The Effect of Forest Habitats on the Traits and Demographic Structure of Cardamine bulbifera (Brassicaceae) Populations

The conservation of plant species requires detailed knowledge of their reproductive behaviour and population demographic structure. This is particularly important for species such as <i>Cardamine bulbifera</i>, which depend on old-growth forest habitats and rely predominantly or entirely on vegetative reproduction through axillary bulbils. Although <i>C. bulbifera</i> has a wide native range, little is known about its population structure and dynamics. The aim of this study was to assess the demographic composition, density and main traits of <i>C. bulbifera</i> individuals in six populations occurring in three types of forest habitats in southern Lithuania: Fennoscandian hemiboreal natural old broadleaved deciduous forests, Fennoscandian herb-rich forests with <i>Picea abies</i> and <i>Galio-Carpinetum</i> oak-hornbeam forests. Field studies were conducted in 2023, during which a total of 20 sampling plots (each 1 m²) were analysed in each population, arranged in a transect. The study revealed an absolute dominance of young (juvenile and immature) individuals in the populations (89.2%), whereas mature individuals comprised only a small fraction (10.8%). The proportion of mature individuals was significantly larger in hornbeam forests than in the other two forest types. The highest density of individuals was recorded in broadleaved forest, while the lowest density was found in spruce forest habitat. Mature <i>C. bulbifera</i> individuals in hornbeam habitats were significantly taller and had longer inflorescences than those in other habitats. The highest mean number of bulbils was produced by individuals of the studied species in spruce habitats, while bulbil production was lowest in hornbeam habitats. The strongest negative contribution to the number of <i>C. bulbifera</i> individuals was the area of bare soil in the sampling plot, whereas herb cover had the strongest positive effect. These results highlight habitat-specific differences in <i>C. bulbifera</i> population structure and suggest that the long-term viability of its populations is closely associated with forest type, as well as stability of the habitat and plant community. The optimum habitat conditions for <i>C. bulbifera</i> are found in old broadleaved forests, and habitats with natural succession are the most favourable for its growth and conservation.