King County hopes to undertake its largest thinning operation to date at Island Center Forest, removing dying alders and tightly packed Douglas firs in an area comprising nearly 100 acres of the popular woodland.

Should the county move forward on the plan, the operation would take place in two different sections of the 363-acre forest — a 60-acre tract and a 33-acre area. The county is holding a public meeting to discuss its plans Tuesday evening at the Land Trust Building.

Neither site, however, would be clearcut under the county’s plan, according to Bill Loeber, the county’s forester. The logging operations would be ecological in nature, he said, geared to improving forest health by selectively thinning in stands that are either too dense or comprised of trees that are dying and ready to topple.

“I think of these things as being like a restoration project,” Loeber said.

David Warren, who heads the Vashon Forest Stewards and who has played an active role in Island Center Forest’s management, concurred.

“There’s this idea that if you just leave the forest alone, it’ll grow back to this natural forest,” he said. Island Center Forest, however, “is at a point where it needs some loving care.”

Much of Island Center Forest was owned by the state Department of Natural Resources, which managed the site commercially for decades, using funds from its management to help pay for school construction. The bulk of the forest was transferred to King County in 2005, after several Islanders advocated for county ownership.

Since then, the county has worked with Vashon groups to develop a stewardship plan for the site that entails ecological thinning, with revenue from the harvests going into the forest’s management. It has also built trails and installed parking lots and signage, transforming the once heavily logged forest into a site popular among horseback riders, cyclists, runners and hikers.

But the forest still holds the remnants of its historical use, Warren and Loeber said. The 60-acre site where the county plans to thin, for instance, contains a mono-crop of Douglas firs planted by the state some 30 years ago; the trees are now so crowded that the area lacks a natural understory and harbors little to no plant diversity.

Once the site gets thinned, Loeber said, the county and Vashon Forest Stewards will fill in some of the openings with cedar, hemlock and white pine, as well as understory species such as hazelnut, cascara and red elderberry — species prized by a range of resident and migratory birds.

The same will happen at the 33-acre site with 70-year-old alders, trees near the end of their lifespan, Loeber said. Some will be allowed to remain as wildlife snags or trees that will eventually topple, providing habitat on the forest floor; others will be removed and sold, again creating openings for other tree and shrub species, he said.

“We’ll keep some of the alder,” Loeber said. “It grows so fast, almost like a weed.”

The county undertook a thinning operation in 2007, but it was much smaller in size. Since then, Loeber noted, recreational use in the forest has grown considerably, and he and other county officials worry that some Islanders who know little of the forest’s history will be troubled if they see logging taking place there.

“We don’t have concerns. But I think the public might have concerns,” Loeber said.

If Islanders attending next week’s meeting express concerns, he said, the county will likely organize some field trips to the site. “Show and tell is the best way to get questions answered,” he said.

Warren noted that the project is a big one — considerably larger than the thinning operation four years ago. What’s more, there will be some disruption; trails will likely have to be closed to ensure the logging can occur safely.

But he said he thinks Islanders will support the effort. The thinning plan is being drafted by Islander Derek Churchill, an ecologist and former member of the Vashon Maury Island Land Trust who developed the 2007 silvicultural plan for Island Center Forest.

The county hopes to make money from the effort, funds that will be returned to the forest for trail maintenance. But the project, Warren said, “isn’t being done to raise revenue. It’s being done for forest health.”

NOTE: The meeting to discuss the county’s plan will be held from 6:30 to 8:30 p.m. Tuesday at the Land Trust Building.