Vegetation dynamics in declining eastern hemlock stands: 9 years of forest response to hemlock woolly adelgid infestation

2006 ◽  
Vol 36 (6) ◽  
pp. 1435-1450 ◽  
Author(s):  
Anne K Eschtruth ◽  
Natalie L Cleavitt ◽  
John J Battles ◽  
Richard A Evans ◽  
Timothy J Fahey
Keyword(s):  
Invasive Plants ◽  
Light Availability ◽  
Hemlock Woolly Adelgid ◽  
Adelges Tsugae ◽  
Eastern Hemlock ◽  
Percent Cover ◽  
Eastern United States ◽  
Transmitted Radiation ◽  
Exotic Invasive ◽  
Exotic Invasive Plants

Hemlock woolly adelgid (HWA; Adelges tsugae Annand) infestations have resulted in the continuing decline of eastern hemlock (Tsuga canadensis (L.) Carrière) throughout much of the eastern United States. In 1994 and 2003, we quantified the vegetation composition and structure of two hemlock ravines in the Delaware Water Gap National Recreation Area. This is the first study to use pre-adelgid disturbance data, annual monitoring of infestation severity, and annual records of hemlock health to assess forest response to HWA infestation. In 2003, 25% of monitored hemlock trees were either dead or in severe decline. Measures of hemlock decline (crown vigor, transparency, density, and dieback) were correlated with HWA infestation severity and changes in light availability over the study period. Average percent total transmitted radiation more than doubled at these sites from 5.0% in 1994 to 11.7% in 2003. The total percent cover of vascular plants increased from 3.1% in 1994 to 11.3% in 2003. Species richness increased significantly, and more species were gained (53) than lost (19) from both ravine floras over the 9-year study period. Though exotic invasive plants were absent from these ravines in 1994, our 2003 resurvey found invasive plants in 35% of the permanent vegetation plots.

Hemlock woolly adelgid impacts on community structure and N cycling rates in eastern hemlock forests

1999 ◽  
Vol 29 (5) ◽  
pp. 630-645 ◽  
Author(s):  
Jennifer C Jenkins ◽  
John D Aber ◽  
Charles D Canham
Keyword(s):  
Community Structure ◽  
New England ◽  
Light Availability ◽  
Ecosystem Processes ◽  
Hemlock Woolly Adelgid ◽  
Adelges Tsugae ◽  
Eastern Hemlock ◽  
N Availability ◽  
Net N Mineralization ◽  
Total N

Mortality of dominant tree species caused by introduced pests and pathogens have been among the most pervasive and visible impacts of humans on eastern U.S. forests in the 20th century, yet little is known about the ecosystem-level consequences of these invasions. In this study we quantified the impacts of the introduced hemlock woolly adelgid (Adelges tsugae Annand) on community structure and ecosystem processes in eastern hemlock (Tsuga canadensis (L.) Carr.) forests in southern New England. Data were collected at six hemlock-dominated sites spanning a continuum from 0 to 99% mortality. Light availability to the understory and seedling regeneration both increased in stands affected by the adelgid. Differences in soil organic matter, total C, and total N pools between infested and noninfested sites were not associated with hemlock decline. Net N mineralization, nitrification, and N turnover increased at sites experiencing hemlock mortality. Inorganic N availability and nitrification rates increased dramatically with adelgid infestation and hemlock mortality, suggesting that nitrate leaching is likely in regions experiencing hemlock mortality. In the longer term, ecosystem processes at infested stands are likely to be driven by the successional dynamics that follow hemlock mortality.

