Effect of various monotypic forest canopies on earthworm biomass and feral pig rooting in Hawaiian wet forests

• Monotypic canopy species strongly affect earthworm biomass in Hawaiian wet forests.
• Canopy species’ effect on earthworms holds across, but is affected by, site climate.
• Earthworm biomass correlates strongly to soil disturbance by feral pigs.
• Canopy impact on pig rooting may inform management of Hawaiian wet forests.

Forestry plantations are functioning ecosystems, and although they differ from natural ecosystems in many important ways they are governed by the same mechanisms and can provide similar ecological habitats and ecosystem services. In this sense, forestry plantations can be viewed as simple forest ecosystems, allowing us to better isolate and understand the mechanisms that drive forest function, structure, and biodiversity. On Hawai‘i Island, 68 forest stands representing 12 species of monotypic forestry plantations, in addition to stands of native forest and grass pastures, were surveyed at three sites to observe the effects of monotypic canopies on earthworm biomass and occurrence of rooting by feral pigs. The canopy species strongly influenced earthworm biomass at each site (r2 = 0.98, 0.99, 0.92; p < 0.001). Earthworm biomass was strongly correlated to underlying soil age when examined by individual canopy species (r2 = 0.96–0.98; p < 0.001). Earthworm biomass was highly correlated to the occurrence of rooting by feral pigs at each site (r2 = 0.92, 0.94, 0.64; p < 0.001). Each site exhibited a different sensitivity of pig rooting in response to earthworms. Canopy and site data could thus be used to estimate total soil disturbance by feral pigs, and inform aspects of forest management regarding soil erosion, biodiversity habitat, and hunting or trapping of feral pigs.