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The cross-hybridization of American chestnut (Castanea dentata (Marsh.) Borkh.) with Chinese chestnut (Castanea mollissima Bl.) is a promising strategy for restoring a blight-resistant strain of this keystone species to the Appalachian mountains. To assess the ecological impacts of hybridization on invertebrate communities, we conducted a study across chestnut plots with varying degrees of hybridization (75%, 94%, or 100% American chestnut). Our findings indicate American chestnut hybridization impacted invertebrate communities above- and belowground. Aboveground insect community composition, insect herbivory, gall infestation, and belowground invertebrate diversity were all altered. While some of these differences could be explained by different growth habits or environmental differences, stark differences in Asian chestnut gall wasp infestation (Dryocosmus kuriphilus Yasumatsu.) suggest a genetic component. These results suggest that chestnut hybridization, and particularly expanded restoration efforts using chestnut hybrids, could impact invertebrate communities above- and belowground in addition to pest dynamics. Understanding these effects is crucial for successful chestnut restoration and ecosystem management. [ABSTRACT FROM AUTHOR]

Gnomoniopsis castaneae is an important, destructive pathogen of Castanea species, initially identified as the primary agent of nut rot in Europe and Oceania. Although a decade of research has focused almost exclusively on its association with and activity in chestnuts, it has been identified as a mild pathogen or endophyte in multiple other hardwood species, whose roles as potential reservoirs and hosts have remained unexplored. Although the origin of the disease is unknown, it is thought to be a ubiquitous endophyte that has potentially shifted to pathogenic activity as a result of global climate change. Yet there is evidence of the expansion of the range of the pathogen as it continues to be identified in new regions, suggesting some degree of introduction is occurring. Its recent discovery in the United States brings a new urgency to the need to understand the full range and epidemiology of G. castaneae and to examine potential methods of detection and mitigation. [ABSTRACT FROM AUTHOR]

For tens of thousands of years, passenger pigeons (Ectopistes migratorius) were a dominant member of eastern North American forest communities, with megaflocks comprising up to several billion individuals. The extinction of passenger pigeons in the early twentieth century undoubtedly influenced associated species and ecosystems as interactions stemming from the pigeons disappeared suddenly. Here, we strive to better understand what was probably one of the most significant of these interactions-that between passenger pigeons and seed bearing trees. Using the band-tailed pigeon (Patagioenas fasciata) and the rock dove (Columba livia) as physical and ecological proxies, we evaluated passenger pigeon dietary range and potential to disperse seeds. Our findings suggest that the passenger pigeon's dietary range, observed historically to be taxonomically broad, was constrained to certain seed sizes due to bill gape size. In addition, we conclude that the digestive process invariably destroyed consumed seeds but the potential for a nutrition/dispersal mutualism might still have existed via regurgitation and post-mortem release of crop contents. Our results highlight the range of ecological interactions that can be lost with species' extinction and the inherent challenge of understanding the consequences of those interactions.

The American chestnut (Castanea dentata Borkh.) was an economically, ecologically, and culturally important tree in eastern American hardwood forests. However, the American chestnut is currently functionally absent from these forests due to the introduction of an invasive fungus (Cryphonectria parasitica (Murr.) Barr) and causal agent of chestnut blight in the early 1900s. Field experiments are being carried out to develop a blight-resistant American chestnut tree, but range-wide restoration will require localized understanding of its current distribution and what factors contribute to suitable American chestnut habitat. While previous studies have researched species distribution of the American chestnut, it is important to understand how species distribution modeling (SDM) technique impacts model results. In this paper we create an ensemble model that combines multiple different SDM techniques to predict areas of suitable American chestnut habitat in Pennsylvania. Results indicate that model accuracy varied considerably by SDM technique – with artificial neural networks performing the worst (Area-Under-the-Curve, AUC = 0.705) and gradient boosting models performing the best (AUC = 0.877). Even though SDM technique accuracy varied, most models identified the same environmental variables as the most important: ratio of sand to clay in the soil, canopy cover, topographic convergence index, and topographic position index. This study offers insight into the best SDM techniques to use, as well as a method of combining SDMs for higher prediction confidence.

Restoration of native hardwood forests through tree planting may provide significant ecological and economic benefits, but reforestation in natural forests and afforestation on open field sites is challenging. Conversion of existing plantations of introduced conifers to hardwoods may provide an alternative opportunity for restoration. In the Midwest US, large areas of mature, introduced pine (Pinus spp.) plantations exist that have little economic and ecological value. These stands may provide ideal sites for planting of native hardwood species that have similar site preferences to pine. We sought to determine optimal management strategies for converting pine plantations by manipulating overstory canopy density and understory competition. We underplanted American chestnut (Castanea dentata (Marsh.) Borkh.) and northern red oak (Quercus rubra L.) seedlings in three overstory canopy treatments: control, shelterwood, and clearcut. Understory competition was either controlled or not through two growing seasons. After three growing seasons, oak performed best in the clearcut and chestnut in the shelterwood, reflecting variation in the species' shade tolerance. Chestnut height and root collar diameter (RCD) were double that of oak, and chestnut leaf N content increased with light availability while oak did not, which can be explained by the species' different adaptive strategies in biomass allocation. Both species had highest photosynthesis in the clearcut. Chestnut seedlings had significantly higher RCD in weeded clearcut and shelterwood plots, and oak in weeded clearcut plots. Weeding in the uncut control plots was ineffective because shade limited competition. Our results indicate that pine plantations offer suitable habitat for these hardwood species and provide insight regarding their growth strategies. Pine shelterwoods and clearcuts are each viable silvicultural conversion options for chestnut and oak if understory competition is controlled. • Evaluated conversion of plantations of non-native conifers to native hardwoods. • Oak performed best in the clearcut (CC) and chestnut in the shelterwood (SW). • Understory weeding increased diameter for chestnut in CC and SW and oak in CC. • Pine plantations offer suitable habitat for restoration of these hardwood species. • CC and SW are viable conversion options if understory competition is controlled. [ABSTRACT FROM AUTHOR]

