Lichen matted seedbeds inhibit while moss dominated seedbeds facilitate black spruce (Picea mariana) seedling regeneration in post-fire boreal forest

Abstract

The subject of conifer regeneration failure after canopy removing disturbance leading to expansion of ericaceous heaths in boreal forests received considerable attention. However, despite seedbed quality being a key factor in tree regeneration, our understanding of the role of lichen and moss dominated seedbeds on tree seedling regeneration after forest fires remains unclear. Objective of this study was to investigate the effect of time since fire and post-fire cryptogamic (lichen and moss) seedbeds with variable organic matter thickness on black spruce regeneration. We conducted black spruce seeding experiment in black spruce – Kalmia forests burned 11, 17 and 37 years ago. In each site we applied three seedbed manipulation treatments (mat-intact, mat-mixed and mat-removed) to test if seedbed manipulation improves spruce regeneration. This experiment was extended to three moss-dominated seedbeds to compare seedbed moisture and temperature effects on spruce regeneration. We also tested potential allelopathic effect of two common lichen and moss species in laboratory bioassay. Seed regeneration was low in all seedbeds. Black spruce germination and seedling growth was lowest in presence of Cladonia cristatella followed by C. stellaris, Polytrichum juniperinnum and Pleurozium schriberi. HPLC analysis of C. cristatella indicated the presence of usnic acid, a common germination inhibiting allelochemical. Moss seedbeds were relatively favourable for spruce regeneration. We conclude that (i) lichen seedbeds inhibit seedling regeneration due to adverse biophysical and chemical (allelopathic) effects, (ii) moss seedbeds facilitate black spruce regeneration by maintaining favourable moisture and temperature, and (iii) seedbed manipulation treatments produce mixed results depending on the dominant cryptogam, organic matter thickness and seedbed moisture and temperature.