The protest on a private lot is the latest episode highlighting tensions behind the tree policy in Seattle as climate change increases temperatures and urban canopy decreases.
The Western red cedar, dubbed “Luma,” is about 24.4 metres tall, with two trunks that are each about 1.2 metres in diameter.
Its age is not known, but activists have estimated it could be as much as 200 years old. The Snoqualmie Indian Tribe is seeking to have the tree preserved for its archaeological significance, saying that Native Americans shaped its branches generations ago to distinguish it as a trail marker.
The protesters have declined to give their names, citing concerns about retaliation.
“We have to win this tree. We have to win because Luma is setting the tone for every other tree that’s under threat in Seattle,” one said from the tree. “We have to show that we mean business.”
The occupation began on 14 July, with each activist taking shifts of several days in the tree.