Sphagnum reintroduction under a warming climate: keys to success

<p>Restoring peatland functioning is closely related to restoring growth of ecosystem engineering Sphagnum species. In strongly degenerated peatlands reintroducing diaspores of Sphagnum is necessary to overcome strong dispersal and establishment bottlenecks. Which reintroduction strategy varies between peatland types, surface properties and/or microclimate. Comparative analyses of restoration techniques is scarce, hampering informed management choices.    </p><p>We set out to assess keys to success for Sphagnum reintroduction on strongly humified bare peat in three degraded and long-time rewetted temperate peatlands in the Netherlands. To this end we experimentally manipulated water table position (control, extra water), type of abiotic shelter (control, nurse plants, mulch), Sphagnum species (S. magellanicum, S. papillosum and S. cuspidatum), species mixture (monoculture, mixed culture), diaspore size (clumped intact plants or fragments) and diaspore density (0, 36, 72, 156 plants/m<sup>2</sup>) and monitored Sphagnum survival, lateral expansion and environmental conditions. The experiment was established in 2018 and repeated in 2019, covering two of the most extreme summers in recorded history.</p><p>Water table close to the surface and shelter of a mulch layer were key to Sphagnum survival and growth irrespective of Sphagnum species, reintroduction method or year. Survival increased linearly with diaspore density. Diaspore size showed an interaction with mulch cover: fragments did best under mulch cover, whereas clumped plants survived better outside shelter.</p><p>Taken together our results suggest that successful reintroduction of Sphagnum is possible under a warming climate, but that strategies should be strongly focussed on amelioration of abiotic stress even when water tables are close to the surface. </p>