As fires continue to rage across Australia, destroying ecosystems and killing millions of animals, it’s hard to imagine any good emerging from such devastation. But it’s long been known that some small plants can benefit from a fire, because they grow back faster than grasses and trees, giving them an advantage in the battle for resources.
A study published on Monday in the Proceedings of the National Academy of Sciences gives another explanation for that success, at least for one prairie plant that has been in decline: reproductive advantage.
Purple coneflowers, also known as echinacea angustifolia, produce more seeds in years following fires, the new study shows, not just because there are fewer competitors for resources, but because a fire “also changes the mating opportunities,” said Stuart Wagenius, a conservation scientist at the Chicago Botanic Garden. Dr. Wagenius, who led the research, tracked a 40-hectare plot, or nearly 100 acres, of prairie land in Minnesota for 21 years as part of the Echinacea Project.
The study found that coneflowers produced more seeds and were more genetically diverse in plots that were burned every few years, compared to those where fires were prevented.
Coneflowers don’t bloom every year because it takes energy to produce a flower. Controlled burning in fall or spring triggered the flowers on the study plot to put out blooms — often more than one — the following summer. Dr. Wagenius found this synchrony both in terms of the years of flowering and the dates within those years. So, in the summer after a fire, more flowers were open at the same time, and bees were better able to pollinate the coneflowers, he said.
“It just makes sense that if there are more plants flowering, there’s going to be better pollination,” he said.
Several other researchers not involved in the work said the group’s findings were surprising and persuasive.
“They show that the effect of fire isn’t what everybody assumed that it is,” said Ingrid Parker, chair of the department of ecology and evolutionary biology at the University of California, Santa Cruz. “It shows that the role of fire is even more interesting than we realized and there’s a lot more to learn.”
Small-scale fires may kill off some pollinators, but the area will readily be recolonized if other pollinators are close enough to discover the new-growth plants, said Elizabeth Crone, a population ecologist and biology professor at Tufts University.
Dr. Crone said the paper confirms in practice what has already been assumed in theory: that fires can be good for prairies.
“I think it’s neat that this was mostly a pollination and reproductive effect, not only a better-nutrients-in-the-soil effect, and I think most of us would have expected it to be the other way around,” Dr. Crone said. “It is the first time I have seen that idea in response to fires.”
The fires that helped the patch of prairie tracked in the new study are not at all like the infernos burning in Australia, or the ones that tore across California last year. Lightning causes frequent fires across the prairies, and prescribed fires have been set for centuries largely for land management and food production, so the prairies have evolved with low-intensity fires every few years.
Without controlled burns or occasional fires, flammable materials like brush and dead grasses accumulate. Then, when a fire does occur, it burns hotter and travels farther, causing more damage, Dr. Wagenius said.
The natural fires tend to come in the spring and fall when many animals are hibernating and many plants are dormant, so they are protected from the blaze, Dr. Wagenius said. The midsummer prairie is green and moist and less likely to burn, he said.
Going forward, Dr. Wagenius plans to continue following his coneflowers, taking a closer look at the reaction of individual plants in burn years versus non-burn years. He also wants to examine other plant species to see how widespread this fire-effect on reproduction might be.
Some of the 778 coneflower plants he mapped in his first year of graduate school more than two decades ago were still alive in his latest count last summer.
“I had no idea of what I was getting myself into,” he said.