Trophic rewilding pumas and guanacos: estimating the potential to enhance carbon sequestration in a Patagonian grassland ecosystem

O_LITrophic rewilding, the practice of restoring animal species to recover lost ecosystem functions, has been proposed as a nature-based climate change solution (NbCS) due to animal biogeochemical influences potentially extending to ecosystem carbon capture. C_LIO_LIWe examined this potential using a case study of puma (Puma concolor) and guanaco (Lama guanicoe) restoration in a grassland ecosystem in Patagonia National Park, Chile. We parameterized a model of animal-driven ecosystem carbon dynamics with published measurements from Patagonian grasslands and compared three scenarios: (1) a no-rewilding baseline; (2) rewilding only guanaco; and (3) rewilding guanaco and puma. We estimated net primary productivity (NPP), net ecosystem carbon balance (NECB), and plant and soil carbon stocks. Using differences among scenarios, we estimated ecosystem carbon gains attributable to rewilding guanacos and pumas, and validated baseline estimates using published carbon capture data for Patagonian grasslands. C_LIO_LIPatagonian grasslands with pumas and guanacos could capture (NPP and NECB) 1.27-2.5 times more carbon, and increase plant carbon by 1.76-3.25 times, above the no-rewilding baseline. Large uncertainties in parameter values make estimating soil carbon challenging, but the rewilded ecosystem could store up to 1.16 times more soil carbon, or up to 0.57 times less. C_LIO_LIThe model estimates that NECB in the rewilded ecosystem could amount to 94.41 t C km-2 y-1 (94.38 t C km-2 y-1-94.44 t C km-2 y-1) of which 23%-43% attributable to animal effects. Plant carbon storage estimates were [~]290 t C km-2 (280-300 t C km-2), of which 43%-67% attributable to animal effects. Finally, the model estimated soil C stock gains up to 178 t C km-2, or losses up to 4300 t C km-2. C_LIO_LIPractical implications. We illustrate how to develop first approximation estimates of carbon capture and storage to help assess the feasibility of trophic rewilding as a NbCS. Our modelling revealed that restoring a puma-guanaco trophic cascade could be a feasible NbCS, and identified looming uncertainties about the fate of carbon that need further empirical exploration. More generally, the modelling identifies key measurements that can inform whether restoring trophic cascades can contribute to NbCS. C_LI