Taking inspiration from a fallen Western red cedar, Seattle-based artist John Grade created the dynamic sculpture “Union” for the Washington Park Arboretum. The long-term, temporary installation is made of two nets suspended between trees and holding cupped resin forms based on the cedar’s cellular structures. Designed to move with the weather, the netted sections separate under the weight of rainwater. When dry, the green and blue forms merge. Over several days this fall, a crew of volunteers helped Grade install the work.