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(a) Late-instar gypsy moth larva. Photograph: Minnesota Department of Natural Resources Archives, www. forestryimages.org. (b) Gypsy moth larvae on a tree trunk during an outbreak in the Catskill Mountains, New York, July 2005. Most of these larvae have died from fungal or viral diseases. Photograph: Lewis De Jaegher. (c) Range of general infestation of gypsy moth in the eastern United States as of 2002 (striped area) and approximate range of susceptible forests (green shaded area). The map is from the USDA Forest Service.
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The forests of eastern North America have been subjected to repeated introductions of exotic insect pests and pathogens over
the last century, and several new pests are currently invading, or threatening to invade, the region. These pests and pathogens
can have major short- and long-term impacts on forest ecosystem processes such as productivity, n...
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Citations
... For over a century, anthropogenic activities have facilitated the biological invasions of exotic pests and pathogens into new habitats throughout the world [1][2][3][4][5][6]. In North ...
... For over a century, anthropogenic activities have facilitated the biological invasions of exotic pests and pathogens into new habitats throughout the world [1][2][3][4][5][6]. In North America, introduced pathogens have caused significant population declines in numerous tree species [2,[5][6][7][8][9][10]. ...
... For over a century, anthropogenic activities have facilitated the biological invasions of exotic pests and pathogens into new habitats throughout the world [1][2][3][4][5][6]. In North America, introduced pathogens have caused significant population declines in numerous tree species [2,[5][6][7][8][9][10]. Laurel wilt is a vascular wilt disease that has plagued various North American members of the Lauraceae dating back to the 2002 introduction of the Asian redbay ambrosia beetle [Xyleborus glabratus Eichhoff (Coleoptera: Curculionidae: Scolytinae)] into the southeastern United States [11][12][13][14][15]. X. glabratus serves as the primary vector of the disease by spreading its fungal symbiont, Harringtonia lauricola T.C. Harr., Fraedrich and Aghayeva, to laurel hosts upon initial attempts to colonize them and subsequently eliciting defensive responses in the host, ultimately leading to mortality [11][12][13][16][17][18]. ...
Laurel wilt, a fungal disease (Harringtonia lauricola T.C. Harr., Fraedrich and Aghayeva) spread by the Asian redbay ambrosia beetle [Xyleborus glabratus Eichhoff (Coleoptera: Curculionidae: Scolytinae)], presents an imminent threat to North American members of the Lauraceae family, having caused extensive mortality in several species, especially redbay (Persea borbonia L. Spreng). Varying levels of disease resistance have been recorded in redbay under controlled conditions. To investigate if previously monitored putatively resistant field redbays have influenced the regeneration and survival of conspecifics within the surrounding 0.08 ha, a survey was conducted in 2018-19 and compared to similar data collected years prior (2008-09, 2013) along the coasts of Florida, Georgia, and South Carolina, United States. Plots were originally established at six disease-infested study sites around large redbay (>7.5-cm diameter at breast height (1.37 m) (DBH)) that had survived the initial laurel wilt disease epidemic that began in approximately 2007. In 2018-19, a subset of 61 plots within 16 m of the original “survivor” redbay were recorded and compared to previous surveys. Among the original redbay selected for resistance, 22 of 61 (36%) survivors across all sites were alive in 2018 with survival rates varying from 0 to 70% between survey periods (average mortality 3.6%/year). Trees that died in years since 2008-09 had their plots reclassified as susceptible or “suscepts”. Changes in mean quadratic diameter at 1.37 m of redbay plots near survivors were significantly greater than those near suscepts, and in 2018-19, the average diameter of redbay near survivors was 7.62 cm vs. 4.90 cm for suscepts. The diameter distribution of dead and live redbay in the whole population showed a decrease in live individuals surviving past 8 cm DBH in 2018–2019, but 20 of 22 survivor candidate trees were larger than 8 cm DBH. Regeneration was occurring both clonally and sexually and tended to be greater near suscepts, but midstory resprouts per hectare and understory seedlings interacted significantly with the site and the latter differed between sites. These findings indicate that redbay is regenerating in these ecosystems, and disease resistance may allow for increased average tree size for some individuals, but an upper size threshold of around 8 cm DBH may still exist for much of the population. In addition, the importance of site variables in regeneration was apparent, making either local genetic or environmental effects an important topic for future research. Continuing to monitor these survivors while locating new candidates for disease screenings and breeding, preventing the introductions of new strains of H. lauricola, shedding light on the nature of resistance and its heritability, and initiating outplanting trials with resistant germplasm are instrumental steps in bringing redbay back to prominence in its historical range.
