Abiotic Factors – How do beaver activities influence the biotic and abiotic characteristics of stream ecosystems?

Expanding Ranges: Beavers’ Effects on New Ecosystems

Scientists today understand the ecological significance of beavers (Castor canadensis or Castor fiber), calling them “ecosystem engineers” because of the widespread impacts of their dams. Before their place in the ecosystems was known, beavers were eradicated from many parts of their historical range. This range included North America, Asia, and Europe, but overhunting led to drastic decreases in their numbers. Now that their importance is understood, beaver reintroduction has been initiated in many parts of their historical range as a method of stream conservation. (Brazier et al., 2020). However, beaver relocation is not always beneficial to the areas’ ecosystems. Whether due to changes in climate or human introduction, beavers can have drastic impacts on stream characteristics.

As the climate changes, beavers are beginning to naturally relocate to areas past their recent historical range. Beavers were overharvested almost to expiration by fur trappers in Alaska (19th – early 20th century). However, even during this time, they were constrained by tundra regions. It is widely believed that the cold temperatures further in the north froze open water, preventing beavers from establishing until recently when temperatures are rising. However, another theory suggests that beavers were present in the tundra in the past, but have not yet returned because historical hunting was so detrimental to their populations.

Whatever the case for their historical absence may be, beavers are beginning to move further into the tundra area. Due to warming air temperatures, the Arctic has had earlier snowmelt and increased warming of the permafrost (ground that is frozen around the year). These effects have been particularly noticeable in streams in particular. When the permafrost melts, it releases sediment and nutrients stored within. It can also release stored gases into the atmosphere, contributing to the changing climate. Melting ice can also break off and move through the water, exposing the stream bank. This encourages growth on the bank and can lead to an overall increase in photosynthesis.(Sturm et al., 2001).

Estimated map of beaver expansion past the tree line (orange line) in Alaskan and Canadian tundra. (Tape et al., 2018).

While changing climate may be the reason for beavers’ range expansion, this expansion also impacts the environment in return. As widely known “eco-system engineers”, this expansion was predicted to strongly impact tundra freshwater ecosystems.

Beaver activity can destabilize arctic streams. As they create dams, they create dynamic wetland ecosystems from these previously stable streams. These changes in the physical characteristics of streams diversify habitat. This can provide ideal conditions for non-native species to expand their own ranges. For example, beaver dams can increase water and sediment temperature downstream. Higher temperatures can improve the survival of fish eggs that are incubating in the sand The effects of these newly colonizing species are yet to be determined (Tape et al., 2018).

A beaver in the snow. (Lockhart, 2024).

In contrast, non-native beavers (Castor canadensis) in Cape Horn, Chile have reduced diversity in streams. In streams invaded by beavers, benthic macroinvertebrate communities were more uniform. Despite this decrease in diversity, the streams became more productive overall. While there were fewer taxa present, the abundance and levels of secondary production greatly increased. Temperatures downstream of the dams were also increased. These results contrasted with what was expected, as species diversity generally increases as habitat diversity increases. The contrasting results observed in Chile were proposed to be a result of increased substrate. While building dams, the beavers may have increased levels of substrate and organic matter on the stream bed, filling spaces where smaller taxa may live. By making the habitat below the streams more uniform, the invasive beavers caused a decrease in biodiversity despite increased productivity (Anderson & Rosemond, 2006).

Whether intentionally introduced or not, the expansion of beaver ranges into new areas can have widespread impacts on stream ecosystems. Beaver habits that are essential to their native ecosystems can have different results in different biomes. As the climate continues to change, beavers may continue to expand their range and may have unprecedented effects. Beaver ranges should be monitored continuously to manage detrimental effects on new ecosystems before irreversible damage is done.

References

Anderson, Christopher B., and Amy D. Rosemond. 2007. “Ecosystem Engineering by Invasive Exotic Beavers Reduces In-Stream Diversity and Enhances Ecosystem Function in Cape Horn, Chile.” Oecologia 154: 141–53. https://doi.org/10.1007/s00442-007-0757-4.

