183; this may be reached between 2028 and 2057. Simulated territory removal, where territories were removed at a fixed rate from the sum of the estimated total population and the population increase for that year, demonstrated large uncertainties in predicted population responses. Simulations with territory removals >3/year all predicted potential population collapse. This finding emphasizes the need for caution when considering population management strategies; translocation of animals out of the catchment or culling should be considered only when populations are established and all alternatives have been considered.
These results provide critical information for the expected rate and magnitude of beaver population change in the River Otter catchment. The methods provide a reproducible and generalizable approach for understanding beaver population change, which can inform policy on the reintroduction of beavers and the potential timing and intensity of future beaver population management.
... Puttock et al. (2017) hypothesized that beaver-constructed features increase water storage within the landscape, with their creation of a stepped profile channel. Dams created by beavers result in ponds along the stream channel that raise the water table in the adjacent riparian zone Macfarlane et al., 2017;Naiman et al., 1988;Pollock et al., 2003Pollock et al., , 2014. Vanderhoof and Burt (2018) quantified increases in reachscale stream surface area upstream of multiple BDAs in the Upper Missouri River Headwaters Basin, as well as decreases in stream surface area for reaches just downstream (through 500 m). ...
... Villarreal et al. (2022) identify locations where NIDS would be most beneficial based on a combination of fire and watershed model predictions. Likewise, beaver restoration can be targeted at suitable sites, more likely to sustain re-introduced beaver populations (Gurnell, 1998;Pollock et al., 2014;Macfarlane et al., 2017;Scamardo et al., 2022). Research to understand how to maximize the benefits from NIDS installations and plan the biggest and most effective chains of soil-water-carbon sinks, will save both financial and environmental resources in the future. ...
In this article we describe the natural hydrogeomorphological and biogeochemical cycles of dryland fluvial ecosystems that make them unique, yet vulnerable to land use activities and climate change. We introduce Natural Infrastructure in Dryland Streams (NIDS), which are structures naturally or anthropogenically created from earth, wood, debris, or rock that can restore implicit function of these systems. This manuscript further discusses the capability of and functional similarities between beaver dams and anthropogenic NIDS, documented by decades of scientific study. In addition, we present the novel, evidence-based finding that NIDS can create wetlands in water-scarce riparian zones, with soil organic carbon stock as much as 200 to 1400 Mg C/ha in the top meter of soil. We identify the key restorative action of NIDS, which is to slow the drainage of water from the landscape such that more of it can infiltrate and be used to facilitate natural physical, chemical, and biological processes in fluvial environments. Specifically, we assert that the rapid drainage of water from such environments can be reversed through the restoration of natural infrastructure that once existed. We then explore how NIDS can be used to restore the natural biogeochemical feedback loops in these systems. We provide examples of how NIDS have been used to restore such feedback loops, the lessons learned from installation of NIDS in the dryland streams of the southwestern United States, how such efforts might be scaled up, and what the implications are for mitigating climate change effects. Our synthesis portrays how restoration using NIDS can support adaptation to and protection from climate-related disturbances and stressors such as drought, water shortages, flooding, heatwaves, dust storms, wildfire, biodiversity losses, and food insecurity.
... The LTPBR manual (Wheaton et al. 2019) and the Beaver Restoration Guidebook (Pollock et al. 2017) recommend using the Beaver Restoration Assessment Tool (BRAT) (MacFarlane et al. 2015) to evaluate restoration feasibility and to select sites. The BRAT, a computer model that predicts the capacity of streams to support beaver dams, was run for Colorado in 2020 by Juli Scamardo (Colorado State University). ...
... The fidelity of the BRAT model to observed beaver dam density reported in Utah (Macfarlane et. al. 2015) did not seem to hold true for Park County, Colorado. The 6-7-fold discrepancy between the BRAT model and our professional assessment of beaver dam capacity is worrisome, especially as more people turn to the model for guidance. We fear it may lead people into unrealistic expectations about restoration potential-or unrealistic fears abou ...
This study outlines a pragmatic professional-judgment assessment of the potential for using low-tech process-based restoration (LTPBR) approaches for restoring riverscapes with beavers in Park County, Colorado. The method allows professionals to apply knowledge and data from many sources in the evaluation of current beaver activity, capacity, limiting factors, and restoration potential to prioritize opportunities.
... According to the 2010 whitebark pine distribution map [40] there are an estimated 10,232 square km of whitebark pine within the GYE, representing 18% of the land cover. LAS has been used to assess beaver dam building habitat [41], map riparian vegetation [42], and to assess whitebark pine mortality [13]. Macfarlane et al. [13] found that LAS combined with the mountain pine beetle-caused mortality rating system (MPBM Rating System) provided an effective assessment of cumulative MPB-caused whitebark pine mortality. ...
An aerial survey method called the Landscape Assessment System (LAS) was used to assess mountain pine beetle (Dendroctonus ponderosae)-caused mortality of whitebark pine (Pinus albicaulis) across the Greater Yellowstone Ecosystem (59,000 km2; GYE). This consisted of 11,942 km of flightlines, along which 4434 geo-tagged, oblique aerial photos were captured and processed. A mortality rating of none to severe (0–4.0 recent attack or 5.0–5.4 old attack) was assigned to each photo based on the amount of red (recent attack) and gray (old attack) trees visible. The method produced a photo inventory of 74 percent of the GYE whitebark pine distribution. For the remaining 26 percent of the distribution, mortality levels were estimated based on an interpolated mortality surface. Catchment-level results combining the photo-inventoried and interpolated mortality indicated that 44 percent of the GYE whitebark pine distribution showed severe old attack mortality (5.3–5.4 rating), 37 percent showed moderate old attack mortality (5.2–5.29 rating), 19 percent showed low old attack mortality (5.1–5.19 rating) and less than 1 percent showed trace levels of old attack mortality (5.0–5.09). No catchments were classified as recent attacks indicating that the outbreak of the early 2000’s has ended. However, mortality continues to occur as chronic sub-outbreak-level mortality. Ground verification using field plots indicates that higher LAS mortality values are moderately correlated with a higher percentage of mortality on the ground.
... Practical applications for forest management have been studied, such as mapping of wet soil areas (Lidberg et al., 2020), low terrain trafficability (Niemi et al., 2017;Salmivaara et al., 2020), and vulnerability to erosion (Frizzle et al., 2021). Accurate DEMs also enable solving spatial optimization problems, such as finding optimal locations for canal blocks in the rewetting of drained peatlands (Urzainki et al., 2020) or modeling suitable locations to support beavers' dam-building activities (Macfarlane et al., 2017). ...
Peatland forest management is an important source of human-induced additional nitrogen, phosphorus, and organic carbon loads to surface waters in Finland. Ditch network maintenance (DNM) is typically used to ensure sufficient soil drainage for profitable timber production on peatland sites, but nutrient mobilization, particularly of phosphorus, and suspended sediment loads from ditches can cause harmful ecological effects on the quality of water courses. Various water protection structures have been developed to capture the loads released after treatments and to decrease the management impacts in forestry. Overland flow fields are efficient mechanisms for water purification, but they are rarely used in practice due to difficulties in finding suitable locations. In addition, leaving breaks between cleaned ditch sections is recommended wherever possible, as uncleaned sections decrease flow velocity and enhance sediment deposition from runoff water. To plan the most adequate protection methods in DNM, new GIS-based tools are needed to propose e.g. appropriate locations for water protection structures. We developed a spatial analysis to suggest locations for overland flow fields and uncleaned ditch sections within the catchment of lake Kovesjärvi (Parkano, Western Finland). Airborne lidar data consisting of 5 pulses m−2 enabled detailed terrain analysis and finding strictly specified terrain properties that satisfied the conditions of the water protection structures. Half of the field-reviewed overland flow fields were evaluated as good suggestions by forest management professionals and researchers. The model for uncleaned ditch sections worked well on the relatively flat study area, as 77% of the field-reviewed suggestions were rated good by expert opinions. Overall, the approach was evaluated to be useful in peatland forest management. Model parameters can be modified for various topographies, but more studies are needed prior to wider use of the model.
... River training works have been widely applied in the inland waterway regulation projects to provide better navigation conditions. Common river training works including dams (Macfarlane et al. 2017), spur dikes (Kiani et al. 2017), dredging works (Mendes et al. 2016), etc. would facilitate navigation conditions improvement and transport safety. In the upper reach of Yangtze river, the stochastic characteristics of turbulent flows and gravel bedload transport are highlighted (Cui et al. 2021). ...
A large number of river training works have been built in the inland waterway regulation projects to improve ship navigation conditions. However, water damages to river training works happen frequently in practice. Technical status evaluation of river training works is regarded as a fundamental content of inland waterway maintenance. Due to the various influencing factors and complex mechanisms, the content involved in the standard files is recognized as qualitative and no quantitative evaluation method is recommended so far. The technical status of river training works is currently evaluated through on-site investigation which is time-consuming and individual-dependent. By means of multi-source sensors, massive status data of river training works could be obtained instantaneously. Study on the technical evaluation model based on the multi-source information fusion theory attracts more attention in recent years. The classical DS evidence theory could fail as evidence conflict occurs. Thus, the Pearson’s correlation coefficient is calculated and utilized to update the probability distribution in the present study. A novel technical status evaluation model based on the improved DS evidence theory is established. The model is further verified through three case studies of traditional river training works (spur dike and flexible mattress belt) in the Yangtze River, China. The model outputs are consistent with the technical survey reports as well as the published research article. Quantitative and accurate evaluation of river training works could be accomplished by applying the proposed evaluation model. Moreover, the model could be embedded in the Inland Electronic Chart Display and Information System. The present study would provide theoretical basis for inland waterway maintenance and infrastructure monitoring in the future.
... A disturbance mechanism operating at small spatial scales that had a large, rapid, and obvious effect on many stream conditions were beavers and their dams (Collen and Gibson 2000;Macfarlane et al. 2017;Larsen et al. 2021). Greater than 10% of stream reaches that underwent a substantial change in at least one habitat attribute had beavers present in the reach. ...
