Thanks, as always, to Conservation for the summary of important scientific findings:
When a serious wildfire rips through a forest, it has a tendency to kill nearly all the trees in its path. Then come the logging companies. On one hand, to log a burned forest makes a good deal of sense. Some of the timber is still useful, and it’s a way to derive some economic benefit from a landscape that’s otherwise devastated. The process, called “salvage” logging, typically operates in two phases. In the first phase, machines called “feller-bunchers” come through, cut down the dead trees, and pile them into bunches. In the second phase, machines called “skidders” are brought in. Their function is to take those piles of felled trees and cart them back down the mountain.
The problem with salvage logging is that its ecological impact is uncertain. The literature is full of contradictory conclusions, and that’s in part because there are so many variables at play, and no landscape is quite the same as another. In addition, it’s hard to disentangle the effects of the post-fire salvage logging from the effects of the fire itself.
In general, it’s thought that post-fire salvage logging can lead to increased runoff and increased erosion. But those alterations are, as Michigan Technological University research Joseph Wagenbrenner writes in the journalForest Ecology and Management, “superimposed on a system that already has been highly altered by fire.” Sometimes logging could exacerbate the underlying problem; other times, theoretically, it could counteract it.
For example, some researchers have written that salvage logging could be beneficial, because it disturbs the soil surface, breaking up the water repellant layer that forms in a fire, and increases the soil’s ability to soak up water. On the other hand, the heavy machinery itself has a tendency to even further compact the soil. Others have argued that salvage logging could be beneficial thanks to the “slash” (the detritus left behind from the logging activity) which increases surface cover and, theoretically at least, decreases erosion. But nobody really knows whether logging increases or decreases surface cover following a fire.
As the frequency and severity of wildfires are increasing – particularly in the western United States – Wagenbrenner and his colleagues brought a decade of scientific observation of unlogged, burned forest ecosystems as well as logged, burned forests to bear on the question. His research sites are scattered through Montana, Colorado, and Washington.
They discovered that the amount of sediment in water runoff increased when a burned forest was logged, at least at smaller scales. Increased sedimentation can lead to flooding, if it disrupts the natural flow of rivers and streams. It can also raise water temperature and alter the aquatic food web, making survival challenging for freshwater fish. And water treatment plants have a more difficult time treating the resulting water…
Read the whole article here.