Table 1. Results from linear mixed model for the main and interacting effects of planting density of black spruce (Picea mariana) and mechanical site preparation on environmental conditions and understory diversity. Df = degrees of freedom. Bold indicates significance at α ≤ 0.05. | ||||||

Response variable | Treatment effects | |||||

Planting density | Mechanical site preparation (MSP) | Planting density × MSP | ||||

Df | p-value | Df | p-value | Df | p-value | |

Environmental conditions | ||||||

Conifer density (stems ha^{–1}) | 1 | 0.28 | 2 | 0.02 | 2 | 0.87 |

Deciduous species density (stems ha^{–1}) | 1 | 0.56 | 2 | 0.036 | 2 | 0.3 |

Shrub density (stems ha^{–1}) | 1 | 0.55 | 2 | 0.65 | 2 | 0.05 |

Vegetation cover (%) | 1 | 0.5 | 2 | 0.01 | 2 | 0.96 |

C/N ratio | 1 | 0.003 | 2 | <0.001 | 2 | 0.3 |

Understory diversity | ||||||

Vascular plant dominance (Simpson index) | 1 | 0.3 | 2 | 0.9 | 2 | 0.65 |

Vascular plant diversity (Shannon index) | 1 | 0.07 | 2 | 0.91 | 2 | 0.09 |

Bryophyte cover (%) | 1 | 0.002 | 2 | 0.11 | 2 | <0.001 |

Bryophyte diversity (Shannon-Wiener index) | 1 | 0.15 | 2 | 0.2 | 2 | 0.46 |

Table 2. Influence of planting density of black spruce (Picea mariana) and mechanical site preparation and their interaction on vascular plant and bryophytes dissimilarity using permutational multivariate analysis of variance (Permanova) based on the Bray–Curtis dissimilarity index. Df = degrees of freedom. Bold indicates significance at α ≤ 0.05. SS = sum of squares. | ||||||

Assemblage | Treatment | Df | SS | F | R^{2} | p-value |

Vascular plant | Planting density | 1 | 0.33 | 1.24 | 0.011 | 0.316 |

Mechanical site preparation (MSP) | 2 | 2.13 | 4.02 | 0.07 | 0.001 | |

Planting × MSP | 2 | 0.84 | 1.58 | 0.02 | 0.048 | |

Residual | 98 | 25.9 | 0.89 | |||

Bryophytes | Planting density | 1 | 0.63 | 2.83 | 0.026 | 0.036 |

Mechanical site preparation (MSP) | 2 | 0.81 | 1.81 | 0.034 | 0.008 | |

Planting × MSP | 2 | 1.14 | 2.56 | 0.048 | 0.016 | |

Residual ^{1} | 94 | 21.10 | 0.89 | |||

^{1} four plots without bryophytes |

Table 3. Results from post-hoc pairwise tests for vascular plant and bryophytes between mechanical site preparation treatments after planting of black spruce (Picea mariana) (CLAAG = careful logging around advanced growth; Plow = plowing; T26 = disk trenching scarification; High = planting density of 2500 seedlings ha^{–1}; Low = planting density of 1100 seedlings ha^{–1}). Df = degrees of freedom; SS = sum of squares. Bold indicates significance at α = 0.05. | |||||||||

Pairs | Df | SS | F | R^{2} | p-value | adjusted p | |||

Vascular plants | |||||||||

CLAAG | vs | PLOW | High | 1 | 1.01 | 3.97 | 0.12 | 0.001 | 0.005 |

CLAAG | vs | T26 | High | 1 | 0.49 | 2.15 | 0.07 | 0.019 | 0.038 |

PLOW | vs | T26 | High | 1 | 0.51 | 2.05 | 0.06 | 0.030 | 0.005 |

CLAAG | vs | PLOW | Low | 1 | 0.64 | 2.16 | 0.05 | 0.012 | 0.035 |

CLAAG | vs | T26 | Low | 1 | 0.47 | 1.74 | 0.04 | 0.083 | 0.13 |

PLOW | vs | T26 | Low | 1 | 1.27 | 4.74 | 0.11 | 0.001 | 0.006 |

Bryophytes | |||||||||

CLAAG | vs | PLOW | High | 1 | 0.76 | 3.12 | 0.10 | 0.028 | 0.1 |

CLAAG | vs | T26 | High | 1 | 1.29 | 6.33 | 0.18 | 0.002 | 0.02 |

PLOW | vs | T26 | High | 1 | 0.20 | 0.71 | 0.02 | 0.605 | 0.68 |

CLAAG | vs | PLOW | Low | 1 | 0.18 | 0.75 | 0.02 | 0.564 | 0.64 |

CLAAG | vs | T26 | Low | 1 | 0.08 | 0.47 | 0.01 | 0.658 | 0.7 |

PLOW | vs | T26 | Low | 1 | 0.42 | 2.08 | 0.05 | 0.090 | 0.26 |

Table 4. Results from linear mixed model for the main and interacting effects of planting density of black spruce (Picea mariana) and mechanical site preparation on functional trait of vascular plant and bryophytes. Df = degrees of freedom. Bold indicates significance at α ≤ 0.05. | ||||||

Response variable | Treatment effect | |||||

Planting density | Mechanical site preparation (MSP) | Planting density × MSP | ||||

Df | p-value | Df | p-value | Df | p-value | |

Functional trait of bryophytes | ||||||

Water content at field capacity (%) | 1 | 0.77 | 2 | 0.02 | 2 | 0.5 |

Colony density (mg cm^{–3}) | 1 | 0.93 | 2 | 0.51 | 2 | 0.09 |

Absorption capacity (ml cm^{–3}) | 1 | 0.13 | 2 | 0.86 | 2 | 0.16 |

Percolation (% cm^{ –3}) | 1 | 0.74 | 2 | 0.95 | 2 | 0.58 |

Functional trait of vascular plants | ||||||

Maximum height (cm) | 1 | 0.86 | 2 | 0.91 | 2 | 0.09 |

Specific leaf area (cm^{2} g^{–1}) | 1 | 0.93 | 2 | 0.43 | 2 | 0.14 |

Small shrubs abundance | 1 | 0.55 | 2 | 0.05 | 2 | 0.055 |

Herbaceous abundance | 1 | 0.01 | 2 | 0.7 | 2 | 0.84 |

Table 5. Results from linear mixed model for the main and interacting effects of planting density of black spruce (Picea mariana) and mechanical site preparation on height, growth, diameter at ground level, N and C foliar concentration of planted trees. Df = degrees of freedom. Bold indicates significance at α ≤ 0.05. | ||||||

Response variable | Treatment effect | |||||

Planting density | Mechanical site preparation (MSP) | Planting density × MSP | ||||

Df | p-value | Df | p-value | Df | p-value | |

Height trees measured in 2020 (cm) | 1 | 0.32 | 2 | 0.75 | 2 | 0.47 |

Diameter at ground-level (mm) | 1 | 0.6 | 2 | 0.35 | 2 | 0.42 |

Sapling growth measured between 2016–2020 (cm) | 1 | 0.89 | 2 | 0.88 | 1 | 0.03 |

N foliar % | 1 | 0.88 | 2 | 0.02 | 2 | 0.29 |

C foliar % | 1 | 0.2 | 2 | 0.001 | 2 | <0.001 |