Brazier, Richard E., Alan Puttock, Hugh A. Graham, Roger E. Auster, Kye H. Davies, and Chryssa M. Brown. 2020. “Beaver: Nature’s Ecosystem Engineers.” WIREs Water 8(1). https://doi.org/10.1002/wat2.1494.

Lockheart, Neil. A beaver sits on a snowy riverbank. 2024. Photograph.

Sturm, Matthew, Charles Racine, and Kenneth Tape. 2001. “Increasing Shrub Abundance in the Arctic.” Nature 411: 546–47. https://doi.org/10.1038/35079180.

Tape, Ken D., Benjamin M. Jones, Christopher D. Arp, Ingmar Nitze, and Guido Grosse. 2018. “Tundra Be Dammed: Beaver Colonization of the Arctic.” Global Change Biology 24: 4478–88. https://doi.org/10.1111/gcb.14332.

Challenges and Benefits of Beaver Reintroduction

Beavers are remarkable animals who transform ecosystems to suit their needs. In doing this, they also create valuable habitats for many other species. They do this by building dams, which create ponds filled with sediment, nutrients, plants, and wildlife. These dams slow down water flow, reducing flooding downstream and storing water during droughts.

A beaver collecting materials for a dam. (WildlifeNYC, 2024).

Beavers also dig canals across floodplains to find food and materials, which helps connect different parts of the landscape. By cutting trees close to the ground to encourage new growth, beavers create habitat for insects, birds, and other animals.

In the past, beavers were common in Europe, Asia, and North America. They played an important role in managing water and supporting freshwater ecosystems. Around 400 years ago, they were hunted extensively and disappeared from some areas, like Great Britain. Now, efforts are being made to reintroduce them to their former habitats.

Understanding the impact of beavers is essential, especially in landscapes that have been heavily impacted by human activities like farming and urban development. This study examines how beavers affect ecosystems, water flow, water quality, freshwater life, and human interactions.

Beavers dig burrows along riverbanks and create networks of shallow channels, known as canals, which affect the distribution of water and the surface of the landscape. As beavers loosen soils from river banks, they can cause sediments to move, which can lead to the collapse of nearby structures like flood embankments.

A beaver dam. (Sowl, 2024).

These beaver constructions also have a huge impact on water flow and storage. Beaver dams affect how water moves both locally and downstream. Their activity slows down water flow, which can flood nearby areas and create wetlands. These wetlands store water and recharge groundwater, helping during dry periods. Additionally, these wetlands provide habitats for many aquatic species.

Beaver dams also hold back sediment and nutrients, which can improve water quality by reducing pollution downstream. They act like filters, trapping particles and chemicals. Additionally, beaver ponds provide habitats for plants and animals, further enhancing water quality. Overall, beavers play a crucial role in shaping freshwater ecosystems and improving water quality by slowing down water, trapping sediment and nutrients, and creating diverse habitats.

Additionally, beavers increase the presence of woody debris in rivers, such as fallen trees, branches, and logs. This creates sheltered areas which act as habitats for many organisms, such as fish, insects, and amphibians. By building dams, beavers create a variety of homes for many species. Their activities lead to more aquatic plants, invertebrates, and fish, increasing biodiversity. Beaver dams create habitat patches, which are distinct areas in an ecosystem that have different characteristics. These habitat patches support fish growth, survival, and diversity.

Diagram of beavers’ interactions with other species as a keystone species. (Rewilding Europe, 2022).

Beavers have many benefits on aquatic ecosystems, but reintroducing beavers into habitats may pose challenges. Conflicts may occur between beavers and humans, especially in areas where beaver activities interfere with human interests, such as agriculture and forestry. In order to effectively manage beaver populations and reintroduction conflicts, it is important to engage with any affected individuals to involve them in decision making processes. There are management strategies which can address conflicts, including dam removal, stabilizing riverbanks, and installing flow devices to control water levels. Overall, while reintroducing beavers can bring significant environmental benefits, effective management and collaboration between stakeholders are essential to address conflicts and maximize the positive impacts of beavers on ecosystems and society.

