Twenty years of stream restoration in finland: Any benefits?

During last few decades, a growing sensitivity toward stream habitat degradation has resulted in a number of stream restoration projects worldwide. These are often based on the assumption that increasing the structural heterogeneity will also increase biological diversity. In Finland, thousands of kilometres of streams were channelized for timber transportation in the 19^th and 20^th centuries, and now these streams are being rehabilitated to their pre-channelization state. In this study, we assessed whether increasing stream bed heterogeneity is beneficial for benthic invertebrates. First, we used Before-After-Control-Impact (BACI) design with data from three years before (1999-2001) and three years after (2001-2003) restoration for six replicate streams, each with randomly-placed restored and control sections. For a longer-term assessment, we sampled streams restored in the early 1990s and compared these to channelized and natural, unmodified streams. In the short-term BACI-approach, macroinvertebrate communities did not show any positive responses to restoration. Furthermore, after a recovery period of almost twenty years, restored and channelized streams supported almost the same variety of species as did the natural streams. Therefore, our results suggest that streambed restoration may have little impact on invertebrate diversity, and a wider, watershed-scale approach to restoration is needed.