Population Persistence and Reproductive Ecology of a Forest Herb: Aster acuminatus

Abstract

Aster acuminatus Michaux, a patchily distributed herb of eastern forests, is commonly represented in all stages of forest succession. To determine its mechanisms of persistence, we carefully examined the distribution patterns of this species as affected by its reproductive ecology and demography. Using A. acuminatus as a model, we hypothesized that 1) availability of propagules and location of adequate recruitment sites impose first-order control over plant distributions in stands of all ages by determining where plants might be found and 2) light and other resources exert a second-order control over herb distributions by determining where established plants cannot persist. Results from our study at the Hubbard Brook Experimental Forest in New Hampshire demonstrated this species' ability to exploit resource-rich disturbances through immediate and profuse ramet and seed production. This ensured rapid colonization of new sites and provided genetic exchange for longer-term survival. Relict colonies which survived the disturbance served as the sole propagule-producing loci for the first year of colonization. After several years, resources became more limiting and the aster shifted to a more conservative asexual reproduction strategy which provided population stability until the next disturbance. The clumped distribution of A. acuminatus in mature forests is explained by strict adherence to asexual ramet replacement in which there is no year-to-year change in aster importance. Location of persistent colonies probably is dictated by location of suitable seedbeds during the first few years of recovery after disturbance. Whereas numerous sites may be colonized initially, timing of colonization and quality of site impose constraints on which colonies persist.