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Overstory basal area, ericaceous shrub cover (Kalmia latifolia L. and Rhododendron maximum L.), and fuels (i.e., woody fuel loads and depths and O Horizon thickness) were assessed within Great Smoky Mountains National Park, USA, in 2003 − 2004. Due to recent wildfire activity within the southern Appalachian Mountain region (including Great Smoky Mountains National Park), the potential spread and expansion of ericaceous shrubs, and the impacts of the hemlock woolly adelgid (Adelges tsugae Annand) on eastern hemlock (Tsuga canadensis (L.) Carrière), these same ecosystem components were again assessed in 2019. Elevation and moisture regime (xeric, intermediate, and mesic) were included in this assessment as potential influential factors. An evaluation of repeated measurements from 40 plots suggested that O Horizon thickness did not change significantly over the 16-year period, but increased as elevation increased, and moisture regime (xeric O Horizon thickness > mesic O Horizon thickness) was a significant, related factor. The sum of 1-, 10-, and 100-h fuel loads (fuels less < 7.6 cm diameter) increased, whereas woody fuel depth decreased over the 16-year period. No significant changes in 1000-h fuel loads (> 7.6 cm diameter), total woody fuel loads, ericaceous shrub cover, total basal area, or live T. canadensis basal area were observed. Live T. canadensis basal area decreased with increasing elevation. Dead, standing T. canadensis basal area increased from 2003–2019, and that increase was most pronounced as elevation increased on xeric and intermediate sites. Overall, we found that: 1. hypothesized increases in total woody fuel loads and ericaceous shrub cover were not present; and 2. elevation and moisture regime were most related to observed changes in vegetation and fuel condition. [ABSTRACT FROM AUTHOR]

The article discusses the article ‘‘Media representation of hemlock woolly adelgid management risks: a case study of sciencecommunication and invasive species control,'' by Leppanen et al. in the September 18, 2018 issue and mentions limitations to media reporting of science. It also mentions the comments made by Salom et al. on this article in terms of scientific communications, methods used in the study, and biological control of insects.

Public support can aid invasive species control and thus reduce negative impacts. Scientific communication can help or hinder efforts when associated risk and uncertainty are exaggerated or neglected, creating fear or distrust. Review of 104 media articles about managing a devastating forest insect, the hemlock woolly adelgid (Adelges tsugae), revealed that uncertainties and value judgments associated with claims of success were usually obscured or omitted, legitimate disagreement among experts about efficacy was omitted, and risks to non-targets were usually unaddressed. Discussion of chemical control in 83 articles included mention of non-target effects (e.g., to water quality, pollinators, and other native taxa) in only 11 articles and specificity was mentioned in only five instances. Biocontrol non-target impacts were mentioned in 11 of 83 cases and agent specificity was not mentioned in 71 of those cases. Ironically, while the value of the native ecosystem is used to justify management, possible non-target impacts of management on native ecosystems are largely ignored, notably hybridization between an introduced non-native biocontrol agent (Laricobius nigrinus) and a native beetle (L. rubidus) and ongoing releases of two non-native beetles, L. osaskensis colonies contaminated with a poorly understood, newly described species (L. naganoensis). To increase the public's ability to make informed decisions, benefits of management techniques should be discussed along with risks, scientific disagreement, and uncertainty. [ABSTRACT FROM AUTHOR]

