REMOVAL OF THE INVASIVE SHRUB, LONICERA MAACKII, FROM RIPARIAN FORESTS INFLUENCES HEADWATER STREAM BIOTA AND ECOSYSTEM FUNCTION

摘要

Riparian forests and streams are interlinked by cross-system subsidies and alterations of the terrestrial environment can have substantial effects on aquatic biota and ecosystem function. In the Midwestern USA, the exotic shrub Lonicera maackii (Amur honeysuckle) has successfully invaded many riparian habitats, creating near-monocultures in some locations. This terrestrial invasion has strong potential to modify cross-system subsidies and impact stream ecosystems. We removed L. maackii from a riparian forest to assess impacts on the aquatic environment. In August 2010, removal occurred along a 150m stream reach, 10m downstream of a non-removal reach, before natural leaf senescence. Over 74 days, in-stream leaf litter [organic matter (OM)] was collected weekly from plots located in riffles (five/reach). Benthic algal biomass, above stream canopy cover, and macroinvertebrate density were measured for 18 months. L. maackii removal was associated with decreased canopy cover and a significant increase in total in-stream leaf OM in early autumn (P ＜ 0.05). Removal also differentially influenced the timing and abundance of specific leaf litter genera within the stream (P ＜ 0.05). Macroinvertebrate density was significantly higher in the removal reach, especially during autumn 1 year after removal (P=0.0294). In both reaches, macroinvertebrate density peaks lagged behind benthic algal biomass peaks. In summary, the removal of an invasive riparian shrub influenced the timing, deposition, quality and abundance of leaf litter habitat into a headwater stream, ostensibly driving bottom-up effects on aquatic primary producer biomass and the macroinvertebrate community.