| Sub Title: | [SUNRISE Edition] |
|---|---|
| Start Page: | C04 |
| Full Text: | |
| Copyright Oregonian Publishing Company May 23, 1997 |
A new federal study of the Siuslaw National Forest reinforces the link between clear-cutting, road building and landslides.
The study of 1,686 slides triggered by the storms of February 1996, covered 1.3 million acres of the forest and adjacent federal, private and state lands. It found that 41 percent of the slides detected through aerial surveys were associated with roads and 36 percent were associated with clear-cut timber harvests. The rest -- 23 percent -- occurred in forested areas free of recent clear-cuts or road building.
The study cautioned that some road and forest slides might have been covered by trees, and therefore hard to detect. But that difficulty does not invalidate the study, agency officials said.
The findings are similar to studies of the past 20 years that have found clear-cutting and road building significantly increase the risks of landslides when unstable terrain is stripped of timber or carved into truck routes.
The studies also are helping trigger a sweeping review of logging policies as state officials ponder ways to reduce the risk of landslides that last winter claimed five lives and destroyed more than a dozen homes.
This new federal study found that landslide rates in clear-cut harvest areas ranged from 1.6 to three times the rates in forested areas. Landslide rates on roads ranged from 19.8 to 26.5 times greater than in forested areas.
The study also noted that federal efforts that reduced logging and stabilized roads helped reduce Siuslaw National forest slide rates.
Although the national forest represented 40 percent of the survey area, it accounted for only 20 percent of the slides. "This gave us the initial impression that our restoration efforts, especially road stabilization, are paying off," according to a Forest Service document.
The study also found that stream improvement projects designed to help fish held up well during the flooding and mudslides of the 1996 storms.
Those efforts involved the placement of woody debris and other stream structures to create pools and help trap sediment. After the storm, more than 80 percent remained in place.