The introduction of the hemlock woolly adelgid ( Adelges tsugae) in the eastern United States has caused extensive damage to eastern hemlock ( Tsuga canadensis) stands. The presence of other herbivores can affect adelgid density and hemlock health. Here, we report the results of long-term work monitoring hemlock forests in a 7,500 km latitudinal transect of southern New England. In biannual surveys between 1997 and 2011, we assessed change in hemlock basal area, stand-level hemlock defoliation, the density of four exotic herbivores ( A. tsugae, Fiorinia externa, Nuculaspis tsugae and an unidentified Nuculaspis sp.) and explored relationships between biotic and abiotic variables. Hemlock basal area decreased by approximately 60 % over the 14 years of the study. Hemlock stand defoliation increased locally in some stands but on average stand defoliation did not change throughout the study period/area. Local increases in defoliation were probably driven by the northward expansion by A. tsugae, and to a certain extent by the co-occurring presence of F. externa and Nuculaspis scales. Average F. externa density increased during the study and also expanded dramatically northward, although its density did not impact hemlock stand defoliation and only reduced hemlock basal area in some stands. Stand-level variation in F. externa densities was most strongly affected by the presence of Nuculaspis scales, which were present in about 80 % of the stands. While A. tsugae continues to be the primary threat to eastern hemlock, its impact needs to be studied in the context of a broader herbivore community. [ABSTRACT FROM AUTHOR]

Key message: Embryogenic cultures of eastern and Carolina hemlocks could be initiated, and somatic embryos and plantlets produced using standard conifer protocols and media. Embryogenic hemlock cultures were cryostored and recovered. Abstract: Eastern hemlock ( Tsuga canadenesis) and Carolina hemlock ( Tsuga caroliniana) are threatened with extirpation from their native ranges in eastern North America by the introduction of the hemlock woolly adelgid (HWA; Adelges tsugae), an exotic insect pest that has already killed millions of hemlock trees. Efforts to conserve and restore these members of the Pinaceae could be greatly enhanced by the availability of an in vitro propagation system. We conducted experiments to initiate embryogenic cultures from eastern and Carolina hemlock zygotic embryos at different stages of development using three media supplemented with 2,4-dichlorophenoxyacetic acid (2,4-D) and 6-Benzylaminopurine (BA). Cone collection date, medium and source tree had significant effects on induction of embryogenic tissue from zygotic embryo explants of both species, which ranged as high as 52 % for eastern hemlock and 17 % for Carolina hemlock. Embryogenic hemlock cultures could be cryostored using a protocol employing sorbitol and DMSO, and recovered following several months of frozen storage. Transfer of embryogenic tissue from proliferation media containing 2, 4-D and BA to a Litvay medium with abscisic acid promoted the development of somatic embryos, which were stimulated to mature by slow drying under semi-permeable plastic film. Embryos moved to an imbibition-germination medium without plant growth regulators and incubated in the light elongated and subsequently germinated. A small number of germinated embryos survived transfer to ex vitro conditions and grew into somatic seedlings. The embryogenesis and cryostorage systems developed in the study are already being integrated with hemlock breeding efforts to develop clones with resistance or tolerance to HWA. [ABSTRACT FROM AUTHOR]

Recent studies have identified a small number of individual eastern hemlock trees that demonstrate relative resistance to the introduced sap-feeding insect, the hemlock woolly adelgid. Using gas chromatography, we compared concentrations of twenty-two terpenoids in susceptible and relatively resistant trees, both in the forest and in propagated cuttings in a common-garden setting. Terpenoid concentrations were higher in twig tissue of resistant versus susceptible trees, across six sampling dates and at both sites. These changes may be particularly important because the hemlock woolly adelgid feeds on twig tissue. Because the common-garden cuttings were free of herbivores, the higher terpenoid concentrations are interpreted as a constitutive defense. Increased levels of monoterpenes and sesquiterpenes imply an overall increase in the input of carbon precursors to both terpenoid synthesis pathways. [ABSTRACT FROM AUTHOR]

