Population development of ground beetles (Carabidae) and epigeal spiders (Arachnidae) five years after conversion towards organic farming in Northern Germany. [German]Original Title Populationsentwicklung von Laufkafern (Carabidae) und epigaisch lebenden Spinnen (Arachnidae) funf Jahre nach der Umstellung auf den Okologischen Landbau in Norddeutschland.

摘要

In 2001 (first year of conversion) and 2005 the population of the ground beetle and epigeal spiders have been assessed on the 600 ha large experimental farm of the Institute of Organic Farming in Northern Germany. In both years the same 14 permanent grassland, 24 crop land and 12 non-agricultural (biotopes) locations have been used to catch the epigeal fauna while spring/summer with Barber traps. Every week the catches have been collected. In the year 2005 21,243 ground beetles (resp. 7.507 in 2001) of 71 species (2001: 63) and 8.083 spiders (2001: 16.040) with 71 species (2001: 88) were catched. This shows that the numbers of individuals and species of beetle have been increased while spiders decrease. Additionally there were substantial changes in the species composition. In 2005 some species could not be found again, others have been catched first time. The habitat demands of the ground beetles have been improved, particularly for species who like open space, low moisture and dry conditions species, with the conversion towards organic farming. The habitat conditions for epigeal spiders have been decreased, mainly because of the change of some plot from fallow land towards crop land. This shows the importance of fallow land for spiders. Intensive fallow land for green manuring and weed control in organic farming can not be compared with fallow land in conventional farming (set aside land). Both farming systems have advantages and disadvantages for epigeal fauna. With the change of the agricultural policy to reduce the share of set aside crop land to zero, organic farming has an advantage.