Hydrologic, terrestrial and biologic disturbances are factors influencing stream channel conditions important to the persistence of aquatic biota. Past studies of how disturbance events alter streams have focused on fires, floods, and debris torrents as the magnitude of these events make them easy to detect. This approach has led to a bias in understanding which disturbances are likely to affect stream conditions. To address this concern, we used stream habitat data to identify where a substantial change in stream conditions had occurred and then used photographs of the evaluated reach to determine the disturbance that potentially caused those changes. We evaluated conditions in over 2000 stream reaches and found nearly a quarter of them had seen a substantial change in at least one of the five stream channel characteristics ‐ bankfull width, wood frequency, median particle size, pool depth, and bank stability – in the two decades these streams were monitored. Although many stream reaches were affected by charismatic disturbance events such as fires, floods, and mass wasting, the majority of the substantial changes we observed in channel conditions were related to small scale disturbances. Mechanisms such as beavers, tree fall, vegetative growth, grazing, and active restoration all played an important role in bringing about large changes in stream channel conditions. While the majority of the disturbances were natural, some channel changes remain tied to anthropogenic activities. Our results suggest no single sampling approach can be used to evaluate how stream conditions respond to all disturbances as they vary in intensity, over space and time, and which stream attribute is measured. By better understanding the full range of possible disturbances, managers should be better able to use such events to improve outcomes for streams and aquatic biota.
... Simulated fluvial corridors were based on streams with alluvial aquifers assumed to be 5-20 m thick. Alluvial aquifers of this size are consistent with second to fourth-order streams in the intermountain west, which also tend to be areas where natural beaver dams persist through high flows (Macfarlane et al. 2017). Floodplain soils that develop from overbank deposition are often dominated by fine-grained deposits. ...
Beaver‐mimicry stream restoration (BMR) involves the alteration of a stream channel to approximate the effects of beaver activity. Project objectives often include increasing groundwater storage and dry‐season streamflow, but limited data are available to understand the nature of its effects on groundwater dynamics. We developed generic groundwater models of mountain headwater streams to investigate the effects of installing a single beaver‐mimicry structure (BMS) using different restoration designs in varied hydrogeologic settings. The magnitude of changes in dry‐season net stream gains from a single BMS was always a minor component of the channel water balance, and would be too small to measure in the field; however, the modeled patterns of change caused by a single BMS help to understand the underlying mechanisms. All tested scenarios caused increases in groundwater recharge from the stream, which resulted in increased groundwater levels, and groundwater outflow from the model domain. For scenarios that did not include evapotranspiration, most treatments in gaining and losing settings caused slight increases in dry‐season net stream gains, but in strongly losing settings net stream gains were reduced. The addition of simulated evapotranspiration often resulted in decreased dry‐season net stream gains, since evapotranspiration increased with groundwater elevations. BMR design and siting influence the types of hydrologic effects that should be anticipated.
... The structure indicator assesses the potential for stream corridors to support dam building beaver and log jam formation by applying the Beaver Restoration Assessment Tool (BRAT) across the Yampa Basin. Although BRAT (Macfarlane et al., 2015) was designed to assess the Yampa River Basin Remote Assessment: Data Synthesis Report ...
In order to characterize physical and biological conditions across the four planning segments of the Yampa Basin that comprise the geographical extent of the Yampa IWMP, a set of hydrogeomorphic and ecological indicators and associated metrics was developed. Each indicator described in this report was assessed based on remotely measurable metrics that together provide a holistic understanding of river health and its degree of functionality. To the extent supported by available data, we have assessed indicators that are either currently used in the Yampa Basin or are otherwise relevant to assessing the hydrogeomorphic and ecological conditions within the basin. The selected indicators account for TSC priorities, project objectives, data availability, riverscape principles, and ability of remote sensing methods to accurately characterizing trends in river health. For each indicator, we include the metrics that support examination of that indicator and assess the quantity and quality of available data to evaluate those variables.
... In other situations, our first step may be policy changes: for example, if floodplains are intact, but beaver management actions (e.g., the lethal removal of beavers that impact the built environment) prevent population persistence sufficient to further recover these landscapes. Regardless of our role in the conversation, beaver inspired or implemented process-based restoration should be a primary strategy to achieving healthy riverscapes (Macfarlane et al., 2015;Pollock et al., 2015). A stream where beavers thrive is a resilient, productive stream (Pollock et al., 2014). ...
Rivers and streams, when fully connected to their floodplains, are naturally resilient systems that are increasingly part of the conversation on nature‐based climate solutions. Reconnecting waterways to their floodplains improves water quality and quantity, supports biodiversity and sensitive species conservation, increases flood, drought and fire resiliency, and bolsters carbon sequestration. But, while the importance of river restoration is clear, beaver‐based restoration—for example, strategic coexistence, relocation, and mimicry—remains an underutilized strategy despite ample data demonstrating its efficacy. Climate‐driven disturbances are actively pushing streams into increasingly degraded states, and the window of opportunity for restoration will not stay open forever. Therefore, now is the perfect time to apply the science of beaver‐based low‐tech process‐based stream restoration to support building climate resilience across the landscape. Not every stream will be a good candidate for beaver‐based restoration, but we have the tools to know which ones are. Let us use them.
This article is categorized under: Science of Water > Hydrological Processes
Water and Life > Nature of Freshwater Ecosystems
Water and Life > Conservation, Management, and Awareness
... An analysis of the existing and historic beaver dam capacity was conducted using the Beaver Restoration Assessment Tool (BRAT; Macfarlane et al., 2015). The model output is a carrying capacity estimate of beaver dams in dams per kilometer. ...
In this report we present a conservation, restoration and monitoring plan for the streams and riparian areas of Dugout Ranch, Utah, owned and operated by The Nature Conservancy (TNC). The plan is intended to help guide conservation, restoration and management of the Dugout Ranch’s riverscapes (streams and riparian areas) over the next several decades and is also developed as an adaptive management plan to facilitate learning. The recommended conservation and restoration actions are intended to maintain and enhance native riparian vegetation and instream biota. Many terrestrial animals that use the riparian zone or migrate through the riverscape are also anticipated to benefit from the plan. The recommended conservation and restoration actions are based on the best available information regarding the current ecological and geomorphic conditions and restoration recovery potential as well as ranch management objectives. We prioritized reaches for conservation and restoration actions using condition assessment models, expert opinion and field observations. We recommend an experimental design for implementation of conservation and restoration actions. Combined with monitoring, the experimental design is aimed at identifying the most successful conservation and restoration actions for maintaining complex instream habitat and a healthy native riparian community.
... Reintroduction of beaver (Castor canadensis), which were once common throughout the northern Rocky Mountains and many bull trout streams, has gained attention for the potential effects on baseflows, meadow restoration, and diversification of stream habitats (Pilliod et al., 2018;Pollock et al., 2014). Beaver reintroductions or the use of beaver dam analogs are relatively inexpensive, could be used to treat many streams, and be targeted effectively using tools that highlight the best potential reintroduction sites (Macfarlane et al., 2017). Concerns exist that beaver ponds and complexes may slow stream velocities and increase temperatures but evidence suggests either minimal impacts or enhanced thermal diversity because hydraulic head pressure on the valley floor creates cold upwelling zones within a warmer overall matrix (Majerova et al., 2020;Weber et al., 2017). ...
Mountain headwater streams have emerged as important climate refuges for native cold-water species due to their slow climate velocities and extreme physical conditions that inhibit many non-native invasions. Species persisting in refuges oftentimes do so as fragmented, relict populations from broader historical distributions that are subject to ongoing habitat reductions and increasing isolation as climate change progresses. Key for conservation planning is determining where remaining populations will persist and how habitat restoration strategies can improve biological resilience to enhance the long-term prospects for species of concern. Studying bull trout, a headwater species in the northwestern U.S., we developed habitat occupancy models using a dataset of population occurrence in 991 natal habitat patches with a suite of novel geospatial covariates derived from high-resolution hydroclimatic scenarios and other sources representing watershed and instream habitat conditions, patch geometry, disturbance, and biological interactions. The best model correctly predicted bull trout occupancy status in 82.6% of the patches and included effects for: patch size estimated as habitat volume, extent of within-patch reaches < 9 °C mean August temperature, distance to nearest occupied patch, road density, invasive brook trout prevalence, patch slope, and frequency of high winter flows. The model was used to assess 16 scenarios of bull trout occurrence within the study streams that represented a range of restoration strategies under three climatic conditions (baseline, moderate change, and extreme change). Results suggested that regional improvements in bull trout status were difficult to achieve in realistic restoration strategies due to the pervasive nature of climate change and the limited extent of restoration actions given their high costs. However, occurrence probabilities in a subset of patches were highly responsive to restoration actions, suggesting that targeted investments to improve the resilience of some populations may be contextually beneficial. A possible strategy, therefore, is focusing effort on responsive populations near more robust population strongholds, thereby contributing to local enclaves where dispersal among populations further enhances resilience. Equally important, strongholds constituted a small numerical percentage of patches (5-21%) yet encompassed the large majority of occupied habitat by volume (72-89%) and their protection could have significant conservation benefits for bull trout.
... This leads to discussions about harm and usefulness, based on a 19th century contradictory categorization of harmful and useful animals. It, therefore, also leads to a focus on individual beaver burrows and not to insights into the geomorphological effects of the beaver at the level of, for example, a river basin [68]. Experiments abroad in which the beaver is used to make rivers more natural again show that the resilience of the beaver can initiate an even stronger resilience in nature. ...
Social resilience and ecological resilience are related and distinguished, and the potential of social resilience to enhance resilience of encompassing social-ecological systems is discussed. The value of resilience thinking is recognized, yet social resilience needs to be better understood in its distinctive qualities, while resisting identification of social resilience with one particular form of governance or organization. Emerging self-organizing citizen’s initiatives in the Netherlands, initiatives involving re-relating to nature in the living environment, are analyzed, using a systems theoretical framework which resists reduction of nature to culture or vice versa. It is argued that space for self-organization needs to be cultivated, that local self-organization and mobilization around themes of nature in daily life and space have the potential to re-link social and ecological systems in a more resilient manner, yet that maintaining the diversity of forms of knowing and organizing in the overall governance system is essential to the maintenance of social resilience and of diverse capacities to know human-environment relations and to reorganize them in an adaptive manner. Conclusions are drawn in the light of the new Biodiversity Strategy.
