Soil organic layer thickness influences the establishment and growth of trembling aspen (Populus tremuloides) in boreal forests

• Aspen establishment was constrained by thick (>25 cm) soil organic layers (SOL).
• Aspen growth was negatively correlated with SOL thickness and black spruce density.
• Aspen growth was positively correlated with soil Ntot.
• Seedlings and suckers responded in a similar manner to SOL thickness and soil Ntot.

In the North American boreal forest, the presence of aspen (Populus tremuloides Michx.) is thought to be constrained on sites where thick (>25 cm) soil organic layers (SOL) prevail. Aspen can reproduce both by seeds and suckers, but it is still unknown how SOL thickness influences both modes of reproduction. In this study, we sought to determine how SOL thickness and chemistry in black spruce dominated stands influences aspen regeneration and growth. Aspen abundance was negatively related to SOL thickness and logistic regression indicated that the probability to detect an aspen declined from 30% at SOL = 0 cm to 10% at 30 cm. Our results also indicated that aspen diameter at breast height was significantly negatively correlated with SOL thickness and black spruce abundance, and positively correlated with soil Ntot, Ca, CEC and pH. Finally, we failed to detect any significant effect of SOL on aspen mode of regeneration (i.e. seeds or suckers). Our study shows that through changes in physical and chemical soil properties, SOL accumulation equally hinders both aspen seedling germination and growth, and sucker development.