The Bees' Needs
The sky darkens above the ruins of a cluster of ponderosa pine that burned 20 years ago. Two women stand amid grass and wildflowers, in a field studded with the charred stumps and downed trunks of dead trees. In the dry hills of Montana’s Helena National Forest, the landscape can take decades to recover after a burn.
But as the sun emerges from behind a blanket of thunderclouds, the air comes alive with buzzing, swooping activity. Bees begin to appear among the blossoms of blanket-flower, yarrow, and vetch. “Here comes a little cutey-pants,” murmurs Elizabeth Reese, a research assistant at Montana State University. She swoops a bee into her net, flicking her wrist to trap it near the top of the cone-shaped mesh. Then she expertly transfers the insect to a clear vial and hands it to me. The black and yellow specimen—a female—squirms inside its plastic prison, orbs of bright yellow jiggling on its hind legs. Bees have evolved brushes of hair designed to trap and carry pollen; this one appears to be carrying a full load.
Over the past 30 years, residents of Montana and neighboring western states have watched and worried as wildfires in their region have grown in both number and intensity. Data collected by the U.S. Forest Service reveal that the average number of fires that burned more than 1,000 acres in Montana and Wyoming has doubled since the 1970s; in Idaho, the number has nearly quadrupled.
And with the increased threat of devastating wildfires comes the increased need to find new ways of fostering biodiversity in their aftermath. That’s why Reese and her supervisor, Laura Burkle, a community ecologist at Montana State, are poking around the wildflowers in a burned-over pine grove on this overcast midsummer day. Much of Burkle’s research focuses on wild pollinators, a group of insects made up largely of the tens of thousands of native bee species that are far different from the honey-makers people usually think of when they hear the word “bee.” For the past few years, she has been looking especially closely at these creatures as part of a larger study on biodiversity’s role in helping landscapes recover after wildfire.
Burkle and many other ecologists have hypothesized that wild pollinators are key to speeding up the process by which burned forests bounce back from barrenness to fecundity. For example, lupine—a wildflower that often pops up on sites recently affected by fire—relies on wild pollinators for reproduction. Once established, the plant’s roots host nitrogen-fixing bacteria that enrich the soil below, paving the way for the sprouting of shrubs and conifer seedlings. Other pollinator-dependent wildflowers and shrubs nourish all manner of woodland creatures, from mice to grizzly bears. (The latter are fond of huckleberries, the fruit of a shrub that relies on bees to carry its pollen.)
Pollination biologists and ecologists are also aware, in a way that many non-scientists aren’t, of the critical yet largely unheralded role that wild pollinators already play in global food production. It’s a role that has grown even more vital to humans as honeybee populations decline. We need wild pollinators to help restore burned forest landscapes, to help feed us, and to help provide a number of other important ecosystem services.
But if we want wild pollinators to keep helping us, we have to start helping them. Because thanks to climate change, their habitats around the globe are being dramatically altered. Sometimes their habitats are disappearing altogether.
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The best-known threat facing bees is colony collapse disorder, the syndrome that has nearly halved the domesticated honeybee populations of North America and Europe in only seven years’ time, leaving millions of hives empty and littering the landscape with tiny carcasses. No single cause for CCD has yet been discovered. But many scientists believe that the syndrome is the result of multiple negative factors, including the widespread use of pesticides, infestation by parasitic mites, and the significant stresses that honeybees undergo when they’re trucked cross-country—thousands of miles from their home bases—to pollinate our crops.
More than one-third of the world’s food crops, in fact, rely on pollinators to enable them to set fruit. But modern agriculture has tried to place the full weight of this monumental task onto the fragile backs of domesticated honeybees. That scenario carries real risks. “If you look at the bigger picture,” Burkle says, “CCD shows the dangers of relying on one type of bee to pollinate our food crops. In nature, there are many bee species doing the work.” Indeed, a 2013 study conducted by an international team of 50 scientists and published in the journal Science noted that across the globe, wild pollinators were actually twice as effective as domesticated honeybees at increasing the proportion of a plant’s flowers that later develop into mature fruits or seeds.
Despite the ecologically essential roles wild pollinators play, most people don’t give them too much thought, aside from the most highly visible species: butterflies, bumblebees, wasps, and flies. But Burkle has been obsessed with them for years. Before she began researching them among the towering ponderosa pines and crystalline lakes of Helena National Forest, she was studying them in a place that couldn’t look or feel any more different: Carlinville, Illinois, a distant exurb of St. Louis whose primary claim to fame is as the nation’s largest repository of Sears Catalog Homes concentrated in a single neighborhood.
