White Ash Trees Research Articles

The persistence of blue ash in the aftermath of emerald ash borer may be due to adult oviposition preferences and reduced larval performance

Abstract We examined the health of mature blue ash, Fraxinus quadrangulata, in two forests in southwestern Ohio in relation to that of mature white ash, F. americana, and examined the potential importance of oviposition preferences and larval resistance in the persistence of blue ash. Both blue ash and white ash were largely unaffected by emerald ash borer in 2012. By 2018, nearly 90% of the blue ash trees observed in these forests had full or nearly full canopies, as opposed to less than 20% of the white ash encountered in our studies. In 2021, blue ash maintained a similar degree of canopy health as in 2018, but no standing live mature white ashes remained. Bark removals revealed no current or past larval feeding attempts in blue ash in 2018 or 2021, except for one attacked and killed tree in 2018. All white ash trees examined were attacked. In a laboratory bioassay with cut stems, emerald ash borer larvae fed less and grew significantly more slowly on blue ash than on white ash. Both reduced larval performance and reduced adult oviposition likely contribute to the persistence of blue ash in forests devastated by emerald ash borer.

Leaf-Level Spectroscopy for Analysis of Invasive Pest Impact on Trees in a Stressed Environment: An Example Using Emerald Ash Borer (Agrilus planipennis Fairmaire) in Ash Trees (Fraxinus spp.), Kansas, USA

The most visible symptoms of emerald ash borer (EAB) (Argilus planipennis Fairmaire) infestation do not usually appear until six years after the borer’s arrival, by which time the prognosis is so grim that many communities have resorted to either heavy chemical use that only slows mortality, or clear-cutting the entire ash tree population. We utilized leaf-level spectroscopy for early detection of invasive pest-related stress, focusing on EAB as it reaches the edges of the geographic range for green and white ash trees (Fraxinus pennsylvanica and Fraxinus americana) in North America. Over the course of two full growing seasons, we sampled trees in three study areas with EAB infestation in Johnson County, Kansas, and two sample groups without infestation in Riley County, Kansas. Our method utilizes field spectrometer readings for reflectance, along with lab spectrophotometry for estimation of leaf chlorophyll and carotenoid content at several points during the growing season. Results show significant differences between pigment ratios and hyperspectral indicators between infested and non-infested ash trees, although the extent of the separation varies across the foliar season. This work has the potential to make stress diagnosis more effective, thereby improving response, and decreasing both chemical application and plant loss.

Captures of Emerald Ash Borer (Agrilus planipennis) Adults in Post-Invasion White Ash Sites with Varying Amounts of Live Phloem

Emerald ash borer (EAB), (Agrilus planipennis Fairmaire), first identified in 2002 in southeast Michigan, has caused catastrophic ash (Fraxinus spp.) mortality in forests within the core of the invasion and has spread to 35 states and five Canadian provinces. Little is known about persistence and densities of EAB populations in post-invasion sites after most ash trees have died. We monitored EAB populations from 2014 to 2016 using double decker (DD) traps set in the midst of white ash (F. americana) trees in 30 post-invasion sites in southeast and south-central Michigan. Two DD traps were deployed at each site. One trap had a dark green upper prism and light purple lower prism, both baited with cis-3-hexenol lures. The other had two dark purple prisms baited with cis-3-hexenol on the upper prism and Manuka oil on the lower prism. In 2014 and 2016, size and condition of ash trees were recorded and area of live white ash phloem was estimated in an 18-m-radius plot centered around each of the DD traps. Area of live white ash phloem per site ranged from approximately 24 to 421 m2 in 2014 and from 24 to 411 m2 in 2016. Canopy condition of live white ash trees generally improved; 65% and 89% of the trees had healthy canopies (<20% dieback) in 2014 and 2016, respectively. Traps in 28, 29 and 30 of the sites captured a total of 580, 585, and 932 EAB adults in 2014–2016, respectively. Area of live ash phloem explained relatively little of the variation in total EAB captures in all three years. Low trap catches, along with relatively stable canopy conditions and continued abundance of live white ash, indicate that EAB populations remain below the carrying capacity of the sites, and ash phloem availability is not a limiting factor for EAB abundance. Further monitoring to track both EAB dynamics and tree condition is needed to determine the long-term outlook for white ash in these sites.

