LAUSR

PREMISE Fire induces flowering in many plant species worldwide, potentially improving reproductive fitness via greater availability of resources, as evident in flowering effort, and improved pollination outcomes, as evident by seed set. Post-fire increases in flowering synchrony, thus mating opportunities, may improve pollination. However, few studies evaluate fire effects on multiple components of fitness. Consequently, the magnitude and mechanism of fire effects on reproductive fitness remain unclear. METHODS Over multiple years and prescribed burns in a prairie preserve, we counted flowering stems, flowers, fruits, and seeds of three prairie perennials, Echinacea angustifolia, Liatris aspera, and Solidago speciosa. We used aster life-history models to assess how fire and mating opportunities influenced annual maternal fitness and its components for individual plants. KEY RESULTS In Echinacea and Liatris but not Solidago: fire increased head counts, and both fire and mating opportunities increased maternal fitness. Burned Echinacea and Liatris plants with many flower heads produced many seeds despite low seed set (fertilization rates). In contrast, plants with an average number of flower heads only had high seed set and produced many seeds when mating opportunities were abundant. CONCLUSIONS Fire increased annual reproductive fitness via resource- and pollination-dependent mechanisms in Echinacea and Liatris but did not affect Solidago fitness. The consistent relationship between synchrony and seed set implies temporal mating opportunities play an important role in pollination. While fire promotes flowering for many plant species, our results reveal that even closely related species exhibit differential responses to fire, which could impact the broader plant community. This article is protected by copyright. All rights reserved.