Made for each other?

When the US Air Force tested its largest conventional weapon, a 21,000-pound behemoth dubbed the "Mother of All Bombs," at Eglin Air Force Base in March, the endangered red-cockaded woodpecker had a ringside seat.

While human observers watched from 30 miles away as a towering column of dust and smoke rose from the blast site, some of the rare birds felt the blast from a forest bordering the bombing range.

Clearly, Eglin is no nature preserve - weapons are developed and tested there. The woodpeckers also must endure campers and hunters on parts of the 463,000-acre base in the Florida panhandle that the military doesn't use.

So viewing the big bomb test as just one more ecological disaster on the road to woodpecker extinction seems a logical conclusion.

But don't tell that to Michael Rosenzweig. The University of Arizona ecologist touts Eglin as a model for saving the planet's endangered species using a new-old approach he calls "reconciliation ecology." It is, he says, the science of planning or reengineering human habitats to accommodate man and nature simultaneously.

While other ecologists dream about pristine wilderness parks, Dr. Rosenzweig's utopia is a nuclear power plant's cooling canals adapted into a breeding ground for rare crocodiles. Or it might be suburban lawns ripped up and replanted with native species so a rare pocket mouse can survive. Or maybe even a bombing range turned into a place where rare woodpeckers thrive.

That's right. Despite all the intense human activity, Eglin's red-cockaded woodpecker population has risen 40 percent in the past decade to 600-plus birds, thanks to a sophisticated management partnership between environmentalists and the Air Force. After the big bomb test, researchers found all birds alive and well.

The idea isn't exactly new. Retooling land still in use by humans into something that animals and plants can better use is something akin to the ideas conservationist Aldo Leopold promoted in the 1950s. But it's getting new attention because some ecologists - Rosenzweig chief among them - believe the Earth is poised to lose far more species than originally thought.

Instead of, say, a 50 percent reduction in species, Rosenzweig's research suggests that the growing human population - in combination with global warning - could wipe out an incredible 95 percent of the planet's biodiversity by century's end. Thus, reconciling human habitat with other species' needs is not just a nice option. It may be the only one able to save a Noah's ark of threatened species, in his view.

"We're going to have to reconcile mankind's habitat needs with the habitat needs of other species," he says. "We already engineer our habitats, the difference is that we must do it with other species in mind."

Rosenzweig's research - and his new book "Win-Win Ecology: How the Earth's Species Can Survive in the Midst of Human Enterprise" - are beginning to attract attention.

"He's coming at it from a different direction, but I absolutely agree that reconciliation ecology is a fundamentally important strategy for preserving species," says Peter Raven, director of the Missouri Botanical Garden and a scientific force in the ecology movement.

"If you're talking about survival of the species you can't just disregard all the rest of the planet [outside of wildlife preserves]. We've all said the same thing for a long time, but we just haven't focused on it. We haven't proposed statistical models or theories to deal with it - and that's what Rosenzweig has done."

That's not to say he agrees entirely with Rosenzweig's dire prediction. Conventional estimates are for the globe to lose half to two-thirds of all species in this century, he notes. So to him, 95 percent seems too high.

"His whole point is really to raise the awareness that every acre counts," adds David Mizejewski, director of National Wildlife Federation's Backyard Wildlife Program. "But it's not something that's been looked at or even concentrated on by the big, powerful cons groups - and they're the ones that have the power to get this out."

Ironically, Rosenzweig's toughest critics may prove to be environmentalists themselves. "The people fighting for more [wildlife] reserves might worry if people bought into Rosenzweig's idea too wholeheartedly," says Gordon Orians, a conservation biologist who recently stepped down from the board of the World Wildlife Fund. "They might worry this would undermine their efforts and, in the long term, hurt biodiversity."

After all, in the battle for scarce dollars, it's far easier to get misty-eyed contributors to open their wallets to save wilderness for caribou, elk, and grizzlies than to pay to save a pine forest on a bombing range. Other groups worry that win-win ecology might be misused by corporate interests to justify battering open wild areas by contending that animals and humans can get along just fine.

While his research is valuable, Rosenzweig "may have oversold the notion that you can save everything or most everything in this manner," says Michael Bean, wildlife director of Environmental Defense, which is one of the most active groups protecting wild lands. "Many species cannot survive in the presence of intensive agriculture.... Someone might draw the inference that we can just get rid of parks and preserves."

The debate comes down to just how much land can be left pristine. Some ecologists have not given up hope that 20 percent of the planet can be set aside for animals. Rosenzweig thinks 5 percent is more likely. In his academic field of evolutionary ecology, the theory of species-area relationships has been scientific bedrock since Alexander von Humboldt laid out the fundamental problem in a speech in Paris in 1805: more land, more species - less land, fewer species.

