Seattle does have a concept of “exceptional trees” (a big old tree worth saving) which are protected by law. But it requires involving the city for them to be recognized and documented.
A friend quashed a developers’ plans in West Seattle by getting ahold of the city to come out and look at what he thought was likely an exceptional tree. The city arborist confirmed that it was and noted that several more were as well.
YMMV, but definitely advocate and engage the city ASAP if there’s any sign of development around big trees.