... Dispersing beavers may need to travel longer distances to find an area to settle with sufficient resources for survival in desert rivers because they have patchier and more unpredictable resources (Gibson and Olden, 2014;Barela and Frey, 2016). Rivers in our study had low existing beaver densities (Macfarlane et al., 2017). This may have allowed RS and translocated beavers to be choosier about selecting high-quality sites for settlement because there was reduced "social resistance" effects (Armansin et al., 2020) with more unoccupied territories and less potential for aggressive encounters with conspecifics (DeStefano et al., 2006). ...
Wildlife translocations alter animal movement behavior, so identifying common movement patterns post-translocation will help set expectations about animal behavior in subsequent efforts. American and Eurasian beavers (Castor canadensis; Castor fiber) are frequently translocated for reintroductions, to mitigate human-wildlife conflict, and as an ecosystem restoration tool. However, little is known about movement behavior of translocated beavers post-release, especially in desert rivers with patchy and dynamic resources. We identified space-use patterns of beaver movement behavior after translocation. We translocated and monitored nuisance American beavers in desert river restoration sites on the Price and San Rafael Rivers, Utah, USA, and compared their space use to resident beavers after tracking both across 2 years. Resident adult (RA) beavers were detected at a mean maximum distance of 0.86 ± 0.21 river kilometers (km; ±1 SE), while resident subadult (RS) (11.00 ± 4.24 km), translocated adult (TA) (19.69 ± 3.76 km), and translocated subadult (TS) (21.09 ± 5.54 km) beavers were detected at substantially greater maximum distances. Based on coarse-scale movement models, translocated and RS beavers moved substantially farther from release sites and faster than RA beavers up to 6 months post-release. In contrast, fine-scale movement models using 5-min location intervals showed similar median distance traveled between RA and translocated beavers. Our findings suggest day-to-day activities, such as foraging and resting, were largely unaltered by translocation, but translocated beavers exhibited coarse-scale movement behavior most similar to dispersal by RSs. Coarse-scale movement rates decreased with time since release, suggesting that translocated beavers adjusted to the novel environment over time and eventually settled into a home range similar to RA beavers. Understanding translocated beaver movement behavior in response to a novel desert system can help future beaver-assisted restoration efforts to identify appropriate release sites and strategies.
... In other situations, our first step may be policy changes: for example, if floodplains are intact, but beaver management actions (e.g., the lethal removal of beavers that impact the built environment) prevent population persistence sufficient to further recover these landscapes. Regardless of our role in the conversation, beaver inspired or implemented process-based restoration should be a primary strategy to achieving healthy riverscapes (Macfarlane et al., 2015;Pollock et al., 2015). A stream where beavers thrive is a resilient, productive stream (Pollock et al., 2014). ...
Rivers and streams, when fully connected to their floodplains, are naturally resilient systems that are increasingly part of the conversation on nature-based climate solutions. Reconnecting waterways to their floodplains improves water quality and quantity, supports biodiversity and sensitive species conservation, increases flood, drought and fire resiliency, and bolsters carbon sequestration. But, while the importance of river restoration is clear, beaver-based restoration - e.g., strategic coexistence, relocation, and mimicry - remains an underutilized strategy despite ample data demonstrating its efficacy.
... Asides from potential management interventions (see Campbell-Palmer et al., 2016 for a summary of techniques), an element of predictability can be applied to beaver populations. Alongside methods of surveying field signs to estimate present beaver population distributions , computerised models which assess beaver foraging habitat availability and the capacity for damming within watercourses are achievable Macfarlane et al., 2017). Although a degree of uncertainty will remain based upon individual animal behaviours (which will need to be made clear), these models make possible a means of predicting likely future beaver impacts at the catchment scale. ...
Natural flood management (NFM) methods work with natural processes to reduce flood risk, while often providing additional benefits such as water quality improvement or habitat provision. Increasingly, the activity of an animal—beavers—is recognised to potentially provide flow attenuation, along with multiple benefits for the environment and society, but there can also be associated challenges. We use Q‐Methodology to elicit and understand human perspectives of beavers and their potential role in flood management among communities living downstream of beavers at three sites in England (Cornwall, Yorkshire and the Forest of Dean). This is the first time a study has focused on downstream communities as the primary stakeholders. We identify diverse perspectives that exhibit a range of value judgements. We suggest a catchment‐based approach to beaver management and public engagement may facilitate deeper recognition of contextual perspectives in decision‐making and enable knowledge dissemination with communities. Further, we examine the relationship between beavers and other NFM methods through these perspectives. In doing so we identify features that relate to the unique element of relying on the natural behaviour of beavers for flood management, rather than human flood managers being the primary decision‐makers.
... These correlations are expected: Beaver dams can facilitate formation of a multithread channel planform (John and Klein, 2004;Polvi and Wohl, 2013), as can channel-spanning logjams (Sear et al., 2010;Wohl, 2011). Multithread channel planform equates to smaller channel cross-sectional area within each channel, which can facilitate trapping and retention of large wood pieces (Ruiz-Villanueva et al., 2016) and construction of beaver dams (MacFarlane et al., 2017). These positive feedbacks progressively increase spatial heterogeneity of the river corridor, hydraulic roughness, and thus the potential for attenuating downstream fluxes of water, solutes, and particulate material. ...
We examine a 9.4-km-long portion of a montane river corridor in the Southern Rockies, the upper 8 km of which burned in 2020. We focus on sediment storage in logjam backwaters and how spatial heterogeneity in the river corridor attenuates downstream fluxes of material following the wildfire. Wider portions of river corridor exhibit greater spatial heterogeneity, as reflected in multithread channel planform and more closely spaced abandoned beaver dams and channel-spanning logjams. Logjams in multithread reaches have greater volumes of backwater storage and store finer sediment than logjams in single-thread reaches. Despite substantial turnover of sediment in backwater storage during the first runoff season after the wildfire, the cumulative volume of sediment stored at 11 monitored logjams following the 2021 runoff season was 71% of the cumulative sediment volume at the logjams immediately after the fire. Floodplain vegetation regrowth was also faster and more complete at multithread reaches. Vegetation recovery contributed to overbank deposition in these reaches, in contrast to the bank erosion observed in single-thread reaches. More spatially heterogeneous portions of the river corridor appear to be disproportionately important in attenuating enhanced inputs of sediment following wildfire, and the cumulative effect of this attenuation across a river network likely enhances watershed-scale resilience to wildfire disturbance.
... To assist salmon conservation better around the North Pacific Rim, Whited et al. (2012) summarized metrics of freshwater habitat from satellite imagery and provided this information online as a 'riverscape analysis' tool. When key habitat features are altered or population declines are observed, restoration actions are typically prescribed and could benefit from the knowledge provided by highresolution spatially comprehensive surveys and modelling (Macfarlane et al., 2017;Wheaton et al., 2019). Recent regional river temperature models (Isaak et al., 2017b;Jackson et al., 2018) or TIR imagery (Dugdale, 2016) could be used to identify reaches that are consistently warmer than other locations or areas influenced by thermal pollution (e.g. from water abstraction, industrial water discharge or river regulation) and inform precisely targeted restoration activities (Kurylyk et al., 2015). ...
Landscape perspectives in riverine ecology have been undertaken increasingly in the last 30 years, leading aquatic ecologists to develop a diverse set of approaches for conceptualizing, mapping and understanding ‘riverscapes’. Spatiotemporally explicit perspectives of rivers and their biota nested within the socio-ecological landscape now provide guiding principles and approaches in inland fisheries and watershed management. During the last two decades, scientific literature on riverscapes has increased rapidly, indicating that the term and associated approaches are serving an important purpose in freshwater science and management. We trace the origins and theoretical foundations of riverscape perspectives and approaches and examine trends in the published literature to assess the state of the science and demonstrate how they are being applied to address recent challenges in the management of riverine ecosystems. We focus on approaches for studying and visualizing rivers and streams with remote sensing, modelling and sampling designs that enable pattern detection as seen from above (e.g. river channel, floodplain, and riparian areas) but also into the water itself (e.g. aquatic organisms and the aqueous environment). Key concepts from landscape ecology that are central to riverscape approaches are heterogeneity, scale (resolution, extent and scope) and connectivity (structural and functional), which underpin spatial and temporal aspects of study design, data collection and analysis. Mapping of physical and biological characteristics of rivers and floodplains with high-resolution, spatially intensive techniques improves understanding of the causes and ecological consequences of spatial patterns at multiple scales. This information is crucial for managing river ecosystems, especially for the successful implementation of conservation, restoration and monitoring programs. Recent advances in remote sensing, field-sampling approaches and geospatial technology are making it increasingly feasible to collect high-resolution data over larger scales in space and time. We highlight challenges and opportunities and discuss future avenues of research with emerging tools that can potentially help to overcome obstacles to collecting, analysing and displaying these data. This synthesis is intended to help researchers and resource managers understand and apply these concepts and approaches to address real-world problems in freshwater management.
... 1 [SD]cm yr -1 ,Butler and Malanson 2005; 15.3 ± 12.6 [SD] cm yr -1 ,Meentemeyer and Butler 1999; 47 cm yr -1 ,Pollock et al. 2007). Dam densities in the middle reach (5.2 dams km -1 in 2018) are higher than reported for other dryland streams in Oregon (1.1 dams km -1 , Gibson and Olden 2014; 3.5 dams km -1 ,Weber et al. 2017), but lower than the modelled potential dam capacity along streams in Utah (8.7 dams km -1 ;Macfarlane et al. 2017). Suitable habitat remains available in the middle reach and continued development of beaver complexes is likely in future years. ...
Abstract
In this study I document the results of 11 years of passive restoration of a small mountain stream in northeastern Oregon. Removal of the main stressors on the system, grazing and agricultural practices, resulted in a strong recovery of the riparian vegetation over the middle two thirds of the reach. Cover of trees and shrubs tripled, tree density increased 7-fold and stream shading 4-fold over the period 2007–2018. Average maximum daily stream temperature declined by 2.1–2.8 oC and average maximum diurnal temperature range narrowed by 3.7–4.6 oC. Recolonizing American beavers (Castor canadensis) played an essential role in improving the condition of the streambed over 18% of the reach. Their dams and ponds initiated the process of streambed aggradation and transformed the single-thread, incised channel into a multi-thread configuration within beaver complexes. Vegetation expansion was much stronger in impounded- than in un-impounded parts of the stream. Passive restoration was not effective in two sections together comprising one third of the reach. In the upper part of the stream recovery stalled because of continued (unauthorized) trespass grazing during late summer and fall. The channelized lower section of the stream was too severely modified for measurable recovery to occur. Using a recently developed Stream Evolution Model I concluded that 11 years of passive restoration improved the condition of the stream from 24% to 32%, and within beaver complexes, up to 57%.
