Impacts of Hydrological Restoration on Lowland River Floodplain Plant Communities

This is a repository copy of Impacts of hydrological restoration on lowland river floodplain plant communities. White Rose Research Online URL for this paper: http://eprints.whiterose.ac.uk/161050/ Version: Published Version Article: Richards, D.R., Moggridge, H.L., Warren, P.H. orcid.org/0000-0002-0550-0886 et al. (1 more author) (2020) Impacts of hydrological restoration on lowland river floodplain plant communities. Wetlands Ecology and Management. ISSN 0923-4861 https://doi.org/10.1007/s11273-020-09717-0 Reuse This article is distributed under the terms of the Creative Commons Attribution (CC BY) licence. This licence allows you to distribute, remix, tweak, and build upon the work, even commercially, as long as you credit the authors for the original work. More information and the full terms of the licence here: https://creativecommons.org/licenses/ Takedown If you consider content in White Rose Research Online to be in breach of UK law, please notify us by emailing [email protected] including the URL of the record and the reason for the withdrawal request. [email protected] https://eprints.whiterose.ac.uk/ Wetlands Ecol Manage https://doi.org/10.1007/s11273-020-09717-0 (0123456789().,-volV)( 0123456789().,-volV) ORIGINAL PAPER Impacts of hydrological restoration on lowland river floodplain plant communities Daniel R. Richards . Helen L. Moggridge . Philip H. Warren . Lorraine Maltby Received: 22 July 2019 / Accepted: 5 March 2020 Ó The Author(s) 2020, corrected publication 2020 Abstract Many lowland floodplain habitats have presence of indicator species from the target flood- been disconnected from their rivers by flood defence plain grazing marsh plant communities. The lowering banks. Removing or lowering these banks can rein- of the flood banks increased the frequency of flood state regular flooding and thus restore these important events, from an estimated average of 1.7 floods per wetland plant communities. In this study we analyse year to 571 floods per year. The increased flooding changes in wetland hydrology and plant community significantly increased the proportion of time that the composition following the lowering of flood defence wetland was submerged, and the heterogeneity in banks at a floodplain of the River Don in the United hydrological conditions within the floodplain. There Kingdom (UK). The aim of the restoration project was were significant differences in composition between to improve the quality of ‘‘floodplain grazing marsh’’ the pre-restoration and restored plant communities. habitat, which is a group of wetland communities that Plants with traits for moisture tolerance became more are of conservation interest in the UK. We analyse abundant, although the communities did not contain changes in species richness and community composi- significantly more ‘target’ floodplain grazing marsh tion over a period of 6 years, and compare the species at the end of the study period than prior to restoration. Colonisation by floodplain grazing marsh species may have been limited because environmental Electronic supplementary material The online version of conditions were not yet suitable, or because of a this article (https://doi.org/10.1007/s11273-020-09717-0) con- shortage of colonising propagules. While the desired tains supplementary material, which is available to authorized target plant community has not been achieved after users. 5 years, it is encouraging that the community has D. R. Richards (&) changed dynamically as a result of hydrological Singapore-ETH Centre, ETH Zurich, Singapore, changes, and that moisture-tolerant species have Singapore increased in occurrence. Over the next few decades, e-mail: [email protected] the restored flood regime may cause further environ- D. R. Richards Á P. H. Warren Á L. Maltby mental change or colonisation events, thus helping Department of Animal and Plant Sciences, The University increase the occurrence of desired floodplain grazing of Sheffield, Sheffield, UK marsh indicator species. H. L. Moggridge Department of Geography, The University of Sheffield, Keywords Functional trait Á Wetland restoration Á Sheffield, UK Hydrological restoration 123 Wetlands Ecol Manage Introduction habitat patches that have been cleared by disturbances (Gurnell et al. 2006). Natural floodplains are a threatened habitat in Europe; There is increasing interest in reversing the degra- it has been estimated that up to 90% of the historical dation of floodplains through restoration projects that floodplain area has been converted to agricultural or reconnect rivers and floodplains hydrologically urban use (Tockner and Stanford 2002). Many low- (Zsuffa and Bogardi 1995; Pedersen et al. 2007; land river floodplains are no longer connected hydro- Toogood et al. 2008; Schaich et al. 