Abstract
Potential for habitat restoration is increasingly used as an argument for reintroducing ecosystem engineers. Beaver have well known effects on hydromorphology through dam construction, but their scope to restore wetland biodiversity in areas degraded by agriculture is largely inferred. Our study presents the first formal monitoring of a planned beaver-assisted restoration, focussing on changes in vegetation over 12years within an agriculturally-degraded fen following beaver release, based on repeated sampling of fixed plots. Effects are compared to ungrazed exclosures which allowed the wider influence of waterlogging to be separated from disturbance through tree felling and herbivory. After 12years of beaver presence mean plant species richness had increased on average by 46% per plot, whilst the cumulative number of species recorded increased on average by 148%. Heterogeneity, measured by dissimilarity of plot composition, increased on average by 71%. Plants associated with high moisture and light conditions increased significantly in coverage, whereas species indicative of high nitrogen decreased. Areas exposed to both grazing and waterlogging generally showed the most pronounced change in composition, with effects of grazing seemingly additive, but secondary, to those of waterlogging.Our study illustrates that a well-known ecosystem engineer, the beaver, can with time transform agricultural land into a comparatively species-rich and heterogeneous wetland environment, thus meeting common restoration objectives. This offers a passive but innovative solution to the problems of wetland habitat loss that complements the value of beavers for water or sediment storage and flow attenuation. The role of larger herbivores has been significantly overlooked in our understanding of freshwater ecosystem function; the use of such species may yet emerge as the missing ingredient in successful restoration.
Highlights
Agricultural activity has impacted most natural ecosystems, often at the expense of their biological and physical diversity (Foley et al, 2005; Strayer and Dudgeon, 2010)
Our study offers an in-depth perspective of the ecological effects of dam building, felling and grazing by beaver introduced explicitly for restoration purposes, based on long-term monitoring
We focus on changes in vegetation and ask ; i) how plant species richness and composition is modified by direct beaverinduced disturbance or indirectly through water level rise, and ii) if beaver are a suitable tool for restoring agriculturally-degraded wetlands
Summary
Agricultural activity has impacted most natural ecosystems, often at the expense of their biological and physical diversity (Foley et al, 2005; Strayer and Dudgeon, 2010). Freshwaters, despite covering b1% of Earth's surface, support disproportionately high biodiversity, including around 12% of the world's known animal species (Collen et al, 2014; Gleick, 1998). These systems can act as carbon sinks (Kayranli et al, 2010), or, by enhancing storage and slowing release of water, can both attenuate flooding and alleviate water shortages (Burchsted et al, 2014). Restoration projects often fail to meet expectations, in-spite of the considerable resources allocated to their planning, execution and monitoring
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