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Tsuga canadensis (Eastern Hemlock) and T. caroliniana (Carolina Hemlock) are important components of western North Carolina forests. The invasive Adelges tsugae (Hemlock Woolly Adelgid [HWA]) was first reported in NC in 1995, and by 2007 the entire range of hemlock in the state was infested. An examination of the Forest Inventory and Analysis (FIA) program data for FIA Unit 4 (21 mountainous counties in western North Carolina), looking at remeasured trees for the time period 1999-2013, demonstrated that diameter net growth of hemlock decreased and mortality increased with increasing duration of HWA infestation. Hemlock trees in this study had a ∼50% chance of survival after 12 years of confirmed HWA infestation in the county where they occur, and growth of surviving trees was reduced by ∼50% over the same time period. This study demonstrates the utility of FIA data for examining effects of an introduced, invasive pest on tree growth and mortality over a relatively small area. Some advantages and limitations to our approach are discussed. [ABSTRACT FROM AUTHOR]

We monitored a population of Carolina Hemlocks in northwestern North Carolina for four years to examine the rate and pattern of decline in response to infestation by Adelges tsugae (Hemlock Woolly Adelgid). Our yearly census of hemlock condition and severity of the adelgid infestation included trees of all sizes. We estimated declines in condition as the portions of the leaf canopy that were lost. Initially, infestation occurred throughout the population but was severe in only a small cluster of individuals. Within 1 year, the area of severe infestation increased in size to encompass 48% of the population. In another region of the population, there was a cluster of relatively healthy individuals comprised largely of seedlings. Of the 4 size-classes of trees, sapling-sized individuals experienced the highest rates of decline in condition. Most trees declined to poor health within 3 years of an observation of moderate to severe infestation. [ABSTRACT FROM AUTHOR]

Abstract: Long-term records from USDA Forest Service Experimental Forests and Ranges (EF&Rs) are exceptionally valuable scientific resources and common ground for research in natural resource management. Coweeta Hydrologic Laboratory, Southern Appalachian Mountains in western North Carolina, is one of 82 EF&Rs located throughout the United States and Puerto Rico. Since its establishment in 1934, the wealth and breadth of scientific knowledge gained from Coweeta Hydrologic Laboratory research has provided both public and private land managers information on forest land management and has added to the knowledge base of natural resource science. We described the early watershed research at Coweeta and used long-term measurements and inventories (from 1934 to 2008) to: (1) explore the influences of large-scale disturbances and vegetation responses on ecosystem processes and (2) assess the long-term and short-term impacts of an exotic, invasive species on a southern Appalachian deciduous forest. We focused on changes in vegetation patterns influenced by natural and managed disturbances and then described the linkages between long-term vegetation measurements and water yield and quality responses. For natural disturbances, we used a network of over 900 permanent vegetation plots established in reference watersheds and unmanaged areas; first measured in 1934 and a subset re-measured in 1969–1972, 1988–1993, and 2003–2008. For the managed disturbances, clearcuts and species conversion experiments, vegetation was measured in permanent plots within treated watersheds before and after treatment. By the time of the 1934 survey, the forest had only 10 years to recover from logging before chestnut blight (Cryphonectria parasitica) induced mortality of virtually all remaining Castanea dentata trees. With the loss of C. dentata as the dominant species, Acer rubrum and Quercus montana became the dominant species and Liriodendron tulipifera and Tsuga canadensis increased in coves and along riparian corridors. T. canadensis is currently threatened by another invasive species, hemlock woolly adelgid (HWA, Adelges tsugae), with 33% tree mortality between 2003 and 2008. Smaller-scale disturbances, such as drought and windthrow, have created canopy gaps and the disturbance agent, gap size, and species-specific demography (dispersal, survival, growth, and mortality) affected colonization and recruitment. In general, the composition of species recruiting into canopy gaps was a reflection of the vegetation already in place at the time of disturbance, because regeneration occurred primarily through saplings or sprouts. In managed forests, where gaps were much larger (9–59ha), early successional species recruit and become established and the long-term vegetation patterns are different than in unmanaged forests. The vegetation data provide a description of changes in forest structure and composition through time and space, and they have been used to develop process-based models to scale-up to the catchment level. Long-term climatic, hydrologic, biogeochemical, and vegetation databases coupled with process-based ecohydrology and ecophysiology models are essential to understanding broader- and more complex environmental issues such as climate change, carbon cycling, atmospheric deposition, and water supply and quality. [Copyright &y& Elsevier]