... Eastern US forests are a globally significant carbon sink, and our results provide no evidence that intrinsic successional dynamics and the current disturbance regimes in those forests should be expected to reduce the strength of that sink over the coming decades. There are clearly potential threats that could reduce the strength of the sink, particularly from introduced forest pests and pathogens (Lovett et al., 2006(Lovett et al., , 2016Peltzer et al., 2010). Climate change can clearly be expected to alter the absolute values of both carbon increment and loss to mortality in all six of the forest types (Dangal et al., 2014) and could well shift the point at which live tree biomass begins to stabilize in an old-growth stand. ...
Carbon sequestration in the forests of the eastern United States is an important offset to the country's CO 2 emissions. Much of the eastern forestland is the product of reforestation of abandoned agricultural land or recovery following clear‐cutting over a century ago. This has led to concerns that eastern forests are even‐aged and that rates of carbon sequestration will decline as forests increase in carbon. Our objective was to examine the successional dynamics of forest carbon sequestration—using live tree carbon stocks as a proxy for successional status—for the six broadly defined forest types present in the region. We used datasets from the National Forest Inventory (NFI) for the 31 US states from Minnesota south to Louisiana and eastward and analyzed live tree net carbon increment for 2007–2021, the period for which NFI plot remeasurement data were available for all 31 states. Spruce–fir and southern pines were the only forest types for which carbon increment declined even modestly over a significant fraction of the range of live tree carbon observed in the region, and southern pine–hardwood forests were the only forests in which predicted sequestration in live tree carbon declined to zero within the range of carbon stocks observed in the region. Northern hardwood–conifer forests, oak–hickory forests, and lowland forests experienced either no decline or a slight increase in sequestration in live tree carbon across the range of successional status observed in the region. Thus, the average stocks of live tree carbon per unit area increased steadily over the study period. At some point in succession, rates of mortality are expected to increase and balance gross growth, leading to zero net sequestration in live tree carbon. Mature and old‐growth stands, however, are rare in all six forest types, and mortality as a fraction of live tree carbon for all six forest types declined across the range of successional status present in the region. Our results thus provide no support for the hypothesis that the successional dynamics of forests in this region can be expected to lead to near‐term declines in net carbon sequestration.
... Changes in climate, acid rain, nitrogen and phosphorus depositions; forestry operations and forest regrowth; rapidly expanding human populations, urbanization and introduction of non-native, plants, animals, pests and diseases are all affecting biota of the region simultaneously (Driscoll et al., 2001(Driscoll et al., , 2003Foster & Aber, 2004;Foster et al., 2002;Lovett et al., 2006). More recently, introduced earthworms and the high browsing pressure exerted by deer (Odocoileus virginianus (Zimmermann, 1780), henceforth deer) have received increasing attention for their capabilities to transform ecosystems. ...
Forests in northeastern North America have undergone dramatic transformations due to losses and gains of species, changes in land use and pollution. Historic stressors combined with new threats of white‐tailed deer and non‐native earthworms are threatening native plant diversity.
We developed a transplant approach to gauge the importance of deer and earthworms in allowing understorey species recovery. This approach, instead of censusing existing individuals, avoids problems imposed by past land use, dispersal limitation or climate change. We selected 20 native species in different taxonomic and functional groups, with different palatability to herbivores, different life‐history strategies and a range of plant traits (%N, specific leaf area [SLA]) and our selection included species indicative of primary or secondary forests.
Using a 2 × 2 full factorial design, we planted species into fenced and unfenced plots with and without existing earthworm invasions in five secondary hardwood forests. We measured survival, plant growth and reproduction over 4–6 years.
