CORVALLIS - A 200-year study of rotting logs in the Oregon Cascade Range is only 10 percent complete, but findings from this research have already helped save hundreds of millions of dollars, improved forest health and shattered conventional wisdom about the decay of woody debris.
It also has attracted the interest of forest managers from around the world.
This work was begun 20 years ago by scientists from the College of Forestry at Oregon State University with 530 logs at the H.J. Andrews Experimental Forest near Blue River, Ore. The research was seen as a way to more rigorously document the process of wood decay and the value it provides in nutrient release, soil enhancement and other issues.
Even though the study is far from complete, it has already achieved many of these goals and raised other important questions that will continue to affect modern silviculture and the understanding of forest ecology, said Mark E. Harmon, the Richardson Chair and Professor of Forest Science at OSU. The work has been funded by the National Science Foundation and the U.S.D.A. Forest Service.
"Much of what we've found has run contrary to the conventional wisdom and is not what we expected," Harmon said. "And this long-term, intensive study of the decay of forest debris and logs has raised considerable awareness of this issue among forest managers."
Two decades ago, forest harvest operations usually "cleaned up" a site after logging, removing most of the debris at considerable cost and effort. As this and other studies showed the compelling ecological value of that material, the debris is now largely left where it is, making the forest healthier in the long run and saving hundreds of millions of dollars in unnecessary work.
"When this study began, we still assumed that most debris and logs decayed in more or less the same way, only releasing their stored-up nutrients after decades or centuries of decay," Harmon said. "It's now understood that there are large differences between the decay rate caused by different decomposers of different tree species, and that some nutrients from dead wood begin to enrich the forest almost immediately.
"That's a huge change in our thinking, and there are still a lot more changes to come," he said.
Among the other findings of the first 20 years of this work:
# As much as one-third of the nitrogen in Pacific Northwest forests, one of the key nutrients that limit vegetation growth, appears to come from nitrogen fixation processes within rotting logs, in addition to that being slowly released from the wood itself.
# Nutrient release begins far more quickly than ever anticipated, from both decaying fungi and the leaching effects of persistent rains.
# The "brown rot" fungi that cannot break down lignin in trees leaves structural material behind to help form the next generations of forest floor and ultimately soil. White rot fungi, by contrast, degrade all parts of the wood, leaving almost nothing behind and decaying far more rapidly but only on some tree species.
# Although some wood (such as Douglas-fir) resists decay, mechanisms such as mushroom growth on downed logs work to drain nitrogen from these logs, much more than had been understood.
# There is a 10-fold difference in wood decay rates among dead trees. True firs such as silver fir will decay far more rapidly than other species, as much as 5-6 percent a year and may be gone in 60 years or less. Other species such as western red cedar or Douglas-fir may persist for hundreds of years.
# Some parts of a log will decay and release nutrients much more quickly than other parts, leading to complex patterns that cannot be predicted by considering just the "average" condition of the wood.
# Decay processes are dynamic and constantly changing, and they affect everything from nutrient release to soil changes, stream sedimentation, and plant, animal and fish habitat.
"In the past we just didn't pay much attention to what was decaying, and how, and what the ecological implications of that were," Harmon said. "We now know there are huge differences between tree species, that some fungi decay some species and not others, and that all of these factors will play a role in sustainable forestry and overall forest health."
In the future, Harmon said, trees increasingly will be planted that are never meant to be harvested - by design, they will be left to decay and play certain roles in forest ecology, for the health of plants, trees, microbes and wildlife. With large trees that have commercial value, it's still not certain exactly how many must be left for the complete range of forest benefits, he said, and findings on that issue will continue to emerge from studies such as this.
Oddly enough, some of today's evolving forest management systems may seem more similar to those in the early days of the Pacific Northwest forest products industry - when large amounts of less-valuable wood was left behind in practices that were later deemed "wasteful" and changed dramatically after the 1940s, in order to harvest more of the wood and leave a clean site behind.
The findings of these studies and their temporal scope have been so compelling, Harmon said, that they have attracted not only forest scientists but artists.
"We originally began this work assuming it would be of interest only to forest researchers and ecologists," Harmon said. "Now people from all over the world are watching these studies, and many experts think of nutrient release as one of the last frontiers in understanding the role of dead trees in forest ecology.
"Writers have done features on the work in national publications. Even artists and sculptors have worked with us to portray the fascinating, natural processes of forest growth and long-term changes."
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