County Fire District 1 spokeswoman Leslie Hynes says the trimmer was cutting limbs from a tree Tuesday afternoon in the backyard of a home in the north Seattle suburb of Mountlake Terrace.
Neighbors who called for help reported seeing a limb the man was cutting come loose, swing around and slam him into the tree trunk. They saw his body go limp.
Hynes says the man, in his mid-30s, regained consciousness but was hurt and stuck, secured with a rope system.
She says a technical rescue team and ladder truck responded. The trimmer was able to walk down the ladder with help from firefighters.
He was taken to Harborview Medical Center in Seattle with injuries that were described as serious but not life-threatening.