Hemlock Woolly Adelgid Research

The Eastern Hemlock tree (Tsuga canadensis) is under assault across almost all of its range by an insect species called the Hemlock Woolly Adelgid (HWA), which was introduced from Southeast Asia (fig. 02). Once the HWA attacks a hemlock, death of the tree is almost inevitable. The HWA has spread across the country over the last 50-60 years, and the end result will likely be that the E. Hemlock forests which covered many sections of the mountainous areas of the eastern US will die. The Eastern Hemlock is probably headed the same way as the American Chestnut went when the Chestnut Blight hit - a lingering semi-extinction.      One of the many results of the Eastern Hemlock going more-or-less extinct, is that the trees will no longer be participants in the soil ecology. For example, the trees will no longer be shedding needles onto the ground where their nutrients are released into the soil via decompostion. We are looking at three types of forest plots in the Appalachian mountains: (1) hemlocks present; (2) hemlocks present, but killed by us; and (3) no hemlocks ever present. We are seeking to track the changes in soil water nutrient availability in each plot. The first type of plot will tell us what a recently-infested forest's nutrients look like; the second type should mimic a forest after the adelgid has killed the hemlocks; and the third type represents the new forest which will replace the dead hemlocks.

Fig. 2: This branch of an Eastern Hemlock tree is under heavy attack by Hemlock Woolly Adelgid insects (the white woolly objects are their egg casings). [Photo by USFS, in public domain]

Fig. 3: One of the many benefits to doing research at Coweeta is the opportunity to be surrounded by nature's beauty. I often remark that I've got the prettiest office of anyone I know. [Photo (c) 2005 M. Parrish]

Our project is scheduled to continue through summer of 2006, at which time our findings will be published.      In the meantime, I suggest that if you, the reader, wish to experience the slow, dark beauty of a hemlock forest, plan your trip soon (fig. 04). The Woolly Adelgid is continuing its rapid spread across the country even as I am writing this. The hemlock forests of the Eastern United States, which have existed for thousands of years, will be gone before most people are even aware that they are threatened. It is not a question of 'if' the forests are going to disappear, but 'when' they will - and the time we are talking about will soon be upon us. Your last chance to see the hemlock is rapidly approaching. -Michael Parrish - Updated January, 2006

Fig. 4: This is a typical hemlock-dominated section of forest on the Coweeta lands. The understory is a nearly impenetrable tangled thicket of mainly Rhododendron maximum which makes these "rhododendron hells" very difficult to traverse. Regardless, this unique habitat is a precious and imperiled resource. [Photo (c) 2006 M. Parrish]