The genus Castanea in North America contains several tree and shrub taxa of conservation concern. The two species within the group, American chestnut (Castanea dentata) and chinquapin (C. pumila sensu lato), display remarkable morphological diversity across their distributions in the eastern United States and southern Ontario. Previous investigators have hypothesized that hybridization between C. dentata and C. pumila has played an important role in generating morphological variation in wild populations. A putative hybrid taxon, Castanea alabamensis, was identified in northern Alabama in the early 20th century; however, the question of its hybridity has been unresolved. We tested the hypothesized hybrid origin of C. alabamensis using genome-wide sequence-based genotyping of C. alabamensis, all currently recognized North American Castanea taxa, and two Asian Castanea species at > 100,000 single-nucleotide polymorphism (SNP) loci. With these data, we generated a high-resolution phylogeny, tested for admixture among taxa, and analyzed population genetic structure of the study taxa. Bayesian clustering and principal components analysis provided no evidence of admixture between C. dentata and C. pumila in C. alabamensis genomes. Phylogenetic analysis of genome-wide SNP data indicated that C. alabamensis forms a distinct group within C. pumila sensu lato. Our results are consistent with the model of a nonhybrid origin for C. alabamensis. Our finding of C. alabamensis as a genetically and morphologically distinct group within the North American chinquapin complex provides further impetus for the study and conservation of the North American Castanea species. [ABSTRACT FROM AUTHOR]

Abstract The iconic American chestnut (Castanea dentata) once spanned a large portion of eastern North America before its functional extinction in the early 20th century due primarily to non‐native fungal pathogens. The pronounced loss of this species likely resulted in an abrupt alteration of many ecological processes, including fire. The potential to resurrect this species through resistance breeding or other methods holds promise, but more information on the fire ecology of American chestnut may provide helpful information to assist restoration. Here we summarize the existing direct and indirect research on the fire history and fire ecology within the former range of American chestnut. We found multiple lines of evidence to suggest fire was frequent throughout much of its historical range. A broadscale analysis of historical fire frequency revealed that 88% of the American chestnut range had a mean fire return interval of 20 yr or less, corresponding to finer‐scale fire history and forest structure studies. In much of the historical range of American chestnut, the stand structure was much more open, fire scar studies of associated species were very frequent (mean fire return interval ranged between 1.9 and 19.8 yr), and, in many cases, charcoal abundance and American chestnut pollen were positively related. This evidence coupled with American chestnut’s suite of traits associated with tolerance of frequent fire, such as highly flammable litter, tall stature, rapid growth, and resprouting ability, reinforce concepts that fire was historically an important component of many woodlands and forests containing American chestnut. While these lines of evidence are strongly suggestive, we provide potential areas of further inquiry to expand and refine our understanding of American chestnut fire ecology.

Historically open oak and pine savannas and woodlands have transitioned to closed forests comprised of increased numbers of tree species throughout the eastern United States. We reviewed evidence for and against a suite of previously postulated drivers of forest transition focused on (1) change in fire regimes, (2) increased precipitation, (3) increased white-tailed deer densities, and (4) loss of American chestnut. We found that fire and fire exclusion provide a parsimonious mechanism for historical dominance by open forests of fire-tolerant oak and/or pine species and subsequent transition to closed forests with fire-sensitive tree species that fill the vertical profile. Based on statistical tests, increased precipitation during the past century was within historical ranges and thus fails to provide an explanation for forest change; additionally, precipitation variability is incongruent with tree traits (i.e., both drought-tolerant and drought-intolerant species have increased and decreased) and patterns of tree establishment. Similarly, current deer densities fail to provide a statistical relationship to explain tree densities at regional scales, species trends are unrelated to deer browse preferences, and both historically open forests and contemporary closed forests contained high deer densities. Functional extinction of the American chestnut had localized impacts but chestnut was not abundant compared to oak or widespread enough in distribution to match forest transitions throughout the eastern United States. Although Euro-American settlement affected many processes, not all changes were consistent enough to cause transitions in forest composition and structure that generally trailed westward expansion by Euro-American settlers. Evidence about these drivers continues to mount and we recognize the need for further research and continual re-evaluation of drivers of historical forests and forest change due to importance for understanding and management of these ecosystems.

