Leaf litter breakdown rates in boreal streams: does shredder species richness matter?

1. Leaf litter breakdown rates were assessed in 23 boreal streams of varyin g size (first-seventh order) in central and northern Sweden. 2. Shredders were most abundant in small streams, while shredder species ri chness showed a hump-shaped relationship with stream order, with most speci es in fourth order streams. 3. In a partial least-squares regression analysis, year, water temperature, shredder species richness and shredder abundance were those factors correl ating most strongly with leaf breakdown rates. Shredder species richness wa s more strongly correlated with leaf lifter breakdown rates than shredder a bundance, and shredder biomass showed no such correlation. 4. These data suggest that shredder species richness is an important variab le in terms of leaf litter dynamics in streams.