Spiders (Araneae) as subtle indicators for successional stages in peat bogs

Assemblages of epigeic spiders were studied in the Dubringer Moor (Saxony, Germany) in 2012 by pitfall-trapping. The Dubringer Moor is a percolation mire that includes (sub-) natural humid habitats such as peat bogs, fens, reeds and birch moor woods. Large areas outside the core zones have been afforested with Pinus sylvestris or Picea abies monocultures. Eight sites were examined: a Sphagnum-rich Erica tetralix-bog (peat bog), a degeneration stage of the bog dominated by Molinia caerulea, four varieties of Picea abies forest and two varieties of birch wood. A total of 130 spider species were collected. A canonical correspondence analysis considering spider occurrence and abundance clearly shows five different groups of species. Their distribution depends on biotic and abiotic environmental factors reflected by habitat type. The results were compared with communities collected at the same peat bog site in 1973 and 1986/1987. The turnover of the most abundant species in each year-Pirata piscatorius in 1973, Piratula hygrophila in 1986/1987 and Aulonia albimana in 2012-illustrates the subtle dehydration that is presumably correlated with heather spreading. We show the actually observed succession and discuss the potential succession based on the 1973, 1986/1987 and 2012 sampling. This study underlines the outstanding indicator value of spiders in peat bogs. This is especially valid for subtle and long-term changes.