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Sisters board debates replacing Swedish aspens on Cascade Avenue, tables final decision
Summary
City staff reported repeated decline of Swedish aspen on Cascade Avenue caused by pests, root girdling and irrigation problems; the Urban Forestry Board discussed alternatives (spacing, bump-outs, alternative species, nematode treatment) and voted to table a final choice until more members can weigh in.
The Sisters Urban Forestry Board discussed how to respond to repeated decline and mortality among Swedish aspen trees lining Cascade Avenue, but tabled a final decision until more members attend a future meeting.
Jackson, a city staff member, told the board that “the downtown corridor on Cascade is lined with primarily Swedish aspens. Those aspens, we have had some decline and die over the years and we have replaced those.” He cited the American hornet moth, root girdling and overwatering caused by dense drip tubing as the primary causes of the recent losses, and said the city is weighing whether to continue planting Swedish aspen and use treatments such as a nematode or to choose alternative columnar species with higher survival rates.
Board members raised concrete options for reducing future loss. Bridget, a board member, said she would “lean towards…try something different,” noting that columnar alternatives may fit the corridor while offering better longevity. Members emphasized defensible-space requirements, with staff noting a minimum 10-foot clearance between trees and buildings. The chair suggested structural changes to planting space—“it would be possible…to build occasional bump outs, put a big tree in each one and get rid of the rest of the trees,” she said—so fewer, larger trees could be accommodated without violating setback rules.
Several members also proposed low-cost steps to improve survival, including checking nursery stock for root girdling before planting, adjusting irrigation density, and testing a nematode treatment that staff said could reduce hornet moth populations but offered no guarantee. The board asked staff to consult further with the arborist (Avery) and to provide visual mockups of alternative species for public and business feedback.
Before making a binding choice, the board voted to table the matter. A board member moved to table the discussion “until there are further members here,” a motion seconded by another member and approved by voice vote. Staff will schedule additional review and return with recommendations at a future meeting.
