Alien invasive insects such as gypsy moth, hemlock woolly adelgid, and emerald ash borer continue to disturb the mixed deciduous and hemlock forests of eastern North America by causing wide-scale ...defoliation, decline and/or mortality of their hosts. Some of the most devastating species are spreading in “defense free space”, causing extensive mortality of hosts that are inherently susceptible, perhaps due to their lack of coevolutionary history with the invader. These disturbances have altered the dynamics of canopy gaps, coarse woody debris, biogeochemical cycling, and ecological interactions among organisms in terrestrial and aquatic systems, with consequent effects on forest composition, structure, and function. Populations of indigenous species specialized to particular habitats and/or host trees are most likely to decrease, while some generalist and opportunistic species may increase in invaded forests, including exotic plants as their facilitation by alien insects sparks an “invasional meltdown”. Although poorly documented, alien insects may induce positive feedback effects on ecological processes and interactions. For example, effects of herbivory on foliar chemistry may indirectly alter tri-trophic interactions of indigenous herbivores on their shared hosts, slow rates of terrestrial nutrient cycling, and decrease productivity of aquatic habitats based on allochthonous inputs. Tactics used to eradicate or suppress alien insects in forests such as insecticide applications, biological control, and silvicultural prescriptions can also have ecological impacts. As alien insects continue to establish and spread in forests of eastern North America, their already pervasive effects on ecological interactions and ecosystem processes will continue to magnify.
Emerald ash borer (Agrilus planipennis Fairmaire) (EAB), an alien invasive wood-boring buprestid beetle, is causing large-scale decline and mortality of the most widely distributed species of ash ...(Fraxinus spp.) trees endemic to eastern North America. We determined which arthropod species that are associated with ash may become threatened, endangered, and co-extinct with the demise of ash as a dominant tree species. A literature survey revealed that 43 native arthropod species in six taxonomic groups (Arachnida: Acari; Hexapoda: Coleoptera, Diptera, Hemiptera, Hymenoptera, and Lepidoptera) are known to be associated only with ash trees for either feeding or breeding purposes, and thus face high risk of endangerment. Most of these species are gall-formers followed by folivores, subcortical phloem/xylem feeders, sap feeders, and seed predators. Another 30 arthropod species are associated with 1-2 host plants in addition to ash, and herbivory on these hosts may increase as these arthropods shift from declining ash trees. Extirpation of arthropods dependent upon ash may unleash multiple extinctions of affiliated species with which they may be inextricably linked. The demise of North American ash species due to EAB is expected to lead to biotic loss with cascading ecological impacts and altered processes within forested ecosystems.
Emerald ash borer (EAB;
Agrilus planipennis
) has killed millions of ash trees and threatens ash throughout North America, and long-term persistence of ash will depend on the potential for ...regeneration. We quantified ash demography, including mortality and regeneration, of
Fraxinus americana
(white ash),
Fraxinus pennsylvanica
(green ash), and
Fraxinus nigra
(black ash) in mixed hardwood forests near the epicenter of the EAB invasion in southeastern Michigan and throughout Ohio. Plots were established across a gradient of ash densities. Ash was the most important species in hydric sites, and ranked second among all species in mesic and xeric sites. In sites nearest the epicenter in Michigan, ash mortality exceeded 99 % by 2009, and few or no newly germinated ash seedlings were observed, leaving only an “orphaned cohort” of established ash seedlings and saplings. As ash mortality increased, the number of viable ash seeds in soil samples decreased sharply, and no viable seeds were collected in 2007 or 2008. In Ohio sites farther from the epicenter, densities of new ash seedlings were much higher in plots with healthy ash trees compared to plots where trees had died. EAB was still present in low densities in Michigan and Ohio stands in 2012 where average mortality of ash was nearly 100 %. The future of ash at these sites will depend on the outcome of the dynamic interaction between the orphaned cohort of previously established ash seedlings and saplings and low density EAB populations.
Manganese (Mn) deficiency is a widespread occurrence across different landscapes, including agricultural systems and managed forests, and causes interruptions in the normal metabolic functioning of ...plants. The microelement is well-characterized for its role in the oxygen-evolving complex in photosystem II and maintenance of photosynthetic structures. Mn is also required for a variety of enzymatic reactions in secondary metabolism, which play a crucial role in defense strategies for trees. Despite the strong relationship between Mn availability and the biosynthesis of defense-related compounds, there are few studies addressing how Mn deficiency can impact tree defense mechanisms and the ensuing ecological patterns and processes. Understanding this relationship and highlighting the potentially deleterious effects of Mn deficiency in trees can also inform silvicultural and management decisions to build more robust forests. In this review, we address this relationship, focusing on forest trees. We describe Mn availability in forest soils, characterize the known impacts of Mn deficiency in plant susceptibility, and discuss the relationship between Mn and defense-related compounds by secondary metabolite class. In our review, we find several lines of evidence that low Mn availability is linked with lowered or altered secondary metabolite activity. Additionally, we compile documented instances where Mn limitation has altered the defense capabilities of the host plant and propose potential ecological repercussions when studies are not available. Ultimately, this review aims to highlight the importance of untangling the effects of Mn limitation on the ecophysiology of plants, with a focus on forest trees in both managed and natural stands.
•Manganese (Mn) is an important element for the functioning of plant secondary metabolism.•Mn deficiency has been linked to decreased concentrations of defense-related secondary metabolites.•Mn deficiency is correlated with increased susceptibility to pests and pathogens.•The ecophysiological impacts of Mn deficiency can be detrimental but few studies assess this relationships in woody systems.
