The emerald ash borer (EAB) is rapidly spreading throughout Eastern North America and devastating ecosystems where ash is a component tree. This rapid and sustained loss of ash trees has already ...resulted in ecological impacts on both terrestrial and aquatic ecosystems and is projected to be even more severe as EAB invades ash dominated wetlands of the western Great Lakes region. We propose a Special Issue that will address current research documenting ecological impacts of EAB in forest ecosystems, as well as management approaches to mitigate those impacts. Prospective authors are invited to contribute original researches to this Special Issue of Forests. Topics may include, but are not limited to: Managements of ash forests and potential replacements, nutrient and vegetation dynamics, greenhouse gas emissions and carbon sequestration and cycling, hydrologic impacts, and pre or post-infestation silvicultural approaches or management strategies.
Emerald ash borer (EAB, Agrilus planipennis) is an invasive phloem feeder from East Asia that has killed millions of ash trees in North America. Currently, effective options for individual tree ...protection are limited to systemic insecticides, in particular neonicotinoids, which have come under increased scrutiny for their nontarget effects. In this study, green ash (Fraxinus pennsylvanica) trees were treated with two neonicotinoid insecticides, imidacloprid and dinotefuran, at full and half label rates based on trunk diameter to evaluate residues and efficacy. Analyzing the leaf, stem, and root tissues, there was no difference in insecticide residues between application rates within each tissue type. However, there were significantly higher residues of imidacloprid in root tissue compared to other plant tissues, and dinotefuran applied at the full label rate resulted in lower residues in stem phloem tissue. Additionally, insecticide-treated stems were artificially infested with EAB eggs to measure larval success (survival and growth). EAB larvae consumed less phloem in treated trees compared to untreated controls. These findings suggest that, in small-diameter ash, lower than label-recommended doses may be a viable component of an integrated management plan for EAB.
•There has been extensive ash regeneration in EAB-invaded regions.•Regeneration is highest on plots with the longest invasion histories.•Seedling densities were generally unchanged between 2007 and ...2018.•Mortality is higher than recruitment on plots invaded for > 10 years.•Current trends indicate that few ashes are likely to survive to reproductive ages.
Non-native insects and pathogens can alter the composition and successional trajectories of forests and, in exceptional cases, drive their host trees functionally extinct. Emerald ash borer has killed millions of ash trees in its invaded range across eastern North America. Predicting the future ecological role of ash requires information on the extent of ash regeneration and recruitment in the wake of invasion. Variable levels of ash regeneration have been observed in stands invaded by emerald ash borer, although recruitment rates of young ash trees into the overstory remain unclear. Here, we used forest inventory data to quantify ash recruitment and regeneration across the eastern United States, and we linked these observed patterns to emerald ash borer invasion history. Inventory data from 2013-2018 indicate there has been extensive ash regeneration in invaded regions, totaling > 1,200 seedlings per ha in counties invaded in 2002–2006. Plots in counties with the longest invasion histories contained the highest densities of ash seedlings and saplings, likely due to the high densities of overstory ash in these areas prior to invasion by emerald ash borer. Seedling densities also remained generally unchanged between inventory periods ending in 2007 and 2018 irrespective of invasion history. Despite this widespread regeneration, ash trees in the smallest overstory class died at faster rates than they were recruited from seedlings or saplings, resulting in negative population trajectories on plots that have been invaded for more than ~ 10 years. This trend suggests that ash will continue to decline in abundance and may become functionally extinct across the invaded range of emerald ash borer. However, the future ecological role of ash will ultimately be determined by the iterative production and survival of ash seeds to reproductive ages in the presence of emerald ash borer populations, along with effective management practices.
Emerald ash borer (EAB) (Agrilus planipennis Fairmaire), an invasive, phloem‐feeding beetle native to Asia, has killed millions of ash (Fraxinus spp.) trees in North America since it was detected in ...southeast Michigan in 2002. Consistently high mortality of black ash (Fraxinus nigra) and green ash (F. pennsylvanica) which often occur in riparian forests is a concern given their role in regulating soil moisture and shallow groundwater levels. We monitored and compared hydrologic processes in a riparian forest impacted by EAB invasion and an adjacent unimpacted riparian forest site in southwest Michigan. From 2018 to 2022, we recorded soil moisture, depth to groundwater and meteorological variables at 15‐min intervals throughout the growing season in a canopy gap following EAB‐caused ash mortality and in adjacent, unaffected forest in the Augusta Creek riparian zone. Groundwater contributions to evapotranspiration (ETG) were estimated using a groundwater level fluctuation (WLF) method. Significant differences in volumetric soil moisture content (16%–26% higher in the gap than forest), average depth to water (10 cm in the gap vs. 70 cm below land surface in the forest) and mean daily ETG (0.6 in the gap vs. 3.0 mm per day in the forest) persisted across four growing seasons. Within the gap, prolonged saturation of the near surface may be contributing to a shift from a forested riparian ecosystem to herb and sedge‐dominated wetland. These differences have implications for an array of riparian zone ecosystem services, a concern given the extent of ash mortality already sustained in much of eastern North America.
This is the first documented longitudinal study of the ecohydrological impacts of emerald ash borer invasion in riparian forests. We demonstrated that there are substantial, significant (p < 0.001), and persistent differences in soil moisture, depth to shallow groundwater, and groundwater contributions to ET between a forested plot unaffected by EAB and a plot where nearly complete mortality of overstory ash trees resulted in a canopy gap in the riparian zone.
