Palaeoecology of <i>Sphagnum riparium</i> (Ångström) in Northern Hemisphere peatlands: Implications for peatland conservation and palaeoecological research

<i>Sphagnum riparium</i> (Ångström) is a rare constituent of modern peatland plant communities and is also very rarely found as a subfossil in peat archives. We present new data on the occurrence of <i>Sphagnum riparium</i> macrofossils in three Northern Hemisphere peatlands from Yellowknife (NWCanada), Abisko (N Sweden), and the Northern Ural Mountains (NWRussia). <i>Sphagnum riparium</i> macrofossils were present in transitional phases between rich fen and oligotrophic bog. <i>Sphagnum riparium</i> was a dominant species in the three sites and was found in combination with <i>Sphagnum angustifolium</i>, <i>Drepanocladus</i> sp., and vascular plants including <i>Andromeda polifolia</i>, <i>Chamedaphne calyculata</i> and <i>Oxycoccus palustris</i>. Testate amoebae indicate that the species occurred in wet to moderately wet conditions (water-table depth inferred from a testate amoeba transfer function model ranged between 25 and 0 cm under the peatland surface). The wet-indicator taxa <i>Archerella flavum</i> and <i>Hyalosphenia papilio</i> dominated the testate amoeba communities in peat horizons containing <i>Sphagnum riparium</i>. The presence of <i>Sphagnum riparium</i> macrofossils in peat profiles in the Northern Hemisphere can be interpreted as an indication of wet minerotrophic conditions, often corresponding to a rise in water-level and establishment of a wet habitat. <i>Sphagnum riparium</i> is a transient species in these peatlands and is replaced by communities dominated by more acidophilic species such as <i>Sphagnum angustifolium</i>, <i>Sphagnum russowii</i>, and <i>Sphagnum fuscum</i>. Our data show that although <i>Sphagnum riparium</i> is a transient peat-forming species, it is widespread in sub-arctic and boreal environments. The subfossil occurrence of <i>Sphagnum riparium</i> in the Northern Hemisphere may indicate that its range has increased during the Late Holocene. The conservation of <i>Sphagnum riparium</i> in peatlands depends on the existence of relatively short-lived transitional communities which potentially can be artificially created.