The Beaver as an Ecosystem Engineer – Effects on Water Quality and Freshwater Ecosystems

The Beaver as an Ecosystem Engineer–Effects on Water Quality and Freshwater Ecosystems

Aqua Viva Fachtagung 2026: Sauberes Wasser

Dr. Leonardo Capitani
Senior Scientist, Department of Aquatic Ecology, Eawag

leomarameo7.github.io

23 October 2026

Slides and links

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Acknowledgments

Photos and names of Christof Angst, Francesco Pomati, Anita C. Risch, Annegret Larsen and Joshua R. Larsen

… and many other researchers and stakeholders!

Main message of this talk

Beaver engineering can create locally climate-resistant wetlands

Photos and effects: Fairfax & Westbrook (2024), Fig. 2; text redrawn

Beavers excavate, build dams and forage; the effects on the wetland are shown as plus or minus

Index of this presentation

Water quality: carbon and nutrients
Biodiversity: habitats and species
Resilience: floods and droughts
Management: living with beavers

International synthesis + Swiss Swiss flag cases

Beaver life history and diet

Slow breeders: few kits, long family life

Eurasian beaver; Table 1.1 and chapters 5, 6 and 10 of Rosell & Campbell-Palmer (2022); photo: Kjell-Erik Moseid, Fig. 5.12

Six life-history numbers for the Eurasian beaver: body mass, gestation, litter size, age at maturity, family size and age at death

Beavers are back across Europe

Distribution of Eurasian and North American beavers in Europe in 2002 (left) and 2020 (right); red circle marks the expansion in Germany and Switzerland

Switzerland, 2022:
4,900 beavers

Info Fauna logo

Beavers are recolonising Europe

Sources: Halley et al. 2020, Mammal Review 51, 1–24 (maps); Angst et al. 2023, Biberbestandeserhebung 2022, info fauna (Switzerland)

How many beavers?

Swiss flag

Number of beavers (Biber) and territories (Reviere) in the canton of Zürich, 2008 to 2022

Data: Nationale Biberfachstelle / info fauna 2023

Info Fauna logo

150 beavers in 2008
400+ beavers in 2022
Growth slows after 2020

Rebound now levelling off

Living with beavers: the cost of damage

Swiss flag info fauna

Damage compensation increased over 30 years (1988–2021)

Source: Angst et al. 2023, Biberbestandeserhebung 2022, info fauna, Fig. 37; damage to crops and forests, 1988–2021

Bar chart of yearly compensation paid for beaver damage in Switzerland, 1988 to 2021, rising from a few thousand to about 87,000 Swiss francs

Hydrological impacts

Beavers reduce longitudinal connectivity, while increasing lateral connectivity

Modified from Brazier et al. (2021), Fig. 2: stages a, c, e, f

Four stages of beaver-driven channel change: incised channel with dam blow-outs, wider channel with stable dams, sediment build-up with rising water table, reconnected floodplain

Water quality · Why nutrient cycling?

Nutrients and organic matter drive ecosystems

Modified from Jansen et al. (2021), Fig. 5: red circles and stream added

Food webs with inorganic nutrients and dissolved organic matter circled in red, rising from a stream

Water quality · International synthesis: C and nutrients

Carbon and nutrient budgets: no unique direction

Modified from Larsen et al. 2021, Earth-Science Reviews 218, 103623, Fig. 15: conceptual model; arrows and counts (studies with that direction of all studies) from their literature review, Fig. 16: 37 water-quality studies, mostly North America, 1982–2021

Conceptual model of how beaver dams change biogeochemical pathways and fluxes from upstream to downstream

Water quality: the Swiss case

Swiss flag

Beaver ponds are local control points of DOC

Capitani et al., in prep., Fig. 4

Beaver effect on DOC in each of 158 streams, ranked

Water quality · drivers of beaver’s influence

Swiss flag

Beavers slow the water; algae and plants add DOC

Capitani et al., in prep., Fig. 3

Stream with several beaver dams, DOC in and out, and the flooded area leading into the causal diagram of downstream DOC

Biodiversity: the Swiss case

Swiss flag

Beavers influence stream biodiversity

Source: Moser et al. 2026, Journal of Applied Ecology

Study design: a beaver pond with dam (pool, 75 m) and a control reach without beavers (100 m) 500 m apart

Radar plots: species richness and abundance of 10 taxa in beaver pools and control sites

Biodiversity · Bats at beaver pools

Swiss flag

Beaver contribution: habitat complexity and more food

Figure: Browning 2025; data: Moser, Capitani et al. 2025; photos: JeanRoulin CC BY-SA, R. Bigonneau CC BY (Wikimedia)

