Wild pigs mediate far-reaching agricultural impacts on tropical forest soil microbial communities

Edge effects, the altered abiotic and biotic conditions on the borders of natural areas, rarely extend more than a few hundred meters. Edge effects have rarely been linked to altered soil biota, which shape ecosystem processes including carbon storage, biogeochemical cycling, and plant performance. Here, we investigated if agriculturally-mediated increased wildlife populations affect soil biotic communities at a distance well over that of estimated edge effects when they move between agriculture and natural habitats using a 22-year fenced exclusion experiment in a primary rainforest in Peninsular Malaysia. We found that the presence of wildlife (mainly native pigs (Sus scrofa) that crop-raid in nearby oil palm plantations) was associated with higher bacterial diversity, and an altered community composition (mediated by changes in soil pH), and reduced abundances of symbiotic ectomycorrhizal fungi compared to soil in exclosures. There were only minor effects of pigs on soil chemistry or microclimate, so we suggest that changes in soil communities are driven by pigs leaf litter removal and alterations to plant composition. Our study highlights that indirect effects from agriculture can be transferred by wildlife >1 km into protected areas and this could have important repercussions for ecosystem processes and plant-soil feedbacks.