Black Spruce (Picea mariana) Regeneration in Post-fire Cryptogamic Mats
Abstract
Post-fire black spruce (Picea mariana Mill.) regeneration has received
considerable attention in management of the boreal forest of eastern Canada. Seedbed
quality is a key factor for seed germination and early seedling establishment. The
objective of this research was to investigate the potential role of cryptogamic seedbeds in
black spruce germination and seedling establishment. To compare lichen-dominated
seedbeds with thin and thick organic matter, in situ seeding experiments were conducted
at three sites in Terra Nova National Park, Newfoundland burned 11 (Rocky Pond, RP),
17 (Spracklin Road, SR) and 37 (Terra Nova Road, TNR) years ago. At each site, three
manipulation treatments (mat-intact, mat-mixed and mat-removed) were applied to the
seedbed with four replications in plots of 30 x 30 cm where 200 black spruce seeds were
broadcasted. To compare lichen vs. moss seedbed, the same experimental design was
extended to moss dominated seedbeds at the SR site. A laboratory germination bioassay
was conducted to test the possible chemical effects of four cryptogamic species on black
spruce germination and primary growth. Seed germination was highest in mat-intact and
mat-removal plots with thick OM at RP, mat-mixed plots with thin OM at SR and matmixed
plots with both thin and thick OM at TNR. There was significantly higher
germination and seedling establishment on moss seedbeds than lichen seedbeds. In moss
seedbeds, mat-mixed plots with thick OM had the highest germination but mat-intact
plots of both thin and thick OM had higher seedling establishment. Moss seedbeds had
higher soil moisture and lower surface temperature than lichen seedbeds. Laboratory
bioassay with lichen Cladonia cristatella Tuck. had significantly lower germination and
seedling growth than control but no difference between the control and moss treatments.
HPLC analysis of C. cristatella indicated the presence of a germination inhibiting
allelochemical, usnic acid. Lichen mat provides physical barrier to seed germination and
seedling growth in late post-fire site TNR but not in early post-fire sites. It appears that
moss dominated seedbeds facilitate black spruce regeneration by increasing seedbed
moisture retention and maintaining low surface temperature, while lichen seedbeds
inhibit seedling regeneration by their adverse physical and chemical effects. Cryptogamic
seedbed type, OM thickness, soil moisture and temperature are limiting factors in poor
black spruce seedling regeneration after fire.