Impacts of Eucalyptus globulus plantations on Atlantic streams: changes in invertebrate density and shredder traits

Abstract

Eucalyptus globulus plantations are spreading in the northern areas of the Iberian Peninsula, substituting natural deciduous riparian vegetation. Whereas laboratory studies with leaf litter of this species have found detri- mental effects on detritivorous species, fi eld studies did not support a strong negative effect. Hence, we compared taxon richness, density and biomass of macroinvertebrate assemblages inhabiting streams fl owing through eucalypt plantations with those fl owing through native oak forest. Moreover, we compared traits of leaf eating macroinver- tebrates (shredders) between the two types of streams. Streams fl owing through eucalypt plantations had lower taxon richness, density and biomass of total invertebrates (and particularly of shredders) compared to those fl owing through native forests. Large shredder taxa, such as Echinogammarus spp. & Limnephilidae, showed a signifi cant negative response (in terms of abundance and biomass) to eucalypt cover whereas smaller taxa displayed similar distribution patterns in both habitat types. The grazer Habroleptoides sp. was the only taxon displaying higher den- sities in eucalypt sites, which might be explained by the reduction of competition/predation by other large shred- ders. Shredders at eucalypt sites showed the following traits: small maximum body size, short life cycles, few re- production cycles per year, active dispersal, and ability to feed on food of lower quality. The shredder assemblages in the eucalypt sites shared similarities with those typical of locations where production is limited due to acidity or oligotrophy of the waters. One stream drained both native and eucalypt forest, but the density and biomass of shredders in the eucalypt (downstream) site was very similar to those found in native streams. This result supports the idea that transport of native organic matter from upstream parts of the basin can maintain native invertebrate assemblages in downstream parts where the land use has been changed.