Simplified scheme: beaver engineering increases canopy heterogeneity, standing deadwood and arthropods, and bat richness, activity and feeding of mid- and long-range echolocators

Mid-range gain most
Driver: deadwood
Endangered bats:

Western barbastelle

Barbastella barbastellus

Geoffroy’s bat

Myotis emarginatus

Resilience: the Belgian case

Belgian flag
Study site: Chevral, Ardennes, Belgium

Flatter peaks, higher low flows

Redrawn from Nyssen et al. 2011, Journal of Hydrology 402, 92–102, Fig. 12 (also Fig. 8 in Larsen et al. 2021)

Inflow and outflow discharge of a beaver pond cascade in Belgium, September 2009 to March 2010

Resilience · Storing water, buffering flow

Dams buffer droughts and floods

Sources: Dittbrenner et al. 2022, Ecosphere 13, e4168; Puttock et al. (2017); Hood 2012 in Rosell & Campbell-Palmer (2022)

Key numbers on water stored, dry-season water, temperature and peak flow with beaver dams

Beaver management: conflicts and solutions

Each conflict has a practical fix

Table 11.1 in Rosell & Campbell-Palmer (2022)

Three kinds of conflict, foraging, burrowing and damming, each paired with solutions

Beaver management: zoning in the Czech Republic

Czech flag

Zoning separates protection from conflict areas

Vorel et al. 2016, as described in Rosell & Campbell-Palmer (2022), pp. 422–423

Czech beaver management zones A (full protection), B (managed, 85.5% of the country) and C (not tolerated, 13.3%)

Beaver management: the Swiss case

Swiss flag

Map of Switzerland showing the net impact (opportunity minus conflict) of modelled beaver floodplains per 1 km² cell

Fig. 6 and Table 4 in Dennis et al. 2024, Global Ecology and Conservation 56, e03304

Info Fauna logo Biber-Auenmodell Science icon

Beaver floodplain: 450 km²

Driver: channel gradient
298 km² (66%) opportunity
132 km² (29%) conflict

Maximise restoration, minimise conflicts

Beaver management: how should we proceed?

Swiss flag

Beaver management should consider social context

Redrawn after Dennis et al. 2024, Global Ecology and Conservation 56, e03304

Decision tree for designating beaver habitat: identify the local extent of the beaver floodplain, check land-use conflict, weigh opportunity against conflict, and check acceptability to local stakeholders

Main message: take-home

Beaver engineering can create locally climate-resistant wetlands

Photos and effects: Fairfax & Westbrook (2024), Fig. 2; text redrawn

Beavers excavate, build dams and forage; the effects on the wetland are shown as plus or minus

Thank you

Two beavers at their dam

Photo: Dominic Tinner

Dr. Leonardo Capitani
leomarameo7.github.io

Acknowledgments

SeeWandel-Klima logo

Dr. Leonardo Capitani is financed by the grant “SeeWandel-Climate: Modelling the consequences of climate change and neobiota for Lake Constance” within the framework of the Interreg VI programme “Alpenrhein-Bodensee-Hochrhein (Germany/Austria/Switzerland/Liechtenstein)”. The funds are provided by the European Regional Development Fund as well as the Swiss cantons.

The funders had no role in the content of this presentation.

Interreg Alpenrhein-Bodensee-Hochrhein, co-financed by the European Union, coats of arms of the Swiss cantons

Supplementary material

Additional slides

Beaver management: a ladder of options

Start with information; remove beavers last

Table 11.2 in Rosell & Campbell-Palmer (2022) (modified from Sjöberg & Belova 2019)

Five management options from informing the public to removing beavers locally, ordered by level of intervention and seriousness of damage

Summer vs winter: change in DOC

Swiss flag

Beavers add DOC in summer, not in winter

Capitani et al., in prep., Fig. 4a

Median relative response of DOC to beaver engineering across 158 streams: about +21% of the seasonal DOC contrast in summer and no clear effect in winter

Sampling design and sites

Swiss flag

Capitani et al., in prep., Fig. 1

Sampling design: a stream flowing left to right with DOC sampled upstream of the first dam and downstream of the last dam, with two beaver ponds, their dams and beavers

Map of Switzerland with the 158 analysed beaver streams

Connectivity and expansion

Isolated northern populations expand slowly

Fig. 3 in Falaschi et al. 2024, Animal Conservation 27, 324–337: connectivity map of Eurasian beaver in Italy and surrounding countries. Source points (beaver occurrences) in black, current flow in red.