Background: Emerald ash borer (EAB), Agrilus planipennis, is an invasive wood-boring beetle that threatens ash trees (Fraxinus spp.) in the urban forest. Methods: We compared the efficacy at which 3 ...different injection systems deliver emamectin benzoate (EB) to the leaf canopy and protect trees. Two of the systems, Arborjet Tree I.V.™ and Rainbow Ecoscience Q-Connect™, used sixteen ports/m of trunk circumference, whereas the third system, Brandt enTREE® EB, used eight. Results: The two systems with more injection ports provided more uniform delivery of insecticide to the leaf canopy. Although all 3 injection systems provided excellent control for the first 2 years, only the 16-port injection systems provided protection for up to 3 years. The number of injection ports affected insecticide delivery because the sectorial structure of the ash vascular system limited lateral product diffusion. Additionally, over the course of an 8-year study, we found trunk injections of EB made in the spring provided better control of EAB than fall injections. Protection afforded by a 2013 application in our study failed by 2016 as EAB populations reached their peak. A second application in 2016 extended protection past the peak of EAB abundance through 2019. Conclusions: We conclude that when the same dose of EB is delivered, efficacy of the application is influenced by the number of injection ports used in the injection system, time of application, and the status of the local EAB population. Arborists need to be aware of these factors when planning their EAB management program.
Black ash wetlands are seriously threatened because of the invasive emerald ash borer (EAB). Wetland hydrology is likely to be modified following ash mortality, but the magnitude of hydrological ...impact following loss via EAB and alternative mitigation harvests is not clear. Our objective was to assess the water table response to simulated EAB and harvesting to determine if management actions will be needed to maintain ecosystem functions following EAB infestation. We applied four replicated treatments to 1.6 ha plots as follows: (1) control, (2) girdling of all black ash trees to simulate loss via EAB mortality, (3) group selection harvests (20% of stand in 0.04 ha gaps), and (4) clear-cut harvest. Water table (WT) elevations were monitored for 1 year pre-treatment and two years post-treatment. Clear-cutting delayed WT drawdown in both years of the study, and the WT was significantly higher than the control treatment, predominantly when WT depth was below 30 cm. The effect of the group selection treatment on WT response was muted compared to clear-cutting and also limited to periods when the WT depth was below 30 cm. These responses were attributed to establishment of shallow-rooted vegetation in cut areas, which would have limited influence on WT dynamics as depth increased. There was little effect of girdling on the WT in the first year post-treatment, but effects on the WT were very similar to clear-cutting in the second year and more pronounced when the WT was within 30 cm of the soil surface. These effects were attributed to reduced transpiration coupled with the presence of a partial canopy following girdling, which would have reduced vegetation establishment and evaporation compared to clear-cutting. Given the large influence of WT depth on vegetation dynamics and associated feedbacks to altered hydrology, these early results indicate a greater risk of ecosystem alteration following EAB mortality compared to clear-cut harvesting. Depending on local hydrologic regime, variation in precipitation patterns, and time for complete canopy loss, it may be necessary for managers to implement active mitigation strategies (e.g., group selection coupled with planting of alternative species) prior to EAB infestation to maintain ecosystem processes in these forested wetland systems.
Black ash (Fraxinus nigra), the most highly preferred and vulnerable host of the invasive emerald ash borer (EAB; Agrilus planipennis) in North America, is of cultural and spiritual importance to ...many Tribal Nations in the US and First Nations in Canada. To date, EAB has invaded nearly 60% of the native range of black ash, with annual spread averaging approximately 50 km per year. On the basis of the predicted expansion of EAB distribution, we estimate that more than 75% of black ash basal area will be lost across 87% of the species’ North American range by 2035. Census data indicate that 98% of Indigenous people currently residing within the geographic range of black ash in the US will be within the area experiencing more than 75% basal area loss by 2035, suggesting broad and multidimensional impacts of EAB invasion for those who value black ash as a cultural keystone species. Collaborative efforts among scientists, resource managers, and Indigenous experts are needed to mitigate EAB impacts and preserve or protect black ash resources, given the species’ vulnerability to EAB and its associated cultural and ecological value.
The gut microbial communities of beetles play crucial roles in their adaptive capacities. Environmental factors such as temperature or nutrition naturally affect the insect microbiome, but a shift in ...local conditions like the population density on a host tree could also lead to changes in the microbiota. The emerald ash borer (EAB), Agrilus planipennis Fairmaire, is an exotic wood borer that causes environmental and economic damage to ash trees in North America. This study aimed to describe the taxonomic structure of the EAB gut microbiome and explore its potential relationship with borer population size. The number of EAB adults collected per tree through a 75 km transect from an epicenter allowed the creation of distinct classes of population density. The Gammaproteobacteria and Ascomycota predominated in bacterial and fungal communities respectively, as determined by sequencing of the bacterial 16S rRNA gene and the fungal internal transcribed spacer ITS2. Species richness and diversity of the bacterial community showed significant dependence on population density. Moreover, α-diversity and β-diversity analysis revealed some indicator amplicon sequence variants suggesting that the plasticity of the gut microbiome could be related to the EAB population density in host trees.
