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12/02/97 13:56 $541 683 6826 EUG PUBLIC WORKS -4-+ -) MAINTENANCE 14002 /003 it just takes time. The younger the tree is exposed to wind, the more windfirm it becomes. Conversely, the older the tree when exposed to wind, the longer it takes to adapt to an increased wind stress. He said older trees can adapt, if they aren't exposed to too much too quickly. When I explained the situation of removal of 120 year -old trees from a 70- 75% stocked stand, professor Mitchell said to proceed with caution. The threshold has already been affected by previous tree removals, and may or may not be exceeded with this entry. Stand history and physical data need collecting for a prediction, and, predicting in a stand that has already been impacted (such as this case) may lessen the reliability of the prediction. If the trees are important to the integrity of the stand, there are options to removal. Of possible mitigative measures to reduce the windthrow hazard, professor Mitchell suggested first to decide whether one is mitigating for endemic wends; or catastrophic winds that occur less frequently. In British Colombia, parks are typically closed when winds exceed a given mph, and are posted as such: Park managers have topped trees, or spiral pruned branches to reduce the exposed crown to the wind. The question with the 19 trees slated for removal is: Will removal of some or all the 19 identified "hazard trees" cause the stand to pass the critical threshold for stability? If so, the removal will have the effect of increasing the instability of this stand, the underlying concern in the first place. Removal in this case creates an even greater hazard to persons and property than existed prior to removal. If the threshold were exceeded, the only option would be 'removal all trees within reach of private property along the east boundary of the park in this critical area. I would not be envious of your position. • I suggest we have time. If what Suzanne Clark of 1898 Fircrest conveyed to me is true, the tree that fell last year was most probably root sprung for some time prior to falling, She indicated she noticed the tree having a greater than normal lean and called Public Works. Suzanne said as the tree lean became -- greater tl- =greater, - -she called Public :Works twice to -.advi se Unfortniiately there was no response until some time later (after the tree fell). We've determined from the literature, mechanical failure as a result of pini infection is almost zero. We've also determined by visual examination there is no incidence of schweinitzii (as identified in the initial July 17th handout) in the area of identified "hazard trees ". Please wait until a management plan is in place prior to any action other than perhaps rescinding the "hazard" label to the 19 trees. • Sincerely, a enc: e-mail Marc J L 1' r e