... How dams can possess such contrasting mitigation abilities is not fully understood. However, since some landscapes have the potential to support significantly more beaver dams than currently present, any drought or flood mitigation effects could be compounded and enhanced in the future if beaver populations increase (Butler and Malanson, 2005;Dittbrenner et al., 2018;Macfarlane et al., 2017). ...
Beaver (Castor canadensis and Castor fiber) are regarded widely as ecosystem engineers and the dams they create are well-known for their ability to drastically alter the hydrology of rivers. As a result, beaver are increasingly being included in green infrastructure practices to combat the effects of climate change and enhance ecosystem resilience. Both drought and flood mitigation capabilities have been observed in watersheds with beaver dam structures; however, how dams possess contrasting mitigation abilities is not fully understood since most studies neglect to acknowledge variation in beaver dam structures. In this study, an extensive cross-site survey of the physical and hydrologic properties of beaver dams was conducted in the Canadian Rocky Mountains in Alberta. This research aimed to improve the understanding of the hydrology of beaver dams by categorizing dams using their intrinsic properties and landscape settings to identify fundamental patterns that may be applicable across landscape types. The dam flow type classification from Woo and Waddington (1990) was evaluated in this new context and adapted to include two new flow types. The survey of intrinsic beaver dam properties revealed significant differences in dam structure across different sites. Physical differences in dam structure altered the dynamics and variance of pond storage and certain dam attributes related to the landscape setting. For instance, dam material influenced dam height and water source influenced dam length. However, a closer analysis of large rain events showed that the physical structure of dams alters seasonal dynamics of pond storage but not the response to rain events. Overall, this research shows that beaver dams can be both structurally and hydrologically very different from each other. Establishing broadly applicable classifications is vital to understanding the ecosystem resilience and mitigation services beaver dams provide.
... Models that are developed from these data to predict dam building sites may be transferable locally (Petro et al. 2015(Petro et al. , 2018, but they ignore the influence nondamming beaver may have on site establishment through meta-population dynamics (Petro et al. 2018). Large scale models developed to predict dam building potential fail to identify non-damming beaver habitat and have not yet been evaluated for transferability across regions and scales (Macfarlane et al. 2017, Dittbrenner et al. 2018. ...
Interest in beaver-related restoration is growing in the western U.S. but understanding the basic ecology of American beaver and their population dynamics is often overlooked when integrating beaver into stream restoration goals. Our study investigated the spatial-temporal distribution of beaver colonies and their damming activities to better inform stream restoration projects in the West Fork Cow Creek Basin of the Umpqua Watershed in southwestern Oregon. During fall 2017, we conducted beaver activity surveys at 144 randomly selected reaches predicted to be either suitable or unsuitable for damming, but suitable for beaver occupation. We categorized beaver use at each reach using assessments of their activities and time of last use. We recorded dam structure and impoundment characteristics at all identified dams. Evidence of beaver activity was documented at 57% of locations suitable for dam establishment and 48% of unsuitable dam sites. Beaver dams were found only in reaches identified as suitable for damming and were concentrated throughout two tributaries located on private ownership. Our beaver activity observations will be combined with other data collected in the Umpqua Watershed, and used to construct a probability of use model that will identify dam and non-dam habitat associations. This work will provide novel insights into the landscape ecology of beaver, and inform critical decisions involving trade-offs of ecological benefits and human-beaver conflicts in freshwater systems of interest.
... Enhancing current summer low flow requires a reduction in domestic or agricultural surface-and groundwater withdrawals or some form of storage (e.g., managed reservoirs or natural wetlands for flow release). Re-establishing channel complexity associated with wetlands and beaver dam complexes can greatly increase floodplain storage and enhance summer baseflows (Bouwes et al. 2016;Macfarlane et al. 2017) and should be a management priority, as is the protection of existing wetlands and recharge zones that contribute disproportionately to baseflow (EPA 2015). Overallocation of water licenses is a serious problem in agricultural regions (Rosenau and Angelo 2003;Grantham and Viers 2014;de Graaf et al. 2019), as are unlicensed water withdrawals (Bauer et al. 2015); active management of surface and groundwater withdrawals must be a key component of hypoxia management. ...
To understand the effects of widespread urbanization and agricultural impacts on recovery of Salish sucker, a federally threatened Catostomid endemic to the lower Fraser Valley of British Columbia, we assessed i) the current extent and effects of hypoxia on the distribution of Salish sucker and juvenile salmonids, ii) potential drivers of hypoxia, and iii) management options for hypoxia mitigation. Over 40% of sucker critical habitat experiences hypoxia (dissolved oxygen (DO) < 4 mg·l-I) by late summer, indicating widespread non-compliance with water quality guidelines. The strong positive relationship between seasonal hypoxia and temperature (R2= 0.53) and negative relationship with streamflow (R2= 0.78) indicates that hypoxia is driven by a synergy between low summer flows, elevated temperatures, and high primary production associated with nutrient enrichment (eutrophication). Sucker show strong selection against high water temperatures and weaker negative selection against low DO; juvenile salmonids show very strong selection against both high temperatures and low DO. Climate projections for declining summer flows and elevated temperatures indicate worsening trends in DO without intensive watershed-scale management to reduce nutrient loads.
... But when beavers do build dams, it is driven by survival needs. Beavers build dams when it is advantageous to their survival, but exactly when and where is subject to several contingencies, including vegetation, geomorphology, and how beavers react to these and other influences (Barnes and Dibble 1988, Johnston and Naiman 1990, Suzuki and McComb 1998, Gibson and Olden 2014, Touihr et al. 2018, Macfarlane et al. 2017, Lapointe St-Pierre et al. 2017, Ritter et al. 2020. North American beaver are generalist herbivores that exploit a wide range of foods and environmental conditions (Jenkins 1975(Jenkins , 1981. ...
Beaver-related restoration is a process-based strategy that seeks to address wide-ranging ecological objectives by reestablishing dam building in degraded stream systems. Although the beaver-related restoration has broad appeal, especially in water-limited systems, its effectiveness is not yet well documented. In this article, we present a process-expectation framework that links beaver-related restoration tactics to commonly expected outcomes by identifying the set of process pathways that must occur to achieve those expected outcomes. We explore the contingency implicit within this framework using social and biophysical data from project and research sites. This analysis reveals that outcomes are often predicated on complex process pathways over which humans have limited control. Consequently, expectations often shift through the course of projects, suggesting that a more useful paradigm for evaluating process-based restoration would be to identify relevant processes and to rigorously document how projects do or do not proceed along expected process pathways using both quantitative and qualitative data.
... Where conditions permit, reintroduction of beavers is likely to be more successful than BDAs in creating desired changes in river corridors. Guidelines for beaver reintroduction and software that can be used to evaluate habitat suitability (Macfarlane et al 2017, Dittbrenner et al 2018, Kornse and Wohl 2020 can assist with these efforts. Extensive modification of river corridors throughout the temperate latitudes limits the remaining areas 1 years after installation, sediment storage increased, but no effect on groundwater levels Scamardo and Wohl (2020) dr A indicates drainage area. ...
Through their modifications of channels and floodplains, beavers are a premier example of ecosystem engineers. Historical and stratigraphic records suggest that hundreds of millions of beavers once modified small to medium rivers throughout the northern hemisphere. Where beavers actively modify the channel and floodplain with dams, ponds, and canals, their activities increase habitat abundance and diversity, biodiversity, nutrient uptake, attenuation of downstream fluxes of water and sediment, and resilience of the river corridor to disturbances. Loss of beavers through commercial trapping and habitat modification occurred simultaneously with other human modifications of uplands and river corridors. The cumulative effects of these human modifications have been to greatly reduce the ecosystem services provided by rivers. Contemporary efforts to re-introduce beavers in North America and Eurasia and to mimic the effects of beaver engineering with beaver dam analogues and Stage 0 restoration represent a good start, but fundamental questions remain about the extent of such restoration efforts needed to create and maintain significant increases in riverine functions.
... In a drainage system network, beavers can affect longitudinal and lateral connectivity by implementing roughness elements that completely alter delivery, timing and storage of sediment, organic matter, nutrients and water (Macfarlane et al. 2017). Due to differences in channel depth, width, gradient and flow rate, sediments accumulate in beaver dams. ...
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.
... (Reproduced with permission from Bouwes et al., 2016) of fish to beaver activity enhances metacommunity resilience but consequently localized fish communities may alter for short periods of time. However, in these upland systems, high flows capable of "blowing out" dams are more frequent (Macfarlane et al., 2017) thus allowing unimpeded fish movement during these periods. In lowland systems, such as those investigated by Virbickas et al. (2015) the increased hydrological stability may result in a longer lasting separation of fish communities up and downstream of beaver dams. ...
Beavers have the ability to modify ecosystems profoundly to meet their ecological needs, with significant associated hydrological, geomorphological, ecological, and societal impacts. To bring together understanding of the role that beavers may play in the management of water resources, freshwater, and terrestrial ecosystems, this article reviews the state‐of‐the‐art scientific understanding of the beaver as the quintessential ecosystem engineer. This review has a European focus but examines key research considering both Castor fiber—the Eurasian beaver and Castor canadensis—its North American counterpart. In recent decades species reintroductions across Europe, concurrent with natural expansion of refugia populations has led to the return of C. fiber to much of its European range with recent reviews estimating that the C. fiber population in Europe numbers over 1.5 million individuals. As such, there is an increasing need for understanding of the impacts of beaver in intensively populated and managed, contemporary European landscapes. This review summarizes how beaver impact: (a) ecosystem structure and geomorphology, (b) hydrology and water resources, (c) water quality, (d) freshwater ecology, and (e) humans and society. It concludes by examining future considerations that may need to be resolved as beavers further expand in the northern hemisphere with an emphasis upon the ecosystem services that they can provide and the associated management that will be necessary to maximize the benefits and minimize conflicts.
