Peat-forming large tussock grasslands on oceanic and sub-Antarctic islands are fundamentally understudied in terms of carbon (C) storage. Here we quantify both plant and soil C and nitrogen (N) storage for the large-tussock grass Poa flabellata in the Falkland Islands, at its most northerly range. In this study we adopt a spatially explicit sampling approach to account for tussock and inter-tussock (between tussocks) areas for three habitats; remnant stands (surviving clearance and overgrazing), restored stands (planted) and eroded bare peat sites. We found that remnant stands of P. flabellata have above-ground C densities of 49.8 ± 9.7 Mg C ha-1 , equivalent to temperate and boreal forests. The majority of aboveground C is stored within the pedestal, a compact accumulation of dead leaves, rhizomes and roots. By surveying restored stands of increasing age we found that such C accrual may take longer than two decades. Soil C stocks were horizontally and vertically spatially variable and did not differ between habitat types. Plant and soil C and N stocks were strongly coupled identifying the important role of N availability for C accrual in this system. Scaling-up our results, planting tussock grass could accrue up to 0.9 million Mg C on a decadal timescale across the islands, yet the impact of planting on soil C storage is likely to be more variable. Our results highlight the local and regional importance of large tussock grasslands as dense C stores and that land management and conservation of these communities needs to be more carbon-conscious.

Remote island ecosystems are vulnerable to human disturbance and habitat destruction, yet they often have limited capacity to revegetate degraded habitats, especially with native species. To revegetate degraded island habitats, practitioners often rely on importing non‐native species, thereby increasing the number of introduced species on islands. In this study, we investigated the effectiveness of sowing wild collected native seeds and locally sourced treatments for revegetating different eroded soil types (clay, peat, and sand) across the Falkland Islands. A seed mixture of 15 native species was sown with different supportive treatments (sheep dung, sheep dags [woolly off‐cuts], and geotextile matting [coir]) and their combinations. After 1 year, native seeds provided up to 70% plant cover and accrued 1.98 kg/m2 in biomass. Three key native species Elymus magellanicus, Poa flabellata, and Poa alopecurus occurred in 64, 50, and 50% of all sown plots. However, supportive treatments equally facilitated the colonization and establishment of non‐native species. At the same time, there was no difference in native plant cover and biomass across different treatments or soil types, although in the absence of supportive treatments there was little to no revegetation. Thus, locally sourced treatments (i.e. sheep dung and dags) may provide an equally effective but low‐cost alternative to imported treatments (i.e. geotextiles). We further discuss challenges of integrating revegetation using native seeds and livestock grazing on the Falkland Islands. Our study demonstrates that native species and local treatments can provide a rapid approach to revegetating degraded island habitats.