关键词: 极小种群野生植物, 钝头杜鹃, 种群结构, 种群动态, Deevey-Ⅱ型存活曲线

Abstract

Aims: Rhododendron farinosum, a plant species with extremely small populations (PSESP) endemic to northeastern Yunnan, China, has been listed as an endangered species. However, its population structure and dynamic characteristics have not yet been reported, and its future trends remain unclear, which hampers the formulation of science-based conservation strategies. This study aims to elucidate the current status, regeneration bottlenecks, and future successional trends of R. farinosum populations, so as to provide a scientific basis for its conservation and population recovery. 

Methods: We selected three natural distribution sites—Langniping (LNP), Yaoshan (YS), and Lengjiaping (LJP) and established four 20 m × 20 m permanent plots. Basal diameter was used as a proxy for age, and all individuals were classified into eight age classes. Growth parameters of all individuals were systematically recorded using the plot survey method. Static life tables were constructed, survival curves were plotted, and comprehensive assessments of age structure, population dynamics, and future trends were conducted through population dynamic quantification analysis (V_pi, V'_pi), survival analysis, and time-series prediction (over 2, 4, 6, and 8-age-class intervals). 

Results: All three populations exhibited a declining age structure, dominated overwhelmingly by middle-aged and old individuals, with a marked scarcity of young individuals. The survival curves of all populations conformed to the Deevey-II type, as confirmed by exponential model fitting, indicating relatively constant mortality rates across age classes. The dynamic indices revealed that V_pi exceeded V'_pi and both were positive for all three populations, suggesting a potential for population growth but a limited buffering capacity against external disturbances. Survival analysis indicated that hazard rates increased progressively with age, cumulative mortality rose steadily, and individual survival capability declined continuously across successive age classes. Time-series predictions showed that over the next 2 to 8 age-class intervals, only age classes III and VIII in the Langniping population, III, IV and VII in the Yaoshan population, and II and VI in the Lengjiaping population were projected to increase, whereas all other age classes were projected to decrease. These projections consistently point to an insufficient recruitment of young individuals across all populations, ultimately leading to population decline. 

Conclusion: Anthropogenic disturbances (grazing and trampling), inhibited seed germination (thick moss layers preventing seed–soil contact, rocky and nutrient-poor substrates, and landslide-induced seed burial), and harsh habitat conditions are the primary causes of the severe shortage of young individuals and the consequent population decline. We recommend four targeted interventions—micro-reserve designation, habitat amelioration, artificial supplementary pollination (to enhance genetic diversity), and artificial propagation with reintroduction to promote population regeneration and recovery. This study provides a population ecology reference for the formulation of conservation strategies for R. farinosum and other endangered Rhododendron shrubs with similar life-history traits.

Key words: plant species with extremely small populations, Rhododendron farinosum, population structure, population dynamics, Deevey-II type survival curves