Biodiversity in logged forests far higher than once believed
New research shows that scientists have significantly overestimated the damage that logging in tropical forests has done to biodiversity, a finding that could change the way conservationists think about how best to preserve species in areas disturbed by humans.
Researchers have discovered a significant flaw in large swaths of ecological research into the impact of logging on tropical forests: Scientists have been dramatically overestimating the damage done by loggers, skewing conservation strategies paid for by the donations of millions of environmentally minded citizens.
Logged tropical forests, new research suggests, are much more valuable for biodiversity than previously thought. Our understandable preoccupation with protecting pristine ecosystems may be blinding us to the fact that the forests that have been selectively logged deserve conservation, too. One immediate and troubling implication is that schemes backed by conservationists in Indonesia and elsewhere to turn “degraded” forests into palm oil plantations will do far more damage to nature’s biodiversity than the original logging.
“Logged forests in the tropics are too vast, vulnerable, and important to ignore, given their large conservation potential,” says William Laurance of James Cook University in Cairns, Australia, who did not participate in the research but backs the importance of the new findings. “It is vital that we recognize their key role for conserving tropical nature.”
The research, published in January in the journal Conservation Biology, finds that at least two-thirds of scientific studies into the impact of logging on forests are guilty of “pseudo-replication.” Horrible word, but it describes a statistical trap that researchers often fall into when comparing sets of data to tease out the effect of some impact.
In this case, it means that ecologists comparing logged forests with nearby unlogged forests have usually assumed that all the differences in species that they find are the result of logging. But this is rarely true. All bits of forest, even close neighbors, are different — often dramatically so. The simple statistical comparisons pick up the pre-existing natural differences as well as the effects of logging. Typically, these flawed analyses have produced figures for the damage caused to forests by logging that are higher than the reality.
The analysis covered 77 studies over the past decade, investigating everything from the butterflies of Thailand and the woodpeckers of Borneo to Kenyan trees, India forest birds, the bryophytes (non-vascular plants) of the Indonesian island of Sulawesi, Amazonian bats, lianas in southern China, the birds of Bolivia, and the termites of the Malaysian state of Sabah. Of these 77 studies, 52 were guilty of pseudoreplication, five were definitely not guilty, and the jury was out on a further 20.
The new research is not from some pro-logging group. The lead authors are Benjamin Ramage, a respected conservation ecologist from the University of California at Berkeley, and Douglas Sheil, a former director of the Institute of Tropical Forest Conservation in Uganda, who is now at the Southern Cross University in Lismore, Australia.
Their discovery of this previously unnoticed flaw at the heart of conservation science is a damning indictment. It undermines the findings of hundreds of research studies published over many years — studies that have underpinned a forest conservation ethos that concentrates almost exclusively on protecting the pristine.
A rethink will be required. Most existing research on the ecological effects of logging “cannot be trusted,” the authors say, adding, “The problem is so pervasive that the severity and precise nature of the bias cannot be reliably calculated.” But they conclude that it means “the effects of logging have been exaggerated and... the current body of literature provides little indication of the true nature of [logging] effects.”
These startling conclusions are supported by forest ecologists who are highly critical of runaway logging, such as Laurance and Jeffrey Sayer of the International Union for the Conservation of Nature.
They also back up research in Sabah on the island of Borneo, by David Edwards of James Cook University in Australia. Reporting in the Proceeding of the Royal Society B in 2010, he found that even after repeated logging, forests there typically retain 75 percent of their biodiversity. Edwards’ study concentrated on birds and dung beetles as representative of overall biodiversity. More than two-thirds of the 179 bird species and a similar proportion of the 53 dung-beetle species survived at 18 sampling sites across a large logging concession covering a million hectares, despite the entire concession being logged over twice.
Sayer goes even further. He says that in Kalimantan, the Indonesian part of Borneo, “biodiversity in logged-over concessions is in better condition than many of the protected areas.” In the concession areas, farmers are kept out, whereas most protected areas are essentially abandoned by the authorities and thus open to invasion. In the Congo basin of Africa, he says, “the intensity of logging is so low that only an expert can really tell the difference between forests in concessions and those in protected areas.”
There is little clear-cutting by loggers in the tropics, except where forests are being razed for agriculture. Most logging is selective, with only the most commercially valuable species cut. Other trees may be damaged by the bulldozers and heavy equipment used to construct roads and remove the timber, but most survive, along with the wildlife that depend on them.
