Three years is not that long for a potted tree to be planted. Unless you have the greatest well draining soil, and you fertilized the Mountain Ash well each year, then the root ball is most likely still pretty much in tack and still easiest enough to remove. A storm broke a friend's 5 or 6 year planted maple tree. It broke about 4 feet up in the middle of the trunk. When he dug around it and pulled the trunk out of the ground with a wench it certainly was amazing how compact the root ball still was. I had another friend whose October Glory Maple had been planted 2 1/2 years before it died in last summer's drought. I dug it up so we could replace it with some ornamental 'Corinthian Pink' peach trees. It was a 9 feet tall tree with a 3 inch diameter trunk, and it still had such a small root ball that I got the tree out of the hole by my self with little effort. For the Ash tree, and if you only planted it no more that 3 inches too deeply, I would suggest you pull away all the dirt from over the rootball; stopping once you can see the root fair. Next remove the grass from around the tree for a distance of about 2 feet out. Then at the edge of the grass free bed dig out the soil until the bed's edge is 3 inches lower than the root flare of the tree. scrape out the dirt starting a little away from the root fair to gradually slant down until it reaches the edge of your bed; once there, simply level the lowest edge of your slant even with the depth of which you dug the trench around the bed's edge. Finally Fill the bed with enough shredded mulch to fill the trenched out edge of the bed only to the height which makes the bed's edge to look level with the rest of the yard. Make certain that the shredded mulch which you apply to the sloping bed is kept at least 4 inches away from the tree's root flair. If you planted the tree way too deep for it to begin growing again after installing the above mentioned bed method, it probably will survive long enough for you to wait and dig up the tree after it goes dormant. That way you will not have to remove so much dirt with the roots. If you choose to move the Ash tree when it is dormant, then wait until mid-Summer to take a spade and slice through the roots all around at about 3 to 4 feet away from the tree's trunk. Then at least once, each following month, repeat that step again in the very same place you first cut the roots with the spade. Once the tree has gone dormant remove as much dirt as possible that is on top of the root flair and from on top of the roots all around; out to where you kept spade cutting the roots during the end of summer and early fall. After that, start near where you spade cut the roots, use a garden pitchfork to help lift out the tree's surface feeder roots. Keep doing that until you are close to the, most likely, still intact root ball; which orginally came out of the pot when you first planted the tree. Once you have reached that spot all the way around the tree, simply use the pitch fork to pry up the rootball. If need be you can cut any roots which are at least 18 inches or more below the root ball. but try to keep intact as many of the closer to the surface growing feeder roots. As long as you are doing this when the tree is dormant, you can lift the tree out of the soil and brush away as much dirt as possible from the tree's roots. That way the tree should not be too heavy to handle. Then you can replant the tree properly where ever you desire, Or you could even set the tree back in the same spot it was growing before, and fill in with good garden soil around and on top of the feeder roots, being certain to keep the root flair just visible above the added soil level. Pound 3 of the larger 6 foot tall metal "t" stakes into the ground at no more than 2 feet distance away from the trunk of the tree. Tie the tree to the stakes with thickly coated and cushioned tree tie wire, or other such non damaging ties. Make certain the ties are taut enough to keep the tree stable in the ground, but also, just loose enough that the tree can sway slightly when winds blow against its canopy. Those stakes will need to remain for 3 full years, but after each of those years you can loosen the tension in the ties just enough each time to let the tree sway just a little more when the wind blows against it. If your lot is big enough, follow dibbits advice for the Willow tree; then dig up the Maple tree you think will not survive. Replace the maple, if you have the space, with a properly planted hardwood sugar maple, or other such quality tree.

IMO, based on that picture, the tree should be pulled out, all of the roots above the flare need to be removed or pulled out and set below the root flare, and then the tree should be replanted with the actual root flare a couple inches above grade.

I did my red maple in earlier in spring, trying to raise it. Mine was planted about 10-12" too deep, but I planted it myself, with the help of a hired hand in fall of 2015. BTW, I'm in Marlboro NJ, zone 7A. The tree in question was a beautiful October Glory maple. I was just aiming to get the top of the burlap bag an inch or 2 above the surrounding soil, not realizing until next spring, that I had made a mistake. It started out a beautiful 'rubrum' in spring, giving me hours of pleasure, as I just stood around it, sometimes nursing a drink. But as a very wet spring progressed, and the leaves were still not opening out fully, my mind raced to a number of things that could have gone wrong in the planting. I definitely had not cut the cage around it as thoroughly as I should have (damn thick guage wire, so hard to cut with pliers!). So, one very wet day, in a very very wet week, I started investigating, prying the dirt away, in an effort to find the wire cage. In the process I discovered that I could not see the root flare at all, instead the trunk was buried, and was discoloring and fraying from the surrounding soil and water. So I decided to raise it. I leaned on the tree, this way and that until it was moving on it's root ball. I shoveled dirt under the root ball, trying to work it in with my foot. Then I had a brainwave! I soaked the root ball and surrounding with water and waited. As the water drained down, the dirt mixed in the water found it's way to the bottom, while I was still wiggling it. It worked, the tree was slowly raised. And then I made the fatal mistake! I also saw roots that were growing from down on up. Now, with the tree raised, these roots were poking into the air. I started cutting them, some of them were big and juicy. I felt horrible, but could not stop! After I had raised and root pruned the tree to my aesthetic satisfaction, I covered it with dirt just so, and mulched and staked it. It looked really nice, with the frayed trunk, previously suffering the indignity of being buried, now finally breathing and recovering, or so I thought. I kept the tree well watered, even spritzing it a few times a day (deputizing my kids in the job as well). But the leaves started drooping. I increased the watering and spritzing, but to no avail. One by one, the leaves gradually turned brown, and then dropped. After a few weeks, in a frantic effort to save the tree, I cut back the branches a couple of inches from the terminal buds to encourage growth. But to no avail. Right now, it's late August, and a scratch test reveals a dead tree. No cambium, no phloem, no nothing! There are leaves growing from the base, but even those are drying up right now. So, I will definitely be replacing the tree. I have a question from this learned group, but I will first let this greek tragedy soak in first.

It's planting 101 for all woodies. When you purchase the replacement, always look for the slight flare at the base of the stem which you want to be at ground level when you set the woody in place. (Easier to notice on trees than on shrubs.) Sometimes container-grown or B&B are already too deep. Another key to success is to dig the hole only as deep as needed for the height of the rootball. If deeper, then filled back in, the woody will sink. It's guaranteed! Have fun shopping.