CORVALLIS, Ore. - A new study done in the area burned in the catastrophic Biscuit Fire in southwestern Oregon in 2002 found that allowing trees to naturally regenerate works about as well or better than logging and replanting, and that undisturbed areas may be at lower fire risk in the future.
The research will be published Friday in Sciencexpress and later presented in the journal Science, by scientists from Oregon State University and the Institute of Pacific Islands Forestry in Hawaii. It provides some of the first actual data about forest regeneration in this vast, burned area.
Even following a severe fire such as this, which covered more than 450,000 acres and was the largest in Oregon history, the natural conifer regeneration on study sites was about 300 seedlings per acre, and 80 percent Douglas fir. However, logging reduced the regeneration by 71 percent, and would necessitate manual planting to restore seedling levels that otherwise would have occurred naturally.
In addition, the study suggested that logging, by itself, would actually increase the levels of material that could fuel another fire in the near future, because of the "pulse" of easily-burned fine fuels and waste wood left behind on the forest floor after trees are felled and processed. Other fuel reduction approaches besides logging would still be needed, the researchers said, with additional expense.
"Surprisingly, it appears that after even the most severe fires, the forest is naturally very resilient, more than it's often given credit for," said Dan Donato, a graduate student in the Department of Forest Science at OSU and lead author on the study.
"And if another of our goals is to reduce the risk of early re-burn, the best strategy may be to leave dead trees standing," he said. "In the absence of post-fire logging, we would expect the fuels to fall to the ground over some protracted period, as opposed to the single pulse of high fire risk we saw after logging alone."
This research was focused on regeneration potential after fire, effects of post-fire logging on regeneration, and fire risks. It did not consider the economics of salvage logging. It also did not address the long-term fate of conifer seedlings in competition with shrubs and hardwoods - although early initial regeneration is one key to winning that battle. Continued research to monitor seedling survival and forest recovery is necessary, the scientists said.
Also of note, the scientists said, is that the years immediately following the Biscuit Fire included a good "seed year" for surviving trees and favorable soil moisture conditions, which is a concern in this comparatively dry region of southwest Oregon, where reforestation has traditionally been difficult.
"What this study does make clear is that natural regeneration does not necessarily fail to achieve our goals for conifer establishment," said Beverly Law, an OSU associate professor of forest science. "Strong numbers of seedlings regenerated naturally, and they have a good foothold. So far, so good. Only time will tell how the conifers will compete with shrubs in the long run."
One of the consequences of logging, the scientists said, is that the use of heavy equipment, log skidding, soil compaction and burial of seedlings by excess woody debris took a heavy toll on naturally regenerated seedlings, which in this case began taking root almost immediately after the fire. The logging of dead, burned trees might add more debris than logging of green trees, researchers said, because without foliage to catch the wind, burned trees often fall more quickly and shatter more readily than living trees.
When left to natural regeneration, trees that did not die acted as a seed source for fairly wide areas around them, researchers say. Contrary to some assumptions, even severe fires rarely kill every tree - rather, they usually move through an area in a mosaic of burned trees and some stands left living.
Fire risk is a different issue, the report said.
"Logging has sometimes been cited as a way to reduce fuels that could feed future fires," said John Campbell, a faculty research associate in the Department of Forest Science. "But not everything leaves on the log truck. We found that the process of logging in this type of situation actually produces a large amount of fine fuels on the ground that, unless removed, could increase fire risk, not decrease it."
Leaving that material up in the air on dead trees that will eventually fall, years or decades in the future, is actually more likely to reduce fire risks during the early stages of forest development, the study said. Mechanical fuel removal can work, the report said, but is often precluded by its expense. After logging, options are to leave the fuels and live with high fire risk, or to treat them, generally by prescribed burning, which can lead to additional impacts such as further soil damage and seedling mortality.
In this study, researchers used a comparison of logged and unlogged plots across the fire area, sampling them before and after logging activities. The study concluded that even if logged areas were replanted at prescribed levels, there would be no net gain over natural, early conifer establishment. But the logging activities did cause a significant increase in both fine and coarse woody fuel loads, elevating the short-term fire risk, the report said.
"Post-fire logging may conflict with ecosystem recovery goals," the authors concluded.