Specifically in Vermont, reintroducing beavers may have various ecological and environmental impacts, both positive and potentially challenging ones. Beavers are considered a keystone species because their activities create and maintain habitats that benefit a wide range of other species. Reintroducing them could enhance biodiversity by creating wetlands that support diverse plant and animal communities. Though beaver dams help improve water quality, these constructions could also lead to a higher risk of flooding, which would need to be managed to minimize conflicts with human activities. This is especially concerning with global warming trends, as Vermont is prone to more extreme precipitation events with increasing temperatures. Beavers would need to be carefully reintroduced to suitable habitats, such as areas with slow-moving streams, ponds, or wetlands. Any reintroduction efforts would need to be monitored to see how successful this project is and foresee any issues that might arise. It’s important to have a long-term plan for managing beaver populations and their impacts.

A beaver swimming. (Howard, 2024).

References

Brazier, Richard E., Alan Puttock, Hugh A. Graham, Roger E. Auster, Kye H. Davies, and Chryssa M. Brown. 2020. “Beaver: Nature’s Ecosystem Engineers.” WIREs Water (8):1. https://doi.org/10.1002/wat2.1494.

Howard, Madalen. 2024. Swimming Beaver. Photograph

Sowl, Kristine. 2024. Beaver Dam. Photograph.

Rewilding Europe. 2022. The Beaver: A Keystone Species. Photograph.

How do beavers affect macroinvertebrate communities, and in turn, ecosystem function?

Macroinvertebrates are small organisms that lack a backbone and are common in aquatic settings. Streams can support diverse communities of macroinvertebrates. Within these communities, each species has different traits, habits, and habitat preferences. Due to this widespread diversity, macroinvertebrates that live in freshwater are classified into six Functional Feeding Groups (FFG). Each FFG is based on the feeding morphology, or the basic shape of their feeding appendages rather than by their relation to other species. There are five basic FFG: shredders (eat leaf litter and coarse particulate organic matter), scrapers (eat algae and other items they “scrape” off rocks), collector/gatherers (which collect and consume fine particulate organic matter from the bottom of the stream), predators (which consume other consumers), and filterers (which use their appendages to filter and consume fine particulate organic matter from the water). While these groups are mostly comprehensive, some species don’t fully fit into any of these groups and are categorized as “others”. West Virginia Government, 2024). These feeding habits also make macroinvertebrates an important step in transferring energy from primary producers and particulate organic matter to consumers at a higher trophic level, such as predatory fish. Their place in the trophic system means that any changes to their abundance or diversity of FFGs can have widespread impacts both on species that they consume and are consumed by (Cummins, 2016).

Example species of the five main macroinvertebrate Functional Feeding Groups. (Coleman et al., 2021).

Macroinvertebrate populations can be affected by a variety of factors from stream water quality to the morphology, or shape, of the stream. Beaver activities such as felling trees and digging canals can change stream morphology (Brazier et al., 2020).

These changes can have a variety of impacts on macroinvertebrate communities within these streams but until 2019, the nature of these impacts has been relatively unstudied in North America, particularly in the West. In 2019, the study “Beavers alter stream macroinvertebrate communities in north-eastern Utah” by Susan Washko, Brett Roper, and Trisha B. Atwood compared the macroinvertebrate communities in beaver altered streams to unaltered streams.

Three main tributaries to the Logan River (Right Hand Fork, Spawn Creek, and Temple Fork) were chosen to model the possible variety of responses, as each stream had a distinguishing characteristic. Temple Fork was the widest stream (average width of 4.0 m). Right Hand Fork was the second widest (average width of 3.9 m) but the most confined stream. Spawn Creek, the least wide stream (average width 1.8 m), was encompassed by a 67-ha cattle exclusion fence. The other large difference between the three streams was the biotic, or alive, aspects of the stream. Only Right Hand Fork had submerged macroinvertebrates present. However, the other two streams had more diverse fish populations, including brown trout (Salmo trutta) which is invasive in the area. In comparison, the fish population of Right Hand Fork is mainly Bonneville cutthroat trout.