In 2009 Burkle and other scientists embarked on a research project that paired their expertise in pollination biology with a penchant for historical sleuthing. For nearly three decades bracketing the turn of the last century, from 1887 until 1916, the American entomologist Charles Robertson had observed and collected bees in the forest surrounding Carlinville, carefully recording which plants the insects visited, when they visited them, and when the plants began to blossom. A century later, Burkle and her colleagues decided to check in on the area’s wild bee population and to look at local pollination patterns, to find out what had changed and what had remained the same.
The striking results of their report were published last year in Science. Half of the bee species that Robertson originally recorded had become locally extinct. Crucial relationships between bees and plants that existed in his time had ended; either the plant or the pollinator had disappeared, or else both organisms had fallen out of sync, their symbiotic rhythms disrupted by the dissonance of climate change. Over the past century, average winter and spring temperatures in Carlinville have risen by more than three degrees. Wildflowers were blooming earlier in the spring, Burkle and her team discovered—but many wild bees were becoming active earlier still. Their accelerated schedules meant that pollinating bees in Carlinville were flying 22.5 fewer days than they had flown in Robertson’s time.
Even so, Burkle and her colleagues got the chance to see for themselves just how flexible wild pollinators could be under highly stressful circumstances. By 2010 whatever fragments of forest were still to be found in and around Carlinville were essentially tiny islands of wildness surrounded by acres of managed agricultural land, retail developments, and homes. Because of the destruction of their habitat, many of Carlinville’s remaining wild bees could be observed collecting pollen from flowers they would never have visited 120 years ago. If one species of wild bee couldn’t find any of the toothwort blossoms that had been its favorite nineteenth-century food, for example, it would make do, gathering pollen from a neighboring snakeroot or spring beauty plant instead.
For many years the assumption in pollination biology had been that plants and pollinators tended to be specifically adapted to one another, with this insect fitting into that blossom like a key fits into a lock. But over the past decade, a new way of looking at plants and pollinators—as large, diverse, holistic communities, rather than as sets of pairs—has shown that the vast majority of flowering plants and the insects that feed from them are actually generalists: each one might have many different partners in the dance of pollination. Models that are based on this insight, which is known as ecological network analysis, suggest that plant communities can respond with surprising resilience whenever they’re faced with the loss of any single species of pollinator, since there are so many other pollinators around to pick up the slack.
But the information Burkle has gathered—much of it from her Carlinville study—complicates this picture. When one bee species disappears from a community, she has found, the surviving species that fill in the gap by visiting a wider variety of plants are actually less efficient as pollinators. Bees can adapt to pollinate new plants, but they are most helpful to their ecosystems when gathering pollen from a single species at a time. Pollen from a gilia blossom doesn’t help an aster plant to set seed. Or, to put it another way: adaptability is a wonderful thing, but biodiversity is even better.
“We need lots of species pollinating our crops and our wild plants,” says Burkle. “Different bees are better pollinators for certain plants, or at certain times of the day or season. Having them all is the safe way to go.”
Berry Brosi, an ecologist at Emory University, has been testing this theory and has found data consistent with it. A few years ago, he and a colleague began tracking the behavior of 11 species of bumblebee that were jointly pollinating a large patch of larkspur, a common wildflower. After dividing the patch into plots, they then captured and temporarily removed the most abundant bumblebee species in each plot.
When a single, dominant bee species was taken out of the picture, Brosi and his colleague discovered that the larkspur tended to set fewer seeds, which translated into fewer flowering plants the following spring. Brosi’s study, recently published in the Proceedings of the National Academy of Sciences, underscores the crucial importance of keeping wild pollinator communities healthy—as well as the importance of keeping them diverse.
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Some wild pollinators are more recognizable than others. It’s relatively easy, for example, to identify a chubby, buzzing bumblebee, carrying bright masses of pollen on its legs. But others are more mysterious. (“That fuzzy-faced one you love so much,” I overhear Reese say to Burkle at one point. “Is that a fly or a bee?”) When I try to describe to Burkle a bumblebee I had seen among the burned-down ponderosa pines, I find myself likening it to a tiny Huey helicopter. She laughs and shares a description of one of her own favorites: a bee with a black-and-white-striped abdomen offset by a stylish metallic green thorax. “She looks all dressed up and ready to go to a party,” she says. “So I call that species Party Pants.”
