SHERIDAN — There were large snowflakes falling on the mountain Tuesday morning, but that wasn’t the only thing landing on the forest floor.

Chainsaws roared as tall Ponderosa Pines fell with a resounding snap. At first glance it looked like the men were cutting down green and healthy trees. But a closer inspection of a felled tree revealed several patches of sap oozing out of the bark along the length of the trunk.

“That’s called a pitch column,” Assistant Engine Captain Ryan Joseph of the Bighorn National Forest said. “This tree was already dead.”

The sap is the tree’s natural defense against the invading mountain pine beetle. The tree releases sap where the beetle enters to try to force it out. Pitch columns were one of the signs members of the USFS looked for when they set out to thin the forest on the face of the Bighorn Mountains near a section of road known as Hairpin Turn off Highway 14 west of Dayton.

Crews have spent the past week thinning areas infected with the mountain pine beetle after receiving a federal grant for this project.

According to Chris Thomas, forester at the Bighorn National Forest, the deaths of the trees are not caused directly by the beetle, but by blue stain fungi, which lives on the mountain pine beetle under a symbiotic relationship. The fungus helps the beetle by softening the wood, making it easier for the beetle to dig deeper into the tree.

Sap oozes out of the bark into what is called a pitch column, an indicator of mountain pine beetle infestation. Justin Sheely | The Sheridan Press

Sap oozes out of the bark into what is called a pitch column, an indicator of mountain pine beetle infestation.
Justin Sheely | The Sheridan Press

The  fungus spreads through the tree phloem, essentially clogging the tree’s ability to draw water up its trunk. The fungus is recognizable by the bluish stain it leaves in the wood. The infected tree will remain green, appearing healthy throughout the winter and into spring, but will die from the fungus by mid-summer.

“By the time we find the brown tree, the beetles will be long gone,” Thomas said. “Cutting the trees down while the beetles are still inside is a more proactive measure.”

The crew members cut down infected trees, then they cut off the branches and divide the trunk into segments so it will dry faster.

“As the wood dries, it becomes less hospitable to the beetles living inside,” Thomas said.

The forester hopes that the weakened beetle won’t reproduce as much after emerging in the spring. Thomas also noted that thinning the forested area on the face of the mountain will strengthen the forest.

“A healthier tree will do a better job fighting the beetle,” he said.

In 2014, the USFS identified 700 acres that indicated beetle activity in the Bighorn Mountains. Beetle activity in the Bighorn Mountains is significantly lower than the rest of the state. This is due partly to the isolation of the mountain range from other forests.

Thomas and others involved with the project hope that the numbers will stay low with the preventative efforts.

“We won’t find out if this works until next year,” he said.