THE INFLUENCE OF RIPARIAN MANAGEMENT ON THE HABITAT STRUCTURE AND MACROINVERTEBRATE COMMUNITIES OF UPLAND STREAMS DRAINING PLANTATION FORESTS

1. Habitat features and macroinvertebrate communities were surveyed in 66 predominantly upland streams throughout Wales and Scotland to assess the efficacy of riparian management (as 'buffer strips') in protecting stream resources during commercial forestry. 2. Habitat data were reduced by principal components analysis (PCA). Macro-invertebrates in the stream margins and riffles were considered separately, and ordination of the community data was by DECORANA. 3. Habitat gradients recognized between the streams from PCA included trends in size, ionic strength, acidity, substratum type, and in the characteristics of marginal habitats. The latter represented a change from margins dominated by 'soft' vegetation features to margins composed of 'hard' features such as tree roots, rock and stones. 4. Marginal habitat characteristics differed between streams with different riparian management. Streams with 'harder' margins occurred where the banks were covered with either conifers or broadleaves. Streams with 'softer' margins occurred in seminatural moorland, and where a 'buffer strip' of moorland vegetation had been retained along the stream at the planting stage. Streams in conifer forest in which a riparian buffer strip had been cleared retrospectively were intermediate. 5. For any given pH, aluminium concentrations were significantly higher in streams draining conifer catchments than in streams draining whole catchments of moorland or deciduous woodland. This effect occurred irrespective of buffer strips in conifer catchments. 6. The taxon richnesses of Ephemeroptera, Plecoptera, Trichoptera and all taxa combined, in both riffles and margins, declined significantly with increasing acidity and aluminium concentration. Primary ordination axes from both habitats correlated with taxon richness, and hence also with pH and aluminium. However, there were significant effects on the ordination scores by riparian management, due mostly to reduced taxon richnesses in conifer sites without buffer strips. Significant effects remained even after accounting for increased aluminium concentration at conifer sites. 7. We conclude that gradients related to acidity are dominant correlates with the composition of invertebrate communities in upland British streams. However, riparian management can influence stream habitat structure and, to some extent, the macroinvertebrate fauna in the stream margins. Buffer strips consisting of broadleaf trees and moorland/grassland vegetation have different effects on taxonomic composition and abundance. They are most effective when implemented at the planting stage, though further data are required to assess succession with time where buffer strips have been cleared retrospectively.