Spawn Creek, Temple Fork, and Right Hand Fork, three tributaries to the Logan River. (Washko et al., 2019).

Each of the three tributaries was sampled in two areas: one area, classified as the “pond area” where the beavers had established and the other area, above the ponds, classified as “lotic reaches”. The lotic reach areas had faster water flow, though were shallower and had larger substrates (cobble). In each stream, five samples were taken from lotic (flowing) areas, and five samples were taken from a nearby beaver pond for a total of 30 samples. However, one sample was left out in the final analysis due to sampling error.

In addition to the macroinvertebrate samples collected, each location was sampled for “environmental characteristics” including elevation, water temperature, levels of dissolved oxygen, velocity, and substrate size. For each stream, each characteristic was averaged separated by pond and lotic reach area.

In comparison to the multiple sampling events for environmental characteristics, macroinvertebrate samples were only taken once per each lotic reach and once per each beaver pond. The lotic reaches were sampled using a surber sampler while the ponds were sampled using a sweep net. This gear and lack of replications were specifically chosen to limit the amount of non-natural disturbance to the communities. Each sample was grouped by taxa and then dried and weighed. Based on these biomass weights and density calculations, the dominant taxa of each sample were found. The number of EPT (Ephemeroptera, Plecoptera, and Trichoptera) taxa was also specifically calculated. EPT taxa are notoriously sensitive to pollutants, so the abundance of these taxa within a stream is often used as an indicator of the water quality. The groups were sorted at the highest level by taxa, they were further identified by the dominant FFG and whether their primary habitat was lentic (still) or lotic (flowing).

Surber net sampling of a stream. (Department of Conservation, 2013).

Sweep net sampling. (Manaaki Whenua Land Care Research, 2024).

The presence of beavers did impact macroinvertebrate communities in the study streams. In all streams, there were significantly higher macroinvertebrate densities, biomass, and densities of EPT taxa collected in the lotic regions than in the pond regions. EPT taxa specifically were also denser in the lotic areas. Additionally, there were more taxa of the scraper FFG in the pond sections than in the reach areas.

These results are believed to be due to changes resulting from the dam building process. However, these changes can vary by stream. The primary reason for these changes is proposed to be a decrease in sediment size in beaver ponds. Smaller sediment sizes can decrease interstitial (or “in-between”) spaces, providing fewer places for macroinvertebrates to live. There may also be less substrate for periphyton (communities of algae and fungi), which can explain the decrease observed in the scraper FFG (Washko et al., 2019).

The results of this study are in contrast to beaver pond-induced effects on fish communities. Beaver ponds were found to increase habitat diversity for fish (Hägglund & Sjöberg, 1999). While beaver dams might have an overall positive effect on fish communities, the negative impacts on macroinvertebrates, an important food source, should be further examined. This contradiction may have unobserved but influential impacts on the ecosystem overall.

References

Coleman, Daniel, Andrew John Brooks, Lauren MacRae, and Tim Haeusler. 2021. The Influence of Unregulated Tributaries on Macroinvertebrate Communities in a Regulated River. Technical Report.

Cummins, Kenneth W. “Combining Taxonomy and Function in the Study of Stream Macroinvertebrates.” Journal of Limnology 75, no. s1 (March 22, 2016). https://doi.org/10.4081/jlimnol.2016.1373.

Department of Environmental Protection. 2024. “Functional Feeding Groups.” https://dep.wv.gov/WWE/getinvolved/sos/Pages/foodweb.aspx#:~:text=The%20major%20functional%20feeding%20groups,using%20a%20variety%20of%20filters%3B.

Gray, Duncan. Rep. 2013. Freshwater Ecology: Quantitative Macroinvertebrate Sampling in Hard-Bottomed Streams Vol. 1.

Manaaki Whenua Landcare Research. 2024. “Sampling Tips”. Freshwater Invertebrates Guide. https://www.landcareresearch.co.nz/tools-and-resources/identification/freshwater-invertebrates-guide/sampling-tips/

Washko, Susan, Brett Roper, and Trisha B. Atwood. “Beavers Alter Stream Macroinvertebrate Communities in North‐eastern Utah.” Freshwater Biology 65, no. 3 (December 15, 2019): 579–91. https://doi.org/10.1111/fwb.13455.

