Feral Ungulate Impacts on Carbon Cycling in a Coastal Floodplain Wetland in Tropical Northern Australia

Abstract

Coastal wetland ecosystems play critical roles in mitigating climate change by sequestering substantial amounts of carbon in vegetation and sediments. The Laynhapuy Indigenous Protected Area, northern Australia, includes culturally significant floodplains that support diverse coastal wetlands. The Yirralka Rangers and Yolŋu Traditional Owners who manage this region have identified invasive ungulates as a key threat to wetlands. Paperbark forests, with species known to Yolŋu as raŋan (Melaleuca viridiflora) and nämbarra (Melaleuca cajuputi), have experienced ungulate damage combined with dieback due to saltwater intrusion. Sedgelands, dominated by culturally significant räkay (Eleocharis dulcis), suffer annual soil and vegetation damage caused by invasive pigs (Sus scrofa) and buffalo (Bubalus bubalis). The Rangers and Macquarie University scientists established an ungulate exclusion fenced plot array in 2018 across a supratidal paperbark forest and sedgeland on the Gurrumuru floodplain. To assess carbon cycle impacts, belowground carbon stocks in sediments and biomass were quantified, along with greenhouse gas (GHG) emissions across the plot array. Our findings revealed fourfold higher GHG emissions (combined CO₂ and CH₄) in locations damaged by invasive ungulates compared to undamaged sites in the early dry season. Belowground biomass increased by 21%–104% within exclusion plots compared with damaged plots. No significant differences in soil organic carbon (SOC) and total nitrogen (TN) stocks or rates of litter decomposition were found between damaged and undamaged plots. This study contributes to potential carbon crediting methods focused on reducing feral ungulate impacts to wetlands, that could help fund coastal floodplain wetland management.