Abstract Working forests comprise a large proportion of forested landscapes in the southeastern United States and are important to the conservation of bats, which rely on forests for roosting and ...foraging. While relationships between bat ecology and forest management are well studied during summer, winter bat ecology remains understudied. Hence, we aimed to identify the diet composition of overwintering bats, compare the composition of prey consumed by bat species, and determine the potential role of forest bats as pest controllers in working forest landscapes of the southeastern U.S. Coastal Plain. During January to March 2021–2022, we captured 264 bats of eight species. We used DNA metabarcoding to obtain diet composition from 126 individuals of seven bat species identifying 22 orders and 174 families of arthropod prey. Although Coleoptera, Diptera, and Lepidoptera were the most consumed orders, we found that bats had a generalist diet but with significant differences among some species. We also documented the consumption of multiple insect pests (e.g., Rhyacionia frustrana) and disease vectors (e.g., Culex spp). Our results provide important information regarding the winter diet of bats in the southeastern U.S. Coastal Plain and their potential role in controlling economically relevant pest species and disease vectors.
1) Many wild bee species interact with soil either as a nesting substrate or material. These soil interactions create a risk of exposure to agrochemicals such as imidacloprid or other neonicotinoid ...pesticides that can persist in soil for months after application. At the landscape level, concentrations of imidacloprid residue in soil are limited to the immediate treatment area, and thus risks to soil-interacting bees could be low if they avoid contaminated soils. 2) We utilized Osmia lignaria (Say), a solitary cavity nesting bee which collects mud to partition and seal nests, and conducted two laboratory experiments to test whether nesting females select or avoid soils containing various levels of imidacloprid residue. For the first experiment, we assessed behavioral responses of females to treated soil utilizing a choice arena and pairing various choices of soil with imidacloprid residues ranging between 0 and 780 ppb. For the second experiment, we developed a laboratory assay to assess soil selection of actively nesting O. lignaria, by providing choices of contaminated soil between 0 and 100 ppb and 0 and 1,000 ppb to nesting females. 3) We found no evidence that O. lignaria females avoided any level of imidacloprid contamination, even at the highest residue level (1,000 ppb) in both the experiments, which may have implications for risk. The in situ nesting methodology developed in this study has future applications for research on soil or pollen preferences of cavity nesting Osmia species, and potential for breeding of O. lignaria in laboratory.
Higher temperatures projected under current climate change models are generally predicted to exert an overall positive effect on the success of invasive insects through increased survivability, ...developmental rates and fecundity, and by facilitating geographic range expansion. However, these effects have primarily focused on the shifts in winter temperatures with limited attention to the role that summer heat may play in shaping species ranges or fitness. We examined the thermal ecology of an ecologically important invasive forest insect, the hemlock woolly adelgid (
Adelges tsugae
), by determining survival during its summer dormancy phase under increasing temperature regimens. From laboratory and field experiments, we documented a positive association between increased temperatures and duration of exposure, and
A. tsugae
mortality.
Adelges tsugae
mortality was minimal (<20%) when exposed to summer temperatures characteristic to its native range (<25 °C), but markedly increased (up to 100%) when exposed to temperatures that occur occasionally or rarely in natural settings (>30 °C). At the warmest, southernmost edge of their range, field mortality of
A. tsugae
ranged from 8.5 to 81.9% and was strongly correlated with site temperature regimens. Further, we found no significant differences in
A. tsugae
survival between populations collected from Maine and Georgia, and over a 3-year period within Georgia, indicating that
A. tsugae
may not be acclimating to heat. These results highlight the importance of including summer temperatures in studies regarding increased temperatures on insect dynamics, and may alter historical predictions of climate change impacts on invasive insects and the conservation of forest ecosystems.
Abstract
Of the more than five hundred and fifty species of North American bark beetles (Coleoptera: Curculionidae, Scolytinae), approximately twenty species occasionally cause large amounts of tree ...mortality in conifer forests. During 2000–2020, trends in bark beetle impacts changed dramatically across North America compared to those observed during the mid- to late 20th century. We review tools and tactics available for bark beetle suppression and prevention and provide an overview of temporal and spatial trends in bark beetle impacts in North American forests during 2000–2020. Higher impacts were observed for several bark beetle species in western North America accompanied by substantial declines in eastern North America driven by large reductions in southern pine beetle (Dendroctonus frontalis) activity in the southeastern United States. Regional differences likely result from a higher species richness of both bark beetles and their hosts in western North America, stronger direct and indirect effects of climate change (warming and drying) on bark beetles in western North America, and differences in forest composition, management history, and other abiotic stressors and disturbances.
Study Implications
Compared to the mid- to late 20th century, bark beetles have had increased impacts in western North America and reduced impacts in eastern North America, the latter driven by large reductions in southern pine beetle (Dendroctonus frontalis) activity in the southeastern United States. We review tools and tactics available to foresters and other natural resource managers to reduce the negative impacts of bark beetles on forests. Furthermore, we provide several potential explanations for recent trends in bark beetle impacts between eastern and western North America.
Society is confronted by interconnected threats to ecological sustainability. Among these is the devastation of forests by destructive non-native pathogens and insects introduced through global ...trade, leading to the loss of critical ecosystem services and a global forest health crisis. We argue that the forest health crisis is a public-good social dilemma and propose a response framework that incorporates principles of collective action. This framework enables scientists to better engage policymakers and empowers the public to advocate for proactive biosecurity and forest health management. Collective action in forest health features broadly inclusive stakeholder engagement to build trust and set goals; accountability for destructive pest introductions; pooled support for weakest-link partners; and inclusion of intrinsic and nonmarket values of forest ecosystems in risk assessment. We provide short-term and longer-term measures that incorporate the above principles to shift the societal and ecological forest health paradigm to a more resilient state.
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