Fire synchronizes flowering and boosts reproduction in a widespread but declining prairie species

Abstract

Fire is an important determinant of habitat structure and biodiversity across ecosystems worldwide. In fire-dependent communities, similar to the North American prairie, fire suppression contributes to local plant extinctions. Yet the demographic mechanisms responsible for species loss have not been directly investigated. We conducted a 21-y longitudinal study of 778 individual plants of Echinacea angustifolia, a widespread perennial species with chronically limited mating opportunities, to explore how fire affects reproduction. In a large preserve, with management units on different burn schedules, we investigated Echinacea mating scenes, which quantify isolation from potential mates and overlap in the timing of flowering, to determine the extent to which fire influences the potential for sexual reproduction. We demonstrate that fire consistently increased mating opportunities by synchronizing reproductive effort. Each fire occurred during fall or spring and stimulated flowering in the subsequent summer, thus synchronizing reproduction among years and increasing the proximity of potential mates after a fire. Greater within-season flowering synchrony in postfire mating scenes further increased mating potential. The improved postfire mating scene enhanced reproduction by increasing pollination efficiency. Seed set in scenes postfire exceeded other scenes by 55%, and annual fecundity nearly doubled (88% increase). We predict the reproductive benefits of synchronized flowering after fire can alleviate mate-finding Allee effects, promote population growth, and forestall local extirpation in small populations of Echinacea and many other prairie species. Furthermore, the synchronization of flowering by burning may improve mating opportunities, reproduction, and the likelihood of persistence for many other plant species in fire-dependent habitats.

A research agenda for the restoration of tropical and subtropical grasslands and savannas

“…Putative causes driving low seed quality in TGB species include nutrient‐limitation (Fujita et al 2014), pollen quality (Rosbakh et al 2018), higher genetic load due to accumulation of deleterious somatic mutations over many disturbance cycles (Lamont & Wiens 2003), harvesting constraints when faced with irregular fruiting phenology, and a combination of these factors. It also remains to be tested to what extent managing fire regimes would create opportunities to improve sourcing seeds from native TGB species where fire‐stimulated flowering typically results in higher and more synchronous seed production and higher seed quality (Young 2004; Le Stradic et al 2015b; Wagenius et al 2020).…”

Flowering synchrony drives reproductive success in a wind‐pollinated tree

“…We define flowering here as the time during which plants are shedding pollen. Flowering synchrony between each pair of plants was calculated using the number of days both individuals were flowering divided by the number of days either individual was available for mating (see Ison et al ., 2014) in the mateable R package version 0.3.1 (Wagenius et al ., 2020). To evaluate the effects of plant density on pollen limitation, we calculated local density of flowering plants, that is, the number of conspecifics within a 50‐m radius (Fig.…”

Restoring tropical forest–grassland mosaics invaded by woody exotics

“…Text within dotted boxes are the research efforts that can help mitigate these challenges. See Dayrell et al (2016), Madsen et al (2016), and Wagenius et al (2020) for more information.…”