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12/02/97 13:56 $541 683 6826 EUG PUBLIC WORKS -+ MA1N'1'L'NANUb i juuciuu.' <br /> it just takes time. The younger the tree is exposed to wind, the more windfirm it <br /> becomes. Conversely, the older the tree when exposed to wind, the longer it takes <br /> to adapt to an increased wind stress. He said older trees can adapt, if they aren't <br /> exposed to too much too quickly. <br /> When I explained the situation of removal of 120 year -old trees from a 70- <br /> 75% stocked stand, professor Mitchell said to proceed with caution. The threshold <br /> has already been affected by previous tree removals, and may or may not be <br /> exceeded with this entry. Stand history and physical data need collecting for a <br /> prediction, and, predicting in a stand that has already been impacted (such as this <br /> case) may lessen the reliability of the prediction. If the trees are important to the <br /> integrity of the stand, there are options to removal. Of possible mitigative <br /> measures to reduce the windthrow hazard, professor Mitchell suggested first to <br /> decide whether one is mitigating for endemic winds, or catastrophic winds that <br /> occur less frequently. In British Colombia, parks are typically closed when winds <br /> exceed a given mph, and are posted as such Park managers have topped trees, or <br /> spiral pruned branches to reduce the exposed crown to the wind. <br /> The question with the 19 trees slated for removal is: Will removal of some <br /> or all the 19 identified "hazard trees" cause the stand to pass the critical <br /> threshold for stability? <br /> If so, the removal will have the effect of increasing the instability of this <br /> stand, the underlying concern in the first place. Removal in this case creates an <br /> even greater hazard to persons and property than existed prior to removal. If the <br /> threshold were exceeded, the only option would be 'removal all trees within reach <br /> of private property along the east boundary of the park in this critical area. I <br /> would not be envious of your position. <br /> I suggest we have time. If what Suzanne Clark of 1898 Fircrest conveyed to <br /> me is true, the tree that fell last year was most probably root sprung for some <br /> time prior to falling, She indicated she noticed the tree having a greater than <br /> normal lean and called Public Works. Suzanne said as the tree lean became <br /> eater -and - greater, - -she .called Public Works -twice .to- advise: IInfor-tunately there <br /> was no response until some time later (after the tree fell). • We've determined from <br /> the literature, mechanical failure as a result of pini infection is almost zero. <br /> We've also determined by visual examination there is no incidence of schweinitzii <br /> (as identified in the initial July 17th handout) in the area of identified "hazard <br /> trees ". Please wait until a management plan is in place prior to any action other <br /> than perhaps rescinding the "hazard" label to the 19 trees. <br /> • <br /> Sincerely, <br /> enc: e-mail <br /> Marc J L • 1' re <br />