Through The Fire, A Bounty of Bees |
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Through The Fire, A Bounty of Bees

At nine a.m. on a perfect late summer day in a series of perfect late summer days, the temperature is starting to climb from a 65-degree low, the dew point is low, and the sky is merry with clouds. As the day goes on, the chirruping crickets will be joined by whining cicadas and the high might touch 80 degrees. It is a good day to go for a hike at southeastern Wisconsin’s Lulu Lake Preserve, and to learn about preserving biodiversity.

Cut through by the Mukwonago River, situated inside a triangle defined by the towns of Eagle, Mukwonago, and East Troy, this gem of a spot sits at the southern tip of the sprawling glacier-formed ridges of the Kettle Moraine. Lulu Lake is a 95-acre kettle lake, formed when a great berg of glacial ice—isolated on the landscape and then buried under sand and rock debris—slowly melted, creating a kettle-shaped and then water-filled depression in the earth. Despite its soft, muddy bottom, the lake has water so pure that even delicate wild rice thrives there—uncommon this far south. The lake is seated amidst a bounty of preserved land, 632 acres of which have been managed and restored by The Nature Conservancy’s Wisconsin arm. Once an ice-harvesting site for Milwaukee’s beer breweries, later the site of a Boys and Girls’ club, and at one point slated to be the location of a convention center, these acres are now home to a precious 50-odd acres of rare oak openings, of 500 remaining in the state, a fraction of the millions of openings that once sprawled across the southern half of Wisconsin. Characterized by a park-like appearance, oak openings—also called oak savannas—consist of wide-branching oaks scattered over native prairie grasslands in varying degrees of density.

It’s bloom time for the prairie plants of Lake Lulu’s oak openings, even as the sumacs are starting to redden in anticipation of fall. Look down and you’re almost certain to see flowers: purples and pinks, lavenders, bright golden yellows, and a dozen variations of white. A black swallowtail butterfly greets us as we get out of the car. Bobbing among the grass are bees, at least half a dozen different colors and sizes and kinds, drifting from flower to flower.

Those bees are why I’m here.

Lasioglossum nelumbonis, a wetland bee. Photo by Sydney Price

In Wisconsin, like elsewhere, bee populations are declining. There are many causes, including parasites and environmental pollutants—particularly a class of pesticides called neonicotinoids. But also to blame is the replacement of the original, complex ecosystems with monocultures of corn, soybeans, and other crops. Research by University of Wisconsin biologist Jeremy Hemberger in 2021 revealed that agriculture has not only expanded to cover more land, but the crops have also become less diverse in the last 150 years. With the loss of diversity of crop species has come an accompanying decline of the Midwest’s native bumblebees.

But a casual observer wouldn’t see that on this August morning. Laura Rericha-Anchor is a wildlife biologist and botanist with the Forest Preserves of Cook County, Illinois, and has spent the last twenty years immersed in the ecologies of the Chicago region, which includes southeastern Wisconsin. In 2021, in a count of bees and other pollinators on preserved lands, she turned up some good news. On the pockets of land she surveyed, she was finding rare bees. And of all such preserves in southeastern Wisconsin that she visited, Lulu Lake had by far the most diversity of native bees.

Past research had previously identified 106 total bee species calling Lulu Lake home. Rericha-Anchor found every single one of them. In contrast, she found only 28 species (out of 152 known) at the site with the next highest count, a portion of the Kettle Moraine Oak Opening State Natural Area.

“I got numerous records (sightings)…things I had not yet collected in the Kettle Moraine area,” she says. “So I knew it was just an incredible area.” When she talks about bees, you may picture a honeybee, the domestic Apis mellifera, with its golden-brown striped abdomen and intensely social hive lifestyle. The honeybee was imported from Europe in the 17th century, arriving on a continent already rich with pollinating bees, moths, wasps, and beetles. The majority of native bees don’t live in hives; they’re solitary, often small, living in small nests or tunnels, and coming together only to mate.

