dyzzypyxxy said:Strongly advise against using river stones as mulch. It will cook the roots, not insulate them while still letting moisture evaporate. Then you will be faced with removing stones from your garden. Trust me, you will regret it SO much if you do that. Stones as mulch belong in a desert where you don't want ANYTHING to grow.
A thick layer of wood chip mulch will insulate the soil to keep it cool, help retain moisture in the soil and add organic material to the soil as it breaks down. Yes, it's not quite as "permanent" as stones but it does a much better job if your goal is to try to make the tree live and be healthy. You will have to buy a couple of new bags of mulch each year to freshen it and keep the layer thick enough to discourage weeds but in the long run it will be better, cheaper and the tree will live.
Please, please remove that black landscape cloth and buy some bags of wood chip mulch to help your tree recover.