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Saturday, April 7, 2018

Regarding Wind Stress and Trees.

We have a report telling us that one timber owner is having difficulty selling his large trees due to "wind stress".  Old growth timber is subject to this and can affect the marketability of the timber.

Let this be a lesson for those who wanted to saw the old growth timber in Watoga.  It could have come at a horrible price to someone, namely those trying to sell timber that the sawmills won't cut.  Thank goodness we dodged this bullet.

By the way,  have you notice that there is very little talk about the "barrel factory" now that the state turned down Watoga.

  Wonder why? see below copied material.

Windthrow mechanics, stand-level instability

Windthrow results when the wind-induced drag force on the tree crown, multiplied over the lever-arm of the stem, results in a turning moment that exceeds the bending resistance of the stem, or the root anchorage. Tree design appears to balance core rigidity with peripheral flexibility.39 The bending and reconfiguration of branches, and consequently tree crowns, during high winds streamlines foliage and reduces the frontal area. Over the range of wind speeds at which this reconfiguration occurs, drag on tree crowns is directly proportional to wind speed rather than to the square of wind speed, as is the case for solid bodies.35,40 The resistance of the stem to failure is proportional to the cube of the stem radius, so small increases in radial growth add substantially to stem strength.5,41 Byrne and Mitchell42 found that the critical moments for trees that fail via stem breakage were similar to the critical moments for trees that failed via uprooting for trees of similar size and form. Root anchorage is a function of root architecture and soil properties, and is empirically very tightly correlated with stem mass.43 The effects of acclimative growth on tree stability in Sitka spruce plantations in Britain were examined by Nicoll et al.30 who found that anchorage increased as wind exposure increased. The stability of trees is affected by precipitation and temperature. Soil moisture affects root anchorage, and uprooting often occurs when high winds coincide with saturated soils.44 Peltola et al.45 found that all of their winched trees failed via stem breakage when soils were frozen, and with higher critical moments than for similar sized trees winched during non-frozen conditions.

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A local archivist who specializes in all things Pocahontas County