Survival probability of white spruce and trembling aspen in boreal pure and mixed stands experiencing self-thinning

• We examine tree and stand variables that affect tree survival in pure and mixed self-thinning stands.
• Tree survival increases as absolute tree size increases regardless of species.
• One-sided rather than two sided competition affects survival of both species.
• Fast growing trees have higher survival probability in both pure and mixed stands irrespective of species.

Tree mortality due to competition is one of the key drivers of forest succession in Canadian boreal mixedwood forests. We analyzed survival probability of trembling aspen (Populus tremuloides Michx.) and white spruce (Picea glauca (Moench) Voss.) trees and saplings, growing in pure and mixed stands experiencing self-thinning, in the Boreal Forest Natural Region of Alberta, Canada. Generalized logistic regression models were utilized to evaluate the effects of tree and stand characteristics on the survival probability of both species. Absolute size of the individuals, characterized by diameter at breast height, had a positive effect on the survival of both aspen and spruce. Aspen experienced decreasing survival with size, which is most likely linked to age rather than competition. Significant effects of basal area of trees larger than the subject tree indicated that one-sided inter- and intra-specific competition, rather than two-sided, is the primary driving force of competition-related mortality for both aspen and spruce. Periodic annual increment in diameter was a better predictor of survival than basal area of larger trees, indicating that growth rate is the most important individual characteristic that defines survival of both aspen and spruce in these self-thinning stands.