Below-ground invasion, the coexistence of exotic and endemic earthworms in New Zealand soils

Abstract

New Zealand has 23 exotic and more than 200 endemic earthworm species. It has been reported that endemic earthworms disappeared quickly from agricultural systems due to environmental changes and soil disruption through agricultural practices. However, little is known about potential competition between endemic and exotic earthworms in New Zealand, and the capacity of exotic earthworms to also colonise native habitats. Using three sites in the South Island, we investigated the impact of aboveground vegetation (exotic vs endemic) on earthworm communities. The study sites were Bankside Reserve (Canterbury Plains), a 2.6 ha dryland reserve surrounded by dairy farms, Quail Island (Banks Peninsula), which has been undergoing native plant restoration for more than 30 years, and the Punakaiki Coastal Restoration Project (West Coast) where 130,000 native trees have been planted in retired pasture in the last seven years. In the Bankside reserve we detected incursions of exotic earthworms throughout the reserve, while endemics were never found in the pasture. In Punakaiki and Quail Island, sequential restoration plantings revealed that recolonisation by endemic earthworms increases with time after restoration. The biomass of endemic earthworm significantly increased with restoration age, and at Punakaiki, abundance did also. However, in both cases, exotic species did not disappear after restoration of native vegetation, leading to the cohabitation of the two assemblages and potential for interspecific competition.