Silver birch and hornbeam

Hi I am back again (having sorted out my camera) to ask your opinion of what could be the cause of the problems I have having with some trees I have. One silver birch has been in for 18 months now and another silver birch and a hornbeam were planted in early December 2008. The 18 month old birch is nearly dead with practically no leaf at all, the other two are really struggling. They were blasted by some cold winds shortly after coming into leaf, but now even the new growth is showing the same browning at the leaf margins and the new growth is very very slow. I wonder I someone could given an opinion as to likely cause. Please see image.