SCIENCE

Berger conducted experiments in 19 areas around the world, including some where native predators of caribou, moose and elk -- such as wolves, grizzly bears and Siberian tigers -- remain in place, and others where those predators had been chased away or killed off years ago.

The results, published in the June 9 early online issue of Conservation Biology, show not only that fear dissipates in the absence of predators but also that it returns in areas where the predators have been reintroduced -- including Grand Teton and Yellowstone national parks, where wolf populations have been replenished at a cost of tens of millions of dollars.

The data are timely, scientists say, because plans are afoot to allow large numbers of wolves to be hunted in some U.S. areas where they were reintroduced. The results suggest it may be important to keep those populations high enough so that prey species maintain proper vigilance levels.

-- Rick Weiss

Case of Missing Carbon Solved

About 8 billion tons of carbon are created every year by vehicles, industry, and burning forests and other natural occurrences, and we could not survive if the carbon stayed where it was. Scientists have known for some time that about 40 percent accumulates in the atmosphere and oceans absorb about 30 percent. The rest is assumed to be taken up by trees and plants in the northern forests and the tropics.

Computer models predicted that about 2.4 billion tons should be taken up by the northern forests, but ground-based studies have tracked only half that amount -- creating one of the bigger mysteries of climate studies. In an effort to better understand how the "carbon sink" works, scientists at the National Center for Atmospheric Research analyzed air samples that had been collected over decades by aircraft around the world but had never been studied.

The samples collected above the tropics contained less carbon than expected; those taken above the northern forests had more than expected. The conclusion: Intact tropical forests are far more effective at removing carbon from the air than ever predicted.

The tropics are still net emitters of carbon, since forest is being cleared at a fast rate. But instead of releasing 1.8 billion tons of carbon yearly, the tropics are releasing only 100 million tons, the researchers found. That means their trees have been capturing much more carbon than was believed.

"Our study will provide researchers with a much better understanding of how trees and other plants respond to industrial emissions of carbon dioxide, which is a critical problem in global warming," said Britton Stephens, leader of an international team. "This will help us better predict climate change and identify possible strategies for mitigating it."

-- Marc Kaufman