Earth & Sky

You can't put all the blame on logging companies

Greg Asner talks about a hidden threat to the rainforest.

A rose is a rose . . . and deforestation is deforestation. But is the taking of single trees – often by local people who are trying to feed their families – as harmful to the Amazon rainforest as clear–cutting to create pastureland? The environmental concerns, combined with the social concerns, make it a complex issue.

In science, a first step toward knowledge usually involves observation. Here’s an interview with Greg Asner, who uses satellite data to analyze the ecological impacts of selective logging in the Brazilian Amazon Basin. Earth & Sky’s Jorge Salazar spoke with him in November, 2005.

Salazar: What is selective logging?

Asner: It’s the thinning of the forest, rather than the wholesale clear–cutting of it.

Typically, a logger will build a very small road into an area and select species of trees to cut down. These are trees that will bring that person some money at the sawmill.

So, you can imagine your average logger going out on the road and walking around in the forest and looking for these few trees, and taking the time to cut them down. That’s an enormous effort to do that. These are really large trees of 100 feet to several hundred feet tall. Imagine cutting down these trees, cutting the crowns off these trees and dragging the main part of the stem out to an area where it can be loaded onto a truck. It’s an extremely manual kind of effort.

Salazar: What’s the problem with selective logging? How does it hurt the forest?

Asner: Selective logging does not cause the same damage to the forest as deforestation by clear–cutting. It causes less damage. It’s a thinning of the forest. It does cause some of the most valuable trees to be taken out. And there is a lot of collateral damage that’s caused inside the forest.

One reason for the collateral damage is that many of the trees are connected by vines in tropical forests. So, when your average logger cuts down one tree, that tree tends to pull down its neighbors.?

But secondly – and probably the biggest concern – is that we and other groups are finding that after selective logging occurs, the understory of the forest tends to dry out. The reason for the drying is that sunlight is usually not easily permitted to get to the forest floor in a tropical forest. The tree canopy generally is closed to sunlight. But after selective logging, sunlight makes it down to the forest floor and tends to dry out the dead material that’s left from the logging event. Dead material includes leaves, branches, tree crowns, stumps, and so forth. That material is easily ignited and tends to burn.

So people ask, “Is selective logging as large a form of damage as deforestation?” And the answer is no, initially, not nearly the same level of damage.

But over the long run, the fact that fire is introduced to a place that really hasn’t had fire historically is a cause of great concern to scientists. The long–term effects of selective logging certainly have the potential to be a rather large problem, although it’s hard to say if it is more or less of a problem than deforestation.

Salazar: How great is the area of the Amazon affected by selective logging?

Asner: Our study shows that across a period from 1999 to 2002, selective logging covered an area anywhere from 5,000 to more than 7,000 square miles each year. Deforestation, a different type of disturbance altogether, ranges anywhere from about 6,000 to nearly 8,000 square miles.

So, suddenly we find that selective logging matches the geographic area of deforestation each year. What that essentially tells us is that the area of disturbance in the Amazon is double what we thought it was prior to our study.

Salazar: So they take the trees one by one essentially. Sounds hard to detect.

Asner: As seen by satellites, selective logging looks very different from other forms of deforestation, which involves the actual clearing of the forest for cattle pasture or agriculture.

The imprint that it leaves in the forest is one in which there might be a small road in any given location. Plus, there’s damage caused by the single tree that got knocked down. Associated with this is an area of disturbance in the understory of the forest caused by the pulling of the tree out to a place where it can be loaded onto trucks.

All of that combined is very, very hard to detect. But now we have a very good method for detecting it.

Salazar: How do you detect it?

Asner: Because of our studies in the field, we started to develop, back in our laboratory, new satellite methods and analytical methods for detecting this thinning of the forest.

During that time, we developed one of the most powerful detection methods ever put together. It uses satellites in orbit to detect the very small but very ubiquitous types of disturbances, even down to a few trees at a time. These types of disturbances are caused by both natural and human activities.

We applied this new method and found that selective logging was extremely widespread in the Brazilian Amazon.

Salazar: Do you have the capability to take real–time images of selective logging?

Asner: There’s a strong call in the scientific community for a near real–time detection system for both deforestation and selective logging. I am in very close coordination with all of the major groups that do remote sensing of deforestation and logging, and we’re quite sure that we could do a global, near real–time system.

The problem is that the availability of satellite data is going down quickly. What we could do, for example, from 1999 to 2002 with the satellite Landsat 7 is not possible today. And the reason is that Landsat 7 suffered a technical failure in 2003. The United States government has not been able to pull together a replacement mission for Landsat 7. It doesn’t think that it will be able to do so until about 2011 or 2012. There’s going to be a large gap in our data. We’re blind at this point to these kind of studies. We cannot do them now.

Other countries are developing satellites very quickly, and it is possible that in an international forum we could pull together our methods with other people’s satellites and try to do a near real–time system. Some of the countries that are moving ahead quickly include Japan, China, the European Union, and India. So, they have the efforts underway and some satellites in orbit that can serve this purpose.

Salazar: Are you planning to expand this work to other places in the world?

Asner: Yes. In fact we have just started a new project in Peru, working on similar issues. We have the ability to go anywhere in the world with our new methods, so we’ll be working with Peruvians on similar issues of logging and forest disturbance.

It’s possible to take this approach anywhere, like to the rainforest in the Congo in Africa or to Southeast Asian rainforests.

We’ll take it one region at a time.

Greg Asner is trained as a “bio–geo–chemist.”? He combines field studies, airborne and satellite remote sensing, and computer simulation modeling to study land use and climate change at the regional level.? He is? a professor in the Department of Geological and Environmental Sciences at Stanford University, as well as a faculty member in the Carnegie Institution’s Department of Global Ecology.