American chestnut (Castanea dentata), a native species of eastern North America, is an economically important deciduous hardwood tree that has been designated as endangered in Canada. The population of American chestnut trees has dwindled significantly across Southern Ontario due to chestnut blight and many of the surviving trees continue to show blight disease symptoms. American chestnut requires efficient strategies for propagation and preservation for species recovery. The objective of this study was to develop a long-term plant conservation program using micropropagation and cryopreservation protocols. An in vitro technology using a liquid-based temporary immersion system (TIS) was developed for micropropagation of American chestnut. The highest rate of shoot multiplication was observed in cultures grown in the DKW (Driver and Kuniyuki 1984) basal medium supplemented with 2.2 µM 6-benzylaminopurine and 1.0 µM gibberellic acid. More than 95% of proliferated microshoots, about 40–50 mm in size, developed roots after 30 days of culture within bioreactor vessels containing DKW basal medium supplemented with 15 µM 3-Indolebutyric acid. Rooted plantlets transplanted to the greenhouse had a survival efficiency of 82% after one month of growth. The cryopreservation protocol for germplasm preservation was developed through droplet vitrification of shoots. Optimal regeneration of shoot tips occurred from explants precultured on stepwise concentrations of sucrose and subsequent dehydration in PVS3 for 30 min. Cryopreserved shoot tips were regenerated to whole plants using pre-optimized conditions of micropropagation. This study confirms the potential of TIS for micropropagation in ex situ conservation and reintroduction of endangered American chestnuts and possibly other woody plant species.

The Asian chestnut gall wasp, Dryocosmus kuriphilus Yasumatsu is an invasive species of global concern that was inadvertently introduced into North America where it induces gall formation on chestnut species including Castanea mollissima Blume, C. crenata Siebold & Zucc., and C. sativa Mill. as well as on the American chestnut, C. dentata (Marshall) Borkh. The gall former was introduced into the United States in the 1970's and since its initial introduction into Georgia, it has been reported to have spread to 13 other states. It has previously been documented as far to the northeast as Connecticut and Massachusetts and as far to the northwest as Michigan. Prior to this study it had been reported in 13 counties within the state of Pennsylvania. The introduction and spread of D. kuriphilus is of particular concern given the intensive efforts to restore American chestnuts into the North American landscape. The purpose of this study was to gain a better understanding of the distribution and spread of the Asian chestnut gall wasp in Eastern Pennsylvania and neighboring states. During the course of this study, specimens of Castanea spp. (Fagaceae) were assessed/monitored for the presence of galls caused by D. kuriphilus at over 100 sites in four states. Herein, galls caused by the Asian chestnut gall wasp are documented, for the first time, on Castanea spp. at several sites in the U.S. states of New Jersey, New York, and Delaware, new state records. Additionally, we report an expansion of the range of the Asian chestnut gall wasp to encompass twenty additional counties within Eastern Pennsylvania. Dispersal of the gall wasps in this study appears to have been influenced by topographical features and wind direction. For further confirmation of identity, we reared D. kuriphilus from galls collected at several sites. These findings establish the range expansion of this gall-forming invasive pest species in the United States to now encompass all of the Mid-Atlantic States. [ABSTRACT FROM AUTHOR]

The iconic American chestnut (Castanea dentata) once spanned a large portion of eastern North America before its functional extinction in the early 20th century due primarily to non‐native fungal pathogens. The pronounced loss of this species likely resulted in an abrupt alteration of many ecological processes, including fire. The potential to resurrect this species through resistance breeding or other methods holds promise, but more information on the fire ecology of American chestnut may provide helpful information to assist restoration. Here we summarize the existing direct and indirect research on the fire history and fire ecology within the former range of American chestnut. We found multiple lines of evidence to suggest fire was frequent throughout much of its historical range. A broadscale analysis of historical fire frequency revealed that 88% of the American chestnut range had a mean fire return interval of 20 yr or less, corresponding to finer‐scale fire history and forest structure studies. In much of the historical range of American chestnut, the stand structure was much more open, fire scar studies of associated species were very frequent (mean fire return interval ranged between 1.9 and 19.8 yr), and, in many cases, charcoal abundance and American chestnut pollen were positively related. This evidence coupled with American chestnut's suite of traits associated with tolerance of frequent fire, such as highly flammable litter, tall stature, rapid growth, and resprouting ability, reinforce concepts that fire was historically an important component of many woodlands and forests containing American chestnut. While these lines of evidence are strongly suggestive, we provide potential areas of further inquiry to expand and refine our understanding of American chestnut fire ecology. [ABSTRACT FROM AUTHOR]

