Over and understory controls on red pine establishment and seedling survival in the largest remaining old-growth red pine forest

The ecological constraints on red pine (Pinus resinosa Ait.) regeneration in multi-cohort stands are not fully understood given the species' long history of even-aged management. In this study a structural equation modelling approach is used to dissect the biotic and abiotic controls on seedling establishment and survival in North America's largest remaining multi-cohort red pine forest. We characterized the under and overstory vegetation as well the soil and litter layer surrounding Wolf Lake in the Wolf Lake Forest Reserve (approx. 1600 ha), Sudbury, ON. The understory of this pine dominated stand was found to be characterized by a feather moss-ericaceous community. Red pine establishment was primarily determined by favourable seed bed conditions, namely limited depth of the litter layer, and to some degree by light availability. Additionally, overstory species composition determined establishment of red pine and other shrub species, likely through distinct contributions to the litter layer. Our model suggests that red pine seedlings compete both in the shaded understory and in well-lit plots. We suspect that the northward migrating species, red maple (Acer rubrum) and white pine (Pinus strobus), exert strong competitive effects especially in canopy gaps. Given that uneven-aged management systems are likely to promote establishment of the competing species, red maple, paper birch (Betula papyrifera) and bracken fern (Pteridium aquilinum var. latiusculum), we suggest successful red pine regeneration is unlikely under these systems.