The invasive hemlock woolly adelgid ( Adelges tsugae Annand, Hemiptera: Sternorrhyncha: Adelgidae) causes significant mortality to eastern and Carolina hemlock ( Tsuga canadensis Carrière and T. caroliniana Engelmann, respectively) throughout the eastern United States. Adelges tsugae produces vast quantities of a wax covering that surrounds most of the instars as well as the adult and eggs. Using direct probe EI mass spectrometry, this wax covering was characterized as a diketoester wax, 17-oxohexatriacontanyl 11-oxotriacontanoate, and accounted for ≈ 42 % of A. tsugae total biomass. The presence of the anthraquinone, chrysophanol, and its precursor anthrone, chrysarobin, in A. tsugae has only been briefly described. Further study confirmed these compounds in all A. tsugae life stages. Additionally, several predatory beetles in use or under consideration as biological control agents for this species appear to ingest and excrete these compounds when feeding on A. tsugae. The production of both a physical and a chemical defense may represent a significant energy investment by A. tsugae. [ABSTRACT FROM AUTHOR]

Spread dynamics of biological invasions are influenced by both the availability and spatial arrangement of suitable habitat. As such, invasive spread can be considered to occur across a network of nodes, representing patches of suitable habitat, with linkages representing the potential for movement between habitat patches. While static network models can provide valuable insight into the potential framework of nodes and linkages across which spread could occur, they offer little information on the actual spatiotemporal dynamics of range expansion processes. Here, we explore the development and application of dynamic network models (DNMs) to model the spread of invasive species. DNMs accommodate temporal dynamics in the utilization of nodes and the connections between them and can flexibly perform simulations at the spatial scales of observational data. As case studies, we develop DNMs to simulate the spread of a generalist forest pathogen and the hemlock woolly adelgid ( Adelges tsugae Annand). We highlight the utility of DNMs for identifying habitat patches that contribute most to spread across the landscape and for visualizing emergent spread dynamics. While currently underutilized in ecology as compared to static network models, DNMs are potentially applicable to numerous research and management questions relevant to biological invasions and the more general phenomena of range expansion. [ABSTRACT FROM AUTHOR]

Although sap-feeding insects are known to negatively affect plant growth and physiology, less is known about sap-feeding insects on woody plants. Adelges tsugae (Annand Hemiptera: Adelgidae), the hemlock woolly adelgid, is an invasive sap-feeding insect in eastern North America that feeds on and kills Tsuga canadensis (L. Carrière), eastern hemlock. Newly hatched adelgid nymphs crawl to young unattacked tissue, settle and immediately enter diapause (aestivation) while attached to hemlock in summer. We assessed the effect of A. tsugae infestation on T. canadensis growth and physiology by analyzing hemlock growth on lateral and terminal branches, water potential, photosynthesis, stomatal conductance, and foliar nitrogen (%N). A. tsugae infestation greatly decreased terminal and lateral growth of eastern hemlock. In addition, A. tsugae presence reduced photosynthesis by 10 % in September and 36 % in October. Adelgid-infested hemlocks also exhibited signs of water stress that included notable reductions in water potential and stomatal conductance. These responses shed light on possible mechanisms of adelgid-induced mortality. [ABSTRACT FROM AUTHOR]

Hemlocks are significant components of temperate forests of Asia and North America, and in eastern North America, they are threatened by an exotic herbivore, the hemlock woolly adelgid, Adelges tsugae. The adelgid is native to Asia and northwestern North America, but is highly invasive in eastern North America where natural enemies are unable to regulate populations and eastern hemlock, Tsuga canadensis, is highly susceptible. In order to gain a better understanding of the metabolic effects of A. tsugae on eastern hemlock, we evaluated its effects on photosynthesis and also evaluated photosynthesis on Tsuga species from various geographic origins. We measured light-saturated photosynthesis ( A) and dark respiration of T. canadensis that were infested with adelgid and found a significant decrease in A and a small but significant increase in dark respiration, suggesting that A. tsugae triggers a physiological response in eastern hemlock by decreasing metabolic activity. In a separate experiment, we also measured A of five different hemlock species, including eastern hemlock, the Pacific Northwestern T. heterophylla and T. mertensiana, and the Asian T. diversifolia and T. chinensis. Only weakly significant differences in A were found, with the highest rate in the eastern North American T. canadensis and the lowest in the Pacific Northwestern T. mertensiana. The relatively high photosynthetic rate of T. canadensis could possibly play a role in its susceptibility to A. tsugae. A better understanding of this metabolic response could help develop effective management strategies for combating the highly invasive A. tsugae. [ABSTRACT FROM AUTHOR]