White ash (Fraxinus americana) survival in the core of the emerald ash borer (Agrilus planipennis) invasion

Despite catastrophic ash (Fraxinus spp.) mortality observed by the mid-2000s in the epicenter of the emerald ash borer (EAB) (Agrilus planipennis Fairmaire) invasion in southeast Michigan, we noticed numerous live white ash (Fraxinus americana L.) in some forests in this region. In 2015, we inventoried overstory trees and regeneration in 28 white ash sites spanning 11 counties. White ash survival ranged from 0% to 100% of stems. Overall, 75% of 821 white ash trees, ranging from 10.0 to 44.0 cm diameter at breast height, and 66% of the white ash basal area, ranging from 0.3 to 3.5 m2·ha–1, were alive. Nearly all live white ash had signs of previous EAB colonization, but 83% had healthy canopies (≤10% canopy dieback). Green ash trees were recorded in 27 sites, but 92% were killed by EAB. Model selection indicated that variation in white ash survival was related to white ash abundance and distance of sites from the original EAB epicenter but not to green ash related variables or to the distance of sites from the Asian parasitoid release or recovery locations. Regeneration strata were dominated by white ash, suggesting that some white ash populations may persist in post-invasion areas.

Optimizing Conservation Strategies for a Threatened Tree Species: In Situ Conservation of White Ash (Fraxinus americana L.) Genetic Diversity through Insecticide Treatment

Forest resources face numerous threats that require costly management. Hence, there is an increasing need for data-informed strategies to guide conservation practices. The introduction of the emerald ash borer to North America has caused rapid declines in ash populations (Fraxinus spp. L.). Natural resource managers are faced with a choice of either allowing ash trees to die, risking forest degradation and reduced functional resilience, or investing in conserving trees to preserve ecosystem structure and standing genetic diversity. The information needed to guide these decisions is not always readily available. Therefore, to address this concern, we used eight microsatellites to genotype 352 white ash trees (Fraxinus americana L.) across 17 populations in the Allegheny National Forest; a subset of individuals sampled are part of an insecticide treatment regimen. Genetic diversity (number of alleles and He) was equivalent in treated and untreated trees, with little evidence of differentiation or inbreeding, suggesting current insecticidal treatment is conserving local, neutral genetic diversity. Using simulations, we demonstrated that best practice is treating more populations rather than more trees in fewer populations. Furthermore, through genetic screening, conservation practitioners can select highly diverse and unique populations to maximize diversity and reduce expenditures (by up to 21%). These findings will help practitioners develop cost-effective strategies to conserve genetic diversity.

Warmest extreme year in U.S. history alters thermal requirements for tree phenology

The frequency of extreme warm years is increasing across the majority of the planet. Shifts in plant phenology in response to extreme years can influence plant survival, productivity, and synchrony with pollinators/herbivores. Despite extensive work on plant phenological responses to climate change, little is known about responses to extreme warm years, particularly at the intraspecific level. Here we investigate 43 populations of white ash trees (Fraxinus americana) from throughout the species range that were all grown in a common garden. We compared the timing of leaf emergence during the warmest year in U.S. history (2012) with relatively non-extreme years. We show that (a) leaf emergence among white ash populations was accelerated by 21 days on average during the extreme warm year of 2012 relative to non-extreme years; (b) rank order for the timing of leaf emergence was maintained among populations across extreme and non-extreme years, with southern populations emerging earlier than northern populations; (c) greater amounts of warming units accumulated prior to leaf emergence during the extreme warm year relative to non-extreme years, and this constrained the potential for even earlier leaf emergence by an average of 9 days among populations; and (d) the extreme warm year reduced the reliability of a relevant phenological model for white ash by producing a consistent bias toward earlier predicted leaf emergence relative to observations. These results demonstrate a critical need to better understand how extreme warm years will impact tree phenology, particularly at the intraspecific level.

Evaluation of Xylem Discoloration in Ash Trees Associated with Macroinjections of a Systemic Insecticide

Emerald ash borer (EAB) (Agrilus planipennis), first identified near Detroit, Michigan, U.S., in 2002, has killed millions of ash trees (Fraxinus spp.) in 28 states and two Canadian provinces to date. Trunk injections of insecticide products containing emamectin benzoate (EB) (e.g., TREE-ageR) are often used to protect ash trees in landscapes from EAB, but wounds and potential injury resulting from injections are a concern. Researchers examined 507 injection sites on 61 trees and recorded evidence of secondary wounding (e.g., external bark cracks, internal xylem necrosis and pathogen infection). Researchers assessed 233 injection sites on 22 green ash and 24 white ash trees macro-injected with a low or a medium-high rate of EB in 2008 only, or in both 2008 and 2009. Only 12 of 233 injection sites (5%) were associated with external bark cracks and there was no evidence of pathogen infection. On 39 of the 46 trees (85%), new xylem was growing over injection sites. Researchers assessed 274 injection sites on 15 green ash trees injected annually with EB from 2008 to 2013 or injected in 2008 and again in 2011. Bark cracks were associated with four injection sites on three trees, but no evidence of injury was found on the other 12 trees. All 15 trees had new xylem laid over injection sites. Confocal laser scanning and polarizing digital microscopy were used to assess the integrity of discolored xylem tissue removed from the immediate area surrounding 140 injection sites on 61 trees. Researchers found no evidence of decay associated with discoloration.