Beavers as Nature’s Engineers

Beavers are doing a fantastic job at purifying rivers, especially in the western United States where it’s getting hotter and drier due to climate change. When beavers construct dams in rivers, they create miniature reservoirs upstream. These reservoirs act as natural filtration systems, capturing sediment, excess nutrients, and contaminants before they can flow downstream. Beavers are ecosystem engineers: their dams purify water in rivers.

Beaver building a dam. (Robert McGouey, 2017).

Water quality refers to how safe and clean water is for a certain purpose, such as drinking or irrigation. The activity of beavers is especially important for preserving water quality with environmental changes from a warming climate. During droughts, water quality declines. Beaver dams can effectively preserve water quality in these conditions by trapping sediment and filtering out pollutants. So, these dams act as protective barriers for water quality. When streams dry out, pollution levels increase because there is not enough water flowing to flush out contaminants. Researchers from Stanford University studied how pollutants move through the environment by taking measurements and using computer models.

It is also important to understand how ecosystems function in response to climate change. Excess nitrogen can promote algae overgrowth, which can block sunlight necessary for photosynthesis. The researchers found that beaver dams played a role in reducing nitrate, a harmful form of nitrogen. This reduction happened because the dams created a sudden drop in water levels, which helped filter out the nitrate from the water.

Comparison of stream health with (left) and without (right) beaver dams. (Shanthanu Bhardwaj, 2024).

While the study specifically focused on rivers in the western United States, these findings have broader implications that could relate to Vermont. Vermont, like many other areas, is experiencing the effects of climate change, including alterations in precipitation patterns and increased instances of extreme weather events.

In Vermont, beavers play a role in shaping local ecosystems. The dams built by beavers in Vermont’s rivers and streams could potentially contribute to water quality improvement by acting as natural filters. This could be especially important during periods of drought or heavy rainfall when water quality may be compromised. Climate change is creating an increase in heavy rainfall and extreme weather events, which can affect water quality and stream habitats.

Understanding the impact of beaver activity on water quality is relevant for Vermont’s ecosystem management and conservation efforts. By recognizing the beneficial role of beavers in maintaining river health, policymakers, conservationists, and local communities in Vermont can consider incorporating beaver management strategies into their plans for mitigating the effects of climate change and preserving water quality.

Beaver dam in a montane stream. (GSA, 2023).

References

Bhardwaj, Shanthanu. Water quality in Chicago’s rivers improving, but still needs work. 2017. Photograph.

Brazier, Richard E., Allen Puttock, Hugh A Graham, Roger E Auster, Kye H Davies. and Chryssa M.L. Brown. 2020. “Beavers: Nature’s Ecosystem Engineers.” WIREs Water 8(1). https://doi.org/https://doi.org/10.1002%2Fwat2.1494.

Dunn, Sarah. EEAGER – The Search for Beavers. March 15, 2023. Photograph.

McGouey, Robert. Beaver Building a Dam. 2017. Photograph.

Exploring the Role of Beavers in Stream Restoration and Climate Adaptation

Many regions are experiencing changes in stream temperatures due to climate change, which alters weather patterns and temperature regimes worldwide. As the air temperature increases, so do the temperatures of bodies of water. This temperature rise can have drastic effects on stream ecosystems. For example, cold water fish, such as trout and salmon, may struggle to survive in a warmer climate. Additionally, altered precipitation patterns, such as changes in the timing and intensity of rainfall, can lead to reduced summer stream flows. This decreases the availability of water for drinking and irrigation; Also, a certain amount of water flow is needed to maintain aquatic ecosystems.

(BBC, 2024)

Scientists are investigating adaptive strategies to mitigate these challenges associated with climate change, such as beaver reintroduction. Beavers can regulate stream environments through dam building. By creating ponds and wetlands, beavers can improve groundwater recharge, increase surface water storage, and moderate stream temperatures.