But the ratio of that relationship has been hard to pin down: How much land equals how many species? What about all the variables, such as birds migrating to new areas? Macro ecologists have also had a persistent credibility problem in warning about species loss, mainly because nobody knows how many species the planet holds. Estimates run from 7 million to 80 million.

In 1995, however, Rosenzweig wrote what is by all accounts a seminal textbook on the issue, "Species Diversity in Space and Time," meshing several theories into one cohesive model. After a complex series of mathematical renderings, it reveals a startlingly simple one-to-one correlation between land available to species and their extinction rates.

His mathematical model shows if 95 percent of the earth is gobbled up for human use - as he and others agree is possible with human population set to grow 50 percent this century - an equal percentage of species will disappear, he says. It's accounted by scientists in the field to be an extreme view - but not beyond the pale.

If Rosenzweig's calculations are correct - and many disagree with him on this - even a far-flung necklace of pristine green nature reserves spanning the globe will not be enough land area to save global biodiversity from crashing. And crashing worse than expected.

That's why Rosenzweig is trying to meet nature halfway. Without backyards, cities, suburbs, farmland, and other human habitation converted to save species, his equations suggest there's little help to save the world's biodiversity. That's also why he's excited about places such as Turkey Point Nuclear Power Station in Florida and its miles of cooling canals.

The growth of Miami and other coastal cities has destroyed much of the mangrove estuary habitats of the endangered American crocodile. But in the early 1980s, studies showed the crocodiles were using the cooling canals. And instead of quietly doing away with the animals to avoid restrictions imposed by the Endangered Species Act (as Rosenzweig says often happens on private lands when a rare animal is found) Florida Power and Light did the right thing: It began a wildlife program. Two decades later more than 3,000 crocodiles have been marked and released and sandbars are being restored. At least 17 other endangered bird and animal species also use the property.

Back at the Eglin base, in the late 1980s, the Air Force formed a partnership with the Nature Conservancy to monitor the red-cockaded woodpeckers. Strangely enough, researchers found the birds actually prefer to nest near Eglin's bombing ranges. Bomb tests ignite fires that burn off small nonnative trees - but not rare long-leaf pines the woodpeckers live in. New ground cover after a fire produces more insects for the birds.

Working with the Air Force at Eglin, the conservancy helped developed a plan to conduct controlled burns, plant millions of long-leaf seedlings, and even drill nesting holes in trees. It's become a model. Today the conservancy has an agreement with the Department of Defense to assist in at least 200 conservation projects on more than 170 bases in 41 states.

Some powerful groups are notably upbeat about expanding on the idea. Steven McCormick, president of the Nature Conservancy, touts "win-win ecology" as an idea in sync with his group's philosophy of moving conservation efforts to "the radical center" where human use, wildlife conservation, and land-use planning all go hand in hand.

Adds Rosenzweig: "If we can do this with the military, we should be able to do this a lot of places. It's something we've got to do."

Trying to save the world's species by making a suburban lawn act more Earth-friendly is fraught with danger. Just ask Jason Spangler.

Mr. Spangler and his wife, Lisa, decided two years ago they were "going natural" - converting their lawn just outside Austin, Texas, into a nature retreat by adding native plants that would attract butterflies, birds - and maybe even some endangered species.

Despite strange looks from neighbors, everything was fine at first. Then, the same local government that advocated water conservationsent them a "mowing needed" notice, and said they were violating zoning laws.

Fortunately, Spangler's was not the first encounter with "bad weed laws," and an Internet search quickly yielded all kinds of legal advice. Some of it came from Brett Rappaport, a Chicago attorney who fought successful legal battles for natural lawn growers in the '80s. Today, the city of Chicago is on board - and a wild plant roof garden adorns the top of city hall.

The New England Wild Flower Society, which promotes natural garden-style lawns, reports a 100 percent surge in membership during the past decade from 3,000 to 6,000 households. Sales of its native plants have gone through the roof.

The "reconciliation ecology" message also might provide a little fresh air to a venerable program at the National Wildlife Federation. For years, one of its most popular efforts has been the Backyard Wildlife Program. Despite its popularity, it hasn't been the focus of fundraising or expansion efforts by the group.

But that may change. David Mizejewski, program director, says win-win ecology has him pondering the impact backyards could make if deployed strategically to save species. "It's not that this is the only solution, or that we are going to save the world in our backyards. But by ignoring it, we would be missing out on a key piece that will help."

As for the Spanglers - well, they won their battle. They also installed a mowed border along the edge of their yard - and signs about the species living there.