Earthworm biomass was associated with increased survival of 13 and decreased survival of five species. Surviving transplants grew taller (eight of 12 species measured) and wider (seven of nine species measured) in earthworm plots but were more likely to be attacked by insects. Excluding deer benefitted most species' survival and growth.
Taxonomic class, SLA or foliar N did not affect species sensitivity to deer or earthworms.
Synthesis . Secondary forests in our region continue to provide suitable habitat for native species. Earthworms and deer are major structuring forces affecting survival and growth of our transplant species, but their impacts are species‐specific and change over time. We observed poorly recognized indirect negative impacts of deer on many unpalatable species. Taxonomic class and differences in plant traits offered no important insights regarding vulnerability to deer or earthworms. Transplanting native species into secondary forests can succeed in restoring understorey communities, but will require fencing or substantial deer population reductions to be successful long term.
... variaciones climáticas extremas, perturbaciones humanas, patógenos y la presencia de plagas(Lovett et al., 2006;Gómez-Guerrero et al., 2021). Estas últimas no solo afectan a la producción de madera(Kurz et al., 2008;Ramsfield et al., 2016), sino también a los servicios ecosistémicos como la captura de carbono, prevención de la erosión del suelo, captación de agua y provisión de hábitats(Schowalter, 2012). ...
Las plagas forestales representan una de las principales causas de disturbio en los bosques templados de México. Ips confusus ataca a Pinus cembroides después de intensas sequías. El objetivo del presente estudio fue evaluar tanto el impacto por I. confusus, como del clima en el crecimiento radial de un bosque de P. cembroides en el municipio Carichí, Chihuahua, México. Se obtuvieron núcleos de crecimiento de árboles atacados (AA) y de no atacados (ANA) de la misma especie. Se dataron 53 series dendrocronológicas con una extensión máxima de 1776 a 2012 (AA=24 y ANA=29). A partir de 1998, se observó un crecimiento diferencial en el área basal entre AA y ANA. Al momento de la muerte del arbolado (2012), se registró una diferencia de más de 100 % (AA=8.03±1.53 cm 2 año-1 , y ANA=17.7±1.74 cm 2 año-1 , p<0.001). Los ANA mostraron una sensibilidad superior a variables climáticas que los AA, con una mayor sincronía en los últimos años. A nivel dosel, se determinó una correlación con el Índice de Vegetación de Diferencia Normalizada (NDVI, r=0.51, p<0.05) exclusivamente para ANA. Sin embargo, los AA fueron más sensibles a condiciones de sequía, con base en el Índice de Severidad de Sequia de Palmer (PDSI, r=0.53, p<0.05). Esto sugiere que condiciones de sequía previas (hasta 10 años) predisponen menor crecimiento radial de P. cembroides y favorece el ataque de plagas.
... Insect-induced defoliation is a significant disturbance affecting tree growth, with consequences ranging from reduced forest productivity (Clark et al., 2010) to alterations in canopy habitats and their climatic buffering capacities (Lovett et al., 2006;De Frenne et al., 2021). Interestingly, insect-induced defoliation events can also trigger beneficial ecological dynamics within forest stands, acting as agents of disturbance. ...
In this study, we investigate the immediate and short-term consequences of defoliation by the spongy moth Lymantria dispar on secondary growth of oaks (Quercus robur L. and Quercus petraea (Matt.) Liebl.), including the interplay between defoliation and water availability during the defoliation period within a large-scale field experiment in southeastern Germany. Furthermore, the impact of defoliation on oak secondary growth is explored retrospectively based on tree core measurements. Within the large-scale filed experiment, secondary growth of 880 oaks in 44 oak-dominated stands was monitored using permanent girth tapes over a three-year period following a spongy moth outbreak. Insecticide treatments were applied to half of the plots to obtain trees without defoliation, and canopy cover dynamics were subsequently monitored ground based and from satellites in all plots. We found that moth defoliation significantly reduced oak secondary growth by 10-60% during the outbreak year, with the impact on secondary growth being directly proportional to defoliation intensity. The negative impact of defoliation on secondary growth was aggravated by increased water availability during the outbreak year. In the post-outbreak year, secondary growth of oaks that had endured mild defoliation was no longer different from that of non-defoliated oaks. In contrast, oaks that had experienced substantial defoliation still exhibited a significant 10-30% reduction in secondary growth. Regardless of defoliation intensity, no further reduction in secondary growth was detected two years after the event compared to control trees. Our complementary retrospective analysis, utilizing core samples from oaks previously subjected to a defoliation event under distinct weather conditions, disclosed a strikingly analogous recovery of secondary growth from defoliation instigated by the spongy moth. Thus, validating that our experimental findings possess broad temporal transferability.
