Seasonal timing of prescribed burns and management of an early successional species enhance flower density and pollinator activity in a pine savanna ecosystem

Background/Question/Methods

Land managers often rely on prescribed burns to promote the diversity of herbaceous plants, yet little is known about how seasonal timing of fire interacts with other ecological factors to maintain or increase floral and flower-visitor density during early restoration of fire-adapted ecosystems. In the southeastern United States, Yankeeweed, Eupatorium compositifolium Walter, often dominates plant communities after soil disturbance for five or more years. Thus, the removal of this species may influence plant community composition with implications for floral resource availability and flower-visitor activity, though this remains unstudied. Using a community-based approach, we asked (1) how do timing of fire and the removal of yankeweed influence floral density and flower-visitor activities across burn treatments and between burn years? and (2) how does plant-pollinator interaction network topology vary between burn years?. We applied a manipulative experimental approach to estimate floral density and flower-visitor frequency across four fire treatments (unburned control, winter-dry season, early wet season, and summer-wet season burns) over two years of a burn cycle in an early-successional longleaf pine savanna restoration. In each burn treatment plot, we manipulated the presence of yankeeweed including one control subplot in which yankeeweed was unmanipulated, and one subplot in which yankeeweed was removed.

Results/Conclusions

Flower density was higher across all seasonal burn treatments compared to unburned controls, particularly during the late summer-fall season, and flower visitors were also more frequent in seasonal burn treatments. During the fire year (year 1), flower density was highest in the early-wet season burn treatment, while in the year following fires (year 2), flower density and flower visitor frequency were highest in the wet season burn treatment. The plant-pollinator interaction network was more diverse in the year following fires (year 2) compared to the fire year (year 1). The removal of yankeeweed enhanced flower visitor activities and the density of other floral resources across all seasonal fire treatments. We conclude that prescribed burns enhance floral resource availability and pollinator activity, but the effectiveness of fire as a management tool depends on applying it outside of the dry season.