Black spruce (Picea mariana) restoration in Kalmia heath by scarification and microsite mulching

• Can microsite mulching (MSM) and scarification improve black spruce seedling growth in Kalmia heath?
• Yes, despite damage from browsing and frost heaving.
• But MSM is preferred for minimum ground disturbance.
• Operational equipment for MSM should be developed.

Canopy removing disturbance such as clearcutting and fire in nutrient-poor boreal and temperate forests often create shrub-dominated vegetation causing significant delay in forest succession. Lack of favourable microsites for black spruce seedling establishment and growth has been identified as the primary cause for conifer regeneration failure in post-fire Kalmia heath in eastern Canada. The aim of this study was to compare the growth performance of black spruce planted in scarified plots and in microsites developed by a novel technique called micro-site mulching (MSM) in Kalmia heaths. We hypothesized that because of vegetation removal and exposure of mineral soil in scarified and MSM treatments, planted black spruce would suffer from frost heaving and animal browsing, but these treatments may offer better seedling growth by ameliorating the inhibitory effects of Kalmia organic matter and providing with favourable soil moisture, soil temperature, soil respiration and nutrient availability. We conducted this study in a 13 year-old post-fire Kalmia heath in Triton Brook, Newfoundland, Canada (48°30′N, 50°00′W). We measured black spruce seedling survival and growth annually for three complete growing seasons and soil nutrient availability one year post-planting. In all three treatments black spruce seedling survival was >90%. About 20% of the seedlings in scarified and MSM treatments suffered herbivore damage and frost heaving with little damage in control plots. Black spruce in scarified and MSM plots were associated with significantly higher growth than control, with differences amplified each consecutive year since planting. Higher seedling growth in scarified and MSM plots was associated with higher soil moisture, lower organic matter content, and lower soil temperature. Soil nutrient differences in treatments had little effect on seedling growth. Since MSM treatment produced substantially less soil disturbance with similar or better seedling growth than scarification, we suggest MSM as a preferred site preparation technique in Kalmia heath in contexts where large-scale soil disturbance by standard mechanized scarification is undesirable. The novelty of his paper is the development of MSM as a potential alternative to scarification in creating suitable microsites for planted black spruce to restore forest cover in ericaceous heaths. However, an operationally suitable MSM tool must be developed and a longer-term (10 years) monitoring is necessary before the method can be applied as a restoration tool.