Many of the bees Rericha-Anchor identified at Lulu Lake do not have common names to accompany the Latin, an ignominy of species that have held little interest for the nonscientific public. But their relationships with the land, and the plants on that land, are well documented and make clear their dependence on a well-conserved prairie or oak opening.

Andrena uvulariae is a small, fuzzy bee with chocolate brown coloring and subtle stripes. It likes bellwort, a small pendulous yellow flower that’s close to the ground and that thrives in the Kettle Moraine.

“I’m talking about tens, hundreds of thousands of plants–an unbelievable weft of blooming,” Rericha-Anchor says. She describes her arrival at the Lulu Lake Preserve, during the bellwort flowering season, as an almost sublime experience of turning a corner and seeing a hill in full sunlight, surrounded by woodland, and covered in yellow bellwort blooms. Within three minutes she had trapped (and shortly thereafter released) Andrena uvulariae, a bee never before recorded in Wisconsin.

Another native bee, Lasioglossum nelumbonis, relies on the pollen of water lilies, which are abundant off the shore of the lake. It requires sandy soils for nesting and is rare throughout the Chicago region. Finding two females during her survey of Lulu Lake, Rericha-Anchor says, “was an amazing surprise.” While it relies on a wetland plant for pollen, it forages for nectar from prairie plants, making it reliant on a unique combination of wetland and prairie.

Other exciting and rare findings at Lulu Lake Preserve include these species:

  • Calliopsis nebraskensis, a rare, pollen-preferring bee that lives in sandy habitats, including dry prairie soils. Where it occurs in Wisconsin, the bee has a strong preference for Verbena stricta, or hoary verbena.
  • Kincaid’s cellophane bee, Colletes kincaidii, depends on the pollen of leadplant, Amorpha canescens, and purple prairie clover, Dalea purpura.
  • The small miner bee, Pseudopanurgus parvus, is rare in our region, and depends on remnant oak savannas and prairies. In Wisconsin, it occurs only in the Kettle Moraine region.

Lulu Lake, oak savanna burned area. Photo by Emily Mills, The Nature Conservancy

This remarkable diversity is in part due to one thing that makes the Lulu Lake Preserve different from many spaces like it. The land here has been managed by fire for more than thirty years.

This is why I’m at Lulu Lake, walking through hip-high grass, collecting three or four different kinds of burrs and hitchhikers on my pants, swooping down at flowers to see who’s visiting them. Brian Miner, The Nature Conservancy’s land steward for southeast Wisconsin, is here to show me the land, the flowers, the bees, and to tell me the story of fire.

It starts with the oak openings, or oak savannas, now reduced to less than one hundredth of one percent of their former glory in Wisconsin. Wisconsin naturalist John Curtis, writing in 1959, defined an oak savanna as a complex of different ecosystems, ranging from a prairie scattered with oak trees grown uncrowded by their fellows to a woodland of oaks with sunlight peeking through the canopy.

Ecosystems like this don’t have stark dividing lines: think instead of a spectrum ranging from an open prairie with no trees, to a forest with a tight, sun-proof canopy. An oak savanna begins when you add a single oak tree to the prairie, and it ends when the land is about 50 percent covered with them. Above 50 percent brings you into a sunny, open-canopied woodland. As the trees crowd closer and the canopy grows, you find yourself in a true forest, where the shade helps retain moisture and cooler temperatures.

“You can’t draw a line and say this is an oak savanna,” Miner says. “It really is transitional.”

It’s this spectrum of different conditions that allows for so much life to flourish, he explains. There’s more opportunity for rare species of flowers to exist in these areas, and also the unique bees that need them. This is particularly true for what are known as specialists: animals with very specific food needs, who cannot subsist on anything else.