The loss of foundational tree species to non-native pests can have far reaching consequences for forest composition and function, yet little is known about the impacts on other ecosystem components such as wildlife. We had the opportunity to observe how the loss of eastern hemlock ( Tsuga canadensis), due to the invasive hemlock woolly adelgid ( Adelges tsugae), influenced the population ecology of the Black-throated Blue Warbler ( Setophaga caerulescens) over a 7 year period. We followed the process of adelgid infestation and subsequent hemlock loss, which allowed us to investigate the patterns and mechanisms of population change. We document a precipitous decline in breeding pairs at one site where hemlock was most abundant in the understory, but not at our other two sites. We observed no changes in reproductive output or apparent survival, yet territory size increased dramatically at the most affected site, suggesting that the decline was due to a lack of colonization by new breeders. Our results demonstrate how an invasive insect pest can indirectly influence wildlife species not believed to be vulnerable and in ways not typically investigated. [ABSTRACT FROM AUTHOR]

The ability to establish successfully in a new area can vary considerably among species. In addition to the well-recognized importance of propagule pressure in driving the rates of establishment of biological invaders, the life history strategy of a species can also affect establishment success, such as in the extent to which Allee effects (positive density-dependence), and environmental and demographic stochasticity manifest themselves. We quantified the establishment success of Adelges tsugae, a non-native insect currently invading North American hemlock. We inoculated eastern hemlock host trees with varying densities of this parthenogenetic insect, from 1 to >500 progrediens ovisacs. The number of settled sistens (the subsequent generation) was positively related to the initial density. More interesting, however, was that we recorded successful establishment from released progrediens ovisacs, and the subsequent initiation of the next generation (sistens), in ≈39 % of host trees inoculated with 1 ovisac. The observation that successful establishment can be accomplished by a single ovisac produced by a single individual has important implications in the invasion dynamics and management of A. tsugae. [ABSTRACT FROM AUTHOR]

Eastern hemlock ( Tsuga canadensis) is in rapid decline because of infestation by the invasive hemlock woolly adelgid ( Adelges tsugae; 'HWA') and, to a lesser extent, the invasive elongate hemlock scale ( Fiorinia externa; 'EHS'). For many conifers, induced oleoresin-based defenses play a central role in their response to herbivorous insects; however, it is unknown whether eastern hemlock mobilizes these inducible defenses. We conducted a study to determine if feeding by HWA or EHS induced changes in the volatile resin compounds of eastern hemlock. Young trees were experimentally infested for 3 years with HWA, EHS, or neither insect. Twig and needle resin volatiles were identified and quantified by gas chromatography/mass spectrometry. We observed a suite of changes in eastern hemlock's volatile profile markedly different from the largely terpenoid-based defense response of similar conifers. Overall, both insects produced a similar effect: most twig volatiles decreased slightly, while most needle volatiles increased slightly. Only HWA feeding led to elevated levels of methyl salicylate, a signal for systemic acquired resistance in many plants, and benzyl alcohol, a strong antimicrobial and aphid deterrent. Green leaf volatiles, often induced in wounded plants, were increased by both insects, but more strongly by EHS. The array of phytochemical changes we observed may reflect manipulation of the tree's biochemistry by HWA, or simply the absence of functional defenses against piercing-sucking insects due to the lack of evolutionary contact with these species. Our findings verify that HWA and EHS both induce changes in eastern hemlock's resin chemistry, and represent the first important step toward understanding the effects of inducible chemical defenses on hemlock susceptibility to these exotic pests. [ABSTRACT FROM AUTHOR]

