Those trees died back for some reason. It could be root injury or drought during or after planting. I suppose if the soil stayed soggy wet for an extended time the roots could have died from lack of oxygen. It could possibly be cold injury if they were growing lushly when a very hard freeze hit. Whatever the cause, they are now regrowing from the living basal parts of the tree. I would give it another few weeks for the tops to start sprouting. If they don't then cut the trunks back to the ground level and let the sprouts grow into the new trunks. You may need to remove some sprouts to direct growth into the "chosen" ones. They should regrow very rapidly and you should have sizeable trunks by the end of the year.
Q&A Library Searching Tips