It’s not just the oak openings themselves that make this place so species-rich, according to Rericha-Anchor. The majority of the Lulu Lake State Natural Area sits on what’s called remnant landscape. Much of it has been untouched, or only minimally disturbed, by post-colonial human activities like mining or logging, agriculture or housing. This means the native plant communities are mostly intact, even where sparse. In addition, the soil itself is whole—it retains the structured complexity of organic matter layered among eroded rock, knit together with microbial species that help dead things decay and help funnel vital nutrients to plant roots.

“The bees can’t be present unless the landscape, the soils are intact,” Rericha-Anchor says.

The difference between a remnant and a restoration—where humans attempt an approximation of the natural order—can be significant. Some species can be found only in the remnants. And at Lulu Lake, the majority of the bee species Rericha-Anchor found were in the remnant, not in the restored prairie and woodland.

“A remnant is the clearing house for biodiversity,” she says. “It’s the template, the launching point. The composition of the remnant was the baseline of species that Native Americans preserved and sustained with regular burnings over thousands of years.

Oak savannas, which once covered much of the state and are now critically endangered, relied on fire, both naturally occurring wildfire and the intentional burning practices of indigenous peoples, suppressed by European settlers upon their arrival.

Miner shows me an area that has burned comparatively little, only eight times in the last thirty years. It’s crowded with small saplings a couple meters tall and low, thick shrubs. It seems unfinished, disorganized, without structure, and I realize there are few flowers here, despite the season.

The unburned land makes a hard, unsubtle transition between forest and prairie, offering few habitats between full shade and full sun, few places for a diversity of life.

Miner also shows me invasive species, like buckthorn and honeysuckle, shrubs that thrive in the absence of a healthy ecosystem. Oriental bittersweet, a woody vine with striking red and orange berries, climbs other plants and smothers them, the weight of its coils able to uproot trees entirely.

Brian Miner showing height of charring on a tree. Photo by Emily Mills, The Nature Conservancy

Elsewhere, in a spot that’s been burned twenty times in the last thirty years, the difference is stark. The oaks thin out from the woodlands to the prairie in a spacing that is elegant. The transition is softer, and there are more varied zones of light and soil moisture, and accompanying gradations of plant communities. There’s no shrubby undergrowth, and many flowers. The oaks have grown for decades with no other trees impeding them, and have the characteristic sprawling branches and massive crowns of leaves for which prairie oaks are known.

Already, a year and a half since the 2021 fire season, young aspen trees are sprouting from the burned land, their root systems producing clones that assault the prairie. Aspens are a native species, but in a land untouched by fire, they quickly strangle the oaks, absorb the sunlight, and destroy the oak savanna ecosystem.

And so, land managers like Miner burn. It’s the easiest way to clear these woody invaders, bring sunlight back to the oak openings, and ensure the prairie remains a habitat for oaks. Burning also makes crucial nutrients easier for plants to access, thus nourishing the entire ecosystem and encouraging flowers to bloom. For example, the roots of the common pale-leaved sunflower, Helianthus strumosus, a perennial, can send up five separate plants capable of blooming every year. But if the land hasn’t burned recently, he says, the sunflower may launch only three stems, and some may be sterile, unblooming.

In August 2022, the land has recovered from its 2021 burn. Historically, Miner says, this land saw fire every three to five years. But now the burn process starts anew every year. “We need to burn more frequently to make up for lost time,” he explains. As a result, every parcel of land has both a long-term fire strategy goal and a specific burn plan for a particular year.

There are three factors Miner’s team considers according to what outcomes they want to achieve: the residence time, or how long an area is burning; the intensity or heat of the burn; and the flame height, which determines how high up a plant might be burned.

They burn in the spring, typically in March, in a window of weeks when the conditions for favorable wind, dry weather and still-dormant vegetation usually, though don’t always, align. Though planning begins a year or more in advance, the burn may never happen. The spring of 2022 was first too wet, and then too windy, for a burn at Lulu Lake. So the burn remains on hold until 2023.

