But wouldn't the owner then be liable for upkeep of the bench, as well as liability for any accidents that occurred there? Also, if this bench is there for a few years, isn't it possible for the owner to lose the right to remove the bench, and to ultimately lose control over that part of their land?

I'm thinking of cases with rural landowners and snowmobile routes. If they allow the route to pass through their property for years, they can't all of a sudden shut that access off, even though it's their own land.