That sounds like an early stage of Hypoxylon canker, caused by a fungus living under the bark. If so, it will probably spread laterally until it girdles and kills the stem. I doubt there's anything to do, other than ask a forester from your excellent state forestry department for advice. There should be help at the County agent office.

The mulch is at the root flare, and it has never had a volcano of mulch around it. Mulch has never touched the places where the bark decay started. It was potted (it was very small when planted), and I consider myself just as professional at planting trees as any other "professional":) No, it wasn't rootbound,but regardless, the root mass was separated and spread out when planted. When I first began inspecting this tree in the spring, I dug down a few inches around the trunk, looking for problems but everything looked healthy and the major roots had a nice spread going away from the trunk. As far as clay, I consider the soil there to be low clay content. I would suspect some of these things if the growth had been stunted or if had looked unhealthy over the years;but it has been a perfect specimen until now. Nary a wilted, scorched leaf or limb dieback; excellent green all summer and the brightest red you can imagine in the fall.

Just so happens I have a Bloodgood Japanese maple under a canopy of a Sugar Maple and a Red Maple. However, I can probably get away with this as my precip tends to be heavy 50-60 inches annually. In your drier climate, I think there would be excessive competition for moisture--Japanese Maples do NOT like drought. Good luck with your Japanese Maple. PS., Despite having lots of exotic plants, that tree always gets all the attention!

Hmmm...where to start. First of all, there are nearly a thousand different cultivars of Japanese maples. About a third (or maybe more) of them have red leaves at least a portion of the year. Secondly, japanese red maple would be a misleading name since a red maple is a native maple to the US that has green leaves and red flowers. Red japanese maple would make more sense. So, "Japanese red maple" could refer to one of hundreds of cultivars that have been reproduced by grafting, or it could be a red seedling that shows good red characteristics. This would mean that 'red select' is a specific cultivar of a red japanese maple. You must also consider whether or not it is a weeping red dissectum (fine lacy leaves) or an upright palmatum (star shaped leaves). 'Red select' is one of many red dissectum cultivars (lacy and weeping). I think 'red select' is a seedling from 'inaba shidare' (guys I know Vertrees claims that they are one in the same, but I have convincing information that says otherwise). They are similar, but some claim there are distinct differences (and by distinct I mean practically with a magnifying glass). Other similar common cultivars include 'crimson queen', 'tamukeyama', 'garnet', and the newer 'red dragon'. A couple of good red upright cultivars include 'bloodgood' and 'fireglow'. Search these names and this should shed some light on what the differences are.