Rabbits, deer, horses, cows, almost any herbivore that could have access to them. Put chicken wire cages round them. Yes, they should start new leaders, unless every bud has been bitten off; check them at the end of the year to make sure than none are developing multiple leaders.

Resin

Thanks. Its most likely Deer because just the tops seem to be eaten. First voles eating the roots, now deer eating the new growth. My poor little pine trees. :-(

I sprayed the remaining undamaged trees with repellent, hoping this will deter future nibbling. And I'll probably pee on the things to see if that helps -- I read that somewhere. I'm really hoping that with all the new spring growth, the deer and voles will eat other things and leave my pine trees alone.

There are too many to cover each one with chix wire. I may swap out the eaten ones with better selections from elsewhere in the yard.

And if the damage continues I may just give up and plant a bunch of leland cyprus. Does anything like to eat those?