As it happens, Montana’s wild pollinators are so little studied that Burkle and her research assistants often come across species previously unknown to science. Walking with Burkle and Reese through their survey plots, I watch them delicately caress the leaves of the many different plants they’re cataloguing. Every bee that visits a blossom will be captured and placed in a plastic vial, which is then carefully labeled. Later, during the winter months—while the next generation of bees is waiting to emerge from nests underground or inside of tree trunks—Burkle and her team will meticulously study each captured insect and identify it to species.
Many of these insects are quite different from what people usually think of as a bee. Unlike hive-dwelling honeybees, native bees are solitary creatures. A female typically creates brood cells underground or in the hollowed-out core of a plant stem, where she lays a few eggs, leaving pollen she has collected to feed her larvae once they hatch. Plenty of wild bees don’t look bee-like: some are iridescent green or blue; others are solid black and resemble stout, hovering ants. “Birders talk about the difficulty of identifying little brown birds,” Burkle notes. “We deal with a lot of little black bees. We can’t tell them apart until they’re pinned under a dissecting scope.” Magnified, a particular species might be identified by the pattern of its wing veins, or the number of spines that are visible on a tiny segment of leg.
A day in the field with Burkle and Reese is a crash course in the dazzling diversity of wild pollinators, and of the plants they service. In midsummer, when I visited Montana, the bright flowers of prairie smoke had already faded, leaving behind the wispy seed heads that give the plant its name. Bees and flies cruised right by them, en route to white clumps of blossoming yarrow, purple bells of campanula flowers, or brilliant blooms of toadflax. Leafcutter bees carried off chunks of greenery to line their nests. Sweat bees lapped salt from my arm. Bee flies moved among the blossoms, feeding on nectar. These flies are masqueraders: they lack a stinger, but their yellow and black stripes are usually enough to keep predators away.
Brosi sees Burkle’s work as emblematic of a relatively new idea in conservation biology: a concerted effort to restore not only single species but also the complex interactions among plants, animals, and phenomena—such as fire—that define the fundamental dynamic of any ecosystem. It’s the same idea that has informed the shift in thinking among forest managers with regard to wildfire suppression: the policy, ironclad for the first half of the twentieth century, dictating that all forest fires be put out as soon as they were discovered. After much debate, ecologists who had long recognized that naturally occurring fire was, in fact, an important ecological process that fostered biodiversity were able to convince the National Park Service to change its policy in 1968. “Historically, we’ve had this very simplistic idea of trying to preserve ‘pristine’ nature,” Brosi says. “But we’ve come to realize that nature isn’t static. Change and development are normal. Fire is essential to many natural communities. It’s just in the last decade that we’ve begun to study plant-pollinator networks, and the ways they change over time.”
After studying how Carlinville’s wild pollinators reacted and adapted to the loss of their habitat because of climate change and development, Burkle says that she is just now beginning to get a good feel for the ways that plant-pollinator networks respond to varying intensities of fire. In some cases, she has discovered, only a limited number of plants will colonize the ravaged land in the first few years following an especially hot burn. But forests that have been hit by what’s known as a mixed-severity fire—very hot in some spots, but relatively cool in others—will often support a greater array of wildflowers, grasses, and shrubs.
“The hypothesis is that more diverse plant communities will host more diverse groups of pollinators,” Burkle says. “We’re excited to get our pollinators identified and to see if that idea proves out.”
What ties this sort of wild-pollinator research to the ongoing debate over wildfire-suppression policies and colony collapse disorder is a shared first principle. The best way—many would say the only way—to ensure healthy ecosystems is to encourage as much biodiversity within habitats as possible. That can mean letting a small wildfire burn, secure in the knowledge that the forest will restore itself once the flames have died out. It definitely means easing the burden placed on honeybees to carry the weight of feeding the world, and letting wild pollinators pitch in at this job they seem to perform so well. Which means, in turn, not undoing through overdevelopment and global warming relationships these insects have forged with plants over millions of years.
The secret life of wild pollinators is complex, fascinating, and as difficult to grasp as a flame. But what Laura Burkle, Elizabeth Reese, Berry Brosi, and other scientists like them have learned is that these tiny, oft-overlooked creatures have disproportionately large impacts on their ecosystems. Bees and wasps and butterflies shape the landscape—just as surely as fire does. When a wild bee flies from a blossoming plant back to its nest, its fuzzy body bright with pollen, it’s carrying the seed of biodiversity.
This article was made possible by the Jonathan and Maxine Marshall Fund for environmental journalism.
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