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Session A3: Think Big: Adding Large Structures To Improve Ecosystem Health

Abstract: The Vindel River is one of the few freeflowing its entire catchment are part of the Natura 2000 network. The river was exploited for timber floating between 1850–1976; rapids in the main channel and tributaries below the alpine tree line were channelized to increase timber transport capacity. Side channels were cut off and the flow was concentrated to a single channel from which boulders and large wood were removed. Hence, previously heterogeneous environments were replaced by more homogeneous systems with limited habitat for riverine species. The Vindel River LIFE project (LIFE08 NAT/S/000266) works with the restoration of 25 tributaries in the Vindel River system. The project strives to alleviate the effects of fragmentation and channelization in affected rapids, to improve the quality of water and riparian habitats. The work has included the construction of over 1000 spawning grounds for brown trout, removal of 17 splash dams, the relocation of rocks into the channels, and the strategic placement of large boulders and dead wood in over 50 km of river. Follow up studies have been done in the channels that have been restored with “demonstration methods,” where previously best-practice restored reaches have been re-restored by adding large boulders and large wood (i.e., entire trees, including root wads) from adjacent upland to the channel. The demonstration restoration has generated wider and more complex streams, which in turn has led to more variable water flow and higher water levels. This will decrease the risk of erosion during high flow and reduce the risk of losing spawning areas. However, fish population data collected by electrofishing before and after restoration show very inconsistent results among tributaries. This highlights the need for considering potential catchment scale degradation and not only concentrating on reach scale problems in order to re-establish ecosystem health.
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