Влияние одиночных деревьев на флористическое разнообразие и популяционную структуру редких видов растений остепненных лугов

Abstract

Steppe meadows preserved in the zone of deciduous forests of European Russia. These meadows have rich floristic composition and contribute significantly in biological diversity of territories. Bryansk region is one of the forest regions, where steppe meadows are sustained. There are meadows with high floristic diversity and big numbers of rare plant species. Trees from the surrounding forest areas insinuate constantly into these meadows. Most of the young trees die from regular fires and human agricultural activity. However, some individuals survive and pass into a generative state, in which they are relatively resistant to ground fires. The influence of single trees on the floristic diversity of steppe meadows was studied at two levels of organization of living systems – coenotic and population. Polydominant steppe meadows and polydominant steppe meadows with single generative trees were studied at the coenotic level. Coenopopulations of Iris aphylla, Anemone sylvestris and Anthericum ramosum were investigated at the population level. Different methods were used in the work: geobotanical, demographic, measuring environmental factors (luminance, steepness of slopes and frequency of fires). The study showed, that polydominant steppe meadows are supported on steep slopes unsuitable for haymaking and grazing and subjected to infrequent fire. These communities have high floristic diversity. Coenopopulations of model plants (Anemone sylvestris, Anthericum ramosum and Iris aphylla) are sustained there. Their ontogenetic spectra belong to left-hand type with maximum number of individuals. Single trees have controversial influence on polidominant steppe meadow vegetation. On the one hand, the species diversity of steppe meadows increases with the appearance of single generative trees because birds use adult trees like habitats and birds carry plant diasporas. On the other hand, mature trees shade grass canopy. It leads to decline of cover and occurrence of steppe and dry-meadow species. Also it affects plants coenopopulation structure. Ontogenetic spectrum of Anemone sylvestris stays full-stages but numbers of individuals is low. Ontogenetic spectrum of Iris aphylla loses ontogenetic stages (g1, g3) with numbers of individuals twice lower than on polidominant steppe meadows. Ontogenetic spectrum of Anthericum ramosum becomes incomplete with extremely low numbers of individuals.