Growing argument

Rainforests are worth protecting. The dense jungles of vegetation cover only about 7 percent of the world's land surface but house, according to some estimates, about half of all plant and animal species.

So it was that a New York Times story last month questioning the importance of old-growth preservation set off a firestorm in the environmentalist community. A buzz of emails and breathless phone calls swirled between biologists from the Amazon to Southeast Asia.

The story quoted Smithsonian senior scientist Joe Wright, who believes that "secondary" forests emerging on the abandoned farmland of once agrarian societies can largely serve to replace the acreage of pristine forests lost each year to fire, logging, or palm oil extraction. That message is not a new one; Wright said as much two years ago. And the UN and Smithsonian Institution have recognized the environmental benefits of new growth since 2005.

But the presence of such a controversial idea on the front page of one of the nation's most-read newspapers triggered more than a little outrage.

Mark Plotkin, president of the Amazon Conservation Team, called the article "one of the worst reported stories I've ever seen." Having studied and worked in the field for three decades from Mexico to Argentina, he says the claim that rainforest is growing back is nonsense: "It's not rainforest. It's trek, secondary forest with very low species diversity and very little in the way of animals living in it."

Plotkin cites the Cambodian forest around the ancient city of Angkor as evidence of just how long habitats can take to return to pristine condition. Populations cleared much of what was rainforest 700 to 1,000 years ago for rice fields and a vast urban settlement. That great society's collapse and migration south in the 15th century allowed jungle to reemerge in much the same way it has in abandoned Latin American farmland over the past few decades.

Centuries later, Plotkin says, "It's still not the equivalent of primary rainforest in species diversity." That's a sentiment shared widely among Plotkin's colleagues on the ground, who witness firsthand the difference between old- and new-growth forests.

But in the popular world of environmentalism, where going green has come to center almost exclusively on carbon footprints, species diversity may prove less important. David Pearson, a tropical biologist and research professor at Arizona State University, says "fast-growing secondary forest uses more carbon dioxide than primary forest does in many cases."

That reality mitigates concerns over the extraction of palm oil from rainforests for biodiesel, a process which some environmentalists charge nets greater CO2 emissions due to deforestation. The encouragement of secondary growth might well restore the perceived value of palm oil extraction in the carbon-cutting game.

But secondary forests are not only carbon-dioxide sinks. They provide a habitat for scores of displaced species, too, albeit not all of those contained in primary forests.

Pearson, who has studied rainforests since 1968, appreciates the hyper-diversity of old growth, having worked alongside Smithsonian entomologist Terry Irwin on a project that discovered 2,000 species of insects inhabiting a single tree. Still, Pearson contends that newer growth deserves celebration and protection as the next best option in a world that has already lost about half of its primary tropical rainforest.

He says scientists who argue that only pristine forest is worthwhile are as misguided as the industry ideologues who contend that secondary forest is just as good: "It's convenient but very inaccurate to go to either extreme. This is a broad sweeping generalization, but the young people coming into this tend to have a much healthier attitude toward these secondary habitats. It's mostly people my age who've got this fixation that pristine is the only way to go."

Pearson sympathizes with his colleagues arguing for pristine only, given the propensity for oversimplification in public discourse. Many biologists fear that any public acknowledgment of value in secondary forests will undermine conservation efforts. "But the public has to know," Pearson said. "If we do this in a way that can be interpreted as a lie or a mistruth, then everything else we say is going to be doubted more and more. Secondary forest by itself is probably not the best approach, but secondary forest is much, much better than a soybean field."