During my morning jog, I saw any number of trees surrounded by landscaping block or stone and then heaped up with soil and mulch, like this:
This is a particularly bad example, but there were a lot more that were not quite as bad. But they will all have the same result: A dead tree.
Don’t do this. Seriously, don’t do this. Mulching the base of trees is a good idea for preventing injury to trunks by string trimmers and lawn mowers, sure. But the proper way to do that is to keep the mulch away from the base and to make sure the root flare is exposed. If your tree looks like a lollipop sticking out of the ground, it is only a matter of time before it rots and dies.
This tree is dead. It just doesn’t know it yet. But this one is figuring it out: