It is not bad luck or bad karma. It means he moved the tree in an "off season," or the roots were exposed for too long or the soil where he is now located was not properly prepared or the soil is not proper for a rowan tree. By "off season," I mean that trees should only be moved and/or planted at certain times of the year. You can't just dig one up at any old time and move it and expect it to live for long. Not all things are magically inclined. In this case, it was simply bad judgement on his part to move the tree. If it were me, I would've left the "old" tree where it stood to keep the past in the past and as a symbol of moving on into the future. I would've planted a new tree to imbue the new home with a new energy.
He should get a new tree (plant it at the right time and make sure the soil is prepared) and bless it as a symbol of his new existence in his new home. Not only is this a good idea in general, but spiritually speaking, it makes up for the tree that was lost. A repayment or atonement so to speak.
If he feels spiritually connected to the old Rowan tree, he could do a blessing over it prior to removal of the dead tree or afterwards (before disposing of it) asking the tree's spirit for forgiveness. Crazy as it sounds, I do that when I'm landscaping and removing or moving trees and bushes. But for those who believe in the ancient treelore, it's good to bless trees in that way.
