Mowing Frequency Influences Number of Flowering Stems but not Population Age Structure of Asclepias viridis, an Important Monarch Host Plant

Milkweeds (Asclepias spp.) are host plants for monarch butterflies (Danaus plexippus), which are currently being considered for listing under the Endangered Species Act. Previous research has documented declines in milkweed availability in the Midwest, but less research has focused on the southern Great Plains. Furthermore, the influence of management practices on the structure of milkweed populations has not been evaluated. We assess the age structure of Asclepias viridis, an important milkweed species for monarchs in the southern Great Plains, in two land uses that differ in the frequency and timing of mowing. Plant age may influence resource availability for larval and adult monarchs by affecting foliar biomass and flower production, and flower production and subsequent seed production may influence the recruitment of new individuals to the population. Using herb-chronology, we found age structure did not differ between roadsides mowed several times during the growing season and grasslands mowed less frequently. However, we did find younger individuals in less frequently mowed grasslands had more stems and more flowering stems than those in more frequently mowed roadsides. Though plant age did not differ among the land uses and mowing regimes included in this study, our results suggest frequent mowing can negatively affect foliar and reproductive biomass of younger A. viridis plants. Limiting mowing during the early summer flowering season for A. viridis could support efforts to maximize host plant and nectar availability for monarchs and other pollinators.