Hoh Tribe’s Planting Effort Using Science To Combat Insect

HOH RIVER (March 21, 2005) – Plant a tree and it will grow.

It’s not that simple though when the tree is a Sitka spruce planted to reforest Olympic coast timberlands.

Populations of spruce-tip weevil, an insect that causes spruce to grow uncharacteristically bushy and low, exploded in spruce forests planted in the mid -1980s. Infestation was so prevalent, that many private timberland owners stopped replanting spruce -the signature species of temperate rainforests – and a key component of salmon habitat.

When the Hoh Tribe wanted to plant spruce in the lower Hoh River corridor as part of their salmon restoration efforts, they consulted Lyle Almond, research silviculturist for the state Department of Natural Resources, to improve their chances of success. Spruce helps promote river channel stability along riverbanks, reducing sediment that can kill salmon eggs. When floods drop spruce into the river, these trees contributes to log jams that help provide important habitat for fish. A weevil-infested spruce will never grow to the dimensions necessary to contribute adequately to salmon habitat.

“Almond found that the weevil infestation in spruce was considerably lower if the trees grew within dense stands of alder,” said Steve Allison, habitat biologist for the Hoh Tribe. “Alder stands keep it too cool for weevil eggs to hatch consistently.”

Almond believes the increase in weevils is solely due to the plantation planting of spruce in clear-cuts. “The open area created an ideal environment for weevils to proliferate,” said Almond. “The eggs need temperatures of 75 degrees or higher to hatch. Without a diversity of other tree species to create shade and lower temperatures, conditions were perfect for weevil production.”

Historically, spruce thrived, despite the presence of a native population of spruce-tip weevil. Today, weevils are able to genetically mutate faster than the host spruce’s ability to create natural defenses. Weevils migrating from the dense stands of spruce have infected native spruce trees, including older trees and those growing close to the ocean – trees previously immune to the weevil. The problem is being made worse by a warming planet that is aiding the northward spread of the pest to areas that were historically too cold.

Almond’s solution, growing spruce within alder stands, was an observation borne out by research. “It gets back to seeking answers in the natural world. Alder and spruce are naturally found together,” said Almond.

“They have similar needs to grow well like the well-drained soil found in dynamic river corridors. They also complement one another well,” said Almond. Alder grows quickly because it’s shade intolerant, but spruce will tolerate shade until an alder has reached most of its adult height, from 15 to 20 years old. During the alder’s rapid growth, the spruce is using the shade to fight off weevil infestation. The alder then stops its rapid growth, relinquishing nutrients and the spruce begins its period of rapid growth.

Equally important to successful spruce growth within the alder stands, however, is the density and age of the alder stands. Young spruce are susceptible to whiplash damage from wind-whipped alders in winter.

“We’re aiming for Almond’s recommended shade percentage of 88 percent per quarter acre, which seems to be optimum for preventing weevil infestation and reducing damage from alder whiplash,” said Allison.

The tribe is planting young spruce in existing dense alder stands along the lower Hoh River and its tributaries and in former river channels. Mature spruce not only benefits fish, but bald eagles, spotted owls and marbled murrelets who prefer mature spruce for nesting.

A channel migration study completed last year for the Hoh River is also being used to help the tribe plant in areas that will be stable long enough to allow the trees to grow to sufficient size. “Eighty years would be good, 150 years would be great,” said Allison.
“If the river comes into an area where the trees are still immature, they won’t hold the channel and consequently, will be too small to contribute to log jams,” said Rod Thysell, natural resources director for the Hoh Tribe.

Tribal biologists and technicians planted more than 15 acres of private and state lands with nearly 2,000 spruce trees in 2004. They will plant nearly 200 acres and more than 16,000 trees this year. Part of their restoration work will include replanting the base of large debris slides along the river, where trees such as silver and grand fir can thrive. The vegetation will help stabilize the debris, reducing the amount of sediment that is washed into the river.

A federal Pacific Coastal Salmon Recovery and Bureau of Indian Affairs watershed restoration grants paid for the work along with donations of some trees from the U.S. Forest Service and Green Crow timber company.


For more information, contact: Rod Thysell, natural resources director, Hoh Tribe,(360) 374-6548; Steve Allison, habitat biologist, Hoh Tribe, (360) 374-5404.