Harvesting tree barks is best done in the late spring/early summer in the pnw, when the sap is really up in the tree. I cut the bark at the edges of the piece i want to take and use my hatchet to pry the corners from the tree, then you can use your hand to seperate it from the tree. this is how i take hemlock, alder, cottonwood, pine, spruce, oak, maple, aspen, fir bark. most of these also have edible cambium in the late spring, so you get bark and a tasty treat. Cedar and juniper are different, you can cut at the bottom and pull out to peel off a tapering piece.