2010; Gonzalez logically to their adjacent floodplains, as flood banks et al. 2015). Such ‘‘restoration’’ projects do not have been constructed to prevent flooding (Jungwirth typically aim to reinstate historical communities, as et al. 2002). The disconnection of rivers and flood- the historical baseline is rarely known and can be hard plains through flood bank construction has led to to define due to long histories of human use (Hilder- degradation of floodplain wetland biodiversity (Tock- brand et al. 2005). Instead, restoration is used as a ner and Stanford 2002). synonym for altering degraded ecological communi- Flooding is important in structuring plant commu- ties into those that are perceived as more desirable. In nity composition at multiple spatial scales; within the United Kingdom (UK), conservationists have habitat patches, across larger mosaics, and between attempted to restore floodplain marshes that are floodplain wetlands at the landscape scale. At the comprised of semi-natural wet grasslands or mire patch scale, the local performance of different species plant communities; these habitats are referred to as depends on their environmental tolerances and ability floodplain grazing marshes (Mountford 1994; Mount- ¨ to compete with each other (Keddy 1992;Hardtle et al. ford et al. 2006). Floodplain grazing marsh is found 2006). Competition and environmental tolerances across North-West Europe, and provides habitat to a have interacting effects on performance, because range of wetland birds, plants, and invertebrates environmental conditions affect the balance of com- (Mountford et al. 2006). The restoration and creation petition between species (Toogood et al. 2008). of floodplain grazing marsh has been a conservation Species that are highly competitive under dry condi- priority for the UK Government for over 20 years tions (referred to here as ‘‘competitive specialists’’ (JNCC 1995) and remains of interest for biodiversity (Grime et al. 1995)) may be negatively affected by conservation and carbon storage (Sozanska-Stanton flood events; for example if they cannot tolerate root et al. 2016). aeration stresses (Gowing & Spoor 1998), or are easily Floodplain restoration projects commonly target damaged by flood disturbance (Bornette and Amoros particular plant species and communities (Matthews 1996). More frequent flooding may therefore benefit and Spyreas 2010), and aim to create the hydrological species that are more flood-tolerant, by decreasing conditions that these species require (Wheeler et al. competition from competitive specialists (Lenssen 2004). There are relatively few cases where the et al. 2004). At the scale of floodplain wetland impacts of floodplain restoration projects on hydrol- mosaics, spatial variation in flood duration and ogy and plant community composition have been frequency creates heterogeneity in hydrological con- analysed and documented (Zedler 2000; Schaich et al. ditions. Hydrological heterogeneity enhances the 2010). Previous studies have shown that plant com- overall biodiversity of floodplain mosaics by main- munities can shift rapidly following the implementa- taining suitable conditions for a diverse range of tion of restoration strategies (Toogood and Joyce species with different niches (Junk et al. 1989; Ward 2008), but that communities often do not develop et al. 2002). Across floodplain landscapes, flood towards the desired target communities following events allow connectivity between different wetland hydrological restoration, at least over the * 5 year patches. Flood water can transport plant matter and timespans during which projects are studied (Trow- seeds from habitats elsewhere in the river network bridge 2007; Matthews and Spyreas 2010). There are ¨ (Holzel and Otte 2001; Gerard et al. 2007), thus adding several ecological mechanisms which can constrain or novel species to the local pool (Moggridge and alter the trajectory of plant community development Gurnell 2010). This process may be important in (Trowbridge 2007; Matthews and Spyreas 2010). maintaining the presence of species across a land- First, the presence of highly competitive species may scape, for example by allowing recolonisation of prevent desirable wetland species from establishing, 123 Wetlands Ecol Manage even if hydrological conditions are suitable (Ho and Methods Richardson 2013). Second, there may be environmental factors other than hydrology that impact commu- Overview of the Fishlake restoration project nity composition, such as grazing pressure (Schaich et al. 2010) or nutrient levels (Donath et al. 2003). The Humberhead Levels were once the third largest Finally, desirable species may not be able to rapidly wetland in England (Rotherham and Harrison 2006), colonise the site by dispersal, even if environmental

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