Forests On The Wane - Science News

In the February 11 Issue:

Forests on the wane

Early last decade, the world’s tree coverage dropped by more than 3 percent

By Sid Perkins

May 22nd, 2010; Vol.177 #11 (p. 10)

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WHEN A TREE FALLSSatellite images indicate that about 3 percent of the world’s forests in 2000 were gone by 2005 (percent deforestation shown on map). Forests vanished largely because of massive wildfires and human-induced deforestation for logging and agriculture.Hansen et al./PNAS

Some people can’t see the forest for the trees, but many can’t see them because they’re truly disappearing: About 3 percent of forests standing in 2000 were gone by 2005, a new analysis of satellite images reveals.

Forests vanish for a variety of reasons, from agriculture and logging to natural phenomena such as wildfires, storms and insect infestations, says study coauthor Matthew Hansen, a geographer at South Dakota State University in Brookings.

For purposes of forest accounting, researchers classify an area as forest if trees cover more than 25 percent of the landscape. In 2000, forests blanketed almost 33 million square kilometers of land worldwide. But by 2005 more than 1 million square kilometers of those forests had disappeared, Hansen and his colleagues report online April 26 and in an upcoming Proceedings of the National Academy of Sciences.

On a percentage basis, forests are vanishing most quickly in the boreal region encircling the Arctic. More than 350,000 square kilometers — about 4 percent of the forests in that ecosystem — fell victim. Fires caused about 60 percent of those losses, says Hansen. Logging accounted for a substantial fraction of the remaining deforestation, which also included losses due to storms and beetle infestations (SN: 5/10/08, p. 9).

More than 58 percent of forest loss worldwide occurred in just four nations — Brazil, Canada, the Russian Federation and the United States. Together, these sprawling nations account for about 45 percent of the world’s forests, Hansen notes.

The new study didn’t measure the spread of forests between 2000 and 2005, so recovery from previous natural disasters such as wildfires or storms wasn’t included. Also, Hansen notes, future analyses by the group will use techniques better able to distinguish natural deforestation from that caused by humans.

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Comments 3

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"The new study didn’t measure the spread of forests between 2000 and 2005, so recovery from previous natural disasters such as wildfires or storms wasn’t included." This is a significant omission as forests are a renewable resource, both naturally and artificially. Also not measured, presumably, is reforestation due to replanting of harvested timber stands especially in the northwestern and southern regions of the United States.

D Killebrew

Apr. 28, 2010 at 8:54am
The current study shows a change (reduction) in forest cover but does not show or define whether this change is meaningful in terms of long term variation of such cover. In the absence of this comparison it is impossible to tell if 3% change over five years is something to worry about or if it is a normal fluctuation in forests.

rudyg

May. 3, 2010 at 8:39pm
Concluding ANYTHING is on the "wane" without including the additions to the system seems a bit grade school to me. I mean really guys, one of the dark areas on the map is here in the Pacific Northwest, where harvesting, planting and growing trees has been a way of life for 120 years. The forests have "disappeared" from this region 2 or 3 or more times before, been replanted, and grown back. The land I live on was harvested in the 1920's, replanted, and now has trees up to 3 feet in diameter. They grow fast, some 2 to 4 feet height per year - commercial size trees can be had in 35 years.

If I take the 5 year time period in question and divide by 3%, that gives me 167 years. This is an easily sustainable harvest rate, given that it takes 35 years here and perhaps several times that in a northern area.

I doubt seriously that the satelite can see the fresh 8 inch tall seedlings that were planted within a year of harvest, it probably looks like a clear cut from space. Well they are there, and they'll be "disappeared" again in a few decades. That is, unless people succeed in saving the trees. In that case, the commercial value of tree farms will decrease (over-supply situation) and the land will be sold for some other use, thus making the disappearance permanent.

So, use "paper" instead of plastic and don't sweat the 3%.

Herb Fecker

Jun. 4, 2010 at 12:28pm

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