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12/02/97 13:56 $541 683 6826 EUG PUBLIC WORKS -+-+ MAINTENANCE 10003/003 <br /> • <br /> From: Stephen Mitchell <smitchel@maiiunixg.ubc.ca> <br /> To: mjI @efn.org <mjI @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 /> -.— _ -- _ -- strips forstream _prszW i rLIEor 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 . incr- ease.1.o.ad residuals. .af ereas...evidence__ _ . -- - <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 />