Societal Impact Statement: Over four billion American chestnut trees have been killed as a result of an introduced pathogen, the chestnut blight fungus. Recently, transgenic blight‐tolerant American chestnut trees have been produced by inserting a gene from wheat into the American chestnut genome. Pending federal approval to use these transgenic trees for large‐scale forest restoration, this would be the first instance where a transgenic approach has been used to restore a tree species that has been rendered functionally extinct by an introduced pathogen. With the help of citizen scientists, we estimate that large‐scale forest restoration using blight‐tolerant American chestnut trees is possible within the next few decades. SummaryBreeding transgenic blight‐tolerant American chestnuts with susceptible wild‐type (WT) trees is potentially an efficient method to rescue the genetic diversity and adaptive capacity of the American chestnut population for large‐scale restoration.To develop a breeding plan to diversify a transgenic blight‐tolerant population, we simulated pedigrees to estimate inbreeding coefficients and effective population size in scenarios involving outcrossing 1–4 transgenic founders to a maximum of 1,500 WT trees over 1–5 generations. We also simulated marker‐assisted introgression scenarios to minimize the extent of the transgenic founder genome, especially on the transgene carrier chromosome.Simulations suggest that the effective population size may be increased to >500, and the average inbreeding coefficient reduced to <0.01, by outcrossing a single transgenic founder over five generations to 2, 25, 50, 150, and 450 (677 total) WT parents. Three generations of marker‐assisted introgression is predicted to decrease the length of the founder genome to between 7% and 13% of the transgene carrier chromosome length as compared to 42% with event selection (ES) only. Transgenic outcross selections may be intercrossed to select progeny homozygous for the transgene for planting in seed orchards.A diversified population of transgenic blight‐tolerant American chestnut is estimated to be available for use in large‐scale forest restoration 20–35 years after federal approval to distribute the trees. In contrast, trees from earlier generations would be available almost immediately after federal approval for personal or horticultural plantings. Methods to accelerate pollen production and outcrossing are discussed. [ABSTRACT FROM AUTHOR]

• Chestnut litter exhibits rapid initial decomposition, despite high lignin:N and C:N ratios. • Chestnut soils had lower N and higher DOC in leachate, but similar respiration flux to cherry and oak. • 13C isotopic analyses in surface soil indicate no difference in new soil organic matter between tree species after 10 years. American chestnut (Castenea dentata), once dominant throughout the eastern deciduous forest of North America, was extirpated from its native range by chestnut blight fungus. Through development of blight-resistant trees, the reintroduction of chestnut is likely, though little is known about the biogeochemistry of forests influenced by chestnut. We performed a one-year laboratory incubation experiment with soil and litter from 10-year-old monoculture plantings of pure American chestnut, black cherry, and northern red oak, in addition to a field-based 13C isotopic analysis of soil C. Parameters included litter decomposition, C respiration, N leaching, soil oxidizable C, extracellular enzyme activity related to nutrient acquisition, and litter chemistry. Results indicate that chestnut litter decayed more rapidly than that of oak or cherry (19.0%, 10.8%, 14.1% mass loss in chestnut, oak, and cherry litter, respectively). Chestnut had lower N leaching rates than soils beneath oak or cherry (7.8, 11.5, and 12.0 mg N kg−1 in chestnut, cherry, and oak soils, respectively), greater dissolved organic C (DOC) in leachate than soils influenced by oak (32.2 and 26.4 mg kg−1 in chestnut and oak soil, respectively). No differences in soil respiration or total soil C by species were detected. We conclude that surface soils influenced by chestnut have large inputs of C through rapid litter decomposition and low inorganic N availability, indicating potential for accumulation of C in surface soil over the long-term. [ABSTRACT FROM AUTHOR]

Abstract As genetic engineering becomes a part of the toolkit for the conservation and restoration of biodiversity, a broad range of social science frameworks are required to understand how different groups of people perceive these emerging technologies. Reciprocal restoration is one such framework that offers Indigenous-specific perspective on new applications of genetic engineering for conservation and restoration. The restoration plan for the American chestnut tree includes the potential wild release of a genetically engineered tree in close proximity to the sovereign Haudenosaunee communities of Central and Upstate New York. This paper uses reciprocal restoration as a framework for evaluating if a restoration project that uses a genetically engineered species could support broader cultural restoration efforts in these communities. Results are complex, but suggest that reciprocal restoration may be possible if certain foundational dimensions – such as kincentric relationships and spiritual responsibilities – are attended to. Reciprocal restoration also offers insight for future cases where Indigenous perspectives on the use of genetic engineering for conservation and restoration are important dimensions of broader governance considerations. Highlights • As genetic technology uses for conservation and restoration increase, they require nuanced frameworks for engaging complexity. • Reciprocal restoration identifies & includes Indigenous perspectives about emerging genetic technologies for conservation. • Genetically engineered American chestnut tree may support cultural revitalization in New York State Indigenous communities. • Insight for projects that intersect genetic technologies for conservation, and Indigenous governance of natural resources. [ABSTRACT FROM AUTHOR]

