Eastern or Canada hemlock (Tsuga canadensis) is another important evergreen needle-leaf conifer that grows along the Appalachian chain from north to south, but is confined to lower elevations than red spruce and the firs. It generally occupies richer and less acidic soils than the spruce and firs and is characteristic of deep, shaded and moist mountain valleys and coves. It is, unfortunately, subject to the hemlock woolly adelgid (Adelges tsugae), an introduced insect, that is rapidly extirpating it as a forest tree. Less abundant, and restricted to the southern Appalachians, is Carolina hemlock (Tsuga caroliniana). Like Canada hemlock, this tree suffers severely from the hemlock woolly adelgid.
What tree contrasted with the Canada hemlock is not affected by the adelgid?