Invasive earthworms shape forest seed bank composition

Aim To assess how non‐native earthworm and non‐native plant invasions shape soil seed bank composition in deciduous temperate forests. Location New York State, USA. Methods We recorded earthworm density, earthworm biomass and vegetation composition in 12 deciduous forests and subsequently collected soil cores and recorded emergence of plant species from the seed bank. We used path analysis to assess direct and indirect contributions of earthworms and vegetation composition (species richness and cover of native and non‐native plants) to the species richness and abundance of emergent seedlings. Results High earthworm populations were positively associated with increased species richness and seedling density of both native and non‐native plant species emerging from the seed bank. This relationship held for all life‐form groups, although the earthworm effect was indirect for non‐native graminoid abundance. Non‐native plants were positively correlated with earthworms and while they influenced both aboveground vegetation cover and species richness, they had no direct influence on emergent abundance or species richness. Main conclusions Our results suggest that forest seed bank composition is strongly influenced by the presence and abundance of non‐native earthworms, and only weakly influenced by non‐native plants. Forest understorey recovery from seed banks is possible following earthworm invasion, but resulting communities bear little similarity to standing vegetation. Recovery of the full desirable and typical complement of aboveground vegetation will require input to seed banks by (1) fostering seed production of existing vegetation and/or (2) planting seed of desired species. We suggest managing understorey vegetation to allow herbaceous species to set seed.