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12/02/97 13:56 2Y541 B&3 6826 EUG PUBLIC WORKS -*-• -► MAINTRNANCR I UU3 /UUJ <br /> r <br /> • <br /> From: Stephen Mitchell <smitchel ©mail.unixg.ubc.ca> <br /> To: mjI ©efn.org <mjl ©efn.org> <br /> Date: Thursday, November 20, 1997 12:01 PM <br /> Subject: windthrow <br /> Hi Mark, <br /> Here are a couple of references from the Pacific Northwest which <br /> attempt to quantify windthrow risk: <br /> Steinblums, IJ, HA Froehlich, JK Lyons 1984. Designing stable buffer <br /> __ ____...— strlps_for sirQam_proted4n_J-EQr 82:49-52. _ _..:__.____ <br /> Andrus, C and H.Froehlich 1992. Wind damage in streamside buffers <br /> and its effect on accelerated sedimentation in coastal Oregon <br /> streams. COPE Report 5:7 -9. Fundamental COPE, Newport OR. <br /> You might also try and track down Michael Lambert with the <br /> USDA Forest Service PNW Research Station. He has done some <br /> work on windfirmness. • <br /> The general principle of windthrow risk assessment is to evaluate <br /> the existing windfirmness of the stand by considering tree <br /> equilibration with periodic peak windloads: for evidence of <br /> equilibration look for deep live crown ratios, lots of taper <br /> open grown stands, lack of current windthrow in stand, sound <br /> stems (stand factors); deep, sound rooting in well drained <br /> soils of medium texture (soil factors); some longterm topographic <br /> exposure, but not ridge line, nor partially sheltered sites which <br /> the wind will work into during peak wind events (topographic factors). <br /> You also need to consider the way new management activities open up <br /> _- the.. stand. and .increase_loading..on residuals... If. #1-iere._is.ev ence. -. - <br /> of instability prior to harvesting, exposed edges are more likely <br /> to be damaged. <br /> Finally, . windthrow risk assessment is not a very exact science, <br /> so make predictions with some caUtion. <br /> Hope this helps, <br /> Steve Mitchell <br /> 11/20/1997 <br />