Abstract: Great Smoky Mountains National Park is using systemic imidacloprid to treat eastern hemlocks (Tsuga canadensis [L.] Carr.) infested with the exotic insect, hemlock woolly adelgid (Adelges tsugae Annand). This study investigated effects of these treatments on insectivorous birds and hemlock canopy arthropod assemblages in the context of food availability for insectivorous birds. Six pairs of treated and untreated hemlock sites were studied in 2007. Territories of three hemlock-associated Neotropical migratory foliage-gleaning bird species were mapped in these six sites, and relationships between bird territory density and hemlock foliar density were examined. Canopy arthropods were sampled by clipping mid-canopy hemlock branches in each paired site. Arthropods were identified to order or suborder and categorized into bird prey guilds and non-target herbivorous insect guilds. Despite being treated within the previous two years, there were no differences in hemlock woolly adelgid infestation between treated and untreated sites. This may reflect recovery or because the imidacloprid is slow-acting. Bird densities also did not differ between treated and untreated sites but were positively related to branch foliage mass, implying a preference in these birds for well-foliated hemlocks. A total of 10,219 hemlock woolly adelgids, and a total of 906 other arthropods from 16 orders were collected. There were no differences in species richness, abundance, or species composition between treated and untreated sites for total arthropods, or for immature arthropods≥3mm. In contrast, non-target herbivorous Hemiptera and larval Lepidoptera were significantly reduced in treated hemlocks. Although larval Lepidoptera are primary prey for insectivorous foliage-gleaning birds, the similarity in bird densities between treated and untreated sites suggests the birds are able to find other food resources in the mixed hemlock-deciduous stands where the study sites were located. Therefore, controlling hemlock woolly adelgid-induced defoliation through use of imidacloprid may have short-term benefits for hemlock-associated birds. While imidacloprid treatments did not appear to be currently affecting most arthropods, primary prey guilds should be monitored for long-term declines that could impact hemlock-associated birds. [Copyright &y& Elsevier]

Forecasting the impact of invasive species can provide valuable insights to land managers and scientists. In this study we examined the threat posed to hemlock Tsuga canadensis forests by an invasive insect, the hemlock woolly adelgid Adelges tsugae (HWA). Our main objective was to determine if paleo-ecological pollen records, showing the response of tree genera to a previous Tsuga decline, could predict contemporary responses to the HWA. To assess this, we matched fossil pollen sites from the Global Pollen Database to sites in the northeastern US that were invaded by the HWA approximately two decades ago. Our analyses showed that several of the same genera responded positively to Tsuga declines at both fossil pollen and contemporary sites. We then applied this methodology to an area currently threatened by the HWA, Great Smoky Mountains National Park (GSMNP), where invasions began just seven years ago. Our analysis suggests that the canopy genera mostly likely to respond positively to declining hemlock abundances in GSMNP are Acer, Betula, Fagus, and Quercus. Our findings provide land managers in GSMNP with the first predictions of likely shifts in canopy composition. We expect that this methodology will have application at other areas threatened by the HWA. Finally, we believe that studies on the impacts of contemporary invasions have underutilized relevant fossil data and that greater efforts should be extended to doing so in the future. [ABSTRACT FROM AUTHOR]

The southern Appalachian forests have been threatened by several large-scale disturbances, such as wildfire and infestation, which alter the forest ecosystem structures and functions. Hemlock Woolly Adelgid (Adelges tsugae Annand, HWA) is a non-native pest that causes widespread foliar damage and eventual mortality, resulting in irreversible tree decline in eastern (Tsuga canadensis) and Carolina (T. caroliniana) hemlocks throughout the eastern United States. It is important to monitor the extent and severity of these disturbances over space and time to better understand their implications in the biogeochemical cycles of forest landscapes. Using all available Landsat images, we investigate and compare the performance of Tasseled Cap Transformation (TCT)-based indices, Normalized Difference Vegetation Index (NDVI), Enhanced Vegetation Index (EVI), and Disturbance Index (DI) in capturing the spectral-temporal trajectory of both abrupt and gradual forest disturbances (e.g., fire and hemlock decline). For each Landsat pixel, the temporal trajectories of these indices were fitted into a time series model, separating the inter-annual disturbance patterns (low frequency) and seasonal phenology (high frequency) signals. We estimated the temporal dynamics of disturbances based on the residuals between the observed and predicted values of the model, investigated the performance of all the indices in capturing the hemlock decline intensity, and further validated the results with the number of individual dead hemlocks identified from high-resolution aerial images. Our results suggested that the overall performance of NDVI, followed by TCT wetness, was most accurate in detecting both the disturbance timing and hemlock decline intensity, explaining over 90% of the variability in the number of dead hemlocks. Despite the overall good performance of TCT wetness in characterizing the disturbance regime, our analysis showed that this index has some limitations in characterizing disturbances due to its recovery patterns following infestation. [ABSTRACT FROM AUTHOR]