... Short-term impacts on trees and forests include defoliation, decreased vigor, and reduced growth (Ellison et al., 2018;Heuss et al., 2018;Engelken et al., 2020). Long-term impacts include ecosystem-wide effects such as species loss, tree death, shifts in nutrient cycling, alterations in wildlife habitat, and changes to above and belowground productivity, with these changes often constituting a lasting driver of processes in an ecosystem (Lovett et al., 2006). Evaluating the potential ecological impacts of a given invasive pest requires consideration of the distinctiveness and abundance of the host species impacted and the short and long-term effects on individual trees and ecosystem functions and dynamics (Lovett et al., 2006). ...
... Long-term impacts include ecosystem-wide effects such as species loss, tree death, shifts in nutrient cycling, alterations in wildlife habitat, and changes to above and belowground productivity, with these changes often constituting a lasting driver of processes in an ecosystem (Lovett et al., 2006). Evaluating the potential ecological impacts of a given invasive pest requires consideration of the distinctiveness and abundance of the host species impacted and the short and long-term effects on individual trees and ecosystem functions and dynamics (Lovett et al., 2006). Asian longhorned beetle (ALB), Anoplophora glabripennis (Coleoptera: Cerambycidae), is an invasive pest that has caused significant ecological and economic effects on urban forests in North America. ...
... Nonnative invasive insects and fungal diseases can functionally eliminate host tree species from a forest and shift overstory species dominance, such as in the historical case of chestnut blight and the ongoing threat of emerald ash borer (Lovett et al. 2006, Herms et al. 2014. Pre-emptive salvage logging or sanitation harvests of host species can have a similar effect (Elliott and Swank, 2008;Herms and McCullough, 2014;Waring and O'Hara, 2005;Kizlinski et al., 2002). ...
The United States has been experiencing an influx of nonnative pests due to increased globalization, and these pests have the potential to permanently alter the composition, structure, and function of forests. Asian long-horned beetle (ALB) is an invasive pest detected in Worcester, MA in 2008, where it invaded both urban and natural forested areas. As a part of the eradication measures (full host removals, herbicide treatments, and stump grinding), all host tree species, primarily Acer spp. were removed to prevent the spread of ALB. While these eradication measures successfully eliminate ALB, little is known about their effects on forest structural and compositional conditions and recovery over time. To address this, we examined forest compositional and structural development following eradication treatments and in adjacent unimpacted forested areas. Overall, our results indicated forest recovery followed similar pathways documented after natural disturbances in southern New England forests. There was little difference among eradication treatments in terms of the resultant forest composition and structure. Overall, forest types shifted to primarily oak-hickory or pine dominance following the removal of all Acer spp. Notably, maple species were present in high numbers in the regeneration layer regardless of treatment, followed by other early colonizing species. Red maple (Acer rubrum) was the most abundant sapling and seedling species and stump sprouting occurred at 60% of sites but was absent in untreated areas. These results suggest that ALB management does not drastically alter forest compositional dynamics in these mixed species forests in the short term, despite significant reductions in the abundance of mature host species through eradication treatments.
... Specifically, studies have demonstrated unprecedented compositional changes in successional and maturing forests throughout the eastern United States (e.g., Abrams, 1998Abrams, , 2003, including in the North Carolina Piedmont (Golubiewski and Urban, 1998;Schwartz, 2007;Israel, 2011;Peet et al., 2014a). These deviations include novel changes brought on by increasing populations of white-tailed deer (Odocoileus virginiana; Stromayer and Warren, 1997;Russell et al., 2001;Côté et al., 2004;Kribel et al., 2011;White, 2012), increasing impacts of exotic species on native flora (Lovett et al., 2006;Israel, 2011;Luken, 2014), increases in atmospheric CO 2 and nitrogen deposition (e.g., Bobbink et al., 2010;Peters et al., 2013), and major disturbances such as hurricanes (Woods, 2004;Xi et al., 2008Xi et al., , 2012Xi et al., , 2019Xi and Peet, 2011). ...
