Assessment of the Status of Cephalanthera longifolia Populations in Lithuania Derived from a Single-Census Study

The study of plant demography is important for identifying ongoing population processes and trends. While single-census studies have limited ability to capture long-term dynamics, they are crucial for establishing baseline data on the status of plant populations. In 2022, four populations of Cephalanthera longifolia (Orchidaceae) in Lithuania were studied using a standardised sampling plot method. Within each population, 20 plots were established along a transect. All plant species within each plot were recorded, and their coverage was estimated. Additionally, the height of the plants, the cover of plant debris, and the amount of bare soil in the sampling plot were assessed. Vegetative individuals of C. longifolia were dominant across all populations, comprising between 58.7% and 85.1% of all individuals. Combining data from all populations revealed that vegetative individuals accounted for 71.8% of the total population, while generative individuals accounted for the remaining 28.2%. The mean density of individuals in the studied populations ranged from 3.8 ± 2.3 to 11.1 ± 4.3 individuals per square metre. A comparison of plant traits (plant height, inflorescence length, number of flowers in inflorescence, number of fruits set, and number of leaves) was performed between populations. Increased cover of plant debris was found to have the strongest negative effect on the number of individuals. We believe that the demographic type of a population (dynamic, normal or regressive) should be assessed in the context of the life cycle of certain species and their ecological traits, rather than mechanistically. Under reduced light availability, most individuals remained in a vegetative state. Therefore, the ratio of generative to vegetative individuals reflects current habitat conditions rather than long-term population trends.