Southeast Alaska's topsoil isn't deep and we have LOTS of rain so almost all of the trees - and we have LOTS of them - pancake instead of sending their roots down to much of any extent. (On the other hand, we also have giant trees, primarily of spruce and cottonwood, so we also have a certain amount of downed trees.)

Just about any lawn up here has a network of roots outlining the tree's system. I remember a few years back when the house museum I was living in got new sodding, a new lawn from start to finish. For a few months it was smooth and even but very quickly the roots became evident and mowing once more became a problem.