Use of near-infrared spectroscopy as an indicator of emerald ash borer infestation in white ash stem tissue

Emerald ash borer (EAB) (Agrilus planipennis), is a non-native beetle responsible for widespread mortality of several North American ash species (Fraxinus sp.). Current non-destructive methods for early detection of EAB in specific trees are limited, which restricts the effectiveness of management efforts to contain this invasive threat. This study explored the application of near-infrared (NIR) spectroscopy as a novel method for detection of EAB in white ash (Fraxinus americana). Increment borers were used to non-destructively and efficiently collect increment cores from visibly healthy and EAB infested white ash trees for subsequent NIR analysis. White ash trees were sampled across sites of different land use categories (i.e., natural forests versus recreational areas) and different latitudinal regions in the eastern Lower Peninsula and in the western Upper Peninsula of Michigan. NIR diffuse reflectance spectra were collected from three stem tissue types (outer bark, phloem, and xylem) using a NIR spectrometer over the wavelength range of 1134–2190nm. Spectral measurements were treated with a Savitzky–Golay smoothing filter, followed by a 1st and 2nd derivative transformation to increase spectral sensitivity. Near-infrared spectroscopy was successfully able to discriminate between EAB infested and visually healthy trees using step-wise linear discriminant analysis for each of the three stem tissue types (outer bark, phloem and xylem). The NIR spectra of xylem tissue transformed using a Savitzky–Golay smoothing filter with a 1st derivative transformation over the full NIR wavelength range (1134–2190nm) had the highest classification accuracy (97%) for discriminating between healthy versus EAB infested trees. This study underscores potential for future research in developing NIR spectroscopy as a cost-effective method of early detection and monitoring of emerald ash borer and other stem-boring insects in support of current detection methods.

Emerald Ash Borer ( Agrilus planipennis) Density and Canopy Dieback in Three North American Ash Species

Emerald ash borer (Agrilus planipennis Fairmaire) (Coleoptera: Buprestidae), a phloem-feeding insect native to Asia, was identified in 2002 as the cause of widespread ash (Fraxinus) mortality in southeast Michigan, U.S. and Windsor, Ontario, Canada. Little information about A. planipennis is available from its native range and it was not known whether this invasive pest would exhibit a preference for a particular North American ash species. We monitored A. planipennis density and canopy condition on green ash (F. pennsylvanica) and white ash (F. americana) street trees in four neighborhoods and on white and blue ash (F. quadrangulata) trees in two woodlots in southeast Michigan. Green ash street trees had significantly more canopy dieback and higher A. planipennis densities than white ash trees growing in the same neighborhood. Density increased by two- to fourfold in both species over a 3-year period. Canopy dieback increased linearly from 2002 to 2005 as A. planipennis density increased (R 2= 0.70). In each of the woodlots, A. planipennis densities were significantly higher on white ash trees than blue ash trees. Woodpecker predation occurred in all sites and accounted for 35% of the A. planipennis that developed on trees we surveyed. Results indicate that surveys for A. planipennis detection in areas with multiple ash species should focus on the relatively preferred species.

Field Note—Comparison of Three Dendrometers in Measuring Diameter at Breast Height Field Note

Abstract Three dendrometers—d-tape, calipers, and Biltmore stick—were used to measure diameter at breast height (dbh), and discrepancies that occurred among these instruments were compared. Three methods of dbh estimation with calipers—the quadratic, arithmetic, and geometric mean of the major and minor axis diameter—were compared. Trees were grouped into four broad dbh classes of 1–5, 6–10, 11–15, and 16–20 in. and three species—northern red oak, sugar maple, and white ash—to determine the effect of tree size and species on discrepancies. The d-tape consistently recorded a larger dbh than the three caliper methods, but was not statistically different nor practically important. The differences in recorded dbh between the d-tape and calipers increased with tree size and were similar among northern red oak and sugar maple trees, but dbh differences in white ash trees were significantly less than in the other two species. The Biltmore stick's accuracy in classifying trees into the same dbh class as determined by the d-tape decreased as tree size increased. When examined by species, the Biltmore stick was less accurate in this regard with northern red oak and most accurate with sugar maple. Because the geometric principle of the d-tape assumes a tree to have a circular shape, its diameter estimation and subsequent basal area will usually be greater than the true diameter and area. The use of calipers reduces this bias, but the differences are not statistically significant.

