Recovery of macroinvertebrate communities from stream habitat restoration

1. Many streams channelized for timber floating in Finland are now being restored to their original condition. The most frequently used restoration structures are boulder dams, flow deflectors, excavations and channel enlargements. By increasing substrate heterogeneity and leaf litter retention, restoration may enhance the formation of detritivore-dominated macroinvertebrate assemblages. In this study, macroinvertebrate communities in streams with differing recovery periods (from 0 to 16 years) from restoration, were compared with those in channelized and near-pristine streams. 2. Water depth and current velocity were lower, and relative bed roughness higher in restored than in dredged channels. Moss cover was negligibly low in recently restored streams, but mosses had recovered well within three years from restoration. The standing stock of leaf litter was lower than in natural streams, but in most cases higher than in channelized streams. 3. Abundances of all invertebrates were highest in natural streams and lowest in streams restored 1 month before sampling. All other restored streams had abundances comparable to, or slightly lower than, those in channelized streams. There was a tendency toward higher abundances of shredders with a long recovery period, but streams restored 8 or 16 years ago still contained relatively sparse shredder populations. 4. Canonical Correspondence Analysis of the October data could be attributed to among-site variation in habitat hydraulics, moss cover and leaf litter. Dredged channels with high velocities and low bed profiles, and natural streams with high retention efficiency were the end points of this gradient. There was little indication of macroinvertebrate assemblages approaching pristine conditions with a longer recovery period. 5. Enhanced litter retention increases the capacity of restored streams to support high abundances of detritivorous invertebrates. Indirectly, restoration may also benefit animals that are not dependent on detrital food. Clearly, macroinvertebrates and other non-vertebrate components of the stream biota should be given a higher priority in the design and execution of stream restoration programmes. (C) 1998 John Wiley & Sons, Ltd.