Prescribed burning is a common management practice for North American prairie remnants and restorations because it decreases the abundance of weeds and woody plants while increasing survival and flowering of fire-adapted native plants. In this study, I investigate the effects of fire on the reproduction and pollination of a widespread, self-incompatible prairie plant with generalist insect pollinators, the purple coneflower, Echinacea angustifolia (Asteraceae). I established a permanent transect with several hundred plants growing in a 40 ha prairie preserve with two management units. Alternating units were burned before the summers of 1996, 1998, and 2007. For each of these years we measured key aspects of the pollination environment, including local density of flowering plants, individual flowering phenology, the number of heads per flowering plant, and the floret count per head. We also measured outcomes of pollination: style persistence (a measure of pollen limitation), the rate of seed set per plant, and progeny vigor.

Results/Conclusions

Prescribed burns appear to reduce both resource and pollen limitation in flowering E. angustifolia plants. The mean count of heads per flowering plant (2.3 vs. 1.5 in 2007) and the mean floret count per head is greater in burn treatments (374 vs. 224 in 2007), suggesting that fires reduce annual resource limitation for individual plants. Many aspects of the pollination environment vary with the burn treatment. Burns increase the local density of flowering plants, alter overall flowering phenology, and increase floral display sizes. Both style persistence and the rate of seed set per plant increase under burn treatments (44 vs. 31% in 2007), demonstrating that that fires reduce pollen limitation of seed set.