Enchytraeid assemblages (Annelida: Clitellata: Enchytraeidae) of two old growth forests in the Porcupine Mountains (Michigan, USA)

ery little is known about enchytraeid assemblages in North American soils. It is difficult to assess to what extent present-day assemblages include introduced species that originally did not occur on the continent. Old growth forests are among the few preserved original habitats that provide the opportunity to study a presumably pristine soil fauna. In May 2011 soil samples were taken in two old growth forest stands on Podzols (Spodosols) in the Porcupine Mountains (Michigan, USA) differing in elevation, soil pH and stand composition (sugar maple vs. hemlock-sugar maple). Enchytraeids were extracted by the wet funnel method and identified alive. Species composition and representation, vertical distribution and density were assessed. In the maple stand, mean enchytraeid density was 32,100 ± 9,000 individuals/m2 (± SE), 74 % of individuals being present in the upper 3 cm of soil. Six enchytraeid taxa were present, in four cases their identity was ascertained to species level. Cognettia sphagnetorum was predominant, comprising at least 82 % of all individuals. The occurrence of C. sphagnetorum in North America had been hitherto known only from a tentative record from Florida. In the hemlock-sugar maple stand (with less acidic soil), mean enchytraeid density was 35,900 ± 7,300 ind./m2 (± SE) and the vertical distribution was more even. Also the representation of the 8 taxa identified was more even than in the maple stand. The genus Marionina was dominant (63 % of all individuals) and represented by 1 or 2 species. M. cf. minutissima is reported for the first time from North America, but may also represent a new species.