资源环境科技发展态势分析平台

Canopy openings resulting from tree death provide opportunities for shade intolerant species such as aspen to establish and grow in the understory leading to development of aspen stands with multiple canopy layers and multiple cohorts. Stand structure is likely to influence survival probability since it will lead to differences in competition intensity and in resource utilization. We examined relationships among stand age (years after stand establishment), age structure (age diversity), and tree size diversity (i.e., diversity of diameter classes), using cores collected from 531 aspen trees in 18 stands distributed across the province of Alberta, Canada. Results show positive relationships between stand age, age diversity, and tree size diversity. Logistic mixed effects survival probability models were developed using data from 199 remeasured permanent sample plots. Results show an inverted U-shaped relationship between survival probability and tree diameter. Survival probability trends varied between young (<= 60), mature (> 60 and <= 100), and old (> 100) age groups in relation to differences in competition intensity and stand structure. Intraspecific competition (deciduous basal area larger) was negatively related to tree survival and the magnitude of the negative impact was stronger in the young age group. Negative effects of structural diversity (tree size diversity) on survival probability were strongest in the mature age group. We suggest that effects of tree size diversity relate to environmental stresses and competition at the stand level while the influence of deciduous basal area larger serves as a measure of competition experienced by individual trees. The significance of mean annual temperature in our models indicates that, under warmer conditions, competition variables (e.g., deciduous basal area larger and tree size diversity) had stronger effects on tree mortality with the magnitude of effects varying between age groups.