Maple Shedding Bark

Question:
There is a mature (sugar?) maple tree in my back yard whose bark is coming off in various sized sheets; from a few inches to a foot long. I have noticed powdery white spots on the tree that are most noticeable where the bark has come off. The spots range in size from pin-point to pin head. I don't know anything about maples but I have never seen a tree whose bark came off like this. The tree is quite large and I would REALLY hate to lose it! Minnesota Master Gardeners say:

Some trees such as sycamore and silver maple shed bark as a normal part of their growth and development. The bark of young silver maples is relatively smooth, but as the trees age they develop furrowed bark that separates into strips that curl on each end. These strips sometimes fall away in pieces the size you have noticed. The amount of bark shed varies among individual trees, but it is a characteristic of the species. If the tree is a silver maple, this is probably what you are observing. The bark underlying the strips on a healthy silver maple is an orangish color. This fades to gray. The powdery white spots sound pretty small. I don't know what causes them, but they may also be part of the tree's bark structure. If the tree appears to be in good health otherwise, you can probably ignore them.