Those conifers have grown to over twenty feet in height and have been spared by the insect damage from Adelges tsugae Woolly Adelgid that has taken down these trees in the wild.    From Wordnik.com.  [Looking For Shade* « Fairegarden] Reference

The introduction of the gypsy moth (Lymantria dispar), spruce budworm (Choristoneura fumiferana), hemlock wooly adelgid (Adelges tsugae), balsam wooly-adelgid (A. piceae), as well as dogwood anthracnost fungi is altering the forest composition and habitat composition.    From Wordnik.com.  [Appalachian-Blue Ridge forests] Reference