(Science Focus, 2023)

This research focused on 13 specific headwater stream reaches where 69 beavers were relocated. In this study, the researchers assessed how the presence of beavers and their dam-building activities influenced water storage in the Snohomish River basin in Washington, USA. To do this, changes in both surface water storage (such as in ponds and wetlands created by beaver dams) and groundwater storage were measured. This was useful for understanding how much more water headwater streams could hold when beavers were relocated to streams.

Another goal of this research was to examine the effects of beaver relocation on stream temperature. Through dam building, beavers create shaded areas and alter the flow dynamics of bodies of water. The researchers assessed changes in stream temperature before and after beaver relocation to determine how beavers influence stream temperatures.

Additionally, the study aimed to evaluate how specific ecosystem changes due to beaver relocation contribute to the ecosystem’s resilience overall. In headwater riparian areas, researchers assessed factors such as habitat quality, species diversity, and ecosystem stability to determine how the activities of beavers influence ecosystems on a broader scale.

The research showed that when beavers were relocated successfully, they created more water storage along the streams. For every 100 meters of stream, an extra 243 cubic meters of water was stored, mostly on the surface. The dams they built also stored groundwater, about 2.4 times more than surface water.

As a result of the dams, downstream areas experienced a cooling effect, with the water temperature dropping by an average of 2.3°C during the summer. This suggests that beaver activities, like building dams, helped to cool down the water in the streams.

The study also looked at different features of the beaver dams, such as age, condition, and how often they were maintained. These factors affected how much the water temperature changed in the streams. Overall, it was found that these dam characteristics played a role in determining the temperature changes observed in the streams.

(Vox, 2023)

These results led the researchers to suggest beaver reintroduction as a helpful strategy for offsetting some negative effects of climate change in aquatic habitats. However, the effectiveness of beaver activities on climate change mitigation can be different based on regional and environmental factors. The researchers reference “regional specificity”, which means that the success of beaver reintroduction can depend on the characteristics of the area where beavers are reintroduced, These characteristics include climate, geography, geology, and existing ecosystem dynamics. For example, the soil in an area can affect how beavers build dams and create ponds. Soil that is rich in clay or silt is ideal for building sturdy dams, whereas sandy soils are far less sturdy and can erode quite easily. So, the soil composition in a region can impact how suitable a habitat is for beaver activity. If a habitat is less suitable for beavers, then beaver reintroduction would be less successful in offsetting climate change.

In Vermont, beaver reintroduction would require planning, community engagement, and continued monitoring. The first step is identifying suitable habitats for beavers in Vermont. Researchers would need to assess certain ecosystem characteristics, such as soil composition. Additionally, researchers would need to consider the environmental impacts that beaver reintroduction would have on existing ecosystems. Beavers would be an introduced species, so they may cause unintended harm to native species or habitats. Engaging with local communities, government agencies, and conservation organizations is important for gaining support for the project. If beavers are reintroduced, it would be important to track beaver populations and assess their impact on both the ecosystem and the landscape. It may also be important to implement strategies to mitigate flooding and protect important habitats. While beaver reintroduction holds promise as a climate adaptation strategy, it is important to consider the specific characteristics of each region and how they may influence the outcomes of beaver activities.

(Vox, 2023)

References

Dittbrenner, Benjamin J., Jason W. Schilling, Christian E. Torgersen, and Joshua J. Lawler. “Relocated Beaver Can Increase Water Storage and Decrease Stream Temperature in Headwater Streams.” Ecosphere 13, no. 7 (July 2022). https://doi.org/10.1002/ecs2.4168.

Jones, Benji. “Beavers Are Heat Wave Heroes.” Vox, July 22, 2022. https://www.vox.com/down-to-earth/23273240/heat-wave-beavers-climate-change.

Stallard, Mark Poynting and Esme. “How Climate Change Worsens Heatwaves, Droughts, Wildfires and Floods.” BBC News, April 25, 2024. https://www.bbc.com/news/science-environment-58073295.

“Why Do Beavers Build Dams?” BBC Science Focus Magazine. Accessed May 1, 2024. https://www.sciencefocus.com/nature/why-do-beavers-build-dams.