The impacts of exotic insects and pathogens on forest ecosystems are increasingly recognized, yet the factors influencing the magnitude of effects remain poorly understood. Eastern hemlock ( Tsuga canadensis) exerts strong control on nitrogen (N) dynamics, and its loss due to infestation by the hemlock woolly adelgid ( Adelges tsugae) is expected to decrease N retention in impacted stands. We evaluated the potential for site variation in N availability to influence the magnitude of effects of hemlock decline on N dynamics in mixed hardwood stands. We measured N pools and fluxes at three elevations (low, mid, high) subjected to increasing atmospheric N deposition where hemlock was declining or absent (as reference), in western North Carolina. Nitrogen pools and fluxes varied substantially with elevation and increasing N availability. Total forest floor and mineral soil N increased ( P < 0.0001, P = 0.0017, resp.) and forest floor and soil carbon (C) to N ratio decreased with elevation ( P < 0.0001, P = 0.0123, resp.), suggesting that these high elevation pools are accumulating available N. Contrary to expectations, subsurface leaching of inorganic N was minimal overall (<1 kg ha 9 months), and was not higher in stands with hemlock mortality. Mean subsurface flux was 0.16 ± 0.04 (SE) (kg N ha 100 days) in reference and 0.17 ± 0.05 (kg N ha 100 days) in declining hemlock stands. Moreover, although subsurface N flux increased with N availability in reference stands, there was no relationship between N availability and flux in stands experiencing hemlock decline. Higher foliar N and observed increases in the growth of hardwood species in high elevation stands suggest that hemlock decline has stimulated N uptake and growth by healthy vegetation within this mixed forest, and may contribute to decoupling the relationship between N deposition and ecosystem N flux. [ABSTRACT FROM AUTHOR]

Plants in nature are often attacked by multiple enemies whose effect on the plant cannot always be predicted based on the outcome of individual attacks. We investigated how two invasive herbivores, the hemlock woolly adelgid ( Adelges tsugae) (HWA) and the elongate hemlock scale ( Fiorinia externa) (EHS), alter host plant quality (measured as amino acid concentration and composition) when feeding individually or jointly on eastern hemlock ( Tsuga canadensis), an important long-lived forest tree that is in severe decline. The joint herbivore treatments included both simultaneous and sequential infestations by the two herbivores. We expected resource depletion over time, particularly in response to feeding by HWA. In contrast, HWA dramatically increased the concentration and altered the composition of individual free amino acids. Compared to control trees, HWA increased total amino acid concentration by 330% after 1 year of infestation. Conversely, EHS had a negligible effect when feeding individually. Interestingly, there was a marginally significant HWA × EHS interaction that suggests the potential for EHS presence to reduce the impact of HWA on foliage quality when the two species co-occur. We suggest indirect effects of water stress as a possible physiological mechanism for our results. Understanding how species interactions change the physiology of a shared host is crucial to making more accurate predictions about host mortality and subsequent changes in affected communities and ecosystems, and to help design appropriate management plans. [ABSTRACT FROM AUTHOR]

Tsuga canadensis is often considered a foundation species because of its influence on the biological and ecological processes of upland forest systems. With hemlock woolly adelgid ( Adelges tsugae; HWA)-induced mortality of T. canadensis in southern Appalachian upland forests, there is a crucial need to understand the regeneration dynamics of this tree species. This research was conducted within mature T. canadensis forests of Great Smoky Mountains National Park (GSMNP) prior to widespread HWA infestation. Tsuga canadensis regeneration abundance is lower than has been reported in more northern locales, but varies widely among sites in the southern Appalachian Mountains. Ordination results suggest landscape-scale patterns of regeneration abundance that are influenced by gradients in understory Rhododendron maximum cover, soil sand and nutrient content. Regression models reinforce the observed gradients in regeneration abundance. Sites with abundant T. canadensis regeneration have less R. maximum cover, soil sand and litter depth, but more soil nutrient availability. Tsuga canadensis seedlings and saplings tend to be spatially aggregated at the 14 × 21 m plot scale. Sites with spatially aggregated seedlings and saplings have greater canopy openness and more species with gap affinity. This research elucidates associations between successful T. canadensis regeneration and site factors such as soil nutrient availability and canopy dynamics. More forest surveys are required to understand the conditions necessary for successful T. canadensis regeneration. Land managers involved in forest restoration efforts may have to utilize appropriate silvicultural techniques conjoined with R. maximum removal operations to regenerate T. canadensis in southern Appalachian upland forests. [ABSTRACT FROM AUTHOR]

