- In an interesting twist, two kinds of rare American freshwater crustaceans have been found to thrive after prescribed burns in their habitats.
- Populations of vernal pool fairy shrimp in Oregon and several species of threatened crayfish on the Gulf Coast increased after the removal of invasive plants, woody shrubs and trees from their habitats using fire or mechanical means.
- Fairy shrimp populations were shown to increase more than fivefold following habitat treatments that featured fire, while speckled burrowing crayfish also responded positively following fires set to favor nesting of sandhill cranes (whose own population has soared since).
- Both areas are savanna ecosystems that have relied on frequent fires over millennia — whether naturally occurring or intentionally set by Indigenous peoples — to maintain the open habitats to which myriad organisms have adapted.
As a field biologist, Keith Perchemlides has often watched flames dance around tiny ponds that mark the remains of a vast wetland that once covered a large part of southwestern Oregon’s Rogue River Valley. Often, he was the one that set fire to the dry grass.
Back then, he was working for The Nature Conservancy (TNC) as a part of a team trying to restore habitat for vernal pool fairy shrimp (Branchinecta lynchi), a translucent invertebrate with walrus-like tusks and a forked, red tail. In the soil, their eggs survive long droughts when their ephemeral pockets of water, called vernal pools, disappear. The inch-long crustacean feeds on small particles in the pools and subsequently serve as food for waterfowl, songbirds and amphibians.
Without fire, invasive weeds or trees will crowd these basins where rainwater collects into seasonal, shallow ponds, limiting where this threatened species can live.
“The worst invasive weed out there right now is medusahead [Taeniatherum caput-medusae]. It builds up this thick, dense layer of thatch that doesn’t break down quickly. Plus, the new growth just dominates the herbaceous plant community,” Perchemlides told Mongabay. “Early season burning, in the spring, does a great job of knocking back invasive grasses, and it stimulates the native seed bank.”
Deliberate burning is an Indigenous practice that the Takelma Tribe applied here for millennia. Like other native communities across the United States who also used fire as a stewardship tool before colonization, their traditional burning regime has since been proven to increase the health of the ecosystem.
If a lightning strike caused a wildfire, they let it burn, clearing overgrown tree canopies and other species that colonize grasslands. If needed, they would set a small, low-intensity fire themselves.
In addition to settler disruption of intentional burning practices, policies that the federal government set forth in the early 20th century mandated the suppression of wildfires. It’s a legacy that land managers and scientists are still trying to reverse from coast to coast in support of wildlife and ecosystems, and it’s especially complicated when it comes to wetlands and crustaceans like the fairy shrimp, which have adapted to frequent fire.
“At this point, we are using prescribed fire as a restoration tool to control invasive species and prepare for seeding of native plants,” Perchemlides said.
“We are not matching what the historic fire regime would likely have been, and I don’t think anyone knows what that used to be. If you go into a forest habitat, you can use various techniques to rebuild historic fire regimes from the fire scars that the trees retain. In the wetlands, we don’t have that,” he said.
Little shrimp, giant result
The present-day landscape will never be the same as it was hundreds of years ago, but conservation and restoration work have resulted in high-quality vernal pool sites for fairy shrimp and other vernal pool-dependent species in the Rogue River Valley.
Perchemlides worked for more than a decade with TNC in partnership with the Oregon Department of Transportation (ODOT) to leverage funds they had for habitat restoration. The latter agency manages the land and led recovery work not just for shrimp, but also for endangered desert parsley (Lomatium cookii) and large-flowered woolly meadowfoam (Limnanthes pumila ssp. grandiflora) at sites like the Whetstone Savanna Vernal Pool Mitigation and Conservation Bank, and Agate Desert Preserve.
Annual monitoring established a baseline that allowed the team to track changes during and after eight years of restoration, that included prescribed burning and careful earth moving. The vernal pool habitat doubled in area and increased in water capacity by 20 acre-feet, or nearly 25,000 cubic meters. This volume kept rainwater onsite for longer, possibly supporting higher stream flows in the Rogue River and its tributaries during arid summers, too.
The larger restored basins also bolstered the fairy shrimp population, which went from occupying just 10% of the vernal pools to more than 60% — a more than fivefold increase. The hydrologic stability boosted the shrimps’ longevity, and more eggs were deposited into the pool.
“It’s exactly what you hope for, but you don’t always expect to see,” Perchemlides said.
“Their whole life strategy is about waiting it out, where their population can just briefly flourish and set the seed or egg bank for the next event, whether that be later that winter or years in the future, and their ability to respond to some of that restored habitat is impressive, I mean the pools were just full of them.”
Crayfish prefer burning over boiling
Returning fire to the Oregon landscape was just one mechanism of the fairy shrimp restoration plan. But when it comes to bringing back open ecosystems heavily disturbed by human activity, prescribed burns are key. The same is true far to the southeast, along the Gulf Coast of southern Mississippi, where a pristine plain is home to a great diversity of crayfish, the crustacean at the heart of regional culinary traditions like crayfish boils. Similar to southwestern Oregon, anthropogenic change and overgrown vegetation in this savanna setting also threaten the ecosystem and its species, including semiaquatic ones.
