<p>The decline in the global biodiversity and the increase in the number of threatened plant species are the extremely unfavorable trends over the past decades. These phenomena determined the need for the thorough and detailed study of the plant population resistance mechanisms, and the development of the methods to predict the risks of their extinction. In the recent years, simultaneous assessment of the ontogenetic and the vital structure of the populations has become the most recognized method of studying populations. This approach has provided a significant increase in the reliability assessment of the population status and led to improved predictions of their dynamics. However, there are a limited number of the papers containing the complex demographic analysis, including the field size of the population, the number of individuals in the population, the population density, as well as genetic, ontogenetic, and vital structure of the populations with their dynamics. The purpose of this work was to determine the current state and to predict the possible trends in the status of seven rare plant species’ populations located on the territory of the National Nature Park “Desnyansko-Starogutsky” (Sumy province, Ukraine). Rare plants <em>Epipactis helleborine</em> (L.) Crantz, <em>Lilium martogon</em> L., <em>Listera ovata</em> (L.) R. Br., <em>Platanthera chlorantha</em> (Cust.) Rchb., and <em>Pulsatilla patens</em> (L.) Mill. are the species listed in the Red Book of Ukraine. Plant species <em>Circaea alpina</em> L. and <em>Pyrola chlorantha</em> Sw. are designated as the rare species on the territory of Sumy region. Integral estimation of the population status has based on the determination of such parameters as population size, population density, the ontogenetic index, and the index of the population vitality. Correlation analysis revealed a high level of correlation (r = 0. 99) not between everyone, but between some of the population parameters only. In our study, the indices that characterize the ontogenetic structure of the populations were the most frequently correlated: renewal index, generative index, as well as indexes of the population age (Δ) and the effectiveness of the population (ω). The regression analysis revealed that the long-term monitoring of the rare plant populations will be an integral character in the case of accounting for such factors as the population size and density dynamics over the years, changes in the population vitality (Q), and the annual changes of the magnitude of ω, which integrates the ontogenetic structure of the populations. It has been established that the populations of <em>L</em><em>.</em><em> martagon</em> from the phytocenoses of <em>Pinetum coryloso-maіanthemosum</em> and <em>Fraxinetum coryloso-convallariosum</em> were stable enough together with the progressive development trend. The populations of the rare species <em>C</em><em>.</em><em> alpina</em>, <em>L</em><em>.</em><em> martagon</em> (habitat between <em>Betuleta corylosa</em> and <em>Pineta corylosa-convallariosum</em>), and <em>P</em><em>.</em><em> patens</em> were estimated as the sustainable. A clear tendency toward a decrease in the individuals’ number was found in rare species represented by only one population (<em>L. ovata</em>, <em>P. chlorantha</em>, and <em>Pl. chlorantha</em>), as well as in one of the several populations of the species <em>C</em><em>.</em><em> alpina</em><em> </em>and <em>E. helleborine</em>. It was confirmed, that the dynamics of the rare plant populations is influenced not only by the internal population processes. The external ecological and coenotic factors, including the ones of a catastrophic nature, which are associated with the succession processes, as well as the level of wildlife conservation in the natural areas of Ukraine can be of decisive importance.</p>
Population status and variation of the rare species Neotinea tridentata (Orchidaceae) under anthropogenic load conditions in the meadow phytocenoses of the Central Caucasus