Highlights • Phytophthora cinnamomi is an introduced pathogen of concern in the eastern US. • P. cinnamomi is traditionally associated with low-lying landscape positions. • P. cinnamomi was detected in drier upland sites as well as moist soils. • P. cinnamomi incidence was correlated with oak abundance. Abstract Invasive pests and pathogens have contributed to widescale forest change around the world, but especially in the eastern US. Phytophthora cinnamomi , one such introduced pathogen, causes root rot in American chestnut (Castanea dentata) and shortleaf pine (Pinus echinata), among other eastern forest species of interest, and has inhibited chestnut restoration efforts in some cases. Traditionally, P. cinnamomi has been associated with low landscape positions and moister soils; however, its distribution patterns in the eastern US are poorly understood. Improved understanding of P. cinnamomi distribution may enable forest managers to prioritize sites with low risk of P. cinnamomi presence for chestnut restoration. To elucidate landscape factors associated with P. cinnamomi distribution, two sets of soil samples from an eastern Kentucky forest (representing two levels of sampling intensity) were screened for P. cinnamomi incidence, and data were analyzed for spatial distribution patterns. In general, sites in which P. cinnamomi was detected tended to be warmer (higher annual solar radiation) and drier (lower moisture indices), than sites in which P. cinnamomi were not detected. P. cinnamomi incidence was also found to be associated with oak (Quercus spp.) abundance and (weakly) negatively associated with soil microbial activity under certain conditions. Overall, P. cinnamomi was found to be distributed across a wide range of landscape variables, including both drier ridge-top sites and moister streamside sites, contrary to traditional associations. In addition, the association with oak abundance suggests that the drier upland sites preferred by oak species in eastern Kentucky are not "safe" from P. cinnamomi. Given that P. cinnamomi was found distributed across a range of environmental conditions, forest managers cannot assume that any landscape position is phytophthora-free, and soil screening should be used for site selection to inform restoration of chestnut and other susceptible species. [ABSTRACT FROM AUTHOR]

Biotechnology offers a new approach for the restoration of tree species affected by exotic pathogens; however, nontarget impacts of this novel strategy on other organisms have not been comprehensively assessed. We evaluated the effect of transgenic American chestnut (Castanea dentata) leaf litter on the growth and survival of larval wood frogs (Lithobates sylvaticus), a forest‐dwelling amphibian species widely sympatric with American chestnut, that forage almost entirely on periphyton and litter detritus that accumulate in temporary vernal pools in forests. We reared wood frog larvae on Castanea leaf litter (American chestnut genetically engineered for blight tolerance, nontransgenic American chestnut, Chinese chestnut [Castanea mollissima], and an American–Chinese chestnut hybrid) and litter from two non‐Castanea, nontransgenic "control" tree species, coupled with two levels of supplementary food. We observed no differences in growth or survival of wood frog larvae reared on transgenic versus nontransgenic American chestnut leaves. Without supplementary food, wood frog larvae provided leaves from American chestnut (both types) developed faster and grew larger than those exposed to other leaf litter treatments. Results of this study provide preliminary evidence that (1) American chestnut may have formerly been an important source of food for forest‐dwelling amphibians and (2) transgenic American chestnut litter generated as part of chestnut restoration efforts is unlikely to present direct novel risks to developing amphibian larvae in the forest environment. [ABSTRACT FROM AUTHOR]

Highlights • BC 3 F 3 hybrids had lower resistance than Chinese chestnut under severe blight pressure. • Differences among BC 3 F 3 families were significant under severe blight pressure. • BC 3 F 3 chestnut had higher pathogen resistance than American chestnut across sites. • Interactions between location and breeding generation were significant. • Disease incidence in chestnut was positively related to tree basal diameter. Abstract The loss of American chestnut (Castanea dentata) in eastern North America to chestnut blight, a disease caused by the fungal pathogen (Cryphonectria parasitica), has devastated ecological and utilitarian processes and functions. A backcross breeding approach has been developed to confer disease resistance to hybrid seedlings, and forest reintroduction trials will provide important information on performance and durability of resistance in real-world forest conditions. Three plantings were established in 2009 in mesic, even-aged regeneration harvests (site index averaged 23 m for Quercus rubra) and were examined for eight-year blight resistance. These plantings are the first forest field trials to test blight resistance of the most advanced breeding generation currently available, the third generation of the third backcross (BC 3 F 3), against less advanced breeding generations (BC 1 F 3 , BC 2 F 3), disease-resistant Chinese chestnut (C. mollissima), and disease-susceptible American chestnut. We also examined if C. parasitica infection was related to tree size and growth. The pathogen infected 36 percent of trees across locations by year 8, but 31 percent of trees died prior to detection of infection. Non-pathogen related mortality was probably due to factors that are typical of hardwood plantings, including repeated deer browsing and native and non-native pest damage. The BC 3 F 3 generation exhibited resistance more similar to the Chinese chestnut than the American chestnut, but exhibited significantly lower resistance than Chinese chestnut at the location with the highest blight incidence; genetic family differences among BC 3 F 3 progeny were significant at this location. Interactions between planting location and breeding generation affected resistance rankings, suggesting additional or longer-term testing is needed to determine resistance of a particular breeding line across a variety of sites. Probability of disease incidence was positively related to ground-line diameter (GLD), but this relationship depended on location and breeding type. At two locations, American chestnut had 50 percent probability of C. parasitica infection when GLD was approximately 70 mm, and the BC 3 F 3 had 50 percent probability when GLD was between 93 and 126 mm. The Chinese chestnut maintained low probability of disease incidence (<35 percent) across all GLD sizes, regardless of location. While a relatively high level of disease resistance was associated with the most advanced breeding generation, BC 3 F 3 , the plantings are too young to determine durable blight resistance. [ABSTRACT FROM AUTHOR]

