Evidence of HWA infestation, Sill Branch.
It seems whenever hiking through a hemlock stand anymore one sees evidence of this infestation. It was so bad near Sill Branch Falls I mistook the occasional bits of white fluff falling through the air to be snow at first.
This from Save Our Hemlocks:
Hemlock Woolly Adelgid (Adeleges tsugae) is native to Asia where it is not a problem to native hemlocks. It was introduced to the United States in the 1920s to the Pacific Northwest, and in the early 1950s to the Washington DC and Richmond, Virginia areas. It lacks natural enemies in North America, so it has since spread throughout the eastern United States creating an extreme amount of damage to natural stands of hemlock, specifically eastern hemlock (Tsuga canadensis) and Carolina hemlock (Tsuga caroliniana).This from Wikipedia:
The hemlock woolly adelgid feeds on the phloem sap of tender Hemlock shoots. Unlike the balsam woolly adelgid that only attacked mature Balsam Fir, HWA infests all age classes of hemlock. In the northern portion of the Hemlock's range, death typically occurs four to ten years after infestation. Where Hemlock occurs in pure stands in that region, the most commonly observed tree species to succeed it is black (sweet) birch. In contrast, in the southern extreme of its range, Hemlock does not typically occur in pure stands but in linear riparian areas and other moist sites. Succession in these areas is vastly different for many reasons, one being the presence of Rhododendron maximum which often co-exists with hemlock, and due to a combination of influences, stricts regeneration to shade and otherwise understory-tolerant plant species. Major changes in ecosystem structure and function, including hydrologic processes, is expected with the loss of hemlock.There are efforts being made to try to prevent the spead of this insect and to possibly fight back using beetles and fungi.
Our forests have already suffered the loss of one great tree. The great chestnut forests are gone. All that remains of them are the occasional stump remnant, rotting trunk, immature sucker or barn siding. The loss of those trees to the blight was and still is a tragedy, but I never knew those forests. The forests I have known will be no more if the hemlocks are lost.