Try posting your question in the garden junk forum as they may know more on this subject.

I never treat stumps where we have cut down trees, just leave them. Eventually they will rot, but I don't like using chemicals any more than I have to. What would be the difference in the mulch we put in our beds.

I've done that before. One of mine lasted 20 years before eventually dwindling to where it fell apart. I didn't treat it with anything. We just recently moved to a new place and had to take down a few trees. So I cut some more pieces the size I needed to put in my flower beds to put pots on and also a bird bath. Great way to reuse and recycle. Gets some height in the flower beds too!