Phytophthora cinnamomi Rands, the causal pathogen of phytophthora root rot (PRR) of chestnut, is one of the main obstacles to growth of american chestnut [Castanea dentata (Marsh.) Bork.] in the southern part of its distribution. To facilitate introgression of PRR resistance of chinese chestnut (C. mollissima Blume) into a C. dentata genetic background, we assessed the disease resistance of 10 interspecific hybrid families derived from potentially resistant C. mollissima cultivars. Hybrid progeny were inoculated with P. cinnamomi in the nursery and assessed for root lesion severity after 1 year of growth. Asymptomatic plants were transplanted to a P. cinnamomi-positive orchard and evaluated for survival midway through the following growing season. During the nursery experiment, 8 of 10 hybrid families were not significantly different from susceptible C. dentata controls for average disease resistance scores. However, multiple asymptomatic individuals were identified in each of the eight families. Two of the 10 hybrid families were not significantly different from the resistant C. mollissima and C. henryi controls. In the P. cinnamomi-positive orchard, the prescreened hybrid families displayed a greater proportion of survivors than backcross families that had not been prescreened for P. cinnamomi resistance. Hybrid plants that have survived 2 years of growth in P. cinnamomi-infested potting media and soils represent an important step toward the production of genetically diverse chestnut populations in the southeastern United States that combine the PRR resistance of C. mollissima with the morphology and local adaptation of C. dentata. [ABSTRACT FROM AUTHOR]

For tens of thousands of years, passenger pigeons (Ectopistes migratorius) were a dominant member of eastern North American forest communities, with megaflocks comprising up to several billion individuals. The extinction of passenger pigeons in the early twentieth century undoubtedly influenced associated species and ecosystems as interactions stemming from the pigeons disappeared suddenly. Here, we strive to better understand what was probably one of the most significant of these interactions—that between passenger pigeons and seed bearing trees. Using the band-tailed pigeon (Patagioenas fasciata) and the rock dove (Columba livia) as physical and ecological proxies, we evaluated passenger pigeon dietary range and potential to disperse seeds. Our findings suggest that the passenger pigeon's dietary range, observed historically to be taxonomically broad, was constrained to certain seed sizes due to bill gape size. In addition, we conclude that the digestive process invariably destroyed consumed seeds but the potential for a nutrition/dispersal mutualism might still have existed via regurgitation and post-mortem release of crop contents. Our results highlight the range of ecological interactions that can be lost with species' extinction and the inherent challenge of understanding the consequences of those interactions.

American chestnut (Castanea dentata) was once an important component forests in the central Appalachians (USA), but it was functionally extirpated nearly a century ago. Attempts are underway to reintroduce blight‐resistant chestnut to its former range, but it is uncertain how current forest composition, climate, and atmospheric changes and disturbance regimes will interact to determine future forest dynamics and ecosystem services. The combination of novel environmental conditions (e.g. climate change), a reintroduced tree species and new disturbance regimes (e.g. exotic insect pests, fire suppression) have no analog in the past that can be used to parameterize phenomenological models. We therefore used a mechanistic approach within the LANDIS‐II forest landscape model that relies on physiological first principles to project forest dynamics as the outcome of competition of tree cohorts for light and water as a function of temperature, precipitation, CO2 concentration, and life history traits. We conducted a factorial landscape simulation experiment to evaluate specific hypotheses about future forest dynamics in two study sites in the center of the former range of chestnut. Our results supported the hypotheses that climate change would favor chestnut because of its optimal temperature range and relative drought resistance, and that chestnut would be less competitive in the more mesic Appalachian Plateau province because competitors will be less stressed. The hypothesis that chestnut will increase carbon stocks was supported, although the increase was modest. Our results confirm that aggressive restoration is needed regardless of climate and soils, and that increased aggressiveness of chestnut restoration increased biomass accumulation. The hypothesis that chestnut restoration will increase both compositional and structural richness was not supported because chestnut displaced some species and age cohorts. Although chestnut restoration did not markedly enhance carbon stocks, our findings provide hope that this formerly important species can be successfully reintroduced and associated ecosystem services recovered. Forests under novel environmental conditions (e.g., climate change), reintroduced species and modified disturbance regimes (e.g., exotic insect pests) with no analog in the past require mechanistic models to robustly project future forest dynamics. We used a forest landscape model based on physiological first principles to test hypotheses about the interactions among climate change, disturbance and land type on nascent efforts to restore blight –resistant American chestnut in the eastern U.S. Climate change should favor chestnut, but chestnut restoration will only modestly increase carbon stocks. Chestnut restoration will likely decrease both compositional and structural richness because chestnut will displaced some species. [ABSTRACT FROM AUTHOR]

