By Henry Fountain
Published: August 1, 2006
'Selective' Logging? Hardly
When you think of logging in the Brazilian Amazon, what comes to mind? Most likely, clear-cutting by ranchers and farmers to create land for crops or grazing. But logging companies in Brazil also practice selective cutting, removing only some of the trees with the goal of sustaining forests (and timber harvests) over a long time.
That's the idea, at least. But a new study of the Brazilian Amazon shows that much selective logging there is anything but sustainable.
The study, led by Gregory P. Asner of the Carnegie Institution of Washington, analyzed high-resolution satellite images of about 17,000 square miles of logged forests over nearly 800,000 square miles of the Brazilian Amazon. It looked for gaps in the canopy cover, indicating that selective logging was taking place, and studied how these areas changed from 1999 to 2004.
The findings, published this week by The Proceedings of the National Academy of Sciences, showed that three-quarters of the areas were logged in a way considered highly damaging: so many trees were removed that the areas were highly susceptible to drought and fire.
Worse, the researchers reported, selective logging often gave way to clear-cutting. A year after selective logging began, about 15 percent of the areas were completely deforested, and the deforestation increased by about 5 percent each year.
The researchers suggested that there was little interest in creating sustainable forests, but rather that these areas were logged to make quick money to support other activities in the Amazon. They say new legislation approved by the Brazilian government to regulate the logging industry may help by moving loggers to lands where forest management can be more tightly controlled.
The March of Trees
Nature can be a deforester, too. The great ice sheets that covered northern North America during the last glacial maximum 17,000 to 25,000 years ago, for instance, did much to strip the landscape of trees.
But scientists have long speculated that some tree species may have survived these colder times in ice-free parts of Beringia, what is now Alaska and the Yukon. The idea was first suggested in the 1930's, but the evidence that such refuges existed was spotty at best.
A new study led by Lynn L. Anderson of the University of Illinois provides genetic evidence that one species, the white spruce, did survive in Alaska during that time. The study is being published this week by The Proceedings of the National Academy of Sciences.
The researchers studied the DNA from white spruces in 24 forests from the northern Great Plains northwest to Alaska. The analysis found great genetic diversity among all the sites, including those in Alaska.
If the spruce trees had been largely wiped out in this area during the glacial maximum, the diversity now would presumably be much lower, because the modern trees would all be descended from those that migrated from areas south of the ice sheets after the climate warmed again.
Instead, the findings suggest that the spruces repopulated the region by migrating from refuges where they survived the ice age. If so, the researchers say, the trees migrated much more slowly than if they had come all the way from the south. And this has implications for how trees may respond to climate change. If they migrate relatively slowly, they may not be able to shift their range fast enough to keep pace as regions get warmer.
Alaska's Fragile Coral
The National Marine Fisheries Service has moved to protect cold-water corals off the Aleutian Islands of Alaska, banning the use of trawls, dredges and other such gear in certain areas across 280,000 square nautical miles.
The ban, which went into effect last week, affects fishing for cod and other bottom-dwelling species. Fragile coral gardens were discovered off the Aleutians in 2002 at depths of about 1,000 feet.
They are thought to be among the most diverse cold-water coral collections anywhere, with at least 25 species or subspecies.
To Pack Them In, Heat Them and Cool Them
Close readers of cereal boxes are familiar with a disclaimer that usually appears in fine print on the side. It is for people who may be concerned when they open the box and it seems less than full. The wording usually points out that the product is sold by weight, not by volume, and that it was packed as full as possible (usually by ''modern equipment'') but that some settling may have occurred in shipment.
The contents settle when the box is shaken, tumbled, bounced or otherwise vibrated in transit. Vibration is one way to get small objects of more or less uniform size to pack more closely in a container.
Close packing of Sugar Smacks may be inadvertent, but deliberate close packing is of practical importance in industries like agribusiness (consider grain in an elevator), pharmaceuticals and mining.
Those industries may be interested in a study by physicists at Penn State.
They have determined that granular materials can become closely packed in a more passive way -- through alternate heating and cooling.
The researchers studied what happened when round glass beads were heated in a plastic container. They found that the ''packing fraction'' -- the percentage of the volume occupied by the material rather than by space, typically around 60 percent for spheres -- increased by about one percentage point after a single cycle in which the temperature was raised and then lowered by 10 degrees Celsius, or 18 Fahrenheit. And the packing fraction increased, though by lesser and lesser amounts, as thermal cycles were repeated.
Peter Schiffer, a physics professor and one of the authors of a brief paper describing the finding in the journal Nature, said that while both the glass and plastic expanded when they were heated and contracted when they were cooled, the plastic did so to a far greater degree. ''As you expand the walls of the container, that gives the glass beads more space so they can settle a bit,'' he said. Then when the walls contract, the beads stay in their new positions.
Dr. Schiffer said he was interested in the phenomenon as a physicist and would leave it to engineers to determine whether there were any practical applications for it.
''I wouldn't want to dismiss the possibility,'' he said, ''but I'd be hesitant to make any claims.''
Photo (Photo by John Passaneau, Penn State)