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Since the discovery of the emerald ash borer (Agrilus planipennis, Coleoptera: Buprestidae) in 2002, it has caused near 100% mortality of North American ash trees (genus Fraxinus). Moreover, uncertainties remain regarding the future of the forest regeneration dynamics after the introduction this prolific forest pathogen. The objectives of this study were to: 1) Assess regeneration potential of green ash (Fraxinus pennsylavnica Marsh.) on the Lake Erie and Lake Tonawanda plains in Western New York State where it was formerly one of the dominant trees; 2) Identify other native tree species that could repopulate depleted ash stands; and 3) Assess factors constraining regeneration like invasive shrub cover and deer browsing pressure. In 32 plots (400 – 3600 m2), proportion of ash trees in c. 2010 pre-ash-borer stands was catalogued (including dead or fallen stems), and all ash trees were assigned into health categories ranging from dead to unimpacted. Stump sprout and seedling recruits were recorded. Canopy and understory stems of all other trees were identified and measured (diameter at breast height). Identity and coverage of invasive shrubs were recorded. Data were analyzed and interpreted along gradients in two important independent variables: 1) stand age at ash borer invasion (from increment counts of fallen dead ash trees, or estimated from aerial imagery), and 2) % of ash in pre-ash-borer stands. Most adult ashes within plots were dead, and with no association with stand age or pre-ash-borer ash dominance. However, 11% of ash trees were completely un-impacted, but were 80%) stands. Stump sprouting was present in 78% of plots, and ash seedlings were noted at most sites, again primarily in young ash-dominated stands. Red and/or silver maples and American elms were the most common native trees and were most important in older less ash-dominated stands. Unfortunately, invasive shrubs were often very abundant, and deer browsing was evident in the majority of plots. This study suggests that green ash within the lake plains of Western New York may be able to regenerate, especially within younger stands, and that other native trees may replenish older stands. However, invasive shrubs and excessive deer browsing may hinder recovery.

Abstract: Hymenopteran parasitoids are widely studied and employed as biological controls to reduce populations of pest insects. Apanteles polychrosidis Vierek (Hymenoptera: Braconidae) is a native parasitoid wasp that has shifted hosts, becoming the primary parasitoid of the ash leaf-cone roller, Caloptilia fraxinella Ely (Lepidoptera: Gracillariidae), an introduced nuisance pest of ash trees (Fraxinus spp.) in Edmonton, Alberta. This project explores two approaches to enhance A. polychrosidis as a biological control agent of C. fraxinella: 1) Baiting trees with synthetic semiochemical lures that release methyl salicylate (MS), and two green leaf volatiles (GLVs) (Z)-3 hexenyl acetate, and (Z)-3-hHexanol to enhance wasp attraction and parasitism in infested ash trees. Mated female wasp attraction to these same compounds was tested also tested in an olfactometer. Male and female wasps were more attracted to ash trees treated with the combination of MS+GLV lures, at the lower release rate tested. Mated females did not demonstrate attraction to VOC compounds in the olfactometer. 2) Nutritional provisioning with 10% and 25% sucrose solution or natural nectar sources to enhance retention of wasps in ash trees and increase parasitism of C. fraxinella. The effect of sucrose nutrition on wasp longevity, female fecundity and parasitism, and offspring fitness were measured in the laboratory. Wasp longevity was greater in virgin male and female A. polychrosidis that were fed either 10 or 25% sucrose solution. Females lived significantly longer than males, when they were both fed 25% sucrose. Virgin female egg load was lower for wasps fed 25% sucrose, and female egg load was negatively correlated with female longevity. Nectar feeding extended virgin female longevity similarly to those fed 25% sucrose. Neither sucrose solution, nor buckwheat flower provision in the field increased wasp retention. Wasp density was negatively correlated with C. fraxinella host density in field experiments.

