Population dynamics of Agrimonia eupatoria and Geum rivale, two perennial grassland species

The population dynamics of two polycarpic perennials, Agrimonia eupatoria and Geum rivale, characteristic of semi-natural grasslands in Scandinavia, were examined in south-eastern Sweden. The perennial forbs were studied for several years in two populations each, located in habitats characteristic for the species in the study area. Demographic transition probabilities varied significantly between populations and among years for the species. Transition matrix modelling yielded lambda-values (population growth rates) that ranged from 0.89 to 1.14 for A. eupatoria and from 0.94 to 1.04 for G. rivale. The elasticity analysis showed that stasis in the adult stage classes contributed most to lambda. The life-table response experiment analysis produced similar results as the elasticity analysis, where stasis together with progression in the adult stage classes made a large contribution to the observed spatial variation in lambda. Simulations of expected time to extinction were in the order of centuries for the study populations. Seedling recruitment was enhanced by seed addition and small scale disturbance in populations. For the intermediately abundant and more patchily distributed A. eupatoria, a regional survey of local populations was conducted in the study area which revealed that most populations were relatively small (< 100 individuals) and restricted to grassland fragments in road verges. Furthermore, an attempt was made to estimate fruit dispersal from local populations.