Study on the Population Structure and Dynamic Characteristics of Kandelia obovata in the Northern Marginal Introduction and Natural Distribution Regions of Mangroves in China

This study aims to provide a scientific basis for the management and conservation of Kandelia obovata forests in the northern marginal introduction and natural distribution regions of mangroves in China, as well as to inform future northward expansion of mangroves. Based on field plot survey data, the population structure and dynamics of K. obovata plantations established since 1957 on Ximen Island, Zhejiang Province, and natural K. obovata populations in Fuding, Fujian Province, were characterized. The results reveal significant differences in height and diameter class structures between the two populations. The artificial population on Ximen Island was dominated by individuals with heights of 1.0-1.5 m and diameter classes Ⅲ-Ⅵ, with no individuals below 0.5 m in height or in diameter class Ⅰ. In contrast, the natural population in Fuding primarily consisted of individuals with heights of 2.0-2.5 m and below 0.5 m, and the diameter classes were mainly distributed in classes Ⅰ and Ⅳ-Ⅵ. Both populations exhibited Deevey Ⅱ-type survival curves, characterized by relatively high mortality rates. The survival rate and cumulative mortality rate curves of both populations were complementary, with peak mortality density occurring at the first age class. The dynamic indices indicate pronounced fluctuations in V_n for both populations, with V_pi > V′_pi > 0, suggesting an overall growth trend but high sensitivity to external disturbances. Long-term projections of the artificial population on Ximen Island showed an increase in older individuals and a decline in younger individuals over 2, 4, 6, 8, and 10 age classes, indicating difficulty in sustaining long-term population growth. In contrast, the natural population in Fuding was projected to increase steadily over extended periods. Spatial analysis show that all four developmental stages of the natural population in Fuding and the small tree group of the artificial population on Ximen Island exhibited aggregated distribution patterns. In contrast, the large tree and old tree groups in the artificial population in Ximen Island displayed uniform distribution patterns. Overall, the growth performance, population development, and structural stability of the K. obovata plantation in Ximen Island were inferior to those of the natural K. obovata forest in Fuding.