Shredder guilds in three Danish forest streams contrasting in forest type

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. Temperature was lowest in the conifer stream reflecting the high degree of shading during winter. The standing stock of coarse particulate 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 Nemoura flexuosa 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 plecopteran 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. flexuosa in the conifer stream than in the deciduous streams. Total shredder guild production was 5982 mg m -2 yr -1 in the beech stream, 4681 mg m -2 yr -1 in the mixed deciduous stream and 1310 mg m -2 yr -1 in the conifer stream. Our results thus suggest that forest stream shredder guilds are influenced 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.