Restoration of plants endangered by introduced pathogens relies in part on the ability to predict geographic variation in the incidence of disease and its impact on tree health. Environmental factors can influence plant-pathogen interactions but large scale, multifactorial analyses of environmental determinants are often lacking. Here we use a multi-year survey of the endangered American chestnut in southern Canada and geospatial data on climatic, edaphic, and landscape characteristics to test for spatial heterogeneity in, and environmental associations with, blight occurrence (current incidence of chestnut blight, infection of healthy individuals over 13 years) and tree health (presence of healing/healed cankers, tree mortality). We detected geographic hotspots for all measures of blight occurrence and tree health, suggesting tree-pathogen interactions are moderated by local conditions. Individual measures of blight occurrence were correlated with nine climatic, edaphic and landscape variables and were consistently related to precipitation, surficial geology and elevation. Measures of tree health were consistently affected by mean annual temperature, and individually correlated with five climatic and landscape variables but no edaphic variables. Overall, environmental variables explained 9–22% of variation in blight and tree health, reflecting the complex processes underlying host -pathogen interactions in a system in which blight persists throughout the range. Nevertheless, environmental correlates are sufficient to guide further research on mechanisms of tolerance and aid conservation priorities and action in this species. [ABSTRACT FROM AUTHOR]

Forest tree species in the eastern US such as American chestnut (Castanea dentata (Marsh.) Borkh) and oaks (Quercus spp.) have been negatively impacted by forest changes over the past century. Many mature, introduced pine (Pinus spp.) plantations exist in the Midwest US following establishment 50-60 years ago yet have little economic and ecological value. As oak and chestnut have similar site preferences to pines, these stands may be ideal sites for hardwood restoration plantings. We sought to determine optimal management strategies for converting pine plantations by manipulating their canopies. We underplanted hybrid American chestnut and northern red oak (Quercus rubra L.) seedlings into three canopy treatments (control, shelterwood, clearcut) and included an open field treatment. For each of two growing seasons, 0, 30, or 60 g 19N-6P-12K of controlled-release fertilizer (CRF) were also applied to seedlings. Soil chemical parameters and leaf nutrients were analyzed throughout the study. Chestnut and oak seedlings had significantly greater height after two growing seasons in the clearcut and shelterwood than the control and open field, and chestnut had significantly greater diameter as well. Chestnut height and RCD growth were threefold that of oak after two growing seasons. In general, fertilization increased seedling growth more in the clearcut and open field than shelterwood and control for both species. Soils had significantly higher pH, K, and S in the open field than in pine stands. Results suggest that pine plantations may serve as target sites for restoration of these hardwood species. Shelterwoods and clearcuts are both favorable conversion options for oak and chestnut, and addition of CRF may augment further growth increase, especially in open environments. [ABSTRACT FROM AUTHOR]

Abstract Chestnut blight cankers, caused by the fungus Cryphonectria parasitica , are prone to invasion by other microorganisms as the canker ages. This microbial community has the potential to alter canker expansion, which may influence the probability that the canker girdles the infected stem. Hypoviruses infect the pathogen mycelium directly and are known to decrease pathogen virulence (i.e. hypovirulent). These viral infections can slow pathogen growth, decreasing the rate of canker expansion and lowering the probability of girdling. Saprophytic fungi also invade the expanding canker and may antagonize C. parasitica leading to reduced pathogen growth. The combined effects of fungal antagonism and a hypovirulent pathogen could work in combination to reduce the probability of girdling the infected stem. We assessed the ability of different fungal taxa, isolated from low severity cankers, to inhibit the growth of virulent and hypovirulent forms of C. parasitica in dual culture tests on two cultural media. Percent growth inhibition of virulent C. parasitica by potentially antagonistic fungi ranged from 2 % to 34 %, while inhibition of hypovirulent C. parasitica ranged from 18 % to 54 %. Only one isolate, identified as Umbelopsis isabellina (Umbelopsis WS) inhibited the virulent form of the pathogen more than the hypovirulent form. All three Trichoderma isolates caused the greatest growth inhibition of virulent C. parasitica , but they, like all other fungal isolates tested, inhibited the hypovirulent form of the pathogen more than the virulent form. These results suggest that commonly occurring fungi in chestnut blight cankers, including Trichoderma , may inhibit the hypovirulent C. parasitica more than virulent C. parasitica. Thus, the presence of other fungi in cankers may not enhance the effect of hypovirulent C. parasitica to delay cankers from girdling a stem but instead intensify canker development. [ABSTRACT FROM AUTHOR]

American chestnut (Castanea dentata) was a dominant species in eastern North America prior to the importation of chestnut blight. In light of recent efforts to restore viable populations of chestnut in eastern forests, an increased understanding of its association with other co‐occurring, disturbance‐adapted oak species is necessary. We evaluated crown architecture and leaf morphology in juvenile chestnut and red oak (Quercus rubra) to assess potential differences in establishment strategies of both species. We also investigated differences in nonstructural carbohydrate reserves and whole tree biomass partitioning between species. Seedlings of both species were planted in forest stands treated either with midstory removal or small patch cuts, simulating potential restoration plantings. After 5–7 years, chestnut's allocation to its root system was lower than red oak's, with chestnut saplings instead diverting resources to branches and foliage. Chestnut had lower leaf area index, greater crown projection area, and higher specific leaf area than red oak, indicating the species may have an advantage in shaded understories. There were only minor differences in nonstructural root carbohydrate reserves, between red oak and American chestnut, indicating that chestnut may respond similarly to oak by resprouting after disturbances topkill young saplings. We suggest that American chestnut has morphological and physiological attributes that allow it to function as an opportunistic and plastic species that can utilize gaps to facilitate its canopy recruitment, yet still persist after occasional surface fire. This knowledge can guide restoration strategies for this iconic species of the eastern temperate forest region. [ABSTRACT FROM AUTHOR]