Digger crayfish (Creaserinus oryktes) are a freshwater species that don’t live in open water but rather in the waterlogged soils of flat, wet landscapes. They carve tunnels as deep as 2 meters (6 feet) in the wet, acidic clay of Mississippi Sandhill Crane National Wildlife Refuge, the last remaining wet pine savanna in the United States. But digging such ambitious burrows has become tougher, as the crayfish must now compete with woody plants’ root masses.
Wildlife biologist Scott Hereford and his staff have overseen the return of fire to this landscape over the past three decades. They burn about 2,250 hectares (6,000 acres), or a third of the refuge, each year, and it’s given the endangered Mississippi sandhill cranes (Grus canadensis pulla) the prairie-like habitat they need to nest. The big bird’s population has accordingly grown from a few dozen to 130 birds, bringing the animals back from near extinction.
“This is a highly disturbance-dependent ecosystem. Going back thousands of years, there was fire in these coastal plains, and if it’s not burned, this landscape dominated by a rich, herbaceous plant community will quickly revert to one dominated by woody vegetation,” Hereford said. “Our goal is to restore and maintain these open areas, and besides the cranes, there’s been work done that shows [benefits for] other important birds like yellow rails [Coturnicops noveboracensis] and Henslow’s sparrows [Passerculus henslowii ].”
Hereford became curious about fire’s impact on the speckled burrowing crayfish (Creaserinus danielae), because a decrease in these native crayfish has the potential to disrupt biodiversity and balance. And if these crayfish lose their habitat, the ecosystem also loses a piece of its hydrologic complexity, because their burrows help aerate dense, wet soil, unearthing nutrients for plants.
So Hereford reached out to astacologist Susan Adams with the U.S. Forest Service, who has studied crayfish in Mississippi for 20 years.
“They started to become more concerned about how their management might be influencing other at-risk species,” Adams said. “What got me thinking was that somebody had, years ago, worked with a related species on an army base, and he had a comment on one of his papers that as soon as you started seeing this dark organic matter in the soil, you stopped seeing these crayfish.”
With Hereford’s help, Adams set up 12 study sites at the refuge that varied in how often they were burned or mulched (a mechanical approach for clearing trees and plants when weather and other conditions are not conducive to fire). The team counted crayfish tunnels and burrow openings, which look like chimneys made of balls of clay.
Two sites within 164 meters (538 feet) of each other were recently compared: one with an open pasture and another with a mature pine forest, and burrow density was found to decrease dramatically at the latter site. It was a finding consistent with Adams’s previous study results showing that unmanaged areas have higher densities of woody vegetation and fewer crayfish burrows.
Adams’s study findings also shed some light on the possible management needs of other rare crayfish in the region. She is part of the research team that recently described species like the lonesome gravedigger (Lacunicambarus mobilensis) and the banded mudbug (L. freudensteini), two crayfish species that also spend their lives burrowed in darkness, with brightly hued shells of blue and orange. Both are considered vulnerable to extinction because of their limited geographical range, being found only between Mobile Bay in Alabama and Mississippi’s Pascagoula River.
“There’s every reason to think that they have the same relationship to open habitat as the Creaserinus oryktes,” Adams said. “It’s why we are super interested in understanding this relationship for conservation in respect to burrowing crayfish.”
The ‘never ending’ work of prescribed burning
While this transformative work has been years in the making, restoration hasn’t ended, because these landscapes need monitoring and frequent fire. Also, crustaceans have been overlooked in terrestrial environments for so long that scientists are still trying to figure out the best way to study them.
But even an introductory analysis like the one at the sandhill crane refuge is helping land managers access funding and resources needed to carry out prescribed burns.
“It reinforced the fact that crayfish need areas even more open and less woody than the cranes,” Hereford said. “Our mechanical and prescribed fire treatments in the last few years, since the crayfish study, have continued to keep areas open for crayfish, but it’s never ending, and a long-term project.”
More robust restoration reports, like the 96-page document that Perchemlides co-authored in Oregon, must also be based on long-lasting effects — especially as climate change compounds existing challenges. Bigger pools of water provide a greater variety in wetland habitat over a range of time, and more resilience to unprecedented weather cycles.
Now working as an independent contractor at Groundtruth Ecological, Perchemlides also continues his work with TNC and ODOT. His study methodology evolves while watching these rehabilitated vernal pools return to a more natural state.
“It’s just great to see water replaced by flowers replaced by fire,” he said.
Ashli Blow covers the intersection of environmental science and policy with an emphasis on climate solutions.
Banner image: Setting a prescribed fire around vernal pools at Agate Desert Preserve. Image courtesy of Evan Barrientos.
See related by this reporter: Another feature about the usefulness of fire via Mongabay’s ongoing series that covers conservation solutions:
As U.S. insurers stop covering prescribed burns, states and communities step up