Birch (Betula papyrifera) × white spruce (Picea glauca) interactions in mixedwood stands: implications for management

Abstract

Current British Columbia forest regulations drive the regeneration management towards pure conifer stands rather than remaining in a mixed-species condition. This approach may result in unnecessary vegetation control. The main objective of this investigation was to study the impact of variable paper birch densities on white spruce growth in 15-20 years old stands for management implications. Regression analysis was used to examine the effect of birch density and two competition indices to predict spruce growth. A mixed model ANOVA showed that spruce mean annual DBH and basal area increment differed significantly among sites and density. From the regression analysis it appears that birch density up to 4,000 stems.ha-1 had no significant influence on spruce growth which is much higher than the current BC reforestation guideline (1,000 stems.ha-1 broadleaves). Similarly, birch relative density index (RDI) had to exceed 3 to affect spruce DBH growth significantly on all sites except one. On most sites, spruce had a larger DBH than birch. Our results also suggest that rather than following the current broadcast approach to vegetation management, a targeted approach could enhance forest productivity and stand diversity.

Keywords

• boreal forest
• competition
• mean annual dbh growth
• productivity
• relative density index (rdi)
• vegetation management