The North American Prairie, a vast grassland that once covered the better part of 14 states, was one of the most complex ecosystems in the world.

Today, most of that prairie has been fenced in or converted to farmland, and the millions of bison, antelope and elk that once grazed on it are mostly gone. However, one can still find a pristine 40,000-hectare piece of that natural wonder in the Flint Hills of eastern Kansas.

Americans who believe that the state of Kansas, in the central United States, is flat and featureless may have never seen the Tallgrass Prairie National Preserve. In the summertime, the sight of its gently undulating rises of shoulder-high grasses - mostly Big Bluestem, Little Bluestem, Indiangrass and switchgrass -- take Ranger Ron Clark's breath away every day he tromps through them on his daily rounds.

"Look at the multitude of colors," he says. "I see Wavy-leaf thistle blooming lavender, yellow coneflower, purple coneflower, both purple and prairie clover, some white prairie clover." Of course, mainly what Ranger Clark sees are the 40 kinds of grasses that make up the palette of greens, which comprise less than 10% of the plant community. With root systems that can reach four meters or more. "That's what enables them to sustain periods of drought, fire and grazing," says Mr. Clark.

The rhythms of fire and grazing are key to understanding the tallgrass prairie, where, for untold millennia, antelope, bison and elk grazed on their migrations, trimming back extra growth while ingesting the rich nutrients they needed to stay strong, mate and move on.

And every five to seven years, natural fires caused by lightning would burn away the dead grass and make way for new shoots. Today, ranchers graze cattle on the prairie to fatten them up, and Ranger Clark says that the ancient fire cycle is renewed every spring, when those ranchers set a controlled prairie burn that nature once set at random.

Once the fires are set, he says, "You'll see fire and smoke everywhere you look, and after the burn, you just see nothing but rock out here - you wonder how anything can grow. But within four or five days, it's green everywhere out here." And within two weeks, he adds, the Tallgrass prairie "looks like a sculptured golf course. Within a month you can turn steers out there and they will put on several pounds a day on this grass. Most people have no idea of the richness of this landscape."

The richness of the soil is largely due to the calcium and other minerals left here by the marine life that lived and died here millions of years ago when this part of North America was covered by a vast inland sea, says. Ranger James Kimo, who specializes in prairie geology.

"And when it was warm, it would be full of crustaceans, bivalves, coral and sponges - animals that absorbed the calcium from the seawater and excreted it to make their skeletons or their shells." And as they died, he says "that mass would drop to the bottom of the sea and would evolve into lime mud and then into limestone. And it makes for a very good soil for these grasses."

Today, grasshoppers are the tallgrass prairie's primary grazer, and Ranger Clark says that grasshoppers make up two thirds of a coyote' summer diet.

"The coyotes in the winter will feed on rabbits and prairie pocket gophers that may be out and so the cycle goes on." Even mosses and lichens get into the act, by converting the lime and the sandstone to soluble use so plants can utilize it. "The herbivores then feed on the grass," says Ranger Clark, "and the carnivores feed on the herbivores, and I guess in that food chain we are in there as well - because we will eat some of the herbivores, particularly the beef cattle."

Ron Clark is a ranger, not a scientist. Still, he often refers to himself as an "oh my" biologist - as in "Oh my, look at this!" and "Oh my, look at that!" He loves to kneel down close to the earth and, in his words, "let the prairie talk to him" even the dangerous parts.

"Occasionally, in rocky areas, you will come across a rattlesnake, but they always are courteous enough to warn me and I just give them their space and walk around. They were here first and they don't bother me at all." He bends down and touches a delicate green leaf called "Catclaw sensitive briar," and it curls up. "This had a nice little red lollipop flower on it a few days ago. Kids love that," he says.

Ranger Clark points a meter farther up the rise. See this lead plant? It was used as medicine by Indians. It'd help a sore heal -- kind of like an antiseptic."

Ranger Clark adds that the prairie heals itself too. He likens the broom weed he is standing in by the side of a dirt road to a "band-aid."

"It's a plant that will grow along this road, which is a damaged site. But the grasses, given time -- no more grazing, no more rocks, no more vans -- they will reclaim and crowd out most of this broom weed and the band-aid will disappear. The prairie is amazingly resilient. There is probably no truer statement that that."

Thanks to the Tallgrass Prairie National Preserve, all visitors to Kansas can have the opportunity to experience the wonder of the North American prairie. All they have to do is simply get out of their cars, listen hard, and let the prairie "talk to them."