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When the bison finally charged, Maryan Smith was ready: One camera had been encased in a specially constructed steel box, covered with Plexiglas, and lowered into a freshly dug 2-foot hole. Two other cameras were positioned at just the right angles to catch the herd of 300 head-on and from the left flank. Finally, Smith and her two assistants—a biologist and a second camera operator—camouflaged themselves in the high grass behind a barbed-wire fence—a relatively flimsy, but likely effective, barrier between them and the behemoths that would soon roar by on this patch of Oklahoma turf.

But with the bison just 100 yards away, Smith, who had spent weeks planning this sequence and half a day setting it up, suddenly had second thoughts. The reason: A few days earlier, while riding in a Jeep on nearby ranchland, she had seen some unruly bison show their disdain for manmade barricades. “I watched them flatten a five-strand barbed-wire fence,” she says. “They trampled it and the whole herd went right through.”

Now those same bison, herded by cowboys on horseback, were thundering toward the trio, and Smith could only focus on the possibility of this fence also being dismantled. “At that moment I thought, “I didn’t think this through well enough,’ ” she says.

If the bison did raze the barbed-wire, Smith and her crew would have to abandon thousands of dollars’ worth of camera equipment and run for the hills. In that instant, she says, she considered calling the whole thing off—about signaling the cowpokes to drive the herd in another direction. But because of the potential danger to the younger animals—the possibility, for example, of their being run down by their massive elders—the cowboys wouldn’t want to repeat this sequence. And besides, says Smith, it’s just that little lag time before a complicated shot like this that invariably gives you pause. But, she adds, it always passes. “When they’re close enough, you have to think about your work. The die is cast.”

Smith says this with only a trace of emotion, as if an onslaught by this continent’s largest land mammals—some of which weigh as much as a ton—was not really reason for concern, that her last-minute heebie-jeebies were actually nothing more than an insignificant case of the butterflies. But when your work has already taken you atop a 70-foot scaffold to film eagle chicks on the Chesapeake Bay and headfirst into a Poconos bear den to get footage of mother and cub, a buffalo stampede may in fact be just another day at the office.

In any case, Smith’s decision to stay prone in the grass ultimately paid off: The buffalo didn’t deviate from the script, and as a result, the opening of her new half-hour film, Fire and Thunder, includes a cloud-of-dust sequence so visceral that the herd seems to be running through the room. It’s heart-stopping footage that gives way to incredible shots of prairie chickens performing their spring mating dance, snakes swallowing eggs and poking around inside the burro of obviously worried cotton mice, and male lizards facing off to do slow-motion battle.

But the real stars of this film about the tall-grass prairie, which airs as part of the “National Geographic Explorer” series, are the bison, whose numbers over the past century dwindled from an estimated 60 million to 541. The slaughter was carried out by European settlers looking to capitalize on bison flesh, hides, and bones, and, some contend, to kill off a vital component of native culture, an animal considered by the tribes to be nothing less than a gift from the Great Creator. The decimation of the bison only stopped when the herds were gone and it was not profitable enough to track down and butcher those that remained. If only for that reason, the species did not become altogether extinct.

Back then, bison used to travel 50 to 100 miles a day in search of good grazing. They cut, tilled, and fertilized as they went, thereby helping to maintain the “fruited plain” wrapped like a cummerbund across the nation’s midsection. This tall-grass prairie exists nowhere else, and it boasts a generous collection of flora and fauna: Mixed in among 150 kinds of grass are 50 different mammals, 201 types of bees, and 301 species of grasshopper.

But the tall-grass prairie has been disappearing; where there were once uninterrupted expanses that let buffalo roam at will, there are now just unconnected islands of heartland. A few years ago, as part of its “Last Great Places” campaign, the Nature Conservancy bought 36,000 acres of this land in Oklahoma’s Flint Hills in hopes of restoring it to its 19th-century condition. That meant returning bison to the land, and last year a donated herd of 300 was trucked 40 miles from a ranch to the restored preserve.

