THE ROLE OF HAIR-CAP MOSSES (POLYTRICHUM SPP) IN NATURAL REGENERATIONOF WHITE SPRUCE (PICEA-GLAUCA (MOENCH) VOSS)

Natural regeneration of many North American conifer species frequently occurs in association with the hair-cap mosses (Polytrichum spp.), co mmon and widely distributed pioneer mosses of boreal and temperate con iferous forests. The role of Polytrichum mosses in the natural regener ation of white spruce (Picea glauca (Moench) Voss) was investigated th rough a comparative study of seedbed effects on seedling emergence, su rvival, morphology and the presence of competing vegetation. Intact mo noliths of Polytrichum moss, mineral soil and undisturbed litter were collected from the forest floor of a mixed conifer stand in Central On tario. Half of the litter seedbeds were later burned with a propane to rch. Replicates of the four seedbeds (n = 24) were placed in a greenho use and hand sown with white spruce seed. Percent effective seedling e mergence was significantly higher on mineral soil than on the other th ree seedbeds but did not differ among moss, liner and burned litter. S eedling survival under a watering regime representative of the seedbed collection site did not differ among seedbeds. Survival of a short dr ought stress treatment, however, was significantly improved in mineral soil and moss as compared with the litter and burned liner seedbeds. Differential survival was related in part to the biomass of herbaceous and woody competition that developed from the seed bank and rhizomes present in the four seedbeds. Above- and below-ground biomass of compe tition on the litter and burned litter seedbeds were significantly hig her and ten times that of mineral soil and moss seedbeds. This differe nce in biomass of competition was associated with lower average daily soil water potentials in the two litter seedbeds. Seedlings growing in mineral soil, and to a lesser extent burned litter, generally exhibit ed larger shoot, root and total dry mass and produced more robust shoo ts of higher mechanical strength (i.e. shoot dry mass/shoot length). S eedlings grown on moss were taller with smaller epicotyls and stem dia meters, indicative of an etiolation response associated with steep lig ht gradients in this seedbed. Seedlings grown in mineral soil and mass had higher root/shoot ratios and showed trends toward greater total r oot length and root branching. The ecological relationship between whi te spruce and Polytrichum mosses and the comparative value of Polytric hum seedbed in silvicultural systems to promote natural regeneration o f white spruce are discussed.