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

Lotta Ström (1) , Roland Jansson (1) , Christer Nilsson (1) , Mats E. Johansson (2) , Shaojun Xiong (3)

1 Department of Ecology and Environmental Science [Umeå]
2 County Administration of Västerbotten
3 Unit of Biomass Technology and Chemistry

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 were inert in their response to new hydrologic conditions. After 6 years, biomass of transplanted turfs did not differ statistically 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. Less area available to riparian plants is expected to result in fewer species, even if no species lose their hydrologic niches. 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 non-linear fashion to external pressures.

Mots clés: Life Sciences

Lotta Ström, Roland Jansson, Christer Nilsson, Mats E. Johansson, Shaojun Xiong. Hydrologic effects on riparian vegetation in a boreal river: an experiment testing climate change predictions. Global Change Biology, 2010, 17 (1), pp.254. ⟨10.1111/j.1365-2486.2010.02230.x⟩. ⟨hal-00599516⟩