isn't it?  those large stately trees are far less vigorous than the smaller trees.  The rule of thumb when dealing with Spruce beetles is that trees eight inches in diameter at breast height or smaller are the ones that the spruce beetles won't be able to defeat.  those larger trees grow at a far slower pace, and have fewer proportional resources with which to protect themselves.  This is why management of forests focuses a lot of attention on the age class distribution of trees.  if you have a ton of large, old trees, there is the potential for an outbreak.  The goal is to maintain a balance of a large number of young and middle aged spruce, and a small number of large mature spruce.  The forest naturally does this in areas that aren't affected by man, but in areas where we suppress fires and don't replace the fire/beetle process with selective thinning, then the beetles will pick up the slack and take care of business.