Impact of natural factors on population changes of herbaceous plants species and assessment of their state in present high-mountain conditions of the Ukrainian Carpathians

Background. Natural ecosystems of the Ukrainian Carpathians have been signi­ficantly transformed during the last few years due to the impact of climate factors and an increased activity of nature restoration processes. The study of the influence of the external environ­mental factors on populations of the herbaceous plant species is particularly topical for the high-mountain ecosystems. As a result of gradual restoration of native plants, specific changes occur in the structural and spatial organization of populations of many herbaceous plant species. Thus, considering the increased climate changes and regenera­tive activity, the assessment of the present condition of the populations of herbaceous plant species, their regenerative ability, response to changing environmental conditions and individual peculiarities of performance in the altered environmental conditions are important. Methods. The conventional stationary and route-field methods were applied in order to determine changes in the structural organization of high-mountain plant populations and their regenerative ability. The initial diagnostic parameters of the populations’ condition include the individual growth peculiarities and the nature of dynamic trends under the changed environmental conditions. During the ontogenetic development of plants, the most important changes occur within the generative phase that ensures the rege­nera­tion and self-maintenance of populations by means of seeds; those changes are a significant indicative feature. The long-term observations of different types of plant communities were applied; these included the records of the main parameters and characteristic features at permanent test sites. The transects are located in the alpine, subalpine and upper forest belts of the Ukrainian Carpathians within 1000–2000 m a.s.l. altitudinal range. The study comprises such behavioral features of the species populations as phenological (intensity phenophase, flowering rhythmics), demographic (number of individuals, spatial differentiation), reproductive (generative reproduction, seed productivity), etc., which enable the determination of their adaptation and ability to exist under the changed environmental conditions. Results. The continuous monitoring of different high-mountain plant aggregations showed that in some cases the number of species which are distinguished by active regenerative strategy aimed at further extension of the habitat is growing, while in other cases the species demonstrated the opposite trend resulting from their inability to adapt to changing habitat conditions. It has been determined that the vegetative development of the populations of high-mountain plant species is closely related to temperature conditions which influence phenology, dynamics of the numbers of individuals and the nature of their reproduction. A significant influence of warming on the processes of seasonal development of populations and flowering abundance is evidenced by their increased number and migration to much higher hypsometric levels of the high-mountain zone. The increased ability to generative reproduction contributes to the dissemination of seeds and formation of new population loci Valeriana simplicifolia, V. transsilvanica, Silene dioica, Astrantia major, Doronicum carpaticum, Euphorbia carniolica, etc. in favourable micro-habitats at significantly higher hypsometric levels of the high-mountain zone (1600–2000 m a.s.l.). Another natural factor of changes in populations of herbaceous plant species is the impact of restoration succesions in different types of plant communities. These changes are usually accompanied by increased shading and crowding of vegetation due to the spread of more competitive tree and shrub species as well as adventive species of tall herbaceous plants. It refers mostly to grassland species that need open sites for the effective population recruitment. Radical changes can be observed in the structural organization of the populations of herbaceous plants species due to an increased cenotic activity of more competitive species. Such changes reduce the regenerative ability of the populations of herbaceous plants species and trigger their fragmentation. Thus, the change of ecological and cenotic conditions of various plant communities along the elevation gradient of the highlands predetermines different charac­teristic features of the populations of herbaceous plant species and their unequal spatial differentiation. Conclusions. It has been determined that present natural processes occurring in the populations of herbaceous plant species of the high-mountain zone controversially influence their regenerative ability and the nature of changes in their structural organization. The dynamics of populations in each separate case is defined by the influence of natural and climate changes and their association with particular plant communities along the elevation gradient of the high-mountain zone. The multi-year dynamics of the numbers of generative individuals represents their regenerative ability in populations and dependence on weather conditions. The important feature of active regeneration of the populations is the development of their local foci in favorable microhabitats at significantly higher hypsometric levels of the high-mountain zone, in particular, the alpine and the upper margin of the alpine. Occurrence of new populations loci is indicative of their ability to reproduce and survive. In some cases, the dynamic trends in populations are accompanied by an increased number of individuals and extension of their habitats, while in other cases, trends are the opposite, which is caused by a decreased number of individuals and their degradation. The processes which are observed during the regeneration of species populations are related to their ascending extension to various hypsometric levels, as well as the strengthening of the positions of the populations of tree and shrub layer species and adventive representatives of tall herbaceous plants which are peculiar to lower layers. Significant overgrowth processes, which result in gradual exclusion of herbaceous plant species typical of meadow communities aggregations, are observed in the habitats of the populations of many types of herbaceous plants and at the upper margin of the forest and subalpine layers. Thus, the changes in ecological and cenotic conditions of various plant communities along the elevation gradient of the highlands predetermines different characteristic features of the populations of herbaceous plant species and their unequal spatial differentiation