Terminal Bud Cluster Pruning Promotes Apical Control in Transplanted Shade Tree Whips

Transplant-induced loss of apical control, as measured by the central leader to total lateral branch caliper ratio, was documented for 'Patmore' green ash (Fraxinus pennsylvanica) and 'Autumn Purple' white ash (F. americana) by measuring trees one, two, five and 10 years after transplanting. For both species, the central leader to total lateral branch caliper ratio ranged from 0.3 to 0.5, regardless of the age from transplanting, indicating that large lower limb development (loss of apical control) was initiated at transplanting and persists for up to 10 years. Transplanted nursery grown 'Patmore green ash and 'Autumn Purple' white ash trees bud pruned to maintain a strong central leader had central leader to total lateral branch caliper ratios of 0.7 and 0.8, respectively. A pruning treatment, removing the lateral buds from the terminal bud cluster, reduced large lower limb development, maintained apical control and resulted in better lateral branch distribution in transplanted red oak {Quercus rubra) and 'Patmore' and 'Autumn Purple' ash whips than leaving the terminal bud cluster intact.

Ash Yellows, Drought, and Decline in Radial Growth of White Ash

The effect of MLO infection and drought on the radial growth of white ash trees was measured using standard dendrochronological techniques. Both MLO infection and drought stress caused reductions in the radial growth of white ash, but not all MLO-infected trees declined in radial growth. The effect of regional drought on the radial growth of white ash was investigated on 15 of 41 permanent research plots by comparing summary tree ring indices of the white ash within these plots with mean Palmer Drought Severity Indices for April through September (.)

Detection of Tobacco Mosaic and Tobacco Ringspot Viruses in White Ash Trees by Enzyme-Linked Immunosorbent Assay

Detection of Tobacco Mosaic and Tobacco Ringspot Viruses in White Ash Trees by Enzyme-Linked Immunosorbent Assay

Detection of Tobacco Mosaic and Tobacco Ringspot Viruses in White Ash Trees by Enzyme-Linked Immunosorbent Assay

Detection of Tobacco Mosaic and Tobacco Ringspot Viruses in White Ash Trees by Enzyme-Linked Immunosorbent Assay

Apical control of branch movements and tension wood in black cherry and white ash trees

We measured x,y coordinates and growth of 2-year-old branches on ash (Fraxinusamericana L.) and cherry (Prunusserotina Ehrh.) trees through one season of growth. We sectioned the branches at the end of the season and calculated stresses developed by new wood cells through the season. There were three treatments: (1) control, (2) stem girdled above the branch, and (3) stem girdled as in (2), with indolebutyric acid in lanolin added to the girdle (IBA). All branches first moved down, then stopped in controls, reversed to relatively rapid upward movement in treatment 2 and moved slowly upward in IBA treatments. In treatment 2, compared with controls, branches grew more in diameter, particularly on the upper side and at the branch base; stem growth below the branch was reduced; tension wood (TW) formed in ash branches and TW with greater tensile stress than in controls formed in cherry branches. Branches in IBA treatments had diameter growth and TW formation intermediate between control and treatment 2 branches.

Properties of a Strain of Tobacco Mosaic Virus Isolated from White Ash Trees

Properties of a Strain of Tobacco Mosaic Virus Isolated from White Ash Trees

Translocation of Herbicides and Assimilates in Red Maple and White Ash

Herbicidal dosages of 3-amino-1,2,4-triazole (amitrole) or 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) were applied to red-maple and white-ash trees. Amitrole applied to either leaves or stems was absorbed and transported throughout the trees. In contrast, 2,4,5-T was not exported from the leaves and did not appear to be symplastically translocated following application to stems. Leaves on similarly treated trees were exposed to 14CO2, and the effect of the herbicides on the movement of 14C-assimilates was noted. Both amitrole and 2,4,5-T caused significant transport of 14C-assimilates into the veins of fully expanded leaves from the 14CO2-treated leaf. Translocation of labeled assimilates to the roots was reduced if the 14CO2-treated leaves had been sprayed previously with either herbicide. When the 14CO2-treated leaf had not been sprayed, transport of labeled assimilates to the roots was only moderately affected by amitrole or 2,4,5-T applied to the remainder of the shoot.