Long-term recovery of stream habitat structure and benthic invertebrate communities from in-stream restoration Original Research Article

Headwater streams channelized for water transport of timber in Finland are being restored to their pre-channelization state. The primary motivation is the enhancement of sport fisheries, but restoration probably has profound impacts also on other stream organisms. We assessed how such “single-goal” restorations affect benthic macroinvertebrate communities. We revisited the streams sampled by Laasonen et al. [Aquatic Conservation: Marine and Freshwater Ecosystems 8 (1998)] in the early 1990s when the streams had been recently restored. In 1997, the recovery period of these streams ranged from 4 to 8 years. Habitat structure among the stream types represented a distinct recovery gradient, with streams restored 1 month before sampling and natural streams being the endpoints of a gradient in moss cover (highest in natural, lowest in recently restored streams). Channelized streams supported a characteristic set of indicator species, whereas shifts in species composition between restored and natural streams were more gradual. Macroinvertebrate communities in unmodified streams changed little between the two surveys, whereas communities in restored streams had undergone considerable changes. In-stream restoration is an unpredictable disturbance, to which stream biota cannot have any evolved responses. Therefore, the relatively rapid recovery of habitat structure and macroinvertebrate communities in restored streams is encouraging. However, long-term monitoring of benthic communities in both restored and natural streams is needed to assess whether restoring rivers by these techniques will enhance the recovery of benthic biodiversity in boreal streams.