POPULATION-DENSITY AND DISTRIBUTION OF THE NEW-ZEALAND INDIGENOUS EARTHWORM OCTOCHAETUS-MULTIPORUS (MEGASCOLECIDAE, OLIGOCHAETA) IN HILL PASTURES

The distribution of the indigenous New Zealand megascolecid earthworm Octochaetus multiporus (Beddard) in hill pastures of different fertili ties in the southern North Island of New Zealand, and the population d ensity throughout a year are described. Octochaetus multiporus was mos t numerous in soils of low to moderate fertility. High fertility soils had a similar population density to that of an adjacent area of nativ e forest, indicating that the exotic pasture environment can favour Oc tochaetus multiporus in some circumstances. Population density of Octo chaetus multiporus was best correlated with soils which were moist in summer. There was no well defined breeding season for this species, ma ture and recently hatched individuals being found in most months of th e year. Octochaetus multiporus is a deeper burrowing indigenous earthw orm species which is successful in an exotic environment. In pastures which have moist soils in summer, this species may be improving soil s tructure and root penetration in the absence of deep burrowing introdu ced lumbricid earthworms.