Wildflower Uprisings

 biennial fourpoint evening primroses
Weakened prairie grasses often make way for insurgent wildflowers. This sand prairie full of biennial fourpoint evening primroses (Oenothera rhombipetala), for instance, took hold two years after the site was burned and grazed during a drought. The primroses germinated and grew rosettes the year following the grazing and bloomed prolifically the year after that. Photo: Chris Helzer

In Nebraska prairies, grasses such as big bluestem (Andropogon gerardii), Indiangrass (Sorghastrum nutans), and non-natives smooth brome (Bromus inermis) and Kentucky bluegrass (Poa pratensis) are like occupying armies. Most wildflower species shrink away from the dominance of those grasses, and without intervention, many of those wildflowers can be driven out of prairies altogether.

One of a land manager’s biggest jobs is to foster diverse plant communities by periodically suppressing the vigor of dominant grasses, giving less competitive plants a chance to reclaim a little territory. When grasses are only slightly debilitated, the response from wildflowers can be muted and difficult to see. However, when the army of grasses is severely weakened, wildflowers often respond with flamboyant riots of color. Sometimes, flowers that take advantage of weak competition are celebrated by locals, as in the case of Texas bluebonnets (Lupinus texensis). Other times, the show features less universally popular species like annual sunflowers (Helianthus annuus) or broomweed (Amphiachyris spp.).

monarch thistle
Many thistle species expand quickly when land management keeps perennial plants at bay. Despite their unfavorable reputation with many landowners, thistles like this Cirsium altissimum (tall thistle) are extremely valuable for pollinators, including some of great conservation concern like monarch butterflies. Photo: Chris Helzer

Floral explosions can be caused by droughts or other weather events, but are often the result of management practices. Prescribed fire, mowing and grazing can all help regulate the dominance of grasses. When grasses are burned up, mowed down or munched off during the growing season, they lose clout both above and below ground. Above ground, leaf canopies that otherwise monopolize access to the sun are depleted. Below ground, massive root systems that rely on energy captured by those leaves follow suit. In short, the loss of leaves results in a comparable loss of roots. Within a day or two of a grass plant being chewed off by a cow or burned up by fire, it abandons large portions of its root mass, opening that space for the colonizing roots of neighboring plants.

shell leaf penstemon
Shell leaf penstemon (Penstemon grandiflorus) is almost never grazed by cattle, allowing the flower (a relatively weak competitor otherwise) to flourish in heavily grazed areas like this one. Photo: Chris Helzer

A weakened grass community benefits most wildflower species, but some are better suited for quick colonization than others. Annuals, biennials and many short-lived perennials are built for this exact opportunity. They can germinate, bloom and produce copious amounts of seed very quickly. As grasses regain strength and dominance, they are literally surrounded by the seeds of the next insurrection.

daisy fleabane
Daisy fleabane (Erigeron strigosus) often thrives in sites of low soil productivity where few other plants can compete strongly. It’s also able to fill in gaps left by a weakened grass community after intensive grazing. Photo: Chris Helzer

Prairie managers (including those at the Wildflower Center) facilitate this kind of  competition among the plant community. We don’t want to debilitate the army of grasses altogether or lawlessness ensues. At the same time, we want to ensure the survival of all the wildflowers and other species that can’t compete with those dominant grasses when they are at full strength. We foster periodic rebellions by weakening dominant grasses but then allow those grasses to recover between uprisings. Often, nature joins in the fun via droughts or floods and we just try not to let any side in the battle gain too much advantage over the others.

showy prairie gentian
One of Mrs. Johnson’s favorite flowers, showy prairie gentian (Eustoma exaltatum) grows well in relatively wet prairie sites. A year of high groundwater flooded out much of the competition in this prairie slough, allowing the annual species to roar to dominance. Photo: Chris Helzer

Prairie plant communities are incredibly strong and resilient. Wildflower riots can be dramatic and beautiful, but they are more than just spectacles. The ability of those wildflowers to rapidly fill the gaps left when the rest of the community is weakened is critically important. Among other things, it helps prevent encroachment by invasive species and provides a relatively constant supply of food and cover for prairie insects and wildlife during tough times. For thousands of years, prairies have survived fires, droughts, bison herds and grasshopper plagues. The coming years will provide even more challenges for prairies, but with careful management they will respond just as they always have — beautifully.

prairie sunflowers
The summer of 2012 was the driest on record in the Nebraska Sandhills. A weakened grass community, combined with already sparse vegetation, opened the door for an explosion of prairie sunflowers (Helianthus petiolaris) across millions of acres the following summer. Photo: Chris Helzer

Chris Helzer is the Nature Conservancy’s director of science in Nebraska. He writes The Prairie Ecologist blog and is the author of “The Ecology and Management of Prairies in the Central United States.”