This article is categorized under:
• Water and Life > Nature of Freshwater Ecosystems
Abstract
This article reviews the state‐of‐the‐art scientific understanding of the beaver as an ecosystem engineer. It summarizes how beaver impact: (a) ecosystem structure and geomorphology, (b) hydrology and water resources, (c) water quality, (d) freshwater ecology, and (e) humans and society.
... Lateral connectivity can be naturally occurring, such as debris dams, wood jams, or beaver dams (Abbe and Montgomery, 1996;Collins et al., 2012); or they can be restoration interventions informed by natural processes, such as mechanically emplaced large woody debris (Abbe and Montgomery, 1996;Stavi et al., 2020;Thomas and Nisbet, 2012). The results of beaver activity demonstrate that landscape modifications of increasing stream complexity and channel-floodplain connectivity support functions of slowing flow, increasing water storage, and increasing base flow (Burchsted et al., 2010;Macfarlane et al., 2015). The valley bottom systems of channels and floodplains are therefore critical buffer zones, and the extent of channel to floodplain connectivity are key indicators of the buffering capacity of dryland watersheds. ...
Increased flooding, droughts, and sediment transport are watershed-scale problems negatively impacting agriculture and ecosystems in drylands worldwide. Vegetation loss in upland watersheds is leading to scouring floods, which in turn decreases infiltration, soil moisture levels, and downstream groundwater recharge. Management to confront these intractable problems has been hindered by a lack of accessible decision support tools for both land and water managers that synthesize the watershed processes that buffer against dryland disturbances. Flood flow connectivities across the landscape create buffer zones through replenishing soil moisture and reducing flood energy, which in turn support multiple functions. This study developed a decision support tool, the Flood Flow Connectivity to the Landscape (FlowCon) framework that quantifies the most efficient management efforts to increase the key watershed buffering functions of increasing infiltration and reducing flow energy. FlowCon links three spatially explicit, process-based, and predictive models to answer two critical management questions: what key processes acting in what optimal areas are drivers of infiltration dynamics and what roles do peak flows of differing scales of energy play. The spatial models delineated the buffer zone to characterize the heterogeneous and optimal infiltration dynamics across the landscape. The hydrologic process model, using a curve number technique, identified the key ecohydrologic processes that affect infiltration and characterized peak flows and flow regime variability. The predictive flood routing model quantified the potential management benefits. We calibrated the models with measured runoff and the corresponding rainfall events for a six-year period, which included thirty-six flow events. The synthesized ecohydrologic indicators provided critical calibrations, improving the relationship between the hydrologic modeling results and observed data by 12% for the linear regression R² and 69% for the root mean square error (RMSE). Implementation of prioritized management is estimated to reduce peak flow by half, with interventions focused on 24% of floodplains that infiltrate three times the flow volume per area than the floodplain average. FlowCon provides an efficient assessment framework that integrates watershed process understanding in an accessible decision support tool to achieve tangible improvements in dryland watershed management.
The Eurasian beaver (Castor fiber) was an important member of Early and Mid-Holocene landscapes and animal communities in Northern Europe. Previous zooarchaeological research has established the alimentary roles of beavers for Mesolithic societies and their importance for fur procurement. In this paper, we develop an integrated biocultural approach to human-beaver interactions, examining the position of humans and beavers in Mesolithic and Early Neolithic multispecies systems. We contextualize beaver landscape agency in hydroactive environments with human behaviour, synthesizing currently available data on mammalian assemblages, ichtyofauna and beaver-related material culture across Northern Europe. This cross-cultural, diachronic analysis reveals previously overlooked facilitations of human behaviour by beaver practices and ecological legacies. We show that long-term trajectories of human-beaver cohabitation differed between northern European regions. While in Southern Scandinavia, human-beaver intersections witnessed major re-organizations during the Mid-Holocene, beavers retained a key role for human societies across Northeastern Europe throughout much of the Holocene and played an important part at the Mesolithic-Neolithic transition in the Dutch wetlands. Divergent pathways are also evidenced by Mesolithic beaver-related material culture, highlighting the cultural keystone status of Castor fiber in higher latitude European landscapes. We argue that this keystone status is grounded in the supply of human hunting, fishing, and gathering affordances by the animals, pointing to the generative commensality between Mesolithic foragers and their beaver neighbours. Taken together, our findings demonstrate the importance of the beaver in the making of Early and Mid-Holocene forager societies in Northern Europe and illustrate the fruitfulness of deploying an integrated multispecies approach.
Idaho's large-river floodplain and riparian forests, especially those dominated by cottonwood (Populus spp.), are crucial ecosystems highly threatened by human land uses and hydrologic shifts resulting from climate change. Once widespread in river valleys of Idaho, the condition, function, and extent of cottonwood riparian and floodplain forests have been greatly diminished. However, prior to this project, no assessment of the conservation status of this ecosystem existed. Goals of this project were to: • describe the distribution and condition of floodplain cottonwood forests in Idaho • analyze potential climate change impacts on the long-term viability of this ecosystem • develop conservation and restoration strategies that incorporate climate change adaptation and resilience concepts We used Maxent to model the current and future extent and distribution of cottonwood habitat using species observations, climate variables, and abiotic predictors. Future habitat was predicted with Maxent by using climate variables modeled for mid-century RCP 4.5 and RCP 8.5 emissions scenarios. The condition of current and future suitable cottonwood habitat occurring in river and large stream valley bottoms was analyzed by applying an existing landscape integrity map. A watershed-scale Flow Modification Index, based on water and land use, was created to characterize the degree of departure from the natural hydrologic regime in each watershed. The flow modification index was applied to predicted current and future habitat to assess constraints on cottonwood sustainability. The potential effects of projected climate induced river flow changes on cottonwood reproduction were also explored. These analyses were then used to develop watershed and river reach-specific conservation and restoration strategies for floodplains predicted to have higher long-term viability for cottonwoods.
Historically, beavers and beaver dams were an important component of dryland riparian systems in the western US and exerted an extraordinary influence on these systems. At the time of Euroamerican settlement of the Eagle Valley, beavers were present along main Daly Creek. Land management activities including diverting water for irrigation, channelizing, and removal of riparian vegetation for agricultural purposes and cattle grazing likely changed the historic multi-thread channel system at Daly Creek into a single-thread channel. Daly Creek was divided in 3
reaches based on past legacy of farming and grazing to evaluate system responses: 1) Lower Daly Creek (1.2 miles [1.9 km]), 2) Middle Daly Creek (5.9 miles [9.5 km]), and 3) Upper Daly Creek (2 miles [3.2 km]). Given the key role that beaver play in the recovery of Daly Creek, beaver dam and pond surveys started in 2009 when beaver activity was first noted as part of a larger study to assess (passive) riparian recovery. Specific objectives were to: 1) annually locate all beaver dams, 2) collect information on location, and physical characteristics of dams (i.e., dam height and length, crossing of stream or partial dam), and 3) survey and map beaver ponds
on at least a 2-year interval. From 2009 through 2018, surveys were conducted annually, although no beaver activity was noted in 2010-2012. In 2009, 2013 and 2014 spring surveys were conducted. In 2014 and following years, fall surveys were conducted when beaver dam numbers peak during low base flows. Beaver ponds were surveyed in 2015 and 2018. Turn-over rates of dams was high, based on new dams constructed annually (𝑥̅=70.7±26.0(STD)%). Number of dams increased quadratically along the Middle Reach (pre-existing and new) from 8 in 2008 to 56 in 2018. Dam densities along the Middle Reach ranged from 0.5 to 5.2 dams/km. Overall, 63.5% of all beaver dams crossed the stream. Average length of a dam was
7.5±6.8(1 STD) m, ranging from 2.25 to 40.0 m and did not differ among reaches. Average height of a dam was 0.96±0.40(1 STD) m, ranging from 0.10 to 2.0 m and was similar among reaches. Ponds averaged 0.05±0.05(1 STD) acres and .13±0.19(1 STD) acres and in 2015 and 2018, respectively, with 9.3% overlap. Location of eaver dam complexes shifted over time. Beaver dams concentrated in the Lower Reach in 2009. The Middle Reach was consistently occupied from 2013 through 2018 and the lower part of the Upper reach in 2015, 2017, and 2018. Sections of the Middle Reach where beaver dams and ponds became established changed from single-thread stream (12% functional) to a sinuous streambed (45-67% functional) between 2007 and 2018. In 2018, there was limited in-channel features and vegetation recovery, and the channel likely reconnected to groundwater and hyporheic zones. Vegetation and floodplain- and hyporheic connectivity may afford moderate flood and drought resilience; furthermore, water clarity and stream temperature amelioration continued to improve. Absence of beavers in the Upper Reach and continued livestock grazing impaired streambed and woody riparian recovery, effectively stalling improvement of the Upper Reach, where the streambed remains a single-thread stream (12% functional). The Lower Reach remained in stasis (12% functional), as beavers did no successfully colonize this reach, because food remained limited for beavers, spring flows removed beaver dams, and beavers were likely highly susceptible to predation in this narrow, incised stream. In the absence of beaver dams and other structures, such as log jams, there is little opportunity for the retention of sediments, aggradation of the stream bed, and recovery from a single-thread to a multi-thread, or sinuous stream bed
Wildlife translocation facilitates conservation efforts, including recovering imperiled species, reducing human–wildlife conflict, and restoring degraded ecosystems. Beaver (American, Castor canadensis ; Eurasian, C. fiber ) translocation may mitigate human–wildlife conflict and facilitate ecosystem restoration. However, few projects measure outcomes of translocations by monitoring beaver postrelease, and translocation to desert streams is relatively rare. We captured, tagged, and monitored 47 American beavers (hereafter, beavers) which we then translocated to two desert rivers in Utah, USA, to assist in passive river restoration. We compared translocated beaver site fidelity, survival, and dam‐building behavior to 24 resident beavers. We observed high apparent survival (i.e., survived and stayed in the study site) for eight weeks postrelease of resident adult beavers (0.88 ± 0.08; standard error) and lower but similar apparent survival rates between resident subadult (0.15 ± 0.15), translocated adult (0.26 ± 0.12), and translocated subadult beavers (0.09 ± 0.08). Neither the pre‐ nor the post‐translocation count of river reaches with beaver dams were predicted well by the Beaver Restoration Assessment Tool, which estimates maximum beaver dam capacity by river reach, suggesting beaver‐related restoration is not maximized in these rivers. Translocated beavers exhibited similar characteristics as resident subadult beavers during dispersal; they were more vulnerable to predation and many emigrated from the study sites. High mortality and low site fidelity should be anticipated when translocating beavers, but even so, translocation may have contributed to additional beaver dams in the restoration sites, which is the common goal of beaver‐assisted river restoration. Multiple releases at targeted restoration sites may eventually result in establishment and meet conservation objectives for desert rivers.
