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 (CO 2 ) when disturbed. Although humans are known to exacerbate soil CO 2 emissions through land-use change, we know little about the global carbon footprint of invasive species. We predict the soil area disturbed and resulting CO 2 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 km 2 (mean of 123,517 km 2 ) in their non-native range, with a 95% prediction interval (PI) of 14,208 km 2 -634,238 km 2 . This soil disturbance results in median emissions of 4.9 million metric tonnes (MMT) CO 2 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 CO 2 ) 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.

Do Invasive Mammal Eradications from Islands Support Climate Change Adaptation and Mitigation?

“…In addition to the potential of invasive mammal eradications for enhancing climate adaptation and resilience, there is also evidence from multiple ecosystems that removing invasive mammals can help mitigate climate change (Tables 1 and 3) by promoting carbon sequestration [70,146]. Estimates of invasive mammal impacts on terrestrial carbon sequestration include a recent study's calculation that by uprooting soil, feral pigs (Sus scrofa), most of which are invasive, release 4.9 million metric tons (MMT) of CO 2 per year globally (equivalent to 1.1 million passenger vehicles) [118]. Yet another study on removing rabbits from Australia proposes that carbon sequestration resulting from their removal could be more cost-effective than planting trees [149].…”

Invasive wild pigs (Sus scrofa) as a human‐mediated source of soil carbon emissions: Uncertainties and future directions

“…We chose the minimum estimated decrease in soil respiration based on Persico et al (2017) and the maximum value to be 0 as there may be cases where soil CO 2 emissions are statistically no different than zero (e.g., Cuevas et al, 2012). For non‐saltmarsh habitats, we retained the uniform distribution originally used in O’Bryan et al (2021). Because values ≤0 are undefined for log transformations, we present these values in the solitary blue bar and histogram subset on the left side of the plot, which represents 0.9% of simulations (min: −341.1 MMT CO 2 , max: −0.0001 MMT CO 2 , mean: −7.9 MMT CO 2 , median: −0.07 MMT CO 2 ).…”

“…Because values ≤0 are undefined for log transformations, we present these values in the solitary blue bar and histogram subset on the left side of the plot, which represents 0.9% of simulations (min: −341.1 MMT CO 2 , max: −0.0001 MMT CO 2 , mean: −7.9 MMT CO 2 , median: −0.07 MMT CO 2 ). The black bars behind the red bars indicate the original results presented in O’Bryan et al (2021)…”

“…Through their uprooting of soil, they are known to affect food security, drive the loss of native plants and animals, and jeopardize cultural resources (Barrios‐Garcia & Ballari, 2012; Risch et al, 2021; Sloane et al, 2021). In our recent article, we explored another threat from their soil disturbance: greenhouse gas emissions (O’Bryan et al, 2021). We discussed that ongoing and future management of wild pigs could bring potential co‐benefits through the reduction of CO 2 emissions, but our analysis revealed a great deal of uncertainty that points to potential wide‐ranging consequences of their management on CO 2 emissions.…”

“…The model that informed this re‐analysis can be obtained from O'Bryan et al (2021). The distribution map of saltmarsh habitat can be obtained from Mcowen et al (2017).…”