Assessing impact of eucalyptus plantations on benthic macroinvertebrate communities by a litter exclusion experiment

Abstract

To test whether leaf litter from eucalyptus plantations affects stream macroinvertebrate communities, we manipulated litter inputs into a small headwater tributary of the Aguera stream (northern Spain) running under mixed deciduous forests. Three contiguous 50 m long reaches were used: the upstream reach was left as a control (site C), whereas the two downstream sites were covered by 1 mm mesh nets to avoid natural litter inputs, and twice a month received litter collected at a deciduous forest (site D, mid) or a eucalyptus plantation (site E, downstream). Benthic Surber samples were taken from the three sites before and after the treatment and density, biomass and structure of the community were compared. Density and biomass of macroinvertebrates did not differ among sites before the treatment. Total density and biomass of macroinvertebrates increased in all the sites during the experimental period but most considerably at the site were deciduous forest inputs were simulated (station D). At the end of the experiment shredders were significantly less abundant at site E (eucalyptus) than at site D (deciduous). In addition, shredder density and biomass per total organic matter amount and per total leaf amount became higher at site D. In conclusion, these results suggest a subtle negative impact of eucalyptus litter on stream macroinvertebrate communities, especially on shredders.