Decomposition of green foliage in eastern hemlock forests of southern New England impacted by hemlock woolly adelgid infestations

2006 ◽  
Vol 36 (5) ◽  
pp. 1331-1341 ◽  
Author(s):  
Richard C Cobb ◽  
David A Orwig ◽  
Steve Currie
Keyword(s):  
Soil Moisture ◽  
New England ◽  
Mass Loss ◽  
Organic Soil ◽  
Hemlock Woolly Adelgid ◽  
Adelges Tsugae ◽  
Eastern Hemlock ◽  
Functional Changes ◽  
Southern New England ◽  
Crown Health

This study examined the impacts of hemlock woolly adelgid (Adelges tsugae Annand) (HWA), a small, invasive insect, on foliar chemistry, forest floor microclimate, and subsequent green foliage decomposition in eastern hemlock (Tsuga canadensis (L.) Carrière) forests. We investigated the direct effects of HWA feeding and indirect changes in microclimate on foliar decomposition by incubating HWA-infested and uninfested foliage across eight eastern hemlock dominated stands in southern New England that had different histories of HWA infestation. Infested stands had much poorer average crown health (3.4 versus 1.4 crown loss ratings), higher percent open sky (10.9 ± 2.4 vs. 5.3 ± 0.5 gap light index), and lower organic soil moisture (0.83 ± 0.02 g·g–1 vs. 1.06 ± 0.05 g·g–1) than uninfested stands. There were no significant differences in percent C, percent N, or percent lignin for the excised foliage at the start of the study. However, after 120 days, decomposing foliage from infested trees had significantly higher N concentrations (1.83% ± 0.05% vs. 1.69% ± 0.02 %) and lower C/N ratios (29.9 ± 0.8 vs. 31.6 ± 0.2) than uninfested foliage, suggesting that HWA herbivory resulted in alterations of litter chemistry as decomposition progressed. Mass loss of common uninfested foliage was lower in uninfested hemlock stands than in infested ones (30.9% ± 0.7% vs. 34.2% ± 0.1%). These rates of mass loss were significantly correlated with microclimate factors and indicate that organic soil moisture levels are controlling decomposition in HWA-infested forests. Infestation by HWA causes virtually no direct feeding damage to foliage, but it does lead to several indirect and significant ecological and functional changes over the 10- to 20-year course of infestation and stand decline.

Eastern hemlock (Tsuga canadensis) regeneration in the presence of hemlock woolly adelgid (Adelges tsugae) and elongate hemlock scale (Fiorinia externa)

2011 ◽  
Vol 41 (12) ◽  
pp. 2433-2439 ◽  
Author(s):  
Evan L. Preisser ◽  
Mailea R. Miller-Pierce ◽  
Jacqueline Vansant ◽  
David A. Orwig
Keyword(s):  
New England ◽  
Tsuga Canadensis ◽  
Hemlock Woolly Adelgid ◽  
Adelges Tsugae ◽  
Eastern Hemlock ◽  
Invasive Pest ◽  
Seedling Density ◽  
Southern New England ◽  
Elongate Hemlock Scale ◽  
Fiorinia Externa

The hemlock woolly adelgid (Adelges tsugae Annand) is an invasive hemipteran that poses a major threat to eastern hemlock (Tsuga canadensis (L.) Carrière) forests in the United States. We conducted three surveys over a five-year period that assessed the density of hemlock woolly adelgid (HWA) and a second invasive pest, the elongate hemlock scale (EHS; Fiorinia externa Ferris), overstory hemlock mortality, and hemlock regeneration in ~140 hemlock stands (mean size, 44 ha; range, 7–305 ha) within a 7500 km2 north–south transect of southern New England (USA). In each stand, we rated HWA and EHS density on 50 hemlock trees using a 0–3 scale (0, none; 1, 1–10 organisms/m branch; 2, 11–100 organisms/m branch; 3, >100 organisms/m branch). Data on the presence or absence of regeneration were taken in 2005; in 2007 and 2009, we quantitatively assessed regeneration by counting the number of hemlock seedlings in three 16 m2 plots per stand. In 2005, 81% of sampled stands had HWA, 72% had EHS, and 66% had hemlock regeneration. In 2007, 86% of sampled stands had HWA, 79% had EHS, and 46% had hemlock regeneration. In 2009, 91% of stands had HWA, 87% had EHS, and 37% had hemlock regeneration. The proportion of stands with hemlock regeneration declined 46% between 2005 and 2009, and hemlock seedling density declined 71% between 2007 and 2009. A best-fit model selection algorithm found that this decrease was inversely correlated with stand-level adelgid density. There was no correlation between the change in seedling density and stand-level density of the elongate hemlock scale. The apparent decline in regeneration suggests that the ecosystem-level changes currently occurring in southern New England may be difficult to reverse.

