A b s t r a c tThe characteristics of phytocenoses developing on light soils in cereal crops of the Łuków Plain are presented in the paper. The studies were carried out between 2003 and 2006 in 182 localities. Cereal crops on light soils were frequently occupied by patches of Arnoserido-Scleranthetum. The association reaches the eastern limit of its geographic range in the mesoregion. The phytocenoses were noted under various moisture conditions and were the floristically poorest cereal communities in the studied area. The paper presents new data on the occurrence of Arnoserido-Scleranthetum on its eastern distributional limits. Quite frequently, the patches of Vicietum tetraspermae scleranthetosum, especially of its variant with Juncus bufonius and Vicietum tetraspermae typicum variant with Rhinanthus serotinus, were also frequently noted in the studied mesoregion. Small patches of Papaveretum argemones were recorded very seldom.

Plant communities of the cultivated fields of the Podlaski Prze³om Bugu mesoregion. Part 2. Cereal communities (Otrzymano: 20.12.2004) S u m m a r yPresence of communities without species characteristic for cereal associations was observed in the cultivations of the Podlaski Prze³om Bugu mesoregion. Community Scleranthus annuus and community with species characteristic for alliance Aperion spica-venti were observed in winter cereals. Phytocoenoses similar in floristic composition to root cultivations were noted in spring cereals of the studied area. Plots of communities with participation of species characteristic for alliance Panico-Setarion were observed on loose soils while on more compact and fertile habitats community with species characteristic for Polygono-Chenopodion was noted.

S u m m a r yCharacteristic of plant communities developing in the cereal cultivations of the Podlaski Prze³om Bugu mesoregion is presented in the paper. This agricultural region is partially situated in the borders of the ,,Podlaski Prze³om Bugu" Landscape Park. Extensive agriculture as well as large soil and microclimatic diversity resulted in occurrence of rich, floristically differentiated agrocoenoses. Three associations from the alliance Aperion spicae-venti were noted in the studied area. Association Vicietum tetraspermae was the most common and inner differentiated. Four subassociations: Vicietum tetraspermae scleranthetosum, Vicietum tetraspermae myosotidetosum, Vicietum tetraspermae typicum, Vicietum tetraspermae consolidetosum and 18 lower syntaxonomic units were distinguished. Plots of Papaveretum argemones, differentiated into 3 subassociations: Papaveretum argemones scleranthetosum, Papaveretum argemones typicum and Papaveretum argemones consolidetosum were noted seldom in the studied area. In the central part of the Podlaski Prze³om Bugu mesoregion occurrence of a single plots of Arnoserido-Scleranthetum was noted.

The work presents the results of studies on the diversity of weed communities in tuber crops as well as in winter and spring cereals under similar climatic and soil conditions. We examined overall species abundance in the groups analysed, the average species number per relevé, as well as weed cover of the study area. Additionally, species composition, number of individual species and their biomass were determined. Dominant species in each crop group were distinguished. Species diversity was determined based on the following ecological indices: the Shannon-Wiener index of biodiversity H’ and Simpson’s index of dominance C. The indices were computed on the biomass and number-of-species basis. The objective of the work was to compare the structure and diversity of weed communities in the crops studied. The communities analysed differed in all the characteristics examined. Differences were found between biodiversity and dominance indices calculated for individual crop groups, but their significance depended on the method applied to calculate the indices

A b s t r a c tThe work presents the results of a study on the biodiversity of agrocenoses using ecological indices. In order to calculate the measures, phytosociological relevés were made and exact methods were applied in winter cereals, spring cereals, tuber crops and stubble fields. The objective of the work was to compare ecological indices (Simpson's index of dominance C, Simpson's index of species richness D, and Shannon-Wiener index of biodiversity H') calculated using the number of plants and their cover determined based on the degree of presence. Moreover, correlation analysis was conducted between the indices computed using the two approaches applied.The results of the study revealed significant differences between all the indices calculated using the exact and approximate methods. In turn, comparisons of the measures computed for individual crops showed significant differences only for potato crops and winter cereals. No significant differences were found between the indicators calculated for spring cereals and stubble fields.