In this article we evaluate a US Forest Service plan to mitigate damages from an invasive insect on public, forested land. We develop a dynamic model of infestation and control to explicitly account for biological interactions, baseline conditions, and uncertainty, thus creating a more complete picture of policy impacts than a static cost benefit analysis could provide. We combine the results of the dynamic model with an empirical study of nonmarket forest benefits to create a bioeconomic model of ecosystem management. Estimating the empirical model in a Bayesian framework allows us to treat the economic coefficients of the dynamic model as random variables. We specify distributions for the biological parameters and examine the effects of both biological and economic uncertainty on the predictive distribution of net benefits. We find that the net benefits of the program are positive, and that uncertainty in the biological model contributes substantially more to the variance of our estimate than does uncertainty over the valuation of the resource. [ABSTRACT FROM AUTHOR]

The objectives of this study were to quantify rates of nitrogen inputs to the forest floor, determine rates of nitrogen losses via leaching and to partition the sources of NO from healthy, declining, and salvage or preemptively cut eastern hemlock ( Tsuga canadensis) stands in both an urban forest at the Arnold Arboretum in Boston, MA and a rural forest at Harvard Forest in Petersham, MA. Rates of nitrogen inputs (NH and NO) to the forest floor were 4-5 times greater, and rates of nitrogen losses via leachate were more than ten times greater, at the Arnold Arboretum compared to Harvard Forest. Nitrate that was lost via leachate at Harvard Forest came predominantly from atmospheric deposition inputs, whereas NO losses at the Arnold Arboretum came predominantly from nitrification. Although our study was limited to one urban and one rural site, our results suggest that current management regimes used to control the hemlock woolly adelgid ( Adelges tsugae), such as salvage cutting, may be reducing nitrogen losses in urban areas due to rapid regrowth of vegetation and uptake of nitrogen by those plants. In contrast, preemptive cutting of trees in rural areas may be leading to proportionately greater losses of nitrogen in those sites, though the total magnitude of nitrogen lost is still smaller than in urban sites. Results of our study suggest that the combination of the hemlock woolly adelgid, nitrogen inputs, and management practices lead to changes in the movement and source of NO losses from eastern hemlock forest ecosystems. [ABSTRACT FROM AUTHOR]

Hemlock Woolly Adelgid ( Adelges tsugae) is spreading across forests in eastern North America, causing mortality of eastern hemlock ( Tsuga canadensis [L.] Carr.) and Carolina hemlock ( Tsuga caroliniana Engelm.). The loss of hemlock from riparian forests in Great Smoky Mountains National Park (GSMNP) may result in significant physical, chemical, and biological alterations to stream environments. To assess the influence of riparian hemlock stands on stream conditions and estimate possible impacts from hemlock loss in GSMNP, we paired hardwood- and hemlock-dominated streams to examine differences in water temperature, nitrate concentrations, pH, discharge, and available photosynthetic light. We used a Geographic Information System (GIS) to identify stream pairs that were similar in topography, geology, land use, and disturbance history in order to isolate forest type as a variable. Differences between hemlock- and hardwood-dominated streams could not be explained by dominant forest type alone as forest type yields no consistent signal on measured conditions of headwater streams in GSMNP. The variability in the results indicate that other landscape variables, such as the influence of understory Rhododendron species, may exert more control on stream conditions than canopy composition. The results of this study suggest that the replacement of hemlock overstory with hardwood species will have minimal impact on long-term stream conditions, however disturbance during the transition is likely to have significant impacts. Management of riparian forests undergoing hemlock decline should, therefore, focus on facilitating a faster transition to hardwood-dominated stands to minimize long-term effects on water quality. [ABSTRACT FROM AUTHOR]