Tracing the story of beaver restoration across California, this paper investigates the emerging discourse of ‘working with nature’ through the lens of animal work and labour, exploring possibilities for, and conceptualising, multispecies collaboration. At the intersection of animal geographies, environmental anthropology, and geographies of conservation, this paper finds three concurrent modes of working with beaver: beaver as labourer, beaver as coworker, and beaver as community. Beaver as labourer emerges as a mode where beavers go from material resource to low‐wage labourer, their liveliness predicated on their ability to be working for humans. Beaver as coworker transitions beavers from labourers to workers, respected for their skills as ecosystem engineers to be working with. Beaver as community emerged as a mode in which beavers and humans live with each other as kin, amidst wider multispecies assemblages. This mode sets the foundation to theorise the concept of multispecies collaboration, a term often used in the literature, but never defined. This paper explores the concept through theories of animal work and labour, challenging the premise of work altogether, while situating multispecies collaboration as an in‐between, a both/and space of working and living with ‘nature.’ This paper serves as an important reflection on the ways in which humans ‘work with nature,’ in a time where various nonhumans are being made to be ‘workers.’ It presents and analyses these relations, ruminates on implications for governance of these multispecies spaces, and develops the concept of multispecies collaboration as a critical consideration for Nature‐based Solutions.
As-built report for Phase 1 of the Bailey Flat Low-tech Process-based Riverscape Restoration.
This report contains reviews and syntheses of scientific literature for the purpose of informing the development of policies related to management of riparian areas and watersheds of Washington State.
Beavers (Castor fiber, Castor canadensis) are one of the most influential mammalian ecosystem engineers, heavily modifying river corridor hydrology, geomorphology, nutrient cycling, and ecosystems. As an agent of disturbance, they achieve this first and foremost through dam construction, which impounds flow and increases the extent of open water, and from which all other landscape and ecosystem impacts follow. After a long period of local and regional eradication, beaver populations have been recovering and expanding throughout Europe and North America, as well as an introduced species in South America, prompting a need to comprehensively review the current state of knowledge on how beavers influence the structure and function of river corridors. Here, we synthesize the overall impacts on hydrology, geomorphology, biogeochemistry, and aquatic and terrestrial ecosystems. Our key findings are that a complex of beaver dams can increase surface and subsurface water storage, modify the reach scale partitioning of water budgets, allow site specific flood attenuation, alter low flow hydrology, increase evaporation, increase water and nutrient residence times, increase geomorphic heterogeneity, delay sediment transport, increase carbon, nutrient and sediment storage, expand the extent of anaerobic conditions and interfaces, increase the downstream export of dissolved organic carbon and ammonium, decrease the downstream export of nitrate, increase lotic to lentic habitat transitions and aquatic primary production, induce ‘reverse’ succession in riparian vegetation assemblages, and increase habitat complexity and biodiversity on reach scales. We then examine the key feedbacks and overlaps between these changes caused by beavers, where the decrease in longitudinal hydrologic connectivity create ponds and wetlands, transitions between lentic to lotic ecosystems, increase vertical hydraulic exchange gradients, and biogeochemical cycling per unit stream length, while increased lateral connectivity will determine the extent of open water area and wetland and littoral zone habitats, and induce changes in aquatic and terrestrial ecosystem assemblages. However, the extent of these impacts depends firstly on the hydro-geomorphic landscape context, which determines the extent of floodplain inundation, a key driver of subsequent changes to hydrologic, geomorphic, biogeochemical, and ecosystem dynamics. Secondly, it depends on the length of time beavers can sustain disturbance at a given site, which is constrained by top down (e.g. predation) and bottom up (e.g. competition) feedbacks, and ultimately determines the pathways of river corridor landscape and ecosystem succession following beaver abandonment. This outsized influence of beavers on river corridor processes and feedbacks is also fundamentally distinct from what occurs in their absence. Current river management and restoration practices are therefore open to re-examination in order to account for the impacts of beavers, both positive and negative, such that they can potentially accommodate and enhance the ecosystem engineering services they provide. It is hoped that our synthesis and holistic framework for evaluating beaver impacts can be used in this endeavor by river scientists and managers into the future as beaver populations continue to expand in both numbers and range.
Abstract
In this study I documented the results of 11 years of passive restoration of a small mountain stream in northeastern Oregon. Removal of the main stressors on the system, grazing and agricultural practices, resulted in a strong recovery of the riparian vegetation over the middle two thirds of the reach. Cover of trees and shrubs tripled, tree density increased sevenfold and stream shading fourfold over the period 2007–2018. Average maximum daily stream temperature declined by 2.1–2.8 oC and average maximum diurnal temperature range narrowed by 3.7–4.6 oC. Recolonizing American beavers (Castor canadensis) played an essential role in improving the condition of the streambed over 18% of the reach. Their dams and ponds initiated the process of streambed aggradation and transformed the single-thread, incised channel into a multi-thread configuration within beaver complexes. Vegetation expansion was much stronger in impounded than in un-impounded parts of the stream. Passive restoration was not effective in two sections together comprising one third of the reach. In the upper part of the stream recovery stalled because of continued (unauthorized) trespass grazing during late summer and fall. The channelized lower section of the stream was too severely modified for measurable recovery to occur. I concluded that 11 years of passive restoration improved the functionality of the stream from 24% to 32%, and within beaver complexes, up to 57% of its pre-disturbance condition.
While many different watershed management strategies have been implemented to improve water quality, relatively few studies empirically tested the combined effects of different strategies on water quality in relation to land cover changes using long-term empirical data at the sub-basin scale. Using 10 years of total suspended solids (TSS) data, we examined how the conversion of wetland, wetland fragmentation, beaver dams, and Best Management Practices (BMPs) affect wet season TSS concentrations for the 25 monitoring stations in the Tualatin River basin, USA. Geographic information systems, Fragstat, and correlation analysis were used to identify the direction of land cover change, degree of wetland fragmentation, and the strength of the relationship between TSS change and explanatory variables. Improvement in TSS concentrations was tightly coupled with the aggregation of wetlands, presence of beaver dams, particularly during the mid-wet season when flows were highest. Other BMPs effectively reduced TSS concentrations for the early and late-wet seasons when flows were not as high as in the middle wet-season. Aggregated wetlands were more effective for improving water quality than smaller disaggregated wetlands of similar total area when combined with the presence of beaver dams and BMPs. These findings offer important scientific and practical implications for management of urbanizing watersheds that seek to achieve the dual goals of improving environmental quality and land development.
Beavers can profoundly alter riparian environments, most conspicuously by creating dams and wetlands. Eurasian beaver (Castor fiber) populations are increasing and it has been suggested they could play a role in the provision of multiple ecosystem services, including natural flood management. Research at different scales, in contrasting ecosystems is required to establish to what extent beavers can impact on flood regimes. Therefore, this study determines whether flow regimes and flow responses to storm events were altered following the building of beaver dams and whether a flow attenuation effect could be significantly attributed to beaver activity. Four sites were monitored where beavers have been reintroduced in England. Continuous monitoring of hydrology, before and after beaver impacts, was undertaken on streams where beavers built sequences of dams. Stream orders ranged from 2nd to 4th, in both agricultural and forest-dominated catchments. Analysis of >1000 storm events, across four sites showed an overall trend of reduced total stormflow, increased peak rainfall to peak flow lag times and reduced peak flows, all suggesting flow attenuation, following beaver impacts. Additionally, reduced high flow to low flow ratios indicated that flow regimes were overall becoming less "flashy" following beaver reintroduction. Statistical analysis, showed the effect of beaver to be statistically significant in reducing peak flows with estimated overall reductions in peak flows from -0.359 to -0.065 m3 s-1 across sites. Analysis showed spatial and temporal variability in the hydrological response to beaver between sites, depending on the level of impact and seasonality. Critically, the effect of beavers in reducing peak flows persists for the largest storms monitored, showing that even in wet conditions, beaver dams can attenuate average flood flows by up to ca. 60%. This research indicates that beavers could play a role in delivering natural flood management.
Billions of dollars are being spent in the United States to restore rivers to a desired, yet often unknown, reference condition. In lieu of a known reference, practitioners typically assume the paradigm of a connected watercourse. Geological and ecological processes, however, create patchy and discontinuous fluvial systems. One of these processes, dam building by North American beavers (Castor canadensis), generated discontinuities throughout precolonial river systems of northern North America. Under modern conditions, beaver dams create dynamic sequences of ponds and wet meadows among free-flowing segments. One beaver impoundment alone can exceed 1000 meters along the river, flood the valley laterally, and fundamentally alter biogeochemical cycles and ecological structures. In this article, we use hierarchical patch dynamics to investigate beaver-mediated discontinuity across spatial and temporal scales. We then use this conceptual model to generate testable hypotheses addressing channel geomorphology, natural flow regime, water quality, and biota, given the importance of these factors in river restoration.
Beaver (Castor canadensis) dam-building activities lead to a cascade of hydrologic, geomorphic and ecological effects that increase stream complexity, which benefits a wide-variety of aquatic and terrestrial species. Depending on biophysical and vegetation conditions present, beaver dam-building activities variously trap sediment; raise incised streambeds, often reconnecting them with their floodplains; subirrigate the valley downstream of a dam; create wetlands; slow runoff; mitigate impacts by floods; extend seasonal stream flow; increase stream complexity; extend riparian woody and other vegetation; and create or increase habitat for diverse and sometimes rare species, including amphibians, fish, small mammals, and birds. As a result, beaver are increasingly being used as a critical component of passive stream and riparian restoration strategies.
