Direct seeding of black spruce in northwestern Ontario: Temporal changes in seedbed coverage and receptivity

Abstract

Temporal changes in black spruce (Picea mariana [Mill.] B.S.P.) seedbed coverage and seedbed receptivity were investigated on coarse-textured upland sites near Thunder Bay (48°25′N 89° 15′W), in northwestern Ontario. Sowing was completed in May for three consecutive years following summer scarification at each of 12 sites. Infilling by organic debris reduced the proportion of receptive soil strata three to five years after scarification by 50–95%. Receptive seedbed coverage declined more quickly on fresh Soil Moisture Regimes with a variety of deciduous trees and shrubs than on moist Soil Moisture Regimes dominated by eracaceous shrubs. Pioneer mosses, which are also good seedbeds, invaded moist sites more readily than fresh sites, and mitigated losses in seedbed coverage. Compact Sphagnum seedbeds in lowland depressions maintained good areal coverage much longer than did receptive upland soil strata. Seedling establishment ratios varied greatly among seeding years, seedbeds and sites, but there was an underlying trend of decreasing seedbed receptivity with time since scarification. Seedlings originating from the first seeding year were taller at age 7–10 than those originating from the second or third seeding years. Key words: direct seeding, seedbed coverage, seedbed receptivity, scarification, black spruce, Picea mariana