Rod Thesium (lněnka) má v České republice zastoupení v osmi druzích, z nichž polovina má status kriticky ohrožených. Informace o jejich populační biologii a ekologii by nám mohly velice pomoci v účinnější ochraně tohoto rodu, avšak informací je zatím velice málo a naše studie byla jednou z prvních zabývajících se specifitou vazby na hostitelské druhy tohoto poloparazita. and Genus Thesium is represented with eight species in the Czech Republic and half of them are critically endangered. Thus information about population biology and ecology would be very useful for effective conservation of this genus. However, this information is very scarce and our study was one of the first dealing with the relationship with host plants at this hemiparasite.
Landscapes are constantly changing and, for plant species, this means that some suitable patches disappear while others emerge. Distribution of species in the landscape depends, therefore, not only on actual distribution of suitable habitat patches but also on a species’ ability to persist in habitats that are already unsuitable and disperse to habitats that have become suitable. Distribution of species in such landscapes thus strongly depends on the spatio-temporal structure of the landscape and species traits. The present study aims to determine to what degree past land use affects the present distribution of dry grassland plant species at a regional scale. We studied the distribution of 52 dry grassland species in 215 grassland patches. Data on bedrock, slope, potential irradiation, area and past land use for two periods (1950s and 1980s) were collected from maps. Multivariate analysis was performed to assess the relative contribution of environmental and historical factors on present species distribution. In addition, analyses were carried out to reveal the relationship between past land use and occurrence of single species. This study shows that dry grasslands are habitats with rapid land-use changes. Distribution of species in these habitats is largely determined by environmental conditions, but past land-use also has a significant effect. In many species, the effect of past land use is even more important than the effect of environmental conditions. For the species investigated, those restricted both to former pastures and fields could be identified. Only a minority of species are restricted to continuous grasslands. This indicates that many species colonized places cultivated in 1950 within 50 years, suggesting that the dynamics of these species is relatively fast. The results suggest that many dry grassland communities in the region are of recent origin and the distribution of species in these habitats is partly determined by past land use. In addition to information on environmental conditions, detailed knowledge of land use history, landscape structure and species attributes is needed in order to understand the distribution of species in dry grassland communities.