The influence of soil rutting severity on regeneration potential and seedling performance for black spruce-dominated peatlands

Abstract

Excessive rutting continues to be recorded in post-harvest compliance inspections in black spruce peatlands across Ontario. These qualitative, visual assessments, however, cannot provide the necessary data to determine a site disturbance threshold that is linked to poor regeneration and seedling growth. In an attempt to provide this quantitative link, harvested black spruce [Picea mariana (Mill.) B.S.P.] peatland sites were surveyed and divided into severely rutted (non-compliant), moderately rutted, and non-rutted (compliant) blocks. In 1995, 2001, and 2006, each block was assessed for areal extent of rutting, number of plantable spots, moisture status, planting medium, competition level, stand density, species composition, and black spruce seedling survival and growth. Black spruce seedling survival in the severely-rutted block was significantly lower when compared with either the moderately rutted or the non-rutted blocks. A derived seedling survival model identified moisture class as having the largest influence on the probability of seedling survival. In terms of seedling growth, however, it was the non-rutted blocks that had the poorest performance. Based on a canonical discriminant analysis (CDA), competition factors, particularly ericaceous shrub cover, were the most important microsite factors influencing black spruce seedling growth. Overall, the moderately rutted block generated conditions that resulted in high conifer recruitment and good seedling survival and growth. Although the inference space of the study is small, the results suggest that black spruce peatland sites may benefit from a moderate level of site disturbance caused during harvest operations. Key words: Rutting severity, black spruce peatlands, survival, growth, microsite assessment