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.

Multi-year ecosystem response to hemlock woolly adelgid infestation in southern New England forests

2008 ◽  
Vol 38 (4) ◽  
pp. 834-843 ◽  
Author(s):  
David A. Orwig ◽  
Richard C. Cobb ◽  
Anthony W. D’Amato ◽  
Matthew L. Kizlinski ◽  
David R. Foster
Keyword(s):  
New England ◽  
Forest Floor ◽  
Hemlock Woolly Adelgid ◽  
Adelges Tsugae ◽  
Net N Mineralization ◽  
Eastern United States ◽  
Ecosystem Response ◽  
Total N ◽  
Invasive Pests ◽  
Southern New England

The introduced hemlock woolly adelgid (HWA) ( Adelges tsugae Annand) has generated widespread tree decline and substantial mortality of eastern hemlock ( Tsuga canadensis (L.) Carrière) throughout the eastern United States. To assess the magnitude of ecosystem response to this disturbance, we conducted a multi-year study of forests with and without damage from HWA. Infested forests had significantly higher HWA-induced foliar loss and significantly lower forest floor C:N ratios and soil organic matter than uninfested forests. There were no significant soil temperature differences among stand types, although infested stands did have lower forest floor soil moisture than uninfested stands. Net nitrification and net N mineralization rates were significantly higher in infested versus uninfested forests by the second and third year of this study, respectively. In addition, total N pools and resin bag capture of NH4 and NO3 were significantly higher in infested versus uninfested forests throughout this study. Increases in N were likely due to a combination of factors including enhanced decomposition, reduced uptake of water and N by declining trees, sparse understory vegetation, and N-enriched throughfall from infested canopies. These results confirm that invasive pests can initiate substantial changes in ecosystem function soon after infestation occurs, prior to substantial overstory mortality or understory reorganization.

scholarly journals Eastern Hemlock Decline in Riparian Areas from Maine to Alabama

2011 ◽  
Vol 28 (2) ◽  
pp. 97-104 ◽  
Author(s):  
Daniel M. Evans ◽  
W. Michael Aust ◽  
C. Andrew Dolloff ◽  
Ben S. Templeton ◽  
John A. Peterson
Keyword(s):  
New England ◽  
Hemlock Woolly Adelgid ◽  
Adelges Tsugae ◽  
Ecosystem Dynamics ◽  
Eastern Hemlock ◽  
Forest Composition ◽  
Mountain Range ◽  
Riparian Areas ◽  
Conifer Species ◽  
Hemlock Decline

Abstract Eastern hemlock (Tsuga canadensis) in the Appalachian mountain range is threatened by the introduced hemlock woolly adelgid (Adelges tsugae). Potential impacts on riparian systems are great because of eastern hemlock's role as a foundation species that influences site soil, vegetation, and stream characteristics. We installed permanent research sites at 49 locations in riparian areas, from Maine to Alabama, to survey eastern hemlock health, measure stand dynamics, and predict near-term forest composition without eastern hemlock. This report summarizes the initial stand measurements from summer of 2008. We found hemlock woolly adelgid present at 25 of 49 stands from Massachusetts to Georgia, and all of these stands had some degree of hemlock decline. New England states, Ohio, western Pennsylvania, Kentucky, and Alabama had good hemlock health and no sign of hemlock woolly adelgid. Eighteen of the 49 sites had no nonhemlock conifer species in the overstory, and 30 of 49 sites had less than 5 m2 ha−1 of nonhemlock conifers. Without eastern hemlock, 25 of the stands would have more than 90% hardwood in the overstory, many of which are in the mid-Atlantic and southern states at sites dominated by shrubs in the understory such as Rhododendron maximum. Competition from shrubs may hinder stand regeneration after disturbance by hemlock woolly adelgid. On the basis of the abundance of hardwood species and lack of conifer species present in the overstory at many infested hemlock-dominated stands, these sites may convert to hardwood-dominated stands, which will affect terrestrial and aquatic ecosystem dynamics.

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.

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.

scholarly journals Hemlock woolly adelgid (Adelges tsugae) infestation affects water and carbon relations of eastern hemlock (Tsuga canadensis) and Carolina hemlock (Tsuga caroliniana)

2013 ◽  
Vol 199 (2) ◽  
pp. 452-463 ◽  
Author(s):  
Jean-Christophe Domec ◽  
Laura N. Rivera ◽  
John S. King ◽  
Ilona Peszlen ◽  
Fred Hain ◽  
...  
Keyword(s):  
Tsuga Canadensis ◽  
Hemlock Woolly Adelgid ◽  
Adelges Tsugae ◽  
Eastern Hemlock
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