Age structure and dynamics of Picea wilsonii population in Datong River basin of Qilian Mountains, China.

Abstract

Taking Picea wilsonii population in the Datong River basin of the Qilian Mountains as research object, we analyzed the age structure, population dynamics, and future development trends of the population by constructing static life tables and survival curves, and combining with survival functions, spectral analysis, and time series models. The results showed that based on the inclusive upper limit method with 5 cm diameter at breast height (DBH) intervals, P. wilsonii population was classified into 15 age classes (Ⅰ-ⅩⅤ), corresponding to four growth stages: juvenile (0 cm60 cm, ⅩⅢ-ⅩⅤ). The abundance of P. wilsonii decreased with age, with juveniles accounting for 58.3%, indicating that the population was in the juvenile forest restoration phase. Throughout the life cycle, both the natural-state dynamic index (V_pi) and disturbance-state dynamic index (V_pi') were greater than 0, but V_pi' was significantly lower than V_pi, reflecting the dual characteristics of growth potential and ecological vulnerability. The survival curve conformed to the Deevey-Ⅱ B₁ subtype, characterized by survival rates fluctuating around the theoretical diagonal and significant differed in survival numbers between developmental stages. Survival function curves revealed a dynamic pattern of initial growth, mid-phase sharp decline, and late-phase gradual recession in population size. Spectral analysis indicated that population dynamics was dominated by the fundamental wave with minor periodic disturbances, and that the late juvenile and middle-aged stages were critical nodes for population fluctuations. Time series predictions showed that within the next 10 age-class periods, individuals in age classes Ⅲ-Ⅵ would decrease, while those in classes Ⅶ-ⅩⅤ would continue to grow. In conclusion, P. wilsonii population in the Datong River basin of Qilian Mountains is a stable and growing population. If not subjected to severe disturbances, it would develop into a mature forest.