Hypovirus-infected Cryphonectria parasitica strains were introduced in a large stand of American chestnut (>4,000 individuals) in western Wisconsin (USA) to evaluate whether hypoviruses can seive as biological control agents. They were deployed by treating cankers from 1992 to 1997 and again from 2004 to 2014. After 17 years of hypovirus introductions within an area of the stand with the longest history of disease, isolation of hypovirus-infected strains increased from 55% in 1994 to 86% in 2014 from cankers that were treated. During the same period, isolation from cankers that arose on trees with treated cankers increased from 29 to 72% and from 15 to 84% for cankers on nearby trees that received no treatment. Tree survivorship over the 23-year study period for trees with treated cankers was 51 % compared with 31% for trees that were not treated. Introduction of hypovirus has resulted in the regrowth of the crowns of many large-diameter U'ees. Putative recovery of American chestnut in this stand provides evidence that prolonged hypovirus treatment can act as a biological control when limited numbers of vegetative compatibility types of C. parasitica exist. [ABSTRACT FROM AUTHOR]

Abstract: Both seed predators and herbivores can have profound effects on individual plant growth, reproduction and survival, but their population‐level effects are less well understood. While most plants interact with a suite of seed predators and herbivores over their life cycle, few studies incorporate the effects of multiple interacting partners and multiple life stages on plant population growth. We constructed a matrix model using 6 years of data from a rare, seed‐producing population of American chestnut (Castanea dentata). We combined field demographic data with published experimental results on the effects of pre‐dispersal seed predators (weevils) and post‐dispersal seed predators (scatter‐hoarding vertebrates) and incorporated the effect of vertebrate herbivores estimated from the field data. We explored the impact of these three different animal interactions for short‐term (transient) and long‐term (asymptotic) tree population growth. In addition, we used the model to explore the conditions under which scatter hoarding would function as a mutualism. Seed predators had greater effect on both short‐ and long‐term population growth than herbivores. Although weevil infestation can greatly reduce the probability of germination, pre‐dispersal seed predators had smaller effects on both short‐ or long‐term population growth than post‐dispersal predators. The elasticities of weevil‐related parameters were also small. The effect of browsers on both the short‐ and long‐term population growth rate were the smallest of the effects studied. Post‐dispersal seed predation affected population growth the most in the interactions studied. The probability of seed removal was among the largest elasticities, similar in magnitude to survival of large trees. Synthesis. Our results indicate that neither weevils nor the intensity of browse damage observed at our study site are likely to hinder tree regeneration or reintroduction, although both reduced population growth. Although researchers and forest managers often assume that seeds are unimportant for long‐lived tree populations, our test of this assumption shows that scatterhoarders and other post‐dispersal seed consumers can significantly limit natural regeneration. Forest management that alters scatterhoarder behaviour could have significant effects on tree population dynamics that are largely unexplored. [ABSTRACT FROM AUTHOR]

Many field planting trials have shown that Appalachian mined lands reclaimed with the FRA provide an opportunity for introducing blight-resistant chestnuts into eastern USA forests. The level of disease resistance in TACF's population of backcross chestnuts will not be known for several years so continued monitoring will be necessary. However, TACF will continue increasing blight resistance in the chestnuts seedlings that it is distributing for planting. Research has found that mine reclamation sites can be planted to establish founder populations of blightresistant chestnuts that could then spread through natural processes into surrounding forests (Jacobs, 2007). There is still much to be learned about establishing chestnuts as a part of a mixed hardwood forest on mined lands; further research is ongoing. The lessons learned from these trials may also play a role in re-establishing other native tree species that are being threatened by exotic pests and diseases. For example, mined lands are currently being tested to re-introduce American elms that are resistant to Dutch elm disease. The American Chestnut Foundation considers efforts by ARRI and other organizations (such as Green Forests Work) to create productive and biodiverse forests on active mining operations, legacy mines, and AMLs a high priority. As larger numbers of Restoration Chestnuts 1.0 are produced, TACF intends to contribute more for reclamation projects. However, demand for blight-resistant chestnuts will outpace supply for many years to come. Full implementation of the FRA will be important to TACF decisions concerning allocation of blight-resistant chestnut stock for mine reclamation plantings. [ABSTRACT FROM AUTHOR]

American chestnut (Castanea dentate) has been described as a towering giant dominating eastern deciduous forests. To determine whether this portrayal was accurate, we compared pre- and postblight descriptions of American chestnut. Preblight sources most frequently reported maximum height of mature American chestnut as 100 ft whereas postblight descriptions most frequently report a maximum height of 120 ft. In preblight sources, the maximum diameter reported for American chestnut was 13 ft, and in postblight sources 17 ft was regularly identified as the maximum diameter. We hypothesize that confusion between tree circumference and diameter and the inability to correct false descriptions with measurements has resulted in an increase in the reported maximum size of American chestnut in postblight sources. [ABSTRACT FROM AUTHOR]