Litter breakdown and invertebrate association with three types of leaves in a temperate rainforest stream

Coniferous forests predominate in the boreal and western North American regions, yet most studies of litter breakdown in streams have focussed on litter from deciduous trees. We studied breakdown rates and invertebrate colonization of leaf litter from two common conifer species (western red cedar and western hemlock), along with red alder (a common riparian, deciduous species) in a small, coastal rainforest stream of British Columbia during two seasons (summer, autumn). Alder lost mass 40- 100% more quickly than the two conifer species. During summer, hemlock lost mass significantly more quickly than cedar, but this trend was reversed in autumn. Measures of relative lignin concentration and carbon content did not differ signifi- cantly between litter species. Nitrogen content was nearly twice as high in alder as the two coniferous species. Decomposition rates were positively related to initial nitrogen content of the litter and negatively related to C:N ratio. Invertebrate species associated with particular types of leaf litter were clearly distinct during the autumn, but less so during summer. In the autumn, invertebrate assemblages on alder and cedar were dis- tinguished from those on hemlock by the high numbers of detritivores on the former litter types. Cedar had more mayflies and fewer orthoclad midges than alder. There were no significant differences between litter types in densities of any invertebrate taxon per gram of leaf tissue, although alder always had higher numbers.