Reproductive ecology of the western silvery aster Symphyotrichum sericeum in Canada

摘要

ABSTRACT: Previous studies suggest that low seed production due to pollinator competition and seed predation may negatively affect the reproduction of the rare forb western silvery aster Symphyotrichum sericeum in Canada. Research was conducted to determine normal flower and seed production and the impact of seed predation, and to ascertain whether clipping surrounding vegetation and/or fertilizing with nitrogen stimulates flower and seed production in S. sericeum. Only 41% of all stems observed produced capitula, and less than 40% of the seeds in each capitulum were filled. Flower production was negatively correlated with percentage vascular plant cover and positively correlated with percentage cryptogamic cover. The main seed predator was a weevil (Anthonomus sp.) that destroyed about one-third of all capitula produced. None of the treatments applied (e.g. clipped, fertilized and clipped × fertilized) significantly increased stem height, the percentage of flowering stems or seed production over the control; clipping actually decreased stem height. Fertilizing was the only treatment that showed some promise as it increased the number of capitula per flowering stem. Flower and seed production in S. sericeum may be facilitated by the presence of other species that modify the microenvironment. Low flower and seed production of plants in Canada is likely due to limited soil resources and pollen, and seed predation.