1. Growth and emergence of the acidification tolerant stonefly Leuctra nigra were studied in four coniferous forest streams with contrasting pH. Invertebrate samples were taken bimonthly during May 1997 to April 1998. Emerging L. nigra were captured in two of the streams during April to July 1998 using pyramidal emergence traps. In addition, a laboratory experiment was conducted to evaluate growth of L. nigra in response to variations in food quality (neutral or acid conditioned leaves) and water pH. 2. The invertebrate community in low pH streams had lower diversity and density compared with neutral streams. Abundance of L. nigra was also lower, despite the dominance of this stonefly in the invertebrate community in the acidic streams. 3. Secondary production of L. nigra was 2.04 and 3.07 g DW m–2 year–1 in the neutral streams compared with 1.02 and 1.27 g DW m–2 year–1 in the acidic streams. The P/B ratio differed only slightly among streams. 4. More adult L. nigra emerged in the neutral stream compared with the acidic stream, despite the density of the pre‐emerging fifth instar nymphs of L. nigra being similar in the two streams. Adult size (expressed as wing length) and female fitness were also significantly greater in the neutral stream. 5. Laboratory growth of L. nigra nymphs was significantly lower when fed acid conditioned alder leaves rather than neutral conditioned leaves. There was no difference in growth when nymphs were fed neutral conditioned leaves in acid and neutral water. 6. Our study shows multiple, sub‐lethal effects on life history of the acidification tolerant stonefly L. nigra in coniferous streams with low pH. The results suggest that these effects could be mediated primarily by low food quality. These findings add to the existing evidence that coniferous plantation forestry has a negative impact on stream ecosystems.

With 4 figures and 7 tables Abstract: We investigated the impact of riparian vegetation type on shredder guilds in three similarly sized Danish forest streams during the period 1992-1994. One stream drained beech forest (Fagus sylvatica L.), one drained mixed, mainly deciduous forest, and one drained conifer plantations. Te mperature was lowest in the conifer stream reflecting the high degree of shading during winter. The standing stock of coarse par ticulate organic matter (CPOM) differed only slightly among streams, although CPOM quality differed more markedly. Leaf litter respiration rates differed significantly among streams, being lowest in the conifer stream. The shredder guild was comprised of 9 species, of which only Nemourajlexuosa AUBERT. was present in all 3 streams. In terms of biomass, the dominant shredders were the amphipod Gammarus pulex L. and the trichopteran Sericostoma personatum SP. in the deciduous streams, and the plecop teran Nemurella picteti KLP. in the conifer stream. Shredder biomass was significantly higher in the two deciduous streams than in the conifer stream. The condition index expressed as mass : head width ratio was significantly lower for Leuctra nigra (OLV.) and N. jlexuosa in the conifer stream than in the deciduous streams. Total shredder guild production was 5982 mg m-2 yr-I in the beech stream, 4681 mg m-2 yr-I in the mixed deciduous stream and 1310 mg m-2 yr-I in the conifer stream. Our results thus suggest that forest stream shredder guilds are infl uenced by forest type, and apparently attributable to a combination of factors including water temperature and chemistry, and the quality of the available food resource. If low secondary production of the shredder guild is a general feature of streams draining conifer plantation forest, it could have important implications for higher trophic levels and ecosystem functioning.