The article presents data on the yield and ontogenetic structure of dominant species of meadow ecosystems in the floodplain of the Sozh river in Chechersk district, Gomel region. Five meadow ecosystems have been studied. The aim of the study was to reveal the yield and ontogenetic structure of the dominant species of the meadow ecosystems in the floodplain of the Sozh river. Geobotanical, ecological, floristic, radiological and agrochemical methods have been used in the research. It was established that soils of three meadow ecosystems (e.i. Poetum angustifoliae, Agrostio vinealis - Calamagrostietum epigeios, Caricetum gracilis) are similar to neutral, while the soils of Deschampsietum cespitosae and Poo - Festucetum pratensis associations are slightly acidic. The soils have low amount of mobile potassium, while the content of mobile phosphorus is medium. The studied soils are characterized by a low content of organic matter. The highest yield was recorded in the Caricetum gracilis association (3.58 t/ha of dry weight), and the lowest was in the Poetum angustifoliae association (1.87 t/ha of dry weight). Two associations, i.e. Deschampsietum cespitosae and Poo-Festucetum pratensis, had almost equal yield (3.06 and 3.13 t/ha of dry weight, respectively). The yield of meadow ecosystems is related to their location in the floodplain and depends on the floristic composition, as well as on the dominant species, which contribute significantly to the formation of the aboveground phytomass yield. Since the specific activity of cesium-137 does not reach 1300 Bq/kg and the content of radiostrontium-90 in the aboveground phytomass did not exceed the accepted level of 260 Bq/kg, then herbal fodder can be used with no limits. The highest density of individuals per m2 was recorded in the Poa angustifolia (60.7 individuals per m2) and Poa pratensis (60.9 individuals per m2) coenopopulations and was almost similar. The lowest density was recorded in the Carex acuta (23.7 individuals per m2) and Deschampsia cespitosa (37.9 individuals per 1 m2) cenopopulations. Middle-aged generative plants prevail in the ontogenetic structure of studied dominant species cenopopulations (37.1-51.1%). Immature, virgin and young generative plants with a small number of old generative ones make it possible for the populations to hold a sustainable position in the associations and maintain a stable yield of grass stand.
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