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Data and code from: Invertebrate responses one year after beaver reintroduction

Sworder, Oliver John12; Jackson, Michelle1; Cameron, Thomas3

Published Nov 03, 2026 on Dryad. https://doi.org/10.5061/dryad.15dv41pc0

Data files

Nov 03, 2026 version files 1.20 MB

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Abstract

Reintroductions of Eurasian beavers (Castor fiber) are gathering pace across the UK after a 400-year local extinction. Amid substantial global invertebrate biodiversity declines, the reintroduction of beavers poses opportunities for gains both for invertebrate and beaver populations, since beavers are “ecosystem engineers”: they create substantial changes in hydrology and therefore instream and riparian habitats. Previous studies on beavers (both C. canadensis in N. America and C. fiber in Europe) have primarily used space-for-time substitutions, due to the lack of opportunity to examine a controlled before/after approach. Other studies have focused on North America or mainland Europe and have not typically included both freshwater and terrestrial invertebrates, or quantified changes in invertebrate communities using biomass. To fill these knowledge gaps, we examined invertebrate communities, algal concentrations, and water quality one year before and after the reintroduction of beavers to enclosures in 2023 at Spains Hall Estate, Essex. We found that beaver introduction increased terrestrial invertebrate abundance and species richness, but had no significant impacts on freshwater invertebrate richness, abundance, or biomass at the community level. On a finer scale, beavers significantly impacted freshwater indicator taxa abundance and biomass and shifted functional feeding group biomass. This was mediated by abiotic shifts, including an increase in dissolved oxygen content throughout the stream and increases in nitrate concentrations in the water near the dams. Downstream, nitrate was nearly completely filtered out from the water following beaver introduction. Our study shows that impacts are felt at least a kilometer downstream of beaver dams, and that beavers’ benefits to water quality and invertebrate biodiversity start to accumulate within only a year. These findings highlight the ecological value of beaver reintroductions and support their consideration in UK conservation planning.