laglaph

Hi, I have a young rowan growing from a root from a neighbour’s rowan tree. Fortunately it is a position in the garden where we wanted to put a tree and a rowan was high on our list so we left it there. It has been growing well for 3 years now but it still appears to be wholly supported by the parent root. I assumed this is a normal way for the tree to propagate naturally therefore I thought it would establish its own root system. So my question is will it support itself with its own roots or be dependent on the parent root? If it is the latter is it viable? Thanks Paul