The age structure of the coenopopulations of Tulipa biebersteiniana Schult. et Schult. fil. (Liliaceae) on the Ergeninsky Upland

Background. Data on the age composition of populations of rare and endangered plant species are necessary for studying succession processes, the structure of plant communities and the life status of species in their natural habitat. The species Tulipa biebersteiniana is listed in the Red Book of Kalmykia and a number of other regions of Russia and the age structure of its coenopopulations has not been sufficiently studied. Purpose. Study of the features of the age structure of Tulipa biebersteiniana coenopopulations on the Yergeni Upland (within the Republic of Kalmykia). Materials and methods. In five coenopopulations of T. biebersteiniana growing on the Ergeninsky upland, studies were conducted during the growing seasons of 2022-2023. When analyzing the age structure of T. biebersteiniana populations, a number of indicators were calculated: the recovery index (Ib), the index of individual optimum (I I.O.), the age coefficient (Δ), the energy efficiency index (ω). The classification of T. biebersteiniana cenopopulations by age structure was carried out using a number of modern approaches. The level of similarity of the age structure of populations was estimated using the similarity index (r) and the identity criterion (I) according. Results. The frequency of occurrence of plants of different age conditions in the coenopopulations of T. biebersteiniana, among which virginal and mature generative individuals prevailed, was determined. The constructed ontogenetic spectra of the populations of the species belonged to two types. The calculated indices characterizing the ontogenetic structure of T. biebersteiniana cenopopulations gradually changed from the northern part of the Ergeninsky upland to the southern one, correlating with the clinality of climatic factors, especially air temperature. The conditions of the second year of the study with lower air temperatures in January-April contributed to a decrease in the proportion of individuals of the generative period in T. biebersteiniana populations and, accordingly, an increase in the proportion of individuals of the pregenerative period. This led to an increase in their ability to recover, but a decrease in the values of the index of individual activity, the age coefficient and the energy efficiency index. All the studied cenopopulations are classified as normal and further, when detailing the type according to the "delta-omega" classification, they are classified as "maturing" and "young" types. Using the similarity index and the identity criterion, the similarity of the ontogenetic structure of the studied cenopopulations was revealed. At the same time, the level of similarity of the ontogenetic structure depended on the territorial proximity of the cenopopulations within the Ergeninsky upland. Conclusion. The ontogenetic structure of T. biebersteiniana cenopopulations on the Ergeninsky upland fits into two ontogenetic types. As we moved from the northern part of the upland to the southern, there was a gradual change in a number of statistical indicators of the ontogenetic structure of the population, which correlated with the climatic conditions of the year of growth, especially with the clinality of air temperature. The degree of similarity in the age structure of the studied coenopopulations of T. biebersteiniana depended on their territorial remoteness.