... Since the early twentieth century, many of the world's temperate forests have been disturbed by introduced pests and pathogens (Lovett et al. 2006). Several of these introductions have resulted in the decline of foundation tree species which has far reaching impacts on forest ecosystem processes and biodiversity (Ellison et al. 2005). ...
Invasive fungal pathogens are an increasing problem globally and can cause strong effects on forest ecosystems. In this study, we contrast vegetation surveys in eutrophic elm (Ulmus glabra) and ash (Fraxinus excelsior) forests in southern Sweden, conducted just prior to the arrival of Dutch elm disease (DED) in 1989, and then again in 2021, several years after ash dieback (ADB) began. At the sample plot scale, species richness (α–diversity) of the upper tree layer strongly decreased from 1989 to 2021, and the mean cover of elm decreased from 27 to 1% and of ash from 29 to 13%. In the lower tree and shrub layers, elm and ash were replaced by other, mainly shade-tolerant, tree species. The cover and richness of the shrub layer increased in previously elm-dominated stands but not in ash-dominated stands. The extensive loss of canopy cover in elm stands caused a larger change in upper tree layer species composition and increased compositional variability (β-diversity) between plots when compared to the ash stands. The direction of the changes in tree layer composition between the surveys varied with soil moisture and nutrient availability. While beech increased in less eutrophic plots, more nutrient-rich plots changed toward hornbeam or small-leaved lime, and wetter plots turned toward alder and bird cherry. Hence, our results indicate increased compositional diversity and alternative successional pathways for community reorganization following DED and ADB. Future research will reveal if these pathways will later merge or further split.
... Forests store 2.4 ± 0.4 Pg carbon (C) annually in biomass and soils (Pan et al., 2011), yet the future of this large C sink is uncertain as global change continues to reshape disturbance regimes (Williams et al., 2016;Keenan and Williams, 2018;Wang et al., 2021). Across the world's forests, disturbance agents including introduced insects, fungal pathogens, and extreme weather are becoming more frequent and spatially extensive (Lovett et al., 2006;Cohen et al., 2016;Williams et al., 2016). Unlike severe disturbances (i.e., killing a larger fraction of trees, sensu Frelich and Reich, 1998) such as stand-replacing wildfires or hurricanes, hostspecific insects and fungal pathogens frequently result in spatially heterogeneous tree mortality and partial, rather than total, canopy loss . ...
Across the globe, the forest carbon sink is increasingly vulnerable to an expanding array of low- to moderate-severity disturbances. However, some forest ecosystems exhibit functional resistance (i.e., the capacity of ecosystems to continue functioning as usual) following disturbances such as extreme weather events and insect or fungal pathogen outbreaks. Unlike severe disturbances (e.g., stand-replacing wildfires), moderate severity disturbances do not always result in near-term declines in forest production because of the potential for compensatory growth, including enhanced subcanopy production. Community-wide shifts in subcanopy plant functional traits, prompted by disturbance-driven environmental change, may play a key mechanistic role in resisting declines in net primary production (NPP) up to thresholds of canopy loss. However, the temporal dynamics of these shifts, as well as the upper limits of disturbance for which subcanopy production can compensate, remain poorly characterized. In this study, we leverage a 4-year dataset from an experimental forest disturbance in northern Michigan to assess subcanopy community trait shifts as well as their utility in predicting ecosystem NPP resistance across a wide range of implemented disturbance severities. Through mechanical girdling of stems, we achieved a gradient of severity from 0% (i.e., control) to 45, 65, and 85% targeted gross canopy defoliation, replicated across four landscape ecosystems broadly representative of the Upper Great Lakes ecoregion. We found that three of four examined subcanopy community weighted mean (CWM) traits including leaf photosynthetic rate ( p = 0.04), stomatal conductance ( p = 0.07), and the red edge normalized difference vegetation index ( p < 0.0001) shifted rapidly following disturbance but before widespread changes in subcanopy light environment triggered by canopy tree mortality. Surprisingly, stimulated subcanopy production fully compensated for upper canopy losses across our gradient of experimental severities, achieving complete resistance (i.e., no significant interannual differences from control) of whole ecosystem NPP even in the 85% disturbance treatment. Additionally, we identified a probable mechanistic switch from nutrient-driven to light-driven trait shifts as disturbance progressed. Our findings suggest that remotely sensed traits such as the red edge normalized difference vegetation index (reNDVI) could be particularly sensitive and robust predictors of production response to disturbance, even across compositionally diverse forests. The potential of leaf spectral indices to predict post-disturbance functional resistance is promising given the capabilities of airborne to satellite remote sensing. We conclude that dynamic functional trait shifts following disturbance can be used to predict production response across a wide range of disturbance severities.