Many forests become permanent timber estates that are repeatedly logged. In a recent paper in Science, Edwards and Laurance estimate that more than 400 million hectares of tropical forests — an area half the size of the contiguous United States — are now part of such estates. Most surviving forests in Southeast Asia have been logged at least once. “Few truly undisturbed forests exist,” they wrote.
Despite their growing importance, logged forests have traditionally been shunned by conservationists in favor of protecting surviving scraps of virgin forest. But Laurance says the new findings about how the conservation value of logged forests has been underestimated will add fuel to the argument that, in the 21st century, logged forests are of increasing value to the planet’s biodiversity and can no longer be shunned.
“Conservationists ignore [logged forests] at their peril,” says Edwards.
This revisionist thinking mirrors that articulated by, among others, Peter Kareiva, chief scientist at The Nature Conservancy, who attacks our romantic notions of the environment as something fragile and separate from humans and questions whether there is any truly pristine nature left anywhere. Even the Amazon was thoroughly worked over by pre-Columbian societies.
Wilderness is a myth, say the new ecologists. They question our obsession with putting nature in a glass cage and poo-poo our antipathy to alien species. We have no choice but to see ourselves as a functioning part of all ecosystems, they argue.
This more sanguine view of forest degradation is hardly embraced by all conservation scientists. Two years ago, the well-known conservation activist, Thomas Lovejoy, now of George Mason University in Virginia, co-authored a letter in Nature that bore the headline “Primary Forests Are Irreplaceable for Sustaining Tropical Biodiversity.” The letter argued that even though few truly undisturbed forests exist, those that remain contain more biodiversity than comparable degraded forests. Ironically, another co-author was Laurance. Yet Laurence points out that logged forests are still more biodiverse than other types of disturbed forests, and given the huge extent of logged areas, he argues that conservation has to embrace them.
Certainly neither Laurance nor his colleagues maintain that the latest research on logging and biodiversity should be treated as a green light for clearing forests. Far from it. For one thing, the roads created by loggers make forests vulnerable to invasions by farmers and ranchers, who may be far more destructive. But it does suggest that well-managed permanent forest estates could be part of the solution to biodiversity loss, rather than the problem — and that conservationists should devote more attention to that task, even if it lacks the romance of protecting the pristine.
By concentrating their attention on what is lost, conservationists have often ignored what survives. And the new study reveals that the statistical failings of their analyses of the losses have served to underestimate how much remains.
All this is a real break from the orthodoxies of conservation ecology and our often simplistic ideas about deforestation. A reevaluation of the conservation of other kinds of degraded ecosystems may be required. Even invasions by farmers may not be the end for forest biodiversity, says Sayer. “Forests that regenerate on abandoned farmland are often surprisingly rich in biodiversity, including some species that are often thought of as [only found in] natural forests,” he says.
There are important implications for practical conservation. Conservationists have traditionally concentrated their lobbying and activities on the ground towards protecting untouched “conservation hotspots,” a term pioneered by Russell Mittermeier, president of Conservation International.
No environmentalist should want to do anything to encourage logging of pristine forest — and some fear that any recognition of the conservation value of logged forests might encourage this. But ignoring logged forests can sometimes be counterproductive to biodiversity conservation.
That is what is happening in Indonesia, where some conservationists are backing a billion-dollar government plan, announced in 2010, to save pristine rainforests by encouraging palm oil and other plantation agriculture to instead move onto “degraded land.” The pristine forests, meanwhile, will be conserved so as to generate carbon credits.
The Washington-based World Resources Institute is among those groups supporting that strategy, by mapping Indonesia’s degraded land. It says this will help the government to divert “new oil palm plantation development onto ‘degraded lands’ instead of expanding production into natural forests.”
Much depends on what the government decides will count as “degraded lands.” And the WRI’s mapping may help protect some logged forests. But Laurance says that a lot of the 36 million hectares — an area larger than Germany — that has been designated as “degraded” in Indonesia is precisely the kind of logged forest that could be almost as rich in species as natural forests.
“Preventing degraded forests from being converted to oil palm should be a priority of policy-makers and conservationists,” says Edwards. The danger is that conservationists end up on the wrong side — complicit in forest destruction and biodiversity loss.
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