Beaver dams affect hydrologic processes, channel complexity, and stream
temperature in part by inundating riparian areas, influencing
groundwater–surface water interactions, and changing fluvial processes
within stream systems. We explored the impacts of beaver dams on hydrologic
and temperature regimes at different spatial and temporal scales within a
mountain stream in northern Utah over a 3-year period spanning pre- and
post-beaver colonization. Using continuous stream discharge, stream
temperature, synoptic tracer experiments, and groundwater elevation
measurements, we documented pre-beaver conditions in the first year of the
study. In the second year, we captured the initial effects of three beaver
dams, while the third year included the effects of ten dams. After beaver
colonization, reach-scale (~ 750 m in length) discharge
observations showed a shift from slightly losing to gaining. However, at the
smaller sub-reach scale (ranging from 56 to 185 m in length), the
discharge gains and losses increased in variability due to more complex flow
pathways with beaver dams forcing overland flow, increasing surface and
subsurface storage, and increasing groundwater elevations. At the reach
scale, temperatures were found to increase by 0.38 °C (3.8 %),
which in part is explained by a 230 % increase in mean reach residence
time. At the smallest, beaver dam scale (including upstream ponded area,
beaver dam structure, and immediate downstream section), there were notable
increases in the thermal heterogeneity where warmer and cooler niches were
created. Through the quantification of hydrologic and thermal changes at
different spatial and temporal scales, we document increased variability
during post-beaver colonization and highlight the need to understand the
impacts of beaver dams on stream ecosystems and their potential role in
stream restoration.
Beaver (Castor canadensis) through their dam building activities, store water, trap sediment, subirrigate vegetation, and subsequently improve habitat for fish, wildlife, and livestock. Many landowners realize the benefits that Beaver can bring to a riparian area and are interested in using them to improve this habitat. From 1994 to 1999 we trapped and relocated 234 Beaver to 14 areas throughout Wyoming to improve riparian habitat and create natural wetlands. We attached radio transmitters to 114 Beaver and subsequently determined movements and mortality of released Beaver, and the overall success of our releases. Mortality and emigration (including transmitter failure) accounted for the loss of 30% and 51%, respectively, of telemetered Beaver within 6 months of release. Kaplan-Meier survival estimates were 0.49 (SE = 0.068) for 180 days and 0.433 (SE = 0.084) for 360 days, and did not differ significantly between age classes. On average, 17 Beaver were transplanted to each release site, and at 11 locations, in an attempt to augment single Beaver that had become established and increase transplant success, we transplanted Beaver in two or more years. Success of an individual Beaver's relocation was unrelated to any of the variables we tested, although 2-3.5 year-old Beaver had higher average success (measured in days of occupancy at the release site) than older animals. Animals < 2 years old had 100% mortality and emigration losses within 6 months of release. High predation and mortality rates of our released Beaver may be due to habitat (our streams were shallow with no ponds and provided little protection) and extensive predator communities. We established Beaver at 13/14 of our release sites and they eventually reproduced. Our results show that Beaver can be relocated successfully but losses from mortality and emigration need to be considered and planned for.
Beaver dams affect hydrologic processes, channel complexity, and stream temperature by increasing inundated areas and influencing groundwater-surface water interactions. We explored the impacts of beaver dams on hydrologic and temperature regimes at different spatial and temporal scales within a mountain stream in northern Utah over a three-year period spanning pre- and post-beaver colonization. Using continuous stream discharge, stream temperature, synoptic tracer experiments, and groundwater elevation measurements we documented pre-beaver conditions in the first year of the study. In the second year, we captured the initial effects of three beaver dams, while the third year included the effects of ten dams. After beaver colonization, reach scale discharge observations showed a shift from slightly losing to gaining. However, at the smaller sub-reach scale, the discharge gains and losses increased in variability due to more complex flow pathways with beaver dams forcing overland flow and increasing surface and subsurface storage. At the reach scale, temperatures were found to increase by 0.38 °C (3.8%), which in part is explained by a 230% increase in mean reach residence time. At the smallest, beaver dam scale, there were notable increases in the thermal heterogeneity where warmer and cooler niches were created. Through the quantification of hydrologic and thermal changes at different spatial and temporal scales, we document increased variability during post-beaver colonization and highlight the need to understand the impacts of beaver dams on stream ecosystems and their potential role in stream restoration.
This report was contracted by the Confederated Tribes of Warm Springs to inventory the existing geomorphic conditions and recovery potential of the Pine Creek Watershed, and to lay out a strategic plan for restoration actions that will inform a later detailed design plan. The report presents the results of a hydrologic and geomorphic assessment undertaken using a simplified version of the River Styles framework (Brierley and Fryirs, 2005). This data informed the condition and recovery potential assessment presented herein. Additionally we present the results of a BRAT (beaver restoration assessment tool: http://brat.joewheaton.org) analysis which assessed existing and potential beaver dam building capacities in the Pine Creek Watershed. This information was synthesized into the strategic restoration plan, which is a simple and cost-effective treatment that seeks to partner with a small extant beaver population to restore geomorphic, hydrologic and ecological processes to improve habitat for aquatic and riparian biota within the incised portions of lower Pine Creek. Beaver Dam Analogues (BDAs) and High-Density Large Woody Debris (HDLWD) structures will be used to produce many of the same benefits as natural beaver dams and achieve additional restoration objectives (e.g., provide stable locations for beaver to establish persistent complexes, restore surface water connectivity, etc.). The strategic restoration plan is not a detailed design plan but provides recommendations for restoration objectives, priorities and reach types throughout the mainstem of Pine Creek. Finally, recommendations are provided on maintaining restoration structures and complexes within an adaptive management framework.
[1] Beaver meadows form when beaver dams promote prolonged overbank flooding and floodplain retention of sediment and organic matter. Extensive beaver meadows form in broad, low-gradient valley segments upstream from glacial terminal moraines. Surveyed sediment volume and total organic carbon content in beaver meadows on the eastern side of Rocky Mountain National Park are extrapolated to create a first-order approximation of landscape-scale carbon storage in these meadows relative to adjacent uplands. Differences in total organic carbon between abandoned and active beaver meadows suggest that valley-bottom carbon storage has declined substantially as beaver have disappeared and meadows have dried. Relict beaver meadows represent ~8% of total carbon storage within the landscape, but the value was closer to 23% when beaver actively maintained wet meadows. These changes reflect the general magnitude of cumulative effects in heterotrophic respiration and organic matter oxidation associated with historical declines in beaver populations across the continent.
Documentation over a 28-year period of beaver (Castor canadensis) habitat use permitted development and testing of two models to predict maximum density of active beaver colonies on streams. Principal components regression, a technique that reduced the confounding effects of closely correlated ecological variables found in earlier studies of this type, and discriminant analysis were used for model development. In mixed coniferous-deciduous forest habitat, the percentage of hardwood vegetation, watershed size, and stream width had significant positive effects on active colony density. Increasing stream gradient and progressively well-drained soils had negative effects. In field-tests, the models were 80% and 75% reliable in predicting active colony density.
Establishment of sampling frameworks to monitor the occurrence of ecological indicators and to identify the covariates that influence occurrence is a high-priority need for natural resource restoration and management efforts. We utilized occupancy modeling to identify patterns of beaver occurrence and factors influencing these patterns (i.e., type and amount of vegetation cover) in the Grand Canyon of the Colorado River ecosystem. We used rafts and kayaks to access a stratified random sample of sites (i.e., 100-m-long sections of riverbank) and used repeated sampling procedures to sample for beaver sign (i.e., lodges, cuttings, tracks, and beaver sightings). We quantified the type and amount of vegetation cover at each sampled section by using a GIS database of remotely sensed information on the riparian vegetation in the Grand Canyon. We first modeled occurrence of beaver sign as a function of the total amount of vegetation cover (summed across classes) and then determined the relative importance score for each of the 7 vegetation classes. Detection probability (p) was 2 times higher when observers traveled in kayaks (0.61) than when they traveled in rafts (0.29). Occurrence of beaver sign (ψ) in sampled transects was widespread throughout the Grand Canyon (ψ = 0.74, SE = 0.06) and positively associated with total vegetation. The relative importance scores for Tamarix and Pluchea vegetation classes were 1.5–2.5 times larger than those for all other vegetation classes, indicating that occurrence of beaver sign was most strongly associated with the cover of these 2 vegetation classes. Our results imply that quantifying the amount of riparian vegetation in close proximity to a river helps determine the occurrence of an important ecological indicator in riparian systems. The results also demonstrate a useful and cost-effective method for monitoring riverine species' usage patterns by explicitly accounting for detectability.
Due to the beaver’s former role as a ubiquitous keystone species, there are increasing efforts in the American West to assist beaver in recolonization. Many interested in reintroduction are using two methods to identify optimal habitat: habitat suitability indexes/models (HSI), and historic occupation. This study details some of the problems inherent in HSIs applied to beaver habitat. The paper then interrogates historical occupation as a relocation tool, and finds that while more logically consistent, this method of habitat identification is also problematic. Historic range does not integrate past or present causes of extirpation and absence. I argue that, specifically in the case of beaver relocation but potentially for other species as well, causes of mortality are as important as are environmental amenities in identifying appropriate habitat.
After near‐extirpation in the early 20th century, beaver populations are increasing throughout many parts of North America. Simultaneously, there is an emerging interest in employing beaver activity for stream restoration in arid and semi‐arid environments (collectively, ‘drylands’), where streams and adjacent riparian ecosystems are expected to face heightened challenges from climate change and human population growth.
Despite growing interest in reintroduction programmes, surprisingly little is known about the ecology of beaver in dryland streams, and science to guide management decisions is often fragmented and incomplete.
This paper reviews the literature addressing the ecological effects and management of beaver activity in drylands of North America, highlighting conservation implications, distinctions between temperate and dryland streams, and knowledge gaps.
Well‐documented effects of beaver activity in drylands include changes to channel morphology and groundwater processes, creation of perennial wetland habitat, and substantial impacts to riparian vegetation. However, many hypothesized effects derived from temperate streams lack empirical evidence from dryland streams.
Topics urgently in need of further study include the distribution and local density of beaver dams; consequences of beaver dams for hydrology and water budgets; and effects of beaver activity on the spread of aquatic and riparian non‐native species.
In summary, this review suggests that beaver activity can create substantial benefits and costs for conservation. Where active beaver introductions or removals are proposed, managers and conservation organizations are urged to implement monitoring programmes and consider the full range of possible ecological effects and trade‐offs.
Copyright © 2014 John Wiley & Sons, Ltd.