“Fire is a big labor project, because you’re not just lighting a match,” says Miner. “You’re also directing it.” Depending on the acreage of the desired burn, this may require anywhere from six people for a small burn unit up to 12 to 15 for a larger parcel. The team must manage the smoke, especially near roads or people’s homes. Wind from the wrong direction can derail a day’s plans. And they have to keep the fire contained to the precise square acreage planned for. The team uses ATVs, UTVs, and trucks to transport crew and pump water to define the edges of the burn and to put out any stray flames.

Team members light the edges with a specially designed gasoline canister. For bringing fire to the interior of a parcel where it may be too dangerous to walk, a PSD (plastic sphere dispenser) gun propels small spheres of highly flammable magnesium-permanganate into the forest, or into wetlands from a canoe or kayak.

Skilled manipulation of fire allows land managers like Miner to target particularly dense stands of brush with more intense waves of flame, while keeping most of the burn at a lower intensity that is easier to control. A backing fire, for example, is a fire that spreads into, or against the wind, a fire that is low-intensity, and low-flamed, but with a longer residence time. A longer-sitting fire can kill the roots of small shrubs, for example, without burning as hot.

But sometimes it can be useful to set head fires—fires that run with the wind—to tackle a particularly pernicious stand of buckthorn, the kind of plant that will take years of repeated efforts to finally eradicate.

“If I can top-kill with fire, then we get native grasses to grow, and it burns a little easier the next time,” Miner says.

The ideal burn plan is one that allows the broadest range of weather conditions to avoid having to cancel the burn, while still being able to both control the fire and have valuable results for the ecosystem.

The goal is not to singe the entire acreage equally, but rather to allow for less- and more-intensely burned patches, as well as occasional spots untouched by fire. In combination with the wind direction and speed, and the manipulations of the human team, all the land’s variations—its shade and sun, moist and dry soil, fast-burning grass and slow-burning trees, even something as seemingly small as an up- or downhill slope—will also shape the fire.

Controlled burn in progress. Photo by Emily Mills, The Nature Conservancy

Miner takes me to an oak tree that stands with a few others on a small rise. It looks healthy, but it’s been marked by fire from the previous spring. There’s a black mark on one side of the trunk—charring. On the other side of the tree is a wide welt in the trunk—a shallow, smooth gash with additional charring, where the bark caught fire and was burned away entirely.

“This is known as a cat face, or burn scar,” Miner says. The tree will likely bear the burn scar the rest of its life, even through the layers of future growth.

These scars and charrings appear only about two feet from the ground, indicating a lower-intensity fire. A few hundred meters away, on other trees, the charring is about twice as high, indicating the fire there was much more intense. Every fire also includes intentionally unburned spots, called refugia, for insects. Early in the year insects are less mobile, more likely to be grubs and nymphs that need shelter from the inferno in order to survive.

Pyrodiversity begets biodiversity, Miner says, and Lulu Lake has biodiversity. Researchers doing plant surveys in the last ten years have found between 140 and 181 different plants in the oak openings and woodlands. In the dry prairies, more than 100; in the wetlands, more than 150. Some species were found in all three habitats. Over 300 plant species thrive in this relatively small parcel of land, including one endangered species, two threatened, and six of special concern in Wisconsin.

Miner introduces me to several species of goldenrod, which look almost identical. Canadian goldenrod and elm-leaved goldenrod, with just a subtle difference in the leaves and a preference for slightly different levels of soil moisture and sunlight, intermingle in the savanna’s mix of sun and shade. Elsewhere on the preserve, he says, you’ll find another five species: tall goldenrod, early goldenrod, gray goldenrod, showy goldenrod, and Ohio goldenrod (the latter a species of ‘special concern’ in Wisconsin, vulnerable in the face of climate change).

Aside from the goldenrods, the list of flowers that Miner pointed out that day includes whorled milkweed, vervain or verbena, flowering spurge, the invasive but lovely pink knapweed, wood betony, northern bedstraw, false Solomon’s seal (no longer in flower, but berries beginning to burgeon), pointed-leaf tick-trefoil, Illinois tick-trefoil, woodland sunflowers, rosinweed, round-headed bush clover, candle flower, native roses, spreading dog’s bane, Culver’s root, forked aster (a state-designated threatened plant), and the brilliant purple spikes of blazing star. A third to half of these are indicators of a remnant oak savanna.

