Earthworm biomass and species diversity in windthrow sites of a temperate lowland forest

In temperate forests, disturbance by uprooting of trees is a key process in maintaining species richness and diversity. Nevertheless, very little is known about the changing role and abundance of earthworm communities in different windthrow microsites. The aim of the study was to find (i) whether single-tree uprooting causes significant changes in earthworm biomass and species composition and (ii) which changes in chemical and physical soil properties can be related to it. Twelve single-tree gap sites in an Ulmo-Fraxinetum aceretosum were selected, six sites locally dominated by beech (Fagus sylvatica) and six by poplar (Populus x euramericana). At each site, 7 microsites were sampled for soil chemical and soil physical properties: undisturbed soil beneath closed canopy, undisturbed soil beneath the gap in the canopy layer, the outer side of the pit, the inner side of the pit, the soil fallen from the mound into and away from the pit, and the mound itself. At six sites also earthworms were collected. The impact of microsite on earthworm biomass and species diversity was more important than the impact of tree species. A significant decrease in earthworm biomass and species number was detected from closed canopy over gaps to zones with soil disturbance and finally to windthrow mounds which never contained earthworms. The most pronounced reaction was the negative impact of uprooting on enclogeic biomass. Epigeic biomass or species number of any ecological group changed more moderately. Six years after uprooting, microsites with direct soil disturbance were still adverse for earthworms though some - epigeic - species could profit from the absence of competitive species. It is concluded that in temperate lowland forests, the early uprooting phases induce changes in earthworm communities due to changes in soil physical parameters and food availability.