Smith spent nine months chronicling the refurbishing of this piece of Oklahoma prairie and the bison’s return to it. Much of her time was spent waiting: waiting for the animals to appear, waiting for good weather, waiting for the right light. But for Smith, who passed the year in a trailer amid 35 acres of pasture, that was not the hard part. “A funny thing people say to me is, “Don’t you get bored?’ Well, the longer you sit, the quieter you are, the more you see. After you’re out there long enough,” she says, “you get a sense of the rhythm. You’re never bored, but rather distracted by everything going on.”

There was also a wait for the right atmospheric conditions to allow the prescribed burning of the grassland—part of the ongoing cycle of destruction and regeneration. In addition to fire, this “disturbance-dependent ecosystem” has also been maintained by the bison, which chewed down the grass and cut the soil with their large hooves. The bison had been gone for a century, however, and the land hadn’t been burned in decades, so the Nature Conservancy called in a six-man crew to systematically torch the parcel.

While the prairie burned, Smith filmed. But the unexpected wind shifts proved more hazardous than the stampeding buffalo: One day, while lighting small backfires in hopes of getting dramatic footage, the winds sent flames racing so close to Smith that her eyebrows were singed. “Another day,” she says, “a gust of wind came up and sent a line of fire up the hill toward us. We were able to grab our equipment and run. If it hadn’t been just a gust, we would have been caught in the flames.

“Another time, we were totally engulfed in smoke. It suddenly came over the hill. I lay on the ground to get air down there. My sound recorder moved to one side and literally stepped out of the cloud. He called to me, but I didn’t have the breath to move.”

Smith seems to relish danger—she offhandedly describes herself as fearless—although a recent conversation made it clear that the real allure for her is the animals. The 43-year-old Fairfax County native recently returned to the place where she grew up—a sprawling tract of woods and pasture—to talk about her filmmaking. This remote property, part of a once-thriving farm community, was formerly home to sheep, cattle, and pigs; today, Smith points out deer tracks, a fox den, and a red-tailed hawk peering down from its nest. It was here, as an 8-year-old, that she learned to drive a tractor and pound nails. “My mother took me to ballet classes,” she says of those years, “and my father took me to mend fences.”

If she had followed her heart, Smith says, she would have pursued a career involving animals. But after college, she instead found herself in a mergers-and-acquisitions job, which in turn was followed by stints in trade journalism and scriptwriting for training films. But 10 years ago, she traded her life savings for a clunky 3/4-inch video system and set out to pursue natural history filmmaking. Six months later, she ended up with a 12-minute video about snow that helped her land a nonpaying internship with the BBC. Her work there on productions about eagles and grey squirrels was in turn parlayed into assignments that included, in 1990, a National Geographic film about black bears, which she both produced and filmed.

For a year, Smith followed a mother bear and her cub around the Poconos. A black bear den is typically the size of a refrigerator, so squeezing in there with the animals tends to not be such a prudent idea. But Smith’s subject had taken up residence in a large crawl space under a homeowner’s deck—enough room, Smith decided, for a photo session. So she slithered inside, then dragged her camera in after her.

“You sort of make a contract with animals,” she says. “I didn’t want help working with the bear; I wanted to keep it one-on-one. She and I had a kind of contract. She’d let me know when I was too close or she was fed up. If I crossed her line, she’d bluff charge—she’d lick her lips and smack her teeth. You want to run, but you have to stand your ground and yell, “No!’ ”

Smith did not get as up-close-and-personal with the bison, in part because she was dealing with an entire herd. Instead, much of the filming was done from an all-terrain vehicle she wangled from Suzuki in exchange for a film credit. (Her business background, she insists, has been a boon to her film-career dealmaking.) But she nonetheless developed a keen fondness and respect for her subjects. “They’re so charismatic,” she says. “They have identifiable faces and personalities. They’re 10 times stronger than a horse. They’re such an American symbol.”

Smith’s next project is still uncertain, but one subject that particularly interests her is fireflies. “The biggest danger in that,” she says, “is the people you might run into while you’re tracking the fireflies at night. Although in Florida, the alligators are also pretty dangerous.”

Fire and Thunder airs at 9 p.m. Sunday, June 4, on WTBS.