The recent infestation of southern Appalachian eastern hemlock stands by hemlock woolly adelgid (HWA) is expected to have dramatic and lasting effects on forest structure and function. We studied the short-term changes to the carbon cycle in a mixed stand of hemlock and hardwoods, where hemlock was declining due to either girdling or HWA infestation. We expected that hemlock would decline more rapidly from girdling than from HWA infestation. Unexpectedly, in response to both girdling and HWA infestation, hemlock basal area increment (BAI) reduced substantially compared to reference hardwoods in 3 years. This decline was concurrent with moderate increases in the BAI of co-occurring hardwoods. Although the girdling treatment resulted in an initial pulse of hemlock needle inputs, cumulative litter inputs and O horizon mass did not differ between treatments over the study period. Following girdling and HWA infestation, very fine root biomass declined by 20–40% in 2 years, which suggests hemlock root mortality in the girdling treatment, and a reduction in hemlock root production in the HWA treatment. Soil CO2 efflux ( Esoil) declined by approximately 20% in 1 year after both girdling and HWA infestation, even after accounting for the intra-annual variability of soil temperature and moisture. The reduction in Esoil and the concurrent declines in BAI and standing very fine root biomass suggest rapid declines in hemlock productivity from HWA infestation. The accelerated inputs of detritus resulting from hemlock mortality are likely to influence carbon and nutrient fluxes, and dictate future patterns of species regeneration in these forest ecosystems. [ABSTRACT FROM AUTHOR]

Tsuga canadensis (L.) Carr. forests of the southern Appalachian Mountains are currently facing imminent decline induced by a nonnative insect pest, the hemlock woolly adelgid ( Adelges tsugae Annand). To effectively manage these forest systems now and in the future, land managers need baseline data on forest structure and dynamics prior to large-scale Tsuga canadensis mortality. Most of our knowledge concerning the dynamics of Tsuga canadensis forests comes from more northern locations such as the Great Lakes region and New England and, therefore, may not pertain to the ecological systems found within the southern Appalachian Mountains. We examined the structure and canopy dynamics of four Tsuga canadensis forest stands within the Cataloochee watershed, in the far eastern part of Great Smoky Mountains National Park (GSMNP). We characterized the environmental settings and vertical forest layers, as well as the diameter and age-structures of each Tsuga canadensis forest stand. These environmental and structural data showed that there were indeed differences between forest stands with and without successful Tsuga canadensis regeneration. The two forest stands exhibiting successful Tsuga canadensis regeneration were located above 1,000 m in elevation on well-drained, moderately steep slopes and had the greatest canopy openness. Structural data from these two forest stands indicated a history of more continuous Tsuga canadensis regeneration. We also constructed disturbance chronologies detailing the history of canopy response to disturbance events and related these to Tsuga canadensis regeneration within each forest stand. Student t-tests adjusted for unequal variances indicated significant differences in the number of release events per tree between forest stands with and without successful Tsuga canadensis regeneration. While forest stands with successful Tsuga canadensis regeneration were more frequently disturbed by minor to major canopy disturbances, events of moderate intensity were found to be most significant in terms of regeneration. These data will be of value to land managers maintaining stands of Tsuga canadensis where treatment for hemlock woolly adelgid infestation has been successful. In areas where treatment is impractical or unsuccessful, land managers will be able to use these data to restore Tsuga canadensis forests after the wave of hemlock woolly adelgid induced mortality has passed. [ABSTRACT FROM AUTHOR]