... Spongy moth outbreaks can be particularly detrimental to chewing herbivores with ecological niche overlap with the spongy moth. Besides the risk of starvation in situations of extreme defoliation (Luciano & Lentini, 1999), outbreaks expose canopy herbivores to elevated concentrations of plant defense compounds, increased hazards from natural enemies and pathogens (Redman & Scriber, 2000), as well as altered light, moisture, and nutrient regimes (Lovett et al., 2006). However, the ecological trade-offs between insecticide-based and "hands-off" management approaches have not been extensively investigated in practical settings. ...
... Because many summer species can exploit alternative host species, admixing tree species that are generally ignored by spongy moth caterpillars may foster the tolerance of herbivore communities to defoliation. Though likely ineffective to preserve oak specialists, the integration and maintenance of resistant tree species should provide refugia for polyphagous species and contribute to maintaining a degree of canopy cover to mitigate the alteration of microclimatic conditions in the forest interior (Lovett et al., 2006). In Bavarian oak stands, the species with the most potential in this regard is the field maple Acer campestre L., as it is well adapted to susceptible forest types, generally avoided by spongy moth caterpillars, and used as a secondary host by many oakfeeding Lepidoptera. ...
Outbreaks of the spongy moth Lymantria dispar can have devastating impacts on forest resources and ecosystems. Lepidoptera‐specific insecticides, such as Bacillus thuringiensis var. kurstaki (BTK) and tebufenozide, are often deployed to prevent heavy defoliation of the forest canopy. While it has been suggested that using BTK poses less risk to non‐target Lepidoptera than leaving an outbreak untreated, in situ testing of this assumption has been impeded by methodological challenges. The trade‐offs between insecticide use and outbreaks have yet to be addressed for tebufenozide, which is believed to have stronger side effects than BTK. We investigated the short‐term trade‐offs between tebufenozide treatments and no‐action strategies for the non‐target herbivore community in forest canopies. Over 3 years, Lepidoptera and Symphyta larvae were sampled by canopy fogging in 48 oak stands in southeast Germany during and after a spongy moth outbreak. Half of the sites were treated with tebufenozide and changes in canopy cover were monitored. We contrasted the impacts of tebufenozide and defoliator outbreaks on the abundance, diversity, and functional structure of chewing herbivore communities. Tebufenozide treatments strongly reduced Lepidoptera up to 6 weeks after spraying. Populations gradually converged back to control levels after 2 years. Shelter‐building species dominated caterpillar assemblages in treated plots in the post‐spray weeks, while flight‐dimorphic species were slow to recover and remained underrepresented in treated stands 2 years post‐treatment. Spongy moth outbreaks had minor effects on leaf chewer communities. Summer Lepidoptera decreased only when severe defoliation occurred, whereas Symphyta declined 1 year after defoliation. Polyphagous species with only partial host plant overlap with the spongy moth were absent from heavily defoliated sites, suggesting greater sensitivity of generalists to defoliation‐induced plant responses. These results demonstrate that both tebufenozide treatments and spongy moth outbreaks alter canopy herbivore communities. Tebufenozide had a stronger and longer lasting impact, but it was restricted to Lepidoptera, whereas the outbreak affected both Lepidoptera and Symphyta. These results are tied to the fact that only half of the outbreak sites experienced severe defoliation. This highlights the limited accuracy of current defoliation forecast methods, which are used as the basis for the decision to spray insecticides.