The invasive emerald ash borer beetle (Agrilus planipennis, EAB) has caused significant ash tree (Fraxinus spp.) declines and forest changes, which include loss of canopy cover and increased numbers of invasive plant species (Hausman et al. 2010). My focus was to assess ash population dynamics and environmental factors that could play a role in ash survival. My research used a population viability analysis (PVA) approach that combined literature review, targeted field studies, and greenhouse experiments to examine green ash trees (F. pennsylvanica) in the post-EAB peak infestation (aftermath) forest. Aftermath forests dynamics between ash and EAB are likely different from the initial infestation. I developed historic and worst case stochastic stage based ash population models as part of a PVA; these scenarios reflect time periods before and after EAB invaded Northwest Ohio. The ash population growth rates were estimated as 0.76 and 1.03, respectively, in worst case versus historic scenarios. Results indicated that population changes were more sensitive to survival and growth of the smallest stage class in the worst case scenario, where ash populations became locally extinct within 41 years. I examined ash parameters with little known information, such as germination, seedling survival and their environmental conditions, and mature ash tree neighbors. My germination experiments from the lab and the field resulted in a very low germination rate from the local population. Seedling survival was high and they were affected by leaf litter, bare ground and dead coarse woody debris. The number of ash neighbors within 6 m was significantly lower for the healthiest ash canopy class compared to declining health classes (p = 0.02). I modeled changes that could occur to the green ash aftermath forest (2010-2017) by introducing EAB periodically as a catastrophe that lowered ash survival and simulated a slow ash survival recovery. Management scenarios included, 1) reduced EAB catastrophes, 2) increase ash survival and growth, 3) individual ash size classes survival increased, and 4) planted EAB-resistant ash trees. Reduced EAB catastrophes, protecting the largest and smallest ash size class, and increase survival and growth provided an improvement for the population. Planting EAB-resistant trees allowed for a partial recovery, where saplings performed better than seedlings. While conservative, these green ash models indicated that increased tree survival improved population recovery, and EAB population fluxes have a large influence on ash population persistence. PVA, as this research demonstrates, allows us to quickly identify factors that influence the population viability of threatened species, allowing for the development of strategies that promote recovery.

Populations of North American ash (Fraxinus sp.) are declining due to the introduction of emerald ash borer (EAB; Agrilus planipennis), a wood-boring beetle native to East Asia. At Oak Openings Preserve Metropark in northwest Ohio, a population of green ash (F. pennsylvanica) exists in which 99% of the trees have succumbed to emerald ash borer, but a small number of trees have remained healthy. These “lingering” ash may be closely related, thus sharing common alleles that may be contributing to EAB resistance. However, relatedness may also indicate an overall lack of genetic diversity in the lingering ash relative to the former intact population. To compare genetic diversity, 39 individuals were sampled from the lingering population as well as from 19 individuals that declined significantly or suffered above-ground mortality due to EAB infestation, but developed stump sprouts. This essentially creates a temporal sampling of the population, with the susceptible and lingering samples allowing estimation of the gene pool pre- and post-EAB arrival, respectively. Genotyping of trees at 12 EST-SSR loci revealed similar levels of allelic diversity and heterozygosity between the two groups. In addition, relatedness was not significantly higher among post-EAB trees (p>0.05), but a spatial autocorrelation analysis revealed that genetically similar trees were clustering close together in geographic space. These results suggest that green ash are buffering population loss and maintaining genetic diversity, probably through life history characteristics (e.g. dioecy, wind-pollination). Knowledge of the lingering ash’s genotypes will aid any breeding efforts undertaken by the US Forest Service to preserve ash on the North American landscape.

Crop tree enhancement is a forest management technique undertaken to maintain, enhance, and improve the species composition, growth rate, and stem quality of stands so that management objectives may be better and more quickly accomplished. In 1996, a crop tree enhancement study involving green ash (Fraxinus pennsylvanica) in a 16-year-old, naturally regenerated, mixed-species, pole-sized, bottomland hardwood stand was initiated at Ames Plantation in West TN. Treatments included a crown-touching release, a crown-touching release plus one-time fertilizer application, and a control, applied in a randomized block design with five 25-crop tree repetitions of the three treatments. Initial crop tree diameters, heights, clear bole lengths, crown dimensions, and crown classes, as determined by the crown rating system for southern hardwoods (Meadows et al. 2001), were recorded at this time. Eighteen years later in 2014, measurements were again recorded. Additionally, competing species, determined with a 10F wedge prism, and the depth to mottled soil horizons for each crop tree were recorded. Growth in diameter, height, crown length, and crown spread over the 18-year study period were calculated. Analysis of variance tested for differences in treatment response. Relationships between the depth to mottled horizons, treatment response, and block layout were examined with chisquare analysis and correlation analysis. Release and release plus fertilize treatments generally did not differ in diameter, height, crown expansion, and crown class. However, both outperformed the control treatment. Release and release plus fertilize treatments maintained a greater percentage of upper canopy green ash crop trees than the control. Crop trees of different crown classes responded to release at varying degrees, with the largest increases in diameter and crown expansion occurring in the codominant class. Releasing dominant crop trees did not yield significantly greater growth, while some intermediate trees benefitted from release. The depth to mottled horizons fluctuated across the study area, but with little relationship to crop tree growth. Competing species composition differed at varying depths to mottled horizons. Crop tree enhancement appears to be a beneficial management strategy for improving growth rates and maintaining the upper canopy status of green ash in mixed-species, bottomland hardwood stands.

