Benthic invertebrate communities in six Danish forest streams: Impact of forest type on structure and function

I investigated the impact of riparian vegetation type on stream invertebrate communities in six Danish forest streams during the period 1992-1993. Two of the streams ran through beech forest Fagus sylvatica, two through mixed, mainly deciduous forest, and two through conifer plantations. Algal biomass and detritus standing stock differed significantly depending on forest type: In mixed deciduous forest streams algal biomass was higher and detritus standing stock lower than in beech and conifer forest streams. Benthic invertebrate community composition was functionally similar in all streams, with detritivores comprising >80% by numbers of the community. Grazer abundance was low in all streams. Shredder abundance in the four deciduous streams was significantly correlated to coarse detritus standing stock. When taking into account both quantitative and qualitative POM parameters for all six streams combined, shredder abundance correlated significantly to the amount of CPOM. There were significantly more invertebrates with a >2 yr life cycle in the conifer and beech forest streams than in the mixed forest streams, probably reflecting the larger and more stable food resource. For all streams combined there was a significant correlation between predator abundance and the abundance of potential prey. My findings suggest that Danish forest streams are regulated by "bottom-up control" at all trophic levels within the invertebrate community, and hence that forest type can structure benthic communities in forest streams.