Selective logging—the practice of removing one or two trees and leaving the rest intact—is often considered a sustainable alternative to clear-cutting, in which a large swath of forest is cut down, leaving little behind except wood debris and a denuded landscape.

New research has found that the destruction of the Amazon rainforest is happening twice as fast as previously estimated. The findings came after researchers realized that earlier satellite photographs of the region missed destruction brought on by “selective logging” and updated imagery revealed the previously unseen destruction. Selective logging (the removal of one or two trees while leaving surrounding trees) while generally illegal, is destroying an area equal to that of conventional logging. They found that selective logging of mahogany and other valuable hardwood trees, which is often illegal, is destroying an area of the Amazon equal to that razed by conventional logging. The thing is during the process up to 30 additional trees can be damaged during the timber harvesting.

According to Dr Asner, a researcher at the Carnegie Institution in Washington and Stanford University in California. "People have been monitoring large-scale deforestation in the Amazon with satellites for more than two decades, but selective logging has been mostly invisible until now."

He went on to state, A tree crown can be 25 meters. When you knock down a tree it causes a lot of damage in the understory. It's a debris field down there,.

A large mahogany tree can fetch hundreds of dollars at the sawmill, making it a tempting target in a country where one in five lives in poverty. "People go in and remove just the merchantable species from the forest," Asner says. "Mahogany is the one everybody knows about, but in the Amazon, there are at least 35 marketable hardwood species, and the damage that occurs from taking out just a few trees at a time is enormous. On average, for every tree removed, up to 30 more can be severely damaged by the timber harvesting operation itself. That's because when trees are cut down, the vines that connect them pull down the neighboring trees."

Previous studies have shown that in logged forests, light penetrates to the understory and dries out the forest floor, making it much more susceptible to burning. "That's probably the biggest environmental concern," Asner says. "But selective logging also involves the use of tractors and skidders that rip up the soil and the forest floor. Loggers also build makeshift dirt roads to get in, and study after study has shown that those frontier roads become larger and larger as more people move in, and that feeds the deforestation process. Think of logging as the first land-use change."

Logging also has a significant impact on the food web, Asner says, noting that nearly a third of the planet's land species inhabit the Amazon rainforest—from insects to jaguars and everything in between. "Studies constantly show declines in primate and other mammal populations following selective logging, and rates of forest re-growth indicate that full restoration of habitats are likely slow for large predators," the authors write.

Another concern is climate change. "When a tree trunk is removed, the crown, wood debris and vines are left behind to decompose, releasing carbon dioxide gas into the atmosphere," Asner says. "Sawmills often have an efficiency level of about 30 to 40 percent, so large amounts of sawdust and scrap also decompose into atmospheric CO2."

Selective logging also involves bringing in heavy equipment using makeshift dirt roads that allows other people to come in later and change the landscape even further, fuelling the process of deforestation.

To make sure their assessments were correct, the scientists went out into the field to compare their satellite data to what they could observe from the ground.

The findings confirmed their worst suspicions - that conventional satellite photography has missed about half of the damage caused by illegal logging.

"The Brazilian government has laws against these logging operations, but they can't enforce them over the enormous geography we're talking about," Dr Asner said. "They can't have a cop on every corner, so our idea is to give them these results in hopes that it might help their law enforcement effort," he said.




The direct impacts of selective logging may include:

* Loss of deep-rooted perennial trees and shrubs
* Reduced canopy cover
* Increased invasion of environmental weeds
* Increased soil compaction
* Increased greenhouse gas emission


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