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

Abstract

The population dynamics of two polycarpic perennials,Agrimonia eupatoria and Geum rivale, characteristic ofsemi-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 populationsand among years for the species. Transition matrix modelling yieldedλ-values (population growth rates) that ranged from 0.89 to 1.14 forA. eupatoria and from 0.94 to 1.04 for G.rivale. The elasticity analysis showed that stasis in the adultstageclasses contributed most to λ. The life-table response experimentanalysis produced similar results as the elasticity analysis, where stasistogether with progression in the adult stage classes made a large contributionto the observed spatial variation in λ. Simulations of expected time toextinction were in the order of centuries for the study populations. Seedlingrecruitment was enhanced by seed addition and small scale disturbance inpopulations. For the intermediately abundant and more patchily distributedA. eupatoria, a regional survey of local populations wasconducted in the study area which revealed that most populations wererelativelysmall (< 100 individuals) and restricted to grassland fragments in roadverges. Furthermore, an attempt was made to estimate fruit dispersal from localpopulations.