This is Sorbus aucuparia, the European mountain ash. It is called 'ash' because of the similar foliage. But it has nothing to do botanically with ash as it is from the rose family while the ash is from the olive family. Anyway, the reason this was repotted way too early is the fungus that attacks this species in the roots. If repotted in April like most other non-conifers the fungus will attack in May and in June the tree is dead. Repotting now is done on the hope that the wounds in the roots are already closed when it gets warm enough for the fungus. We also used good protectant on the wounds: milking fat!