Hemlock Fluting

abiotic cause (environmental factors and tree genetics)

Affected tree in Alaska:

western hemlock (Tsuga heterophyla)

Affected tree part(s): tree bole/stem from the roots to the crown

Current Status & Distribution in Alaska 

Hemlock fluting is characterized by deeply incised grooves and ridges that extend vertically along boles of western hemlock. Fluting can be distinguished from other defects on tree boles, such as old callusing wounds and root flaring, because fluted trees have more than one groove and fluting extends close to or into the tree crown. This condition, especially common in coastal stands in Southeast Alaska (see Map), reduces the merchantable volume of hemlock logs because bark is contained in some of the wood. The cause of fluting is not completely understood, but fluting is associated with increased wind-firmness and sites with shallow soils. Fluting may be triggered during growth release by some stand management treatments or natural disturbances, and trees and stands may be genetically predisposed to fluting. The asymmetrical radial growth typical of fluted trees appears to be caused by unequal distribution of carbohydrates, with less allocated near branches and more allocated between branches. After several centuries, fluting may not be outwardly visible in trees, because branch scars have healed over and fluting patterns have been engulfed within the stem.

Historic Activity

This condition, especially common in coastal stands in Southeast Alaska, reduces the merchantable volume of hemlock logs because bark is contained in some of the wood. After several centuries, fluting may not be outwardly visible because fluting patterns have been engulfed within the stem. The economic impacts of bole fluting on National Forest System timber harvest are probably less significant than in the past, since minimal harvest now occurs within the 1000-foot beach buffer where fluted trees are most concentrated.

Symptoms, Biology & Impacts

The economic impacts of bole fluting on National Forest System timber harvest are thought to be less significant than in the past, since the most severely fluted trees are often located in beach buffer land management units that are no longer open to timber harvest. One study found insignificant differences between the volume and grade of fluted hemlocks compared to unfluted (Christensen et al. 2002). Fluting is believed to have few ecological consequences beyond adding to wind firmness; the deep folds on fluted stems of western hemlock may provide important habitat for some arthropods and the birds that feed upon them (e.g., winter wren). Planting seed from severely fluted trees on protected, productive sites with stable soils could help to discern genetic causes of fluting from environmental causes.