Study shows forestry best management practices prevent erosion
JEFFERSON CITY–John Tuttle and David Gwaze were prepared for bad news when they launched a seven-year study of how controlled logging to achieve forest-management objectives affects erosion and water quality in Missouri’s Ozark forests. Instead, they got a pleasant surprise.
Tuttle is forestry field programs supervisor for the Missouri Department of Conservation. Gwaze is a resource scientist for the agency. Both were concerned about criticisms of timber harvesting on conservation areas.
“There was a time when our critics examined our timber-sale sites and criticized us, and we probably deserved it,” said Tuttle. “It’s not surprising that people are suspicious of logging. Historically, Missouri has mined the forest resource real hard.”
By “mining,” Tuttle means logging with no thought for the future of the forests, wildlife, streams or anything except immediate profits. Recovering from the brand of cut-and-run logging and abusive farming practices in the late 19th and early 20th centuries took decades in the steep hills of the Ozarks. Streams there still are lined with gravel that washed off denuded hillsides with soil during generations of land abuse. When the Conservation Department acquired some of that abused land, it worked to restore and maintain healthy forests, streams, fish and wildlife.
The science of forestry was still in its infancy when Conservation Department stewardship began. Developing sustainable forest management practices involved years of trial and error along with scientific research. By the late 20th century, foresters around the nation were compiling their accumulated knowledge of forest management in books of “best management practices,” or BMPs.
“We got our book the same way other states did,” said Tuttle. “We started with our own, and then we looked at what other states were doing and said ‘Oh, this looks good, let’s put that in our book.’ So then we had this BMP book, and it looked really good on paper. But people were still telling us that our timber sales caused erosion. We said, ‘Let’s see if we have erosion, and if we do, let’s change our BMPs.’”
To determine how effective Missouri’s forestry BMPs were, the Conservation Department enlisted the help of John Bowders, a professor of civil and environmental engineering at the University of Missouri. Together, they designed a seven-year study to determine how clear-cuts on conservation areas affected water quality in adjacent wet-weather streams.
The study involved four master’s degree candidates and two PhD students. They focused mainly on the amount of sediment entering streams. However, they also studied 11 other measures of water quality, including the amount of nitrogen and phosphorus compounds that was washing into streams.
They worked on 15 study sites on Angeline and Current River conservation areas. Five of the sites served as controls, where no timber harvest occurred. On the other 10, loggers conducted regeneration harvests, commonly called clearcuts. Researchers sampled water captured as it ran down hillsides and also in streams.
Field work began four years before the clear-cuts took place, so researchers could gather information about runoff from the healthy, intact forests. Then they gathered comparable data during and after clear-cuts.
“We were very lucky to do the study when we did,” said Gwaze. “2008 was the wettest year in Missouri history, so we got a good test of how our BMPs work.”
Prior to the study, conventional wisdom held that 90 percent of soil erosion comes from haul roads, skid trails (the paths along which loggers drag trees) and landings (where trees are piled up until they are loaded onto trucks). Even with careful construction and revegetation work to minimize erosion, it was assumed these high-traffic areas contributed significantly to erosion.
Gwaze and Tuttle were pleasantly surprised when researchers reported they had found no significant difference in erosion between the harvested and unharvested sites.
“We went to a lot of trouble to be sure we knew if our BMPs work,” said Tuttle. “We didn’t just do it in-house. We brought in academics who had their own ideas and didn’t have a vested interest in forestry. We didn’t know what the outcome would be.
“We hear from our critics all the time that timber sales cause a lot of erosion and that we basically don’t care. We do care. If this study had suggested changes were needed, we were going to change.”
Gwaze said Missouri is not the only state that has BMPs, but it is one of the few that have taken the bold step of evaluating how effective its BMPs are.
“What we have found is that they are really good, we are doing the right thing,” said Gwaze. “To me, that is really important.”
Gwaze said the importance of this study goes far beyond its implications for managing public land. More than 80 percent of Missouri’s forestland is privately owned, and most of this land is not under active management. That is partly because private landowners want to take good care of their forests, and they fear that cutting trees is a bad thing. A study demonstrating that trees can be harvested in an environmentally responsible way could result in better management of private forests, with benefits for wildlife and landowners.
“We have these standards that we try to meet on our land,” said Gwaze, “and we encourage landowners to do the same. But if we aren’t sure how effective they are, it’s a bit difficult to sell. We have to be able to prove these BMPs actually work.”
To learn how the Conservation Department manages its forests to protect streams and water quality, visit mdc4.mdc.mo.gov/Documents/20867.pdfs.