Polytrichum strictum as a nurse-plant in peatland restoration

Polytrichum strictum is a pioneer plant frequently found on bare peat substrate after perturbations (fire, peat extraction). Can this moss facilitate the return of Sphagnum species or other boreal plants after disturbances? Field surveys of abandoned peatlands after peat extraction revealed that Sphagnum was always found in association with P. strictum carpets. We conducted field experiments in abandoned peatlands and showed that P. strictum carpets were able to keep Sphagnum fragments more humid than bare peat but only when the P. strictum carpets were not totally bone dry. In general, daytime temperatures beneath P. strictum carpets and fragments were reduced during the day and increased during the night compared to bare peat. Polytrichum strictum carpets acted as a seed trap, retaining more artificial seeds than bare peat. Polytrichum strictum can be a nurse-plant: after 16 months, vascular plants transplanted in the P. strictum carpet were healthier than the ones planted on bare peat. The use of P. strictum as a nurse-plant in boreal forest or peatland restoration is recommended for sites prone to frost heaving and with harsh microclimatic conditions.