Predicting the impact of hemlock woolly adelgid on carbon dynamics of eastern United States forests

2010 ◽  
Vol 40 (1) ◽  
pp. 119-133 ◽  
Author(s):  
Marco Albani ◽  
Paul R. Moorcroft ◽  
Aaron M. Ellison ◽  
David A. Orwig ◽  
David R. Foster
Keyword(s):  
United States ◽  
Insect Pest ◽  
Hemlock Woolly Adelgid ◽  
Adelges Tsugae ◽  
Eastern Hemlock ◽  
Forest Composition ◽  
Eastern United States ◽  
Regional Patterns ◽  
Spread Model ◽  
The Impact

The hemlock woolly adelgid (HWA; Adelges tsugae Annand) is an introduced insect pest that threatens to decimate eastern hemlock ( Tsuga canadensis (L.) Carriere) populations. In this study, we used the ecosystem demography model in conjunction with a stochastic model of HWA spread to predict the impact of HWA infestation on the current and future forest composition, structure, and carbon (C) dynamics in the eastern United States. The spread model predicted that on average the hemlock stands south and east of the Great Lakes would be infested by 2015, southern Michigan would be reached by 2020, and northeastern Minnesota by 2030. For the period 2000–2040, the ecosystem demography model predicted a mean reduction of 0.011 Pg C·year–1 (Pg C = 1015 g C), an 8% decrease, in the uptake of carbon from eastern United States forests as a result of HWA-caused mortality, followed by an increased uptake of 0.015 Pg C·year–1 (a 12% increase) in the period 2040–2100, as the area recovers from the loss of hemlock. Overall, we conclude that while locally severe, HWA infestation is unlikely to have a significant impact on the regional patterns of carbon fluxes, given that eastern hemlock represents a limited fraction of the standing biomass of eastern forests and that it has relatively low productivity compared with the tree species that are likely to replace it.

scholarly journals Potential of Alternative Tsuga spp. as Landscape Replacements for T. canadensis: Longer-Term Evaluation and Propagation of T. chinensis.

2016 ◽  
Vol 42 (5) ◽  
Author(s):  
Richard Harper ◽  
Paul Weston
Keyword(s):  
United States ◽  
New York ◽  
North America ◽  
Tsuga Canadensis ◽  
Hemlock Woolly Adelgid ◽  
Adelges Tsugae ◽  
Eastern Hemlock ◽  
Eastern United States ◽  
Term Evaluation ◽  
Plant Hardiness

Seven species of hemlock (Tsuga spp.)—four from North America and three from Asia—were evaluated in replicated plots in Katonah, New York, United States (USDA Plant Hardiness Zone 6b) as potential replacements for eastern hemlock (Tsuga canadensis), which is gradually being extirpated from landscapes in the eastern United States. by the invasive hemlock woolly adelgid (Adelges tsugae). Trends reported in an earlier study (Weston and Harper 2009) continued but were exaggerated after an additional three years of observation. For example, Chinese hemlock (T. chinensis) continued to show the greatest potential as a replacement for T. canadensis as mortality was very low, overall plant health was exceptional, and tolerance to A. tsugae was robust. Early indicators suggest that T. chinensis may also be readily propagated from hardwood cuttings under appropriate greenhouse conditions. These characteristics suggest that T. chinensis may indeed become a viable replacement for T. canadensis, and a valuable addition to landscapes in the eastern U.S.

scholarly journals ASSESSMENT OF A 5-YEAR-OLD REHABILITATED RIPARIAN FOREST: IS IT ALREADY SUSTAINABLE?

2015 ◽  
Vol 39 (4) ◽  
pp. 603-610
Author(s):  
Vinícius Londe ◽  
Hildeberto Caldas de Sousa ◽  
Alessandra Rodrigues Kozovits
Keyword(s):  
Invasive Species ◽  
Invasive Plants ◽  
Riparian Forest ◽  
Canopy Openness ◽  
Management Actions ◽  
Minas Gerais State ◽  
Hemispherical Photographs ◽  
Exotic Invasive ◽  
Exotic Invasive Plants ◽  
Over Time

ABSTRACTAs important as the establishment of projects of ecological restoration is its assessment post-implementation to know whether the area is becoming self-sustainable or need to be redirected. In this way, this study aimed to know the current situation of a 5-year-old rehabilitated riparian forest,inserted in an anthropogenic impacted region,at the das Velhas River, Minas Gerais State, studying the canopy openness and recruitment of seedlings as plant indicators. 15 plots were allocated in the forest, where hemispherical photographs were taken to analyze the canopy openness and evaluate all seedlings from 0.30 m to 1.30 m height.Canopy openness ranged from 23.7% to 38.8% between seasons and only 192 seedlings were found,from 13 species, five of them exotic and aggressive. Although canopy openness was low, it seems that lateral penetration of light has been favoring the development and dominancy of plants from invasive species, whereas few native ones have been recruited. The exotic/invasive plants may compromise the success of restoration mainly by competition with native planted species. The outcomes evidenced an unsustainability of the riparian forest and the requirement of some management actions to control exotic and invasive plants and ensure the preservation of the area and its ecological roles over time.

