The role of climate and hydrology fluctuations in shaping Northern Alaska plant community over the last three millennia

Abstract

Rising temperatures observed in recent decades are driving changes in the development of wetland ecosystems in Arctic regions. Therefore, there is a need to assess the current ecological state of peatlands in the Arctic zone to predict their development in the future. This study uses high-resolution multi-proxy palaeoecological analyses (plant macrofossils, pollen, testate amoebae, peat stoichiometry and stable isotopes), supported by radiocarbon (¹⁴C) and lead (²¹⁰Pb and ^239+240Pu), from two peat profiles covering the last 3200 and 1350 years, respectively, located on the northern part of Alaska. We aim to (i) determine the timing of the peat initiation process; ii) identify predominant peat-forming plant species; iii) reconstruct local and regional vegetation changes; iv) reconstruct hydrological changes and v) explore the role of climate-induced hydrological changes on the development of Arctic peat-forming and shrubs plant communities. Our studies revealed that 1) peat initiation occurred at ca. 1200 BCE and 350 BCE through a paludification process; 2) plant communities dominated by sedges and brown mosses played a key role as a main peat-forming species and remained stable for centuries; 3) changes in the composition of dominant peat-forming plants, from sedges and brown mosses, common in wet habitats to Sphagnum and brown mosses typical of drier habitats, were linked to climate warming between 1940 CE and 1960 CE and 4) the drop of the water table depth level during warm climate phases facilitated the spread of shrub and dwarf shrubs in the Arctic plain. Our study shows that the recent surge in woody vegetation exceeds any recorded expansion in the past three millennia, documenting the rapid changes occurring in Arctic plant communities from Northern Alaska.