Emerald Ash Borer (EAB) is more damaging to North American ashes than Asian ashes. Variation in the resistance of ash species to feeding by larvae of EAB may be related to variation in levels of chemical defenses in the phloem. I compared constitutive and methyl jasmonate (MeJA)-inducible levels of several chemical defenses in the phloem of young Manchurian, Chinese, white, and green ashes. Manchurian ash is known to be highly resistant to attack by EAB in the field, while white and green ashes are both susceptible. The hypotheses of this experiment were that: (1) Manchurian (Fraxinus mandshurica) and Chinese ash (Fraxinus chinensis) trees’ phloem or bark contains concentrations of unique secondary compounds and higher level of defense protein activities than white and green ash. (2) MeJA treatment will induce increases in content of protein, Peroxidase (POD), polyphenol oxidase (PPO) content and most of the secondary compounds in all species. Phloem extracts of Manchurian ash showed higher total soluble protein content and significantly faster browning than white and green ash, but lower peroxidase activity and polyphenoloxidase activity. Activities of PPO, POD, phenolic and lignin content, and the rate of browning reactions were not found to exhibit differences between MeJA treated and untreated groups. However, our HPLC results revealed Manchurian ash contained nine unique phenolic compounds: Homovanillic Alcohol, Esculetin, Esculin Related Cmpd, Esculin, Fraxin, Fraxidin hexoside, Pinoresinol dihexoside, Calceolarioside A, Calceolarioside B. We also found obvious increases in specific compounds (of the 20 compounds we reanalyzed in the four ash species) in Green ash, Chinese ash and Manchurian ash in the MeJA treated group. Also, Canonical Discriminant Function Analysis of five common compounds (Tyrosol Hexoside, Mandshurin, Pinoresinol compound, Syringaresinol and Oleuropein) revealed that Manchurian ash was different from the other three ashes, but closer to Green ash and Chinese ash. Green ash and Chinese ash were similar to each other. White ash was very different from all other three ashes. In this study, the highly resistant Manchurian ash was distinguishable from the highly susceptible white ash by having higher total soluble protein content and a significantly faster browning. The susceptible green ash was distinguishable from Manchurian ash by having lower total protein levels and a lower degree of browning. The phloem chemistry of green and Chinese ash was largely similar in this study, indicating that they may be similar in their resistance to EAB, and White ash showed had levels of peroxidase activity, polyphenoloxidase activity, content of phenolic and lower rate of browning reaction than the other three species. From the result of Discriminate Function Analysis, White ash also showed maximal separation from the others. Since White ash is as susceptible as Green ash in North America, White ash may contain different compounds or enzymes than Green that may be attractive to EAB.

In order to assess the enhancement of seedling survival and growth during drought conditions, five-hundred bare-root seedlings each of Shumard oak (Quercus shumardii Buckl.) and green ash (Fraxinus pennsylvanica Marsh.) were planted each with four soil amendments at a Wildlife Management Area in Lewisville, Texas. The treatments were a mycorrhizal inoculant, mulch fabric, and two superabsorbent gels (TerraSorb® and DRiWATER®). Survival and growth measurements were assessed periodically for two years. Research was conducted on vegetation, soil, and site history for baseline data. Both superabsorbent gels gave significant results for Shumard oak survival, and one increased green ash diameter. For overall growth, significant results were found among DRiWATER®, mycorrhizae, and mulch treatments.