Exotic insect pests may strongly disrupt forest ecosystems and trigger major shifts in nutrient cycling, structure, and composition. We examined the relationship between these diverse effects for the hemlock woolly adelgid (HWA, Adelges tsugae Annand) in New England forests by studying its impacts on local canopy processes in stands differing in infestation levels and linking these impacts to shifts in canopy nutrient cycling and stand and landscape effects. HWA initiated major changes in canopy biomass and distribution. Whereas uninfested trees exhibit a significant decline in canopy biomass from the center to the periphery and a positive correlation between total needle litter and estimated biomass, infested trees have significantly less total canopy biomass, produce less new foliage, shed relatively more needles, and exhibit no correlation between litter and canopy biomass. Foliar N content of infested trees was 20%–40% higher than reference trees, with the strongest increase in young foliage supporting the highest densities of HWA. Foliar %C was unaffected by HWA or foliar age. Epiphytic microorganisms on hemlock needles exhibited little variation in abundance within canopies, but colony-forming units of bacteria, yeast, and filamentous fungi were 2–3 orders of magnitude more abundant on medium and heavily infested than uninfested trees. Throughfall chemistry, quantity, and spatial pattern were strongly altered by HWA. Throughfall exhibits a strong gradient beneath uninfested trees, decreasing in volumes from the canopy periphery to the trunk by more than 45%. The amount of throughfall beneath infested trees exhibits no spatial pattern, reaches 80%–90% of the bulk precipitation, and is characterized by significantly higher concentrations of nitrogen compounds, dissolved organic carbon, and cations. Across the southern New England landscape there is a strong south-to-north gradient of decreasing hemlock tree and sapling mortality and understory compositional change that corresponds to the duration of infestation. Regionally, black birch ( Betula lenta L.) is profiting most from hemlock decline by significantly increasing in density and cover. These findings suggest that it is necessary to study the connections between fast/small-scale processes such as changes in nutrient cycling in tree canopies and slow/integrative processes like shifts in biogeochemieal cycling and compositional changes at forest stands and landscapes to better understand the effects of an exotic pest species like HWA on forest ecosystem structure and function. [ABSTRACT FROM AUTHOR]

The objective of this study was to develop a technique to classify health of eastern hemlock stands using historical satellite images. While remote sensing and geographic information systems have been used successfully to classify forest health using recent images, applying this process to older images is problematic because contemporaneous field data are not available to measure the accuracy of the classification of historical images. Data ranges were established for each hemlock health class using a contemporary image and field data. These ranges were used to level-slice archived images to create a series of health-class maps that show changes in forest health over time. By applying cross-tabulation procedures to pairs of classified images, it is possible to construct a transition map that indicates how the hemlock health class of each pixel in the images of the study area has changed over time. The resulting maps provide a look back at forest conditions of the past and can be used to identify areas of special interest. [ABSTRACT FROM AUTHOR]

A method is described to classify stands of eastern hemlock by health condition, at the landscape level, using remote sensing. The hemlock woolly adelgid has been a major cause of hemlock decline in Connecticut since 1985, resulting in varying degrees of defoliation in the region. A 1985 Landsat Thematic Mapper (TM) image was classified to develop a base line of once healthy hemlock stands. Radiance normalization and non-hemlock masking techniques were used to pre-process a 1995 TM image. Several techniques were used to transform the 1995 TM image; each was followed by cluster analysis to separate hemlocks into four levels of tree vigor. We evaluated 600 trees at 150 sites across the study area using the USFS Crown Condition Rating Guide. These field data were used to measure the accuracy of various health classification techniques. The Modified Soil Adjusted Vegetation Index-2 (MSAVI2) transform provided the best overall accuracy, 82.1%, for classifying hemlock according to tree vigor. Non-parametric statistics were used to determine if there were any significant variations in distribution of hemlock pixels by health class in association with features in the landscape. Several features were found to be statistically significant at a confidence level of 0.001. These were aspect of slope, hydrology group (infiltration rate), depth to bedrock, soil order, drainage class (hydraulic conductivity), and surface texture. [ABSTRACT FROM AUTHOR]