The aftermath of an invasion: Structure and composition of Central Appalachian hemlock forests following establishment of the hemlock woolly adelgid, Adelges tsugae

摘要

As the highly invasive hemlock woollyadelgid, Adelges tsugae, continues to expand itsdistribution in eastern North America, affectedforests will incur drastic changes in compositionand structure. While these changes have been well-studied in dense hemlock forests in the Northeast,relatively little work is known about the effects of theadelgid at the western edge of the range of easternhemlock, Tsuga canadensis. We evaluated the natureand extent of these changes using vegetation assess-ments coupled with growth simulations. The woodyplant community was assessed in three strata (upper,mid- and lower) and was used to predict forestsuccession. Using the Forest Vegetation Simulator(FVS), we then projected the growth of hemlockforests 20 years into the future with and without theeffects of the adelgid. In forest simulations lackingadelgid invasion, little change in composition orstructure is forecast. In contrast, our projectionspredict a near complete loss of the hemlock foresttype within 20 years of adelgid establishment, withwidespread conversion to hardwood forest types,most notably white oak-red oak-hickory, chestnutoak-black oak-scarlet oak, and yellow poplar-whiteoak-red oak. Hemlock loss will result in denserdeciduous forests with thinner canopies and multiple gaps, and significant alterations to terrestrial andaquatic wildlife habitat.