The study of the transformation of segetal flora richness and diversity in selected habitats of southern Poland over a 20-year interval

The aim of study was to evaluate diversity of segetal flora and its transformations over a more than 20-year period in 19 field habitats representative for cereal crops of southern Poland. The research hypothesis assumed that: (i) the diversity of habitat conditions determines the abundance of arable land flora, (ii) it also affects farming intensity which is the main cause of the decline in the biodiversity of agrocoenoses.Based on 415 phytosociological relevés (sampled using the Braun-Blanquet method), weed species richness (Sr), phytosociological constancy of species (S), cover index (D), Shannon’s diversity index (H) and Simpson’s dominance index (C) were determined. Measurements were done for each habitat during two research periods. The results were subjected to ANOVA analysis. To assess the similarities of the studied habitats’ weed flora in each period and their changes over time, Ward’s hierarchical cluster analysis was used. The distance matrix was calculated from Jaccard’s similarity indices. The results are presented in the form of hierarchical trees.The study showed that species richness of the weed communities and their diversity were strongly determined by habitat conditions. Preservation of the value of the diversity index and even its increase (especially in a considerable part of mountain habitats) showed that extensive methods of reducing weed infestation had remained at a similar level of efficacy during the 20-year interval. Hierarchical cluster analysis showed differences between the first and second study period in the weed communities for habitats of lowland soil complexes. The exception were the habitats with the greatest potential for crop cultivation, located on chernozems and rendzinas. In the mountain habitats, there were no significant changes in the segetal flora during the study interval. An increase in weed flora abundance indicates a lack of threats to the diversity of agrophytocoenoses in this part of Poland.