At one point I am distracted from admiring the magenta flares of wood betony by the nearby coil of a gray coral fungus, with the white lace of northern bedstraw just inches away. “What’s interesting about a savanna is there’s a lot going on in really small areas,” Miner says.

Andrena uvulariae, Female specimen.

We encounter berry-rich mammal scat, and he tells me bear have been seen here. And as we traverse the preserve we are delighted by the overhead antics of osprey and their spring chicks, who are now flying juveniles. We hear the dinosaur-like rattles of the sandhill cranes we’ll later see strutting casually along the highway as we leave Lulu Lake

It’s not just the array of plant species with their wealth of pollen and nectar that makes a burned ecosystem better for bees. In a landscape with so many different kinds of habitat, the food is more abundant, and available over a longer period of time, even from a single species of flower. This is possible because dips and rises in the topography create small spaces of warmer or cooler air, higher moisture, or more or less direct sunlight. So depending upon their location, individual plants may bloom at different times from their kin, enabling their species to cover even more of the blooming season with their flowers.

“Seeing a high diversity of bees (including specialist pollinators) means you also have rare plants and healthy populations of them,” says Rericha-Anchor. And those benefits flow downstream in the ecosystem. It’s not just Lulu Lake, with its wild rice, that boasts beautiful water.

The Mukwonago River is one of the cleanest streams in this part of the state and has some of the highest diversity of fish and mussels, earning it the Department of Natural Resources’ designation as an exceptional water resource. These waters host species that are struggling elsewhere. The water passing into Lulu Lake and down the river, filtered through Lulu Lake’s wetlands, benefits everyone downstream, from the Muckwonago River to the Fox, to the Mississippi itself. Lulu Lake and other kettle lakes tend to be points where the groundwater recharges, Miner says. So protecting the land around Lulu Lake benefits the spring-fed river system twice—as runoff enters the river from above, and when the water that soaks into the ground eventually reemerges via springs.

Climate change is affecting Lulu Lake, like the rest of the state. The Wisconsin Initiative on Climate Change has flagged rainfall, in particular, as a major concern for ecosystems. More intense but less frequent rainfall events will mean a greater whiplash between summer drought and flood. And the rain from one intense storm is more likely to run off into rivers and streams, as opposed to replenishing dry soil, than when the same amount of rain is spread across several milder storms.

The changing climate may affect the ability of land managers like Miner to burn during that ideal spring weather window, making it harder to target invasive species. And like the pollinators whose populations struggle against multiple stressors, ecosystems themselves are vulnerable to cumulative pressures. Oak trees, for instance, weakened by competition with invasive buckthorn, may find drought harder to weather and struggle to fight off their natural pests. This is why land managers need to use every tool they have to promote the health of the oak stands, including prescribed fire. “As the climate changes, the habitat will change,” Miner says. “I want to make sure the functionality is here and the diversity of habitat opportunities is here.”

The specific plants and animals at Lulu Lake may change as a result of temperature and water changes. Species that prefer the dry, warm southern slope of a prairie may drift towards the northern side to avoid extreme heat or disappear entirely. Chestnut oaks may drift in from the south and replace the white oaks. “We always have a diverse understory of wildflowers, but it might not be the same wildflowers over time,” Miner says. “And the more fire we put into (the ecosystem), the more it’s going to adapt to climate change.”

Fostering biodiversity with tools like controlled burns increases the odds that existing species will thrive and continue to perform the functions that keep their ecosystem vibrant and diverse–-good for the bees, but also for everything else, big and small, that depends on this lake, this prairie, and its precious acreage of oaks.


Christie Taylor is a Madison-born science writer and essayist, and former producer of the national radio show Science Friday. She lives in Brooklyn, New York, and misses the prairie.

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