Ecological Applications, 21(6), 2011, pp. 1950–1961 Ó 2011 by the Ecological Society of America Twenty years of stream restoration in Finland: little response by benthic macroinvertebrate communities PAULIINA LOUHI, 1,6 HEIKKI MYKRA ¨ , 2 RIKU PAAVOLA, 3 ARI HUUSKO, 4 TEPPO VEHANEN, 5 AKI MA ¨ KI-PETA ¨ YS, 5 AND TIMO MUOTKA 1,2 1 University of Oulu, Department of Biology, FIN-90014 University of Oulu, Finland 2 Finnish Environment Institute, FIN-90014 University of Oulu, Finland 3 Oulanka Research Station, University of Oulu, FIN-93999 Kuusamo, Finland 4 Finnish Game and Fisheries Research Institute, Kainuu Fisheries Research, FIN-88300, Paltamo, Finland 5 Finnish Game and Fisheries Research Institute, Oulu Game and Fisheries, FIN-90570 Oulu, Finland Abstract. The primary focus of many in-stream restoration projects is to enhance habitat diversity for salmonid fishes, yet the lack of properly designed monitoring studies, particularly ones with pre-restoration data, limits any attempts to assess whether restoration has succeeded in improving salmonid habitat. Even less is known about the impacts of fisheries-related restoration on other, non-target biota. We examined how restoration aiming at the enhancement of juvenile brown trout (Salmo trutta L.) affects benthic macroinvertebrates, using two separate data sets: (1) a before after control impact (BACI) design with three years before and three after restoration in differently restored and control reaches of six streams; and (2) a space–time substitution design including channelized, restored, and near- natural streams with an almost 20-year perspective on the recovery of invertebrate communities. In the BACI design, total macroinvertebrate density differed significantly from before to after restoration. Following restoration, densities decreased in all treatments, but less so in the controls than in restored sections. Taxonomic richness also decreased from before to after restoration, but this happened similarly in all treatments. In the long-term comparative study, macroinvertebrate species richness showed no difference between the channel types. Community composition differed significantly between the restored and natural streams, but not between restored and channelized streams. Overall, the in-stream restoration measures used increased stream habitat diversity but did not enhance benthic biodiversity. While many macroinvertebrates may be dispersal limited, our study sites should not have been too distant to reach within almost two decades. A key explanation for the weak responses by macroinvertebrate communities may have been historical. When Fennoscandian streams were channelized for log floating, the loss of habitat heterogeneity was only partial. Therefore, habitat may not have been limiting the macroinvertebrate communities to begin with. Stream restoration to support trout fisheries has strong public acceptance in Finland and will likely continue to increase in the near future. Therefore, more effort should be placed on assessing restoration success from a biodiversity perspective using multiple organism groups in both stream and riparian ecosystems. Key words: BACI design; benthic macroinvertebrates; fisheries restoration; long-term effects; restoration assessment; stream habitat enhancement. INTRODUCTION During the last two decades, restoration ecology has emerged as a novel scientific discipline with substantial applied importance for environmental managers and decision makers (Ormerod 2003). Few other branches of ecology attract as much interest among the public as does restoration ecology. Ecosystem restoration has raised great optimism among both environmental managers and academics, not only as a way of mitigating the detrimental impacts of humans on natural ecosystems, but even as a means of preventing the loss of biodiversity (Wilson 1992). Running waters are among the most impacted ecosystems in the world, and restoration of degraded rivers and streams is a key component of many freshwater management programs. For example, the EU Water Framework Directive requires member countries to target restoration mea- sures on streams that fail to reach good ecological status by year 2015. It is therefore alarming to notice that more than 90% of stream restorations in the United States, Australia, and Europe are still not monitored beyond Manuscript received 26 March 2010; revised 16 August 2010; accepted 26 August 2010. Corresponding Editor: C. Nilsson. For reprints of this Invited Feature, see footnote 1, p. 1925. 6 E-mail: pauliina.louhi@oulu.fi 1950 INVITED FEATURE Ecological Applications Vol. 21, No. 6