Unrecognized threat to global soil carbon by a widespread invasive species

Abstract

Most of Earth's terrestrial carbon is stored in the soil and can be released as carbon dioxide (CO₂ ) when disturbed. Although humans are known to exacerbate soil CO₂ emissions through land-use change, we know little about the global carbon footprint of invasive species. We predict the soil area disturbed and resulting CO₂ emissions from wild pigs (Sus scrofa), a pervasive human-spread vertebrate that uproots soil. We do this using models of wild pig population density, soil damage, and their effect on soil carbon emissions. Our models suggest that wild pigs are uprooting a median area of 36,214 km² (mean of 123,517 km² ) in their non-native range, with a 95% prediction interval (PI) of 14,208 km² -634,238 km² . This soil disturbance results in median emissions of 4.9 million metric tonnes (MMT) CO₂ per year (equivalent to 1.1 million passenger vehicles or 0.4% of annual emissions from land use, land-use change, and forestry; mean of 16.7 MMT) but that it is highly uncertain (95% PI, 0.3-94 MMT CO₂ ) due to variability in wild pig density and soil dynamics. This uncertainty points to an urgent need for more research on the contribution of wild pigs to soil damage, not only for the reduction of anthropogenically related carbon emissions, but also for co-benefits to biodiversity and food security that are crucial for sustainable development.

Keywords: Sus scrofa; CO2 emissions; biological invasion; bioturbation; climate change; ecosystem engineer; soil disturbance; ungulate; wild boar; wild pig.