A $1.5 million study by the state Department of Natural Resource to see whether current logging restrictions were reducing landslides is more than two years behind schedule as scientists argue over the report's conclusions.

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Four years ago, the Washington Department of Natural Resources launched a $1.5 million study to find out if state logging restrictions on unstable slopes were helping reduce the frequency and size of landslides.

Field crews tramped through the steep backcountry of Western Washington to catalog 1,147 landslides triggered during powerful storms of December 2007.

But the study is some two years overdue. It’s now bogged down by a bitter dispute among scientists over what knowledge can be gleaned from the formidable accumulation of data, preventing it from being finalized.

The study is intended to help guide state rule-makers in the high-stakes effort to determine which trees should be left behind on slide-prone timberlands to help protect streams and other public resources.

The draft conclusion appears relatively tame, noting that the findings support “the hypothesis that avoidance of clear cut harvests on unstable terrain reduces the size and frequency of landslides,” according to a draft copy obtained by The Seattle Times.

Critics say the study has numerous problems and doesn’t offer evidence to back up the key conclusion that buffers reduce landslides.

“Correct the misinterpretations, and make it clear that the unstable slope buffer effectiveness could not be determined,” wrote A.J. Kroll, a scientist for Weyerhaeuser, which owns Southwest Washington timberlands that were hit by many of the slides.

The study “simply does not address the rules. … In fact, the effectiveness of the rules may be much better or much worse than indicated in this study,” wrote Leslie Lingley, a geologist with the state Division of Forestry that regulates the timber industry.

The five scientists who authored the study include two who work as private consultants, two who at the time of the study were employed by tribal organizations, and a timber-industry geologist with Rayonier.

They note the study already has gone through peer review and say much of the criticism was raised “well after the appropriate stage.”

“The authors are not convinced that further dialogue is likely to be productive,” they wrote in response to their critics. “We do not see a path forward with respect to issues raised.”

The study focused on 55,000 acres of timberlands in the Willapa Hills, the epicenter of 2007 storms, and some 550 miles of logging roads.

The slides dumped mud and debris into swollen rivers, helping fuel the floods that slammed houses, barns and farm fields downstream

The scientific clash over the study unfolds amid continuing controversy over logging on slide-prone landscapes.

Current rules typically require buffers of uncut trees to remain on unstable slopes where landslides might send mud and debris into waterways or other public resources. Unstable slopes are defined under rules put into place in 2001 as steep inner gorges, bedrock hollows and other terrain prone to slide.

The study found that the current rules often did not appear to be followed, identifying some 47 slides that occurred on slopes that had been clear-cut since 2001, even though the land met the state definition for unstable terrain.

The study also found that more than 40 percent of the landslides occurred on slopes that did not meet the state definition.

Environmentalists who have reviewed the study believe it offers ammunition for tougher enforcement of current rules and for expansion of the definitions of unstable slopes to cover more land.

“This study is evidence that steep and unstable slope rules and regulations are inadequate and enforcement is appalling,” said Peter Goldman, of the Washington Forest Law Center.

Kevin Godbout, a Weyerhaeuser official, says that his company already has taken a number of steps since the 2007 slides to improve identification of unstable terrain that could be buffered with uncut trees.

“We have beefed up our staff of geologists, and reviewed the whole process of how we screen for unstable slopes,” Godbout said.

The future of the study remains unclear.

It emerged from a scientific research committee established by the state to develop studies that can guide review and potential change to state forestry rules.

Chris Mendoza, a co-chair of that committee, says that many of the objections to the study were raised after a vote was taken to end the formal review process, and that it should now become final.

Others disagree. To resolve the dispute, a state policy group, at a meeting earlier this month, recently discussed whether the state should eventually hire a mediator.

Bridget Moran, a Department of Natural Resources deputy supervisor, is confident that common ground eventually will be found.

“We’re trying to resolve whatever issues are out there, so we can proceed ahead and finalize the report,” Moran said. “This is a big important study, and we want to get it right.”

Hal Bernton: 206-464-2581 or hbernton@seattletimes.com