INFLUENCE OF SINGLE TREES ON FLORISTIC DIVERSITY OF STEPPE MEADOWS AND POPULATION STRUCTURE OF SOME RARE PLANT SPECIES

Abstract

In the zone of broad-leaved forests of the European Russia, steppe meadows have been preserved showing rich floristic composition and making a significant contribution to the biological diversity of the territories. Bryansk oblast is one of the forest regions in Russia where such meadows are found. Here, steppe meadows with high floristic diversity and a large number of rare plant species have survived. Trees from surrounding forest areas are constantly encroaching on these meadows. Most of the young trees die from regular grass fires and economic activity. However, some individuals survive and reach a generative state, becoming relatively resistant to ground fires. The influence of single trees on the floristic diversity of steppe meadows was studied at two levels of living system organization – coenotic and population levels. Polydominant steppe meadows and polydominant steppe meadows with single generative trees were studied at the coenotic level; and coenopopulations of Iris aphylla, Anemone sylvestris, and Anthericum ramosum were studied at the population level. Collecting the material, we used different methods: geobotanical, demographic, and measurements of environmental factors (illumination, slope steepness, and the frequency of grass fires). Polydominant steppe meadows were found to be were preserved in the middle part of steep slopes unsuitable for haymaking and grazing and subjected to infrequent grass fires. These communities have high floristic diversity and stable coenopopulations of model species. Ontogenetic spectra of Anemone sylvestris, Anthericum ramosum, and Iris aphylla are of the complete left-hand type with the maximum number of individuals. Single trees (Quercus robur, Tilia cordata) have controversial influence on the vegetation of polydominant steppe meadows. On the one hand, with the introduction of trees, species diversity of communities increases. This is due to the fact that trees offer resting places and shelter for birds that spread plant diaspores. On the other hand, mature trees shade the herb cover. This leads to cover reduction and occurrence of steppe and dry meadow species, as well as affects their population structure. The ontogenetic spectrum of Anemone sylvestris is still complete, whereas that of Iris aphylla becomes incomplete, and the spectrum of Anthericum ramosum becomes unfinished.