Carbon and corms: Introduced ungulates and saltwater intrusion variably impact coastal floodplain ecosystem services in the Laynhapuy Indigenous Protected Area, northern Australia

Abstract Carbon and biodiversity offset markets have been proposed to finance management solutions for introduced ungulates across northern Australian coastal wetlands. However, few studies have quantified how ungulate removal may affect ecosystem services important to local Indigenous communities, especially considering coincident saltwater intrusion. Using a mixed‐method, two‐eyed seeing approach, we deployed Yolŋu Knowledge and Western scientific assessments to understand the effects of introduced ungulates and saltwater intrusion on a coastal floodplain fringe in the Laynhapuy Indigenous Protected Area, northern Australia. Collectively, dirramu (male) Yolŋu knowledge holders described the socio‐ecological impacts of introduced ungulates, including declines in bush foods, räkay ( Eleocharis dulcis ) sedgeland and Melaleuca forest, and how this affected their well‐being, culture, songlines and floodplain carbon stores. They noted the interactions between introduced ungulates and saltwater intrusion as channel incision, mangrove encroachment and soil damage. The miyalk (women) attributed ungulate invasion to declines in räkay corm abundance, size and harvestability, with some suggestion that salinity also affected corm size. Using existing ungulate exclusion plots, quantitative Western scientific assessments of above‐ground carbon stocks, forest tree structure and räkay corms largely aligned with the Yolŋu knowledge; however, the Western science did not detect interactions between saltwater intrusion and ungulates, only different significant main effects. In the ungulate exclusion plot array, above‐ground carbon was significantly higher in the healthy Melaleuca forest upper zone (74 ± 14.39 Mg C ha −1 ), compared with the mid (32.8 ± 20.91 Mg C ha −1 ) and lower (7.2 ± 0.84 Mg C ha −1 ) elevation zones where Melaleuca dieback occurred, suggesting a salinity effect. Feral ungulate exclusion resulted in greater understorey carbon in the upper (healthy Melaleuca forest) and lower ( räkay sedgeland) zones. The two‐eyed seeing approach allowed for the collection of quantitative carbon and ecological data alongside locally meaningful Indigenous eco‐cultural perspectives. Nuanced understanding of the impacts of introduced ungulates and saltwater intrusion on regulating and cultural ecosystem services highlighted the potential for ecological, cultural and socio‐economic outcomes from proposed market‐based solutions to managing introduced ungulates on coastal floodplains of northern Australia. Read the free Plain Language Summary for this article on the Journal blog.