scholarly journals The Past, Present, and Future of the Hemlock Woolly Adelgid (Adelges tsugae) and Its Ecological Interactions with Eastern Hemlock (Tsuga canadensis) Forests

Insects ◽  
2018 ◽  
Vol 9 (4) ◽  
pp. 172 ◽  
Author(s):  
Aaron Ellison ◽  
David Orwig ◽  
Matthew Fitzpatrick ◽  
Evan Preisser
Keyword(s):  
Biological Diversity ◽  
Carbon Sources ◽  
Hemlock Woolly Adelgid ◽  
Adelges Tsugae ◽  
Ecosystem Dynamics ◽  
Eastern Hemlock ◽  
Carbon Sinks ◽  
The North ◽  
Spread Dynamics ◽  
Landscape Scales

The nonnative hemlock woolly adelgid is steadily killing eastern hemlock trees in many parts of eastern North America. We summarize impacts of the adelgid on these forest foundation species; review previous models and analyses of adelgid spread dynamics; and examine how previous forecasts of adelgid spread and ecosystem dynamics compare with current conditions. The adelgid has reset successional sequences, homogenized biological diversity at landscape scales, altered hydrological dynamics, and changed forest stands from carbon sinks into carbon sources. A new model better predicts spread of the adelgid in the south and west of the range of hemlock, but still under-predicts its spread in the north and east. Whether these underpredictions result from inadequately modeling accelerating climate change or accounting for people inadvertently moving the adelgid into new locales needs further study. Ecosystem models of adelgid-driven hemlock dynamics have consistently forecast that forest carbon stocks will be little affected by the shift from hemlock to early-successional mixed hardwood stands, but these forecasts have assumed that the intermediate stages will remain carbon sinks. New forecasting models of adelgid-driven hemlock decline should account for observed abrupt changes in carbon flux and ongoing and accelerating human-driven land-use and climatic changes.

Combined Effects of Hemlock Woolly Adelgid (Adelges tsugae) Infestation and Treatment with Imidacloprid on Eastern Hemlock (Tsuga canadensis) Leaf Radiometry

2019 ◽  
Vol 117 (4) ◽  
pp. 340-350 ◽  
Author(s):  
Heath W Garris ◽  
Thomas H Settle ◽  
Jonathan E Crossman ◽  
Stephen J Grider ◽  
Shawnté L Michaels
Keyword(s):  
Optical Properties ◽  
Tsuga Canadensis ◽  
Hemlock Woolly Adelgid ◽  
Adelges Tsugae ◽  
Eastern Hemlock ◽  
Abiotic Stressors ◽  
Leaf Optical Properties ◽  
Photosynthetic Potential ◽  
And Control ◽  
Potential Efficiency

Abstract The neonicotinoid systemic insecticide imidacloprid has proven to be an effective treatment for the prevention and control of hemlock woolly adelgid (Adelges tsugae Annand) in southeastern populations of eastern hemlock (Tsuga canadensis L.). Recent studies have demonstrated that imidacloprid and A. tsugae both stimulate salicylic acid-dependent physiological responses in plant tissues responsible for plant defenses against pathogens, timing of developmental outcomes including flowering and leaf senescence, and resilience to abiotic stressors. We evaluated the interacting effects of A. tsugae presence/absence and treatment with imidacloprid on leaf optical properties indicative of photosynthetic potential, photosynthetic efficiency, and tissue senescence. Our results indicated that A. tsugae changes lower canopy leaf optical properties indicative of reduced photosynthetic potential/efficiency and accelerated senescence in mature leaves. Imidacloprid was associated with declines in photosynthetic potential and showed a largely similar, though less pronounced, effect on leaf spectral properties to that of A. tsugae.

