The question is whether you are mounding or not, and the method of compaction. A lot of assumptions cloudy up the conversation.
If you are making mounds by raising the planting area up (as opposed to digging the surrounding area lower, as I did), you are now using “disturbed” soil. If you were to simply mound up the dirt and maybe lightly compact it by walking on it, you’re looking at 30-50% “settling” and a whole bunch of runoff once it starts raining. What might have seemed like a large mound will be reduced to a lump at best. You would also most likely need to stake all but the smallest trees in windy areas.
Now unless one is using industrial compaction equipment and applying the dirt in “lifts” of several inches at a time, you aren’t going to re-compact the earth back to an “undisturbed” approximation. What you will more likely end up with is a mound where the top few inches are quite well compacted, but the dirt in the middle of the mound (vertically) is only moderately compacted. You’ll get a lot less settling from time and rain if you do some of the compacting yourself as well. But the dirt in the mound will still be quite loose compared to undisturbed and very suitable for new root growth. It will also support the new tree better, but staking may still be required.
Again, if you have access to a bulldozer I would not recommend using it to make tree mounds, as you will not have loose soil in that case. But the weight of a pickup truck or even a bobcat over 12 to 24 inches of soil is going to leave quite a bit of space for roots, but will greatly reduce the settling that you have to plan for when building mounds for trees. The water content of the soil when you compress it is also a difficult to control factor. Too wet or too dry and you won’t get good results
This is a mulberry planted in March in a compacted mound, it sat around for approximately two and a half months and has now put on about 50% of what you see there in the last month.
This is a Scarlet Prince peach planted about 1 year ago. Same type of mound, so it’s got about 4 to 6 in of mulch on top.
What I like so much about mounding up the soil is that you effectively get away with anything. You are not going to recompact the soil to what it was when it was undisturbed, unless again you are using industrial construction equipment. But the drainage benefits are immense, not to mention just how good it looks. And with clay the mounds will hold enough moisture, especially with mulch. I might not mound at all if I had fast draining soil, but clay mounds seem to drain off any amount of excess water while keeping an ideal amount for the tree.
I agree with Alan. Replant the trees if you can, and if you don’t compact the soil, have a plan to maintain the mound as time compresses it and rain erodes it.