Papulation ecology is a currently developing direction of studies in plant ecology. The paper presents the state of the art in research on the population of meadow plants. Distinguishing of a individual and evaluation of its age creates many methodical challenges in the case of perennial herbaceous plants. Progress in population studies of many species of perennial plants occurred when criteria allowing determination of the age of a individual and the distinguishing of agestates in its life cycle were adopted. Age structure, dynamics of abundance and developmental phases of the population embracing many species of plants in meadow phytocenoses have been studied. The shaping of phytocenoses, their fluctuations and cyclic variability, as well as exchange of species in the course of succession results from transformation within populations, mutual relations between populations of differentspecies and changes in environmental conditions.
Grasses are the clonal plants of modular structure. Formation of the tussock grasses and the system of numerous branching in stoloniferous grasses is realized by multiple repeatibility of the basic units - modules. The clonal growth is accompanied by simultaneous processes of plant growth and death. Persistence, understood as a sustained maintenance of the species in meadow plant community, is the notion very wide and complicated; it includes the complex of problems to be considered just on the onthogenetic and population levels.
The processes determining the formation and structure of grassland community are realised at threee levels: the genetic individual (genet, clone), the population and the community. Clonal plants are the dominant species in a grassland community. Clonal growth, modular structure of the plants, as weil morphological and physiological properties and adaptations such as: modification of shoots to form stolons and rhizomes, morphological and physiological integration of modules (ramets), disintegration of the clone and independence of rooted ramets, and growth and death of ramets in the life cycle of clonal plants, inlfuence the life span of the genet, the way of the clone's spreading and the position in the community. The above traits have a significant influence on the regeneration of plants after mowing and grazing, as weil as on the resistance to environmental disturbances. The possibility of increased population abundance through generative and vegetative reproduction is a characteristic trait of clonal plants. Clonal growth of plants, the pattern of spatial formation of the clone, interactions and reciprocal compromises between the species in the neighbourhood have a significant influence on the coexistence of various species in a grassland community. Clonal plants are adapted to mowing and grazing. The abandonment of seminatural grassland causes unfavourable changes to the community structure and its species composition.