Work started yesterday on a six-month project to cut down 115 rotting or termite-eaten trees along Pali Highway and prune back 50 more.

Many of the trees being cut down are at risk of falling on the highway or pose other dangers, said certified arborist David Rohner.

The trees will be removed on both sides of the roadway from the Wyllie Street bridge to the Pali tunnel, and drivers should expect single right-lane closures during the day through the duration of the project. Crews will start the work on the right-hand side of the Kailua-bound lanes, then move to the right-hand side of the town-bound lanes.

Tammy Mori, spokeswoman for the state Department of Transportation, said once the project is finished, arborists will survey trees past the Pali Tunnel.

The state is kicking off the project now to be prepared when the rainy season returns, bringing rain, wind — and the potential for fallen trees. In January, two ironwoods fell across the Pali, damaging two cars and blocking traffic for hours. And after heavy rainfall in April, another ironwood tree fell onto the highway, blocking traffic again for hours.

"These earlier incidents raised some red flags," Mori said.

The project is one of the largest tree removal projects on the Pali in several years.

Mori said similar tree removal and trimming work has already been done on the Likelike Highway and on H-2 Freeway in recent years. On H-2, though, the state ran into trouble last summer when it cut down more than 70 trees along the roadway, leaving bald spots in the landscape and spurring complaints from residents and The Outdoor Circle.

The state agreed to replant some 40 trees to fill in the gaps.

The Pali plan has the blessing of The Outdoor Circle, which said yesterday that the removal or pruning back of the 165 trees will not make a big difference in the lush forest along the highway.

"We're trying to strike a balance between public safety and the beauty of Hawai'i," said Bob Loy, spokesman for The Outdoor Circle, which will be regularly monitoring the Pali project as it progresses. "The trees really make the Pali."

Some 10,000 trees were surveyed in the project area for rot, termite damage or other problems, said Rohner, an arborist for Steve Nimz and Associates, which conducted the tree survey for the state. Most of the trees that will be cut down are invasive, and include albizzia, mahogany, ironwood and Chinese banyan trees.

Two koa trees also need to be removed, Mori said, and those will be replaced.

Rohner said the survey area extended 50 feet from the roadway.

It's unclear when tree removal work on the other side of the Pali — past the tunnel — will start.