Native and exotic invasive plants have fundamentally similar carbon capture strategies

2010 ◽  
Vol 98 (1) ◽  
pp. 28-42 ◽  
Author(s):  
Michelle R. Leishman ◽  
Vivien P. Thomson ◽  
Julia Cooke
Keyword(s):  
Invasive Plants ◽  
Carbon Capture ◽  
Exotic Invasive ◽  
Exotic Invasive Plants

Seasonal abundance and synchrony between Laricobius nigrinus (Coleoptera: Derodontidae) and its prey, the hemlock woolly adelgid (Hemiptera: Adelgidae)

2003 ◽  
Vol 135 (1) ◽  
pp. 103-115 ◽  
Author(s):  
G.M.G. Zilahi-Balogh ◽  
L.M. Humble ◽  
A.B. Lamb ◽  
S.M. Salom ◽  
L.T. Kok
Keyword(s):  
North America ◽  
Pacific Northwest ◽  
Biological Control Agent ◽  
Seed Orchard ◽  
Hemlock Woolly Adelgid ◽  
Control Agent ◽  
Adelges Tsugae ◽  
Seasonal Abundance ◽  
Eastern United States ◽  
Laricobius Nigrinus

AbstractLaricobius nigrinus Fender, native to the Pacific Northwest, is being evaluated as a potential biological control agent of the hemlock woolly adelgid, Adelges tsugae Annand, in the eastern United States. Members of the genus Laricobius feed exclusively on adelgids. Adelges tsugae is found on hemlocks (Tsuga sp.) in North America and Asia, but is considered only a pest of eastern [Tsuga canadensis (L.) Carrière] and Carolina (Tsuga caroliniana Engelmann) hemlocks in eastern North America. This is the first detailed study of the life history of L. nigrinus and its interaction with A. tsugae. Results of a 2-year field study conducted in a seed orchard in British Columbia on the seasonal abundance of L. nigrinus and its prey, A. tsugae, revealed that (i) the sistens generation of A. tsugae matures 2-3 months earlier than previously reported in Virginia and Connecticut, (ii) no A. tsugae sexuparae were observed, which differs from findings in Virginia and Connecticut, (iii) L. nigrinus adults undergo an aestival diapause that coincides with diapausing first instar A. tsugae sistens, and (iv) oviposition and subsequent larval development of L. nigrinus coincides with oviposition by the A. tsugae sistens adults, indicating good synchrony between L. nigrinus and suitable prey stages of A. tsugae.

scholarly journals Potential of Tsuga spp. from Western North America and Asia as Replacements for Eastern Hemlock ( Tsuga canadensis )

2009 ◽  
Vol 35 (1) ◽  
pp. 5-9
Author(s):  
Paul Weston ◽  
Richard Harper
Keyword(s):  
United States ◽  
New York ◽  
New York State ◽  
Tsuga Canadensis ◽  
Hemlock Woolly Adelgid ◽  
Adelges Tsugae ◽  
Eastern United States ◽  
Growth And Survival ◽  
Managed Landscapes ◽  
Species Being

Hemlock woolly adelgid (Adelges tsugae) has had a devastating impact on Tsuga canadensis and T. caroliniana in forests and managed landscapes in the eastern United States. Species of Tsuga from the western United States and Asia are reported to be tolerant or resistant to A. tsugae. We established plots containing T. canadensis, T. caroliniana, T. chinensis, T. diversifolia, T. heterophylla, T. mertensiana, and T. sieboldii in Katonah, New York, U.S., an area with high populations of A. tsugae, and monitored tree growth and infestation by adelgids over a 4-year period. Growth and survival of the hemlock species varied widely, the most vigorous species being T. canadensis and T. chinensis. Susceptibility to the adelgid also varied widely among species; some species (particularly T. canadensis) became readily infested, whereas others (e.g., T. chinensis) were apparently entirely resistant. Given the ability of T. chinensis to thrive in the climate of southeastern New York State and its apparent resistance to hemlock woolly adelgid, this species might be an appropriate replacement species, especially in managed landscapes.

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