Silaum silaus (L.) Schinz and Thell.—Habitat Conditions and Variation in Selected Characteristics of Populations at Different Densities

Grasslands are one of the most diverse and species-rich ecosystems in the agricultural landscape of Central Europe. However, they are gradually being overgrown or transformed into arable fields due to their abandonment and the intensification of economic activities. This leads to a drastic decline in biodiversity and the disappearance of many rare species, e.g., Silaum silaus . Research on Silaum silaus populations was conducted in the years 2020 and 2022. Data were obtained from two Natura 2000 sites. The Jaćmierz site is located in a dispersed range of Silaum silaus in south-eastern Poland. The site at Zagórzyce is located in a dense range of the species in the south-western part of the country. Research on the habitat conditions was conducted on two permanent study surfaces with the dimensions of 10 × 10 m. This research included a soil study and measurements of herbaceous vegetation. To determine the habitat conditions, use was also made of Ellenberg ecological indicator values. At each site, 10 phytosociological relevés were conducted with the Braun-Blanquet method. In each study year, the manner of land use was determined. For detailed population study, one permanent surface of the dimensions 10 × 10 m was marked out, on which each year the generative and vegetative specimens were counted and biometric studies were conducted on 30 randomly chosen generative specimens. The species occurred in two different meadow communities ( Arrhenatheretum elatioris , Molinietum caeruleae ), which were characterised by different habitat conditions, and the greatest differences were evident in the chemical properties of the soil and in the method of management. The meadows at Jaćmierz were mowed twice a year, while at Zagórzyce mowing was performed once every two years. The communities were also varied in terms of flora, characterised by a high species richness and a high Shannon–Wiener index. Silaum silaus had significantly greater numbers and an over four times higher cover coefficient at Jaćmierz. The largest differences in the analysed traits of the species occurred in the case of generative traits. It was observed that management practices at Jaćmierz had a strong influence on the condition of specimens and the population size of Silaum silaus , which was much better preserved at this site.