Shrub Encroachment Following Wetland Creation in Mixedgrass Prairie Alters Grassland Vegetation and Soil
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Shrub Encroachment Following Wetland Creation in Mixedgrass Prairie Alters Grassland Vegetation and Soil Regina Dahl1 Tommy Dalgaard2 Edward W. Bork ●
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Received: 21 May 2020 / Accepted: 17 October 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract Wetland decline under post-European settlement and land use change across western Canada has led to mitigation strategies, including wetland creation. Created wetlands can trigger environmental change, including woody species encroachment, in turn altering vegetation and soil. We quantify changes in shrub abundance from prior to wetland creation (1949) until 60 years later (2012) within a Mixedgrass ecosystem of the Verger watershed in Alberta, Canada. In addition, we compare remaining grassland with areas colonized by shrubland on similar ecosites for differences in (1) plant composition, including native and introduced flora, (2) herbage yield and forage accessibility for livestock, and (3) soil properties (surface organic depth, bulk density, mineral nitrogen (N), and carbon (C) concentration). Repeat photos show Shepherdia argentea shrublands increased from 0 to 88 ha (to 1.15% of study area) following wetland creation, with the greatest increase in the last 20 years. Relative to grasslands, shrublands had lower total plant diversity but greater presence of introduced plant species. Shrub patches were 94% lower in herbaceous production, with 77% of shrublands non-utilized by cattle, collectively leading to reduced grazing capacity. Relative to grasslands, shrublands had a thicker soil surface mulch layer, and where cattle were present, had increased mineral soil N and C. Overall, shrub encroachment following wetland creation has markedly altered vegetation and soils in this once grassland landscape, with negative impacts on native plant diversity, herbage production and forage accessibility, and has implications for the management of shrub encroachment. Keywords Carbon Forage accessibility Herbage production Native plant diversity Species invasion Soil nitrogen ●
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Introduction Encroachment of woody species into grasslands is a worldwide phenomenon (Archer et al. 1995; Ratajczak et al. 2012) and was described in detail for North American semiarid regions by Van Auken (2000). Changes from grassland to shrubland include progression from initial colonization, through suppression of the understory, and eventually transition to near monocultures of shrubs (D’Odorico et al. 2012). Several mechanisms have been implicated as causing
* Edward W. Bork [email protected] 1
Zum Heiligenplatz 1, 66663 Merzig, Germany
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Department of Agroecology, Aarhus University, Blichers Allé 20, Postboks 50, DK-8830 Tjele, Denmark
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Department of Agricultural, Food and Nutritional Science, University of Alberta, 410E Agriculture/Forestry Center, T6G 2P5 Edmonton, Alberta, Canada
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encroachment, including climatic alteration (MacDonald 1989), changes in atmospheric CO2 (Tjetjen et al. 2010), industrial n
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