A decade of studies indicates logging practices that follow the Oregon Forest Practices Act have no adverse effects on Coho salmon or coastal cutthroat trout.

The study was conducted by researchers from Oregon and Colorado state universities, the US. Geological Survey and the forest services industry.

Studies of logging practices prior to the passage of the 1971 act showed changes to fish habitat from the use of stream channels as transportation corridors for logs, and other changes to nearby riparian areas. The Alsea River watershed work was considered one of the landmark studies in the late 1960s by providing a baseline by which to measure future changes.

The team replicated the work, compiling data from the Needle Branch and Flynn creeks watersheds of the Alsea River in northern Oregon.

“In the 1960s, the stream channel in Needle Branch got hammered, and the cutthroat took it in the shorts,” Doug Bateman, the lead author of the paper published last month in the journal Forest Ecology and Management.

Each year, the group counted the number of trout that were older than one year and documented forest cover, stream habitat conditions, temperatures and discharge.

The site was a lesson in comparatives, as logging took place in Needle Branch Creek in 2009, but Flynn Creek was left alone, as it had been in the 1960s.

The number of fish in Needle Branch actually increased after the tree harvesting, in which nearly all the trees were cut with the exception of a required buffer strip along the fish-bearing part of the stream, the study indicates.

Juvenile coho salmon found downstream from harvested areas were not affected, most likely because they wee downstream from the logged area.

“Salmon numbers are also complicated,” Bateman said. “Their migratory behavior exposes them to a variety of factors such as sport and commercial harvesting and conditions in the ocean and estuaries that most cutthroat trout do not experience.”

But trout excelled.

By monitoring their movements, the researchers determined their increased numbers was due to local changes and not influxes of fish from other areas.

“It’s rare to be able to say that,” Bateman said. “In other studies, it is often unknown whether changes in population size are associated with fish movement, but here we show that the fish responded to conditions in the harvested portion of the channel.”

They weren’t sure why, he admitted.

“We weren’t set up to study the causes of the increase, so we can’t really say for sure,” he said. “It’s possible that increases in sunlight or increased export of invertebrates from upstream areas contributed to the increased fish biomass, but it could also be related to any number of other factors, such as stream temperatures, changes in predators or disease.”

Bateman also admitted that other watersheds may very well differ from the Alsea River.

“We’re cautious about generalizing these results to other watersheds since conditions can vary so much,” he said. “Still, these fish are probably well adapted to changes in the streams, and forests provide some of the best remaining habitat for them. When you move downstream into areas adjacent to farm fields and urban areas, the changes to rivers and streams can pose significant challenges. It’s important to look at the watershed as a whole.”

Reach Jane Stebbins at jstebbins@currypilot.com .