Abies alba and Senecio rivularis - two of 44 mountain species reported from the Roztocze Highlands, SE Poland were objects of the study. Both species reach the north-eastern limits of their occurrence in this region. In case of Abies alba, the extent of its habitat niche and possibility of adaptation to alternative niches at the range limits were investigated in two areas of the Roztocze Highlands - the Roztocze National Park (RNP) and gorge sections of four river valleys (RV) of a mountainous

more »

... haracter. In both landscapes, fir prefers mineral soils that are too leachy for deciduous species and even for spruce. In the RV sites, fir seems to have a much broader ecological scale and often colonizes organic soils with wet mixed coniferous forests with spruce, ash-alder, and bog alder forests. The studies on Senecio rivularis are an example of long-term ecological studies at the population level, conducted in the RNP since 1987, e.g., in terms of changes in the size structure of individuals compared to the changes in the surface area covered by this population. A nearly 3-fold increase in the area inhabited by the population was accompanied by changes in the spatial organisation of the population and individual size structure dynamics, which reflects the intensification of intra- and interspecific competition, and indicates condition changes in the population area.