Late-Holocene expansion of <i>Sphagnum</i> in Central Arctic Alaska

Climate change and hydrological disturbances strongly influence the development of Arctic wetland ecosystems. Palaeoecological studies of high-latitude peatlands provide insights into long-term plant succession under such environmental pressures. Here, we conducted high-resolution plant macrofossil analyses, supported by radiocarbon dating, on three new Sphagnum -peat monoliths sampled along the Dalton Highway in central Arctic Alaska. Our aim was to determine the timing of peat initiation, local vegetation succession and their drivers, with a particular focus on mosses. Our results show that: (i) the initiation of peat formation varied among sites, ranging from ca. 150 CE to ca. 1850 CE; (ii) climate-induced hydrological changes, including water table declines, created drier habitats colonized by Sphagnum and brown mosses; (iii) minerotrophic Sphagnum species, such as S. warnstorfii and S. lenense , underwent massive expansion after the Little Ice Age and in recent decades; and (iv) Sphagnum mosses have recently emerged as key peat-forming species, with their ecological role likely to increase in the future; (v) the first subfossils presence of Sphagnum kenaiense in Alaska was documented. Our study provides evidence of the effects of recent Sphagnum growth on changes in local plant communities, highlighting the critical implications for altered carbon accumulation capacity and increased fire activity.