Tamarisk removal is a widespread restoration practice on rivers in the southwestern USA, but impacts of removal on fish habitat have rarely been investigated. We examined whether tamarisk removal, in combination with a large spring flood, had the potential to improve fish habitat on the San Rafael River in southeastern Utah. We quantified habitat complexity and the distribution of wood accumulation in a tamarisk removal site (treated) and a non-removal site (untreated) in 2010, 1 year prior to a large magnitude and long-duration spring flood. We used aerial imagery to analyze river changes in the treated and untreated sites. Areas of channel movement were significantly larger in the treated site compared to the untreated site, primarily because of geomorphic characteristics of the channel, including higher sinuosity and the presence of an ephemeral tributary. However, results suggest that tamarisk removal on the outside of meander bends, where it grows directly on the channel margins, can promote increased channel movement. Prior to the flood, wood accumulations were concentrated in sections of channel where tamarisk had been removed. Pools, riffles, and backwaters occurred more frequently within 30 m upstream and downstream of wood accumulations compared to areas within 30 m of random points. Pools associated with wood accumulations were also significantly larger and deeper than those associated with random points. These results suggest that the combination of tamarisk removal and wood input can increase the potential for channel movement during spring floods thereby diversifying river habitat and improving conditions for native fish.
Instream wood is a driver of geomorphic change in low-order streams, frequently altering morphodynamic processes. Instream wood is a frequently measured component of streams, yet it is a complex metric, responding to ecological and geomorphic forcings at a variety of scales. Here we seek to disentangle the relative importance of physical and biological processes that drive wood growth and delivery to streams across broad spatial extents. In so doing, we ask two primary questions: (1) is riparian vegetation a composite variable that captures the indirect effects of climate and disturbance on instream wood dynamics? (2) What are the direct and indirect relationships between geomorphic setting, vegetation, climate, disturbance, and instream wood dynamics? We measured riparian vegetation composition and wood frequency and volume at 720 headwater reaches within the American interior Pacific Northwest. We used ordination to identify relationships between vegetation and environmental attributes, and subsequently built a structural equation model to identify how climate and disturbance directly affect vegetation composition and how vegetation and geomorphic setting directly affect instream wood volume and frequency. We found that large wood volume and frequency are directly driven by vegetation composition and positively correlated to wildfire, elevation, stream gradient, and channel bankfull width. Indicator species at reaches with high volumes of wood were generally long-lived, conifer trees that persist for extended durations once delivered to stream habitats. Wood dynamics were also indirectly mediated by factors that shape vegetation: wildfire, precipitation, elevation, and temperature. We conclude that wood volume and frequency are driven by multiple interrelated climatic, geomorphic, and ecological variables. Vegetation composition and geomorphic setting directly mediate indirect relationships between landscape environmental processes and instream large wood. Where climate or geomorphic setting preclude tree establishment, reaches may remain naturally depauperate of instream wood unless wood is transported from elsewhere in the stream network.
Dams created by North American beavers Castor canadensis (hereafter, “beavers”) have numerous effects on stream habitat use by trout. Many of these changes to the stream are seen as positive, and many stream restoration projects seek either to reintroduce beavers or to mimic the habitat that they create. The extent to which beaver dams act as movement barriers to salmonids and whether successful dam passage differs among species are topics of frequent speculation and warrant further research. We investigated beaver dam passage by three trout species in two northern Utah streams. We captured 1,375 trout above and below 21 beaver dams and fitted them with PIT tags to establish whether fish passed the dams and to identify downstream and upstream passage; 187 individual trout were observed to make 481 passes of the 21 beaver dams. Native Bonneville Cutthroat Trout Oncorhynchus clarkii utah passed dams more frequently than nonnative Brown Trout Salmo trutta and nonnative Brook Trout Salvelinus fontinalis. We determined that spawn timing affected seasonal changes in dam passage for each species. Physical characteristics of dams, such as height and upstream location, affected the passage of each species. Movement behaviors of each trout species were also evaluated to help explain the observed patterns of dam passage. Our results suggest that beaver dams are not acting as movement barriers for Bonneville Cutthroat Trout or Brook Trout but may be impeding the movements of invasive Brown Trout.Received November 26, 2012; accepted April 15, 2013
We compared physical and vegetative habitat characteristics at 14 dam sites occupied by beaver (Castor canadensis) with those at 41 random unoccupied reaches to identiiy features important to dam-site selection in the Long Creek basin, Grant County, Oregon. Stream reaches with dams were shallower and had a lower gradient than unoccupied reaches. Beaver did not build dams at sites with a rock substrate. Bank slopes at occupied reaches were not as steep as those at unoccupied reaches; and occupied stream reaches had greater tree canopy cover, especially of thinleaf alder (Alnus tenuifolia), than did unused reaches. A discriminant model using transformations of bank slope, stream gradient, and hardwood cover classified all beaver dam sites correctly and 35 of 41 random sites as unoccupied sites. The 6 misclassified sites had rock substrates. We also tested four habitat suitability models for beaver in this basin. Three models produced significantly different (P < .05) scores between occupied and random unoccupied reaches, suggesting that they might have some utility for this region.
The plugging of highway culverts by beavers (Castor canadensis) creates roadside impoundments that damage and sometimes flood the roadbed. Continually mitigating these problem sites requires considerable time, money, and resources from town, county, and state highway departments. We initiated this study to develop proactive and longterm approaches to deal with nuisance beavers along roadsides. Our specific objective was to compare culvert and habitat features at plugged and nonplugged culverts. From June to October 1997 and 1998, we sampled 216 roadside sites in New York state: 113 sites where beavers plugged the highway culvert and 103 sites where beavers did not plug the culvert but instead constructed an upstream or downstream dam. We used stepwise logistic regression (SLR) to identify key variables associated with plugged culverts. We evaluated classification rates of regression models with measures of sensitivity and specificity. For the combined data set, the logistic function retained culvert inlet opening area $({\rm m}^{2})$ and stream gradient in the final model. Based on these 2 variables, the model correctly classified 79% of the sites. Our results indicated that installing oversized culverts would have the greatest influence on discouraging beaver plugging activity. Prorated over the service life of culverts, the installation of oversized culverts by highway departments may be more cost-effective than trapping, debris removal, or other short-term options to manage beaver damage to roads.
Biogenic features such as beaver dams, large wood, and live vegetation are essential to the maintenance of complex stream ecosystems, but these features are largely absent from models of how streams change over time. Many streams have incised because of changing climate or land-use practices. Because incised streams provide limited benefits to biota, they are a common focus of restoration efforts. Contemporary models of long-term change in streams are focused primarily on physical characteristics, and most restoration efforts are also focused on manipulating physical rather than ecological processes. We present an alternative view, that stream restoration is an ecosystem process, and suggest that the recovery of incised streams is largely dependent on the interaction of biogenic structures with physical fluvial processes. In particular, we propose that live vegetation and beaver dams or beaver dam analogues can substantially accelerate the recovery of incised streams and can help create and maintain complex fluvial ecosystems.
Riparian vegetation may recover quickly from disturbance when the disturbance vector is removed or reduced. Grazing is a disturbance that removes plant biomass through herbivory, while overgrazing is a more severe disturbance that can deplete plant propagule pools and inhibit plant community recovery. We tested the hypothesis that riparian vegetation communities can shift quickly from ruderal grasslands to hydrophytic shrubs and graminoids when grazing is largely eliminated from riparian areas. We used a before-after-control study design to collect vegetation community data at six restored reaches and two grazed control reaches prior to and immediately following the construction of a cattle exclosure. We identified trends in Carex and Salix species abundance and quantified shifts in riparian vegetation community composition across time at each reach using PERMANOVA, multi-level pattern analysis and non-metric multidimensional scaling. Vegetation composition changed rapidly in the four years following removal of grazing disturbance. Indicator species for all impact reaches shifted away from grazing tolerant graminoids and forbs, and toward hydrophytic graminoid and shrub species. Over the same timespan control reach indicator species remained grazing-tolerant graminoids and forbs. There was little change in Salix abundance over time at control or impact reaches but Carex abundance increased at restored reaches. We conclude that herbaceous plant communities may recover rapidly following the removal of grazing disturbance, but that woody species may lag in recovery without active vegetation manipulation. We postulate that low woody-species recruitment may affect the potential of the riparian zone to quickly shade stream channels and facilitate undercut bank formation, common riparian restoration objectives. To prevent halted riparian succession, designers should proactively identify potential limitations to woody vegetation colonization. We close discussing active approaches to overcome stalled riparian ecosystem development and suggest metrics for assessing woody species recovery.
Includes supplemental file.
Two centuries of human activities in the Greater Yellowstone Ecosystem (GYE) have strongly influenced beaver activity on small streams, raising questions about the suitability of the historical (Euro-American) period for establishing stream reference conditions. We used beaver-pond deposits as proxy records of beaver occupation to compare historical beaver activity to that throughout the Holocene. Forty-nine carbon-14 (14C) ages on beaver-pond deposits from Grand Teton National Park indicate that beaver activity was episodic, where multi-century periods lacking dated beaver-pond deposits have similar timing to those previously documented in Yellowstone National Park. These gaps in the sequence of dated deposits coincide with episodes of severe, prolonged drought, e.g. within the Medieval Climatic Anomaly 1000–600 cal yr bp, when small streams likely became ephemeral. In contrast, many beaver-pond deposits date to 500–100 cal yr bp, corresponding to the colder, effectively wetter Little Ice Age. Abundant historical beaver activity in the early 1900s is coincident with a climate cooler and wetter than present and more abundant willow and aspen, but also regulation of beaver trapping and the removal of wolves (the beaver's main predator), all favorable for expanded beaver populations. Reduced beaver populations after the 1920s, particularly in the northern Yellowstone winter range, are in part a response to elk overbrowsing of willow and aspen that later stemmed from wolf extirpation. Beaver populations on small streams were also impacted by low streamflows during severe droughts in the 1930s and late 1980s to present. Thus, both abundant beaver in the 1920s and reduced beaver activity at present reflect the combined influence of management practices and climate, and underscore the limitations of the early historical period for defining reference conditions. The Holocene record of beaver activity prior to Euro-American activities provides a better indication of the natural range of variability in beaver-influenced small stream systems of the GYE. Copyright © 2012 John Wiley & Sons, Ltd.
