EFFECTS OF GRASSLAND EXTENSIFICATION ON THE POPULATION-DYNAMICS OF THE INVASIVE SPECIES CHAEROPHYLLUM-AUREUM

The consequences of extensification on grassland invasion by weeds was studied in French Pyrenean hay-meadows through a survey of the popula tion dynamics of one very successful colonizer: Chaerophyllum aureum. Experiments established in natural permanent grasslands allow us to te st the effect of different intensities of cutting on the demography of adult and seedling populations and on the production of seeds and the ir survival in soil. Although an early cut can control population dens ity by drastically reducing invasion by new genotypes, the results rev eal a positive effect of early cutting on adult and seedling survival probably by decreasing intraspecific competition. Allocation of resour ces to sexual reproduction in response to cutting is limited, affectin g especially the seed viability in soil. Nevertheless, the invasive ab ility of this species is due largely to a strategy whereby those adult s showing a high survival rate tend to be perennial.