We have an African Sumac in our backyard that had grown out of control. The landscaper we hired to trim the branches went a little aggressive for my taste, but assured me that the tree was strong enough to come back quickly. Well, two weeks later, the tree looks dead: all the leaves are completely dry. What are the chances of saving this tree? (In other words, how strong is the root system — can it overpower the lack of leaves?) We are in Las Vegas, NV.
Ugh. Generally pruning off up to 1/3 of the foliage away at one time is fine although doing that at the peak of summer heat is a bad idea. Taking more than that will (and it sounds like it has) send the tree into shock. The best you can do now is to keep it watered and hope for the best. It may actually die but may also send up new growth from the roots as the weather cools off in the fall. Give it some time (and water) and then cut it back to where the new growth appear. It is also possible that they are dead completely from shock from being pruned too hard at the wrong time of year.