Connectivity map of Eurasian beaver in Italy and surrounding countries, with source points and current flow

Beavers dam streams in human-used landscapes

Swiss flag info fauna

Beavers dam streams right next to farmland

Photo: Christof Angst, in Angst et al. 2023, Biberbestandeserhebung 2022, info fauna, p. 99

Aerial photo of a beaver territory at Hersiwil, canton Solothurn: dams (red lines) and a lodge (red circle) beside a field

Beaver dams beside paths and railways

Swiss flag info fauna

Beaver territories can sit next to infrastructure

Photos: Christof Angst, in Angst et al. 2023, Biberbestandeserhebung 2022, info fauna, p. 101

Two photos of a beaver territory at Herzogenbuchsee, canton Bern, between a footpath and a railway, with dams marked by red lines and a lodge by a red circle

References (1/2)

Angst, C., Auberson, C. & Nienhuis, C. (2023). Biberbestandeserhebung 2022 in der Schweiz und Liechtenstein.
Brazier, R.E., Puttock, A., Graham, H.A., Auster, R.E., Davies, K.H. & Brown, C.M.L. (2021). Beaver: Nature’s ecosystem engineers. Wires. Water, 8, e1494.
Browning, E. (2025). Direct and indirect impacts of beaver ecosystem engineering have mixed effects on bats across feeding guilds. Journal of Animal Ecology.
Dennis, M., Angst, C., Larsen, J.R., Rey, E. & Larsen, A. (2024). A national scale floodplain model revealing channel gradient as a key determinant of beaver dam occurrence and inundation potential can anticipate land-use based opportunities and conflicts for river restoration. Global Ecology and Conservation, 56, e03304.
Dittbrenner, B.J., Schilling, J.W., Torgersen, C.E. & Lawler, J.J. (2022). Relocated beaver can increase water storage and decrease stream temperature in headwater streams. Ecosphere, 13, e4168.
Fairfax, E. & Westbrook, C. (2024). The Ecology and Evolution of Beavers: Ecosystem Engineers that Ameliorate Climate Change. Annual Review of Ecology, Evolution, and Systematics, 55, 323–345.
Falaschi, M., Ficetola, G.F., Viviano, A., Mazza, G. & Mori, E. (2024). Environmental suitability and potential range expansion of the Eurasian beaver in Italy. Animal Conservation, 27, 324–337.
Halley, D.J., Saveljev, A.P. & Rosell, F. (2020). Population and distribution of beavers Castor fiber and Castor canadensis in Eurasia. Mammal Review, 51, 1–24.

References (2/2)

Jansen, J., MacIntyre, S., Barrett, D.C., Chin, Y.-P., Cortés, A., Forrest, A.L., et al. (2021). Winter limnology: How do hydrodynamics and biogeochemistry shape ecosystems under ice? Journal of Geophysical Research: Biogeosciences, 126, e2020JG006237.
Moser, V., Capitani, L., Zehnder, L., Hürbin, A., Obrist, M.K., Ecker, K., et al. (2025). Habitat heterogeneity and food availability in beaver-engineered streams foster bat richness, activity and feeding. Journal of Animal Ecology.
Moser, V., Minnig, S., Capitani, L., Boch, S., Cramer, N., Edman, O., et al. (2026). Rewilding beyond the wilderness: Beavers can restore stream biodiversity from urban to agricultural to natural landscapes. Journal of Applied Ecology.
Nationale Biberfachstelle / info fauna. (2023). Beaver counts in the canton of Zürich, 2008–2022.
Nyssen, J., Pontzeele, J. & Billi, P. (2011). Effect of beaver dams on the hydrology of small mountain streams: Example from the Chevral in the Ourthe Orientale basin, Ardennes, Belgium. Journal of Hydrology, 402, 92–102.
Puttock, A., Graham, H.A., Cunliffe, A.M., Elliott, M. & Brazier, R.E. (2017). Eurasian beaver activity increases water storage, attenuates flow and mitigates diffuse pollution from intensively-managed grasslands. Science of The Total Environment, 576, 430–443.
Rosell, F. & Campbell-Palmer, R. (2022). Beavers: Ecology, Behaviour, Conservation, and Management. Oxford University Press.
Sheppy, J., Sudduth, E.B., Clinton, S., Riveros-Iregui, D. & Ledford, S.H. (2024). Urban beaver ponds show limited impact on stream carbon quantity in contrast to stormwater ponds. Urban Ecosystems, 27, 1477–1491.