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Hydrologic effects on riparian vegetation in a boreal river: an experiment testing climate change predictions

Authors

  • LOTTA STRÖM,

    1. Landscape Ecology Group, Department of Ecology and Environmental Science, Umeå University, SE-901 87 Umeå, Sweden
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  • ROLAND JANSSON,

    1. Landscape Ecology Group, Department of Ecology and Environmental Science, Umeå University, SE-901 87 Umeå, Sweden
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  • CHRISTER NILSSON,

    1. Landscape Ecology Group, Department of Ecology and Environmental Science, Umeå University, SE-901 87 Umeå, Sweden
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  • MATS E. JOHANSSON,

    1. Landscape Ecology Group, Department of Ecology and Environmental Science, Umeå University, SE-901 87 Umeå, Sweden
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    • 1Present address: Mats E. Johansson, County Administration of Västerbotten, SE-901 86 Umeå, Sweden.

  • SHAOJUN XIONG

    1. Landscape Ecology Group, Department of Ecology and Environmental Science, Umeå University, SE-901 87 Umeå, Sweden
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    • 2Present address: Shaojun Xiong, Unit of Biomass Technology and Chemistry, Swedish University of Agricultural Sciences, SE-904 03 Umeå, Sweden.


L. Ström, tel. +46 90 7867151, fax +46 90 7867860, e-mail: lotta.strom@emg.umu.se

Abstract

Climate change is expected to alter the magnitude and variation of flow in streams and rivers, hence providing new conditions for riverine communities. We evaluated plant ecological responses to climate change by transplanting turfs of riparian vegetation to new elevations in the riparian zone, thus simulating expected changes in water-level variation, and monitored the results over 6 years. Turfs moved to higher elevations decreased in biomass and increased in species richness, whereas turfs transplanted to lower elevations gained biomass but lost species. Transplanted plant communities responded slowly to the new hydrologic conditions. After 6 years, biomass of transplanted turfs was statistically indistinguishable from target level controls, but species richness and species composition of transplants were intermediate between original and target levels. By using projections of future stream flow according to IPCC climate change scenarios, we predict likely changes to riparian vegetation in boreal rivers. Climate-driven hydrologic changes are predicted to result in narrower riparian zones along the studied Vindel River in northern Sweden towards the end of the 21st century. Present riparian plant communities are projected to be replaced by terrestrial communities at high elevations as a result of lower-magnitude spring floods, and by amphibious or aquatic communities at low elevations as a result of higher autumn and winter flows. Changes to riparian vegetation may be larger in other boreal climate regions: snow melt fed spring floods are predicted to disappear in southern parts of the boreal zone, which would result in considerable loss of riparian habitat. Our study emphasizes the importance of long-term ecological field experiments given that plant communities often respond slowly and in a nonlinear fashion to external pressures.

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