Burning questions raised over logging
Clearing the remaining trees after a forest fire can increase the chance of further flames.
Common assumptions about the ecological benefits of 'salvage' logging following forest fires are wrong, according to a study of the aftermath of a 2002 fire in Oregon.
Culling any remaining timber after a forest fire is sometimes thought to be good for forests, because it removes dead trees that might spark future fires, and because it clears the ground for more seedlings to grow. But these ideas aren't backed up by the facts, says Dan Donato, a forest ecologist from Oregon State University, Corvallis.
Donato and his colleagues studied the largest forest fire in Oregon's history: the Biscuit Fire (named after a mountain close to where the fire started). This fire raged for 120 days through the Siskiyou National Forest, which is largely composed of Douglas fir (Pseudotsuga menziesii), and destroyed roughly 200,000 hectares.
After the fire, the US Forest Service proposed a programme of salvage logging. This conservation effort boosted the local economy, providing jobs in both forest and timber mills. Some of the money was then fed back into forest management. The scientists followed the progress of the logging both before and after it began in October 2004.
Dead wood best left
The team found that when tree trunks were removed, this tended to scatter smaller chunks of debris around the forest. "Basically, all the branches get left behind and actually increase the fire risk," says Donato.
They also found that the unlogged sites saw excellent regeneration, with an average of 767 seedlings per hectare, greater than the regional standard for what is considered a 'fully stocked' forest. In contrast, logged areas saw a mere 224 seedlings per hectare. The researchers suggest that this is because dragging logs through the forest tends to disturb the soil and hinder regrowth.
They conclude that the best way to reduce the fire risk of burnt-out forests is actually to leave dead trees standing for as long as possible, they report in Science1. "That's how forests have been recovering from fire for a very long time," says Donato.
"Natural recovery is possible," agrees Jim Goldin, a US Forest Service forester based in the Pacific Northwest. But he adds that a lot of forests are no longer in a 'natural state' in the first place, and so may not have the same ability to recover after a fire.
Many forests are managed to avoid small fires, for example, so they never thin out in the way they would do in the absence of mankind. When a fire does take hold it tends to be bigger and more destructive. "The consequences are more severe, and recovery is more uncertain," says Goldin.
He adds that it is important not to generalize these findings, because different tree species will have different forest ecologies.
Although the scientists' conclusions may seem straightforward, salvage logging has become enormously controversial. Environmental campaigners have argued that the Biscuit Fire logging was simply an opportunity for logging companies to cultivate their profit margin. "The trouble is that the debate's been going on based on assumptions, with no real data," says Donato.
Some of that debate has surrounded a piece of legislation currently working its way through Congress, which aims to clear red tape so that logging companies can gain access to burnt forest land as soon as possible. This would help them get to the wood before it rots.
Donato says his study indicates it makes little difference to the ecology of a forest whether loggers go in months or years after a fire. He adds that economic and environmental factors should be balanced when dealing with the aftermath of a forest fire. "I just hope that no matter which way the policy decisions go, this study will inform the debate," he says.
- Donato D. C., et al. Science, published online doi:10.1126/science.1122855 (2006).