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Toward development of silvical strategies for forest restoration of American chestnut (Castanea dentata) using blight-resistant hybrids
Abstract
Backcross breeding has provided a viable means to restore American chestnut (Castanea dentata (Marsh.) Borkh.) to eastern North American forests, where the foundation species was essentially extirpated by an introduced pathogen. With the prospect of American chestnut reintroduction imminent, it is critical to formulate restoration strategies based on the ecology and silvics of the species, operational confines, social or policy limitations, and ecological implications. American chestnut was apparently adapted to a relatively wide range of site conditions, has evolved a capacity to survive for prolonged periods beneath forest canopies yet respond rapidly to disturbance, and demonstrates extraordi-nary growth and competitive ability. These characteristics are discussed in reference to operative planting techniques and potential for migration of regeneration from hybrid chestnut plantings into forests of the original American chestnut range. The use of hybrid trees for American chestnut reintroduction may generate social and policy ambiguities that require conciliation. Additionally, potential long-term ecological implications associated with reintroduction of American chestnut to the original species range, or introduction to areas outside its original range, must be realized and integrated into reintroduction strategies. Limitations in genetic fitness, potential for disease mutation, and threats from other exotic insects and pathogens may serve as continual challenges to American chest-nut restoration. This paper helps establish preliminary guidelines for restoration plantings and creates awareness of imposing ecological issues and barriers that must be overcome to successfully restore American chestnut to its natural range, while simultaneously main-taining ecological integrity and ensuring conservation benefits to eastern North American forests.
... The demise of the mighty American chestnut is regarded as the worst ecological disaster in post-glacial eastern North American history (Jacobs, 2007), leading to a vast restructuring of the forests where it once dominated (Stephenson, 1986;Parker et al., 1993;Vandermast and Van Lear, 2002). American chestnut was regarded as a foundation species for its influence on forest community dynamics and ecosystem processes, particularly with regards to the resource provided by its seed and its role in nutrient cycling (Ellison et al., 2005;Dalgleish and Swihart, 2012). ...
... Several challenges exist, however, to this approach that remain to be solved regardless of its efficacy (Strauss et al., 2009;Jacobs et al., 2013). It is unclear whether the public will accept a widely spread genetically modified organism (GMO) on public lands as the solution to restoring American chestnut (Jacobs, 2007;Merkle et al., 2007), and this genetically modified chestnut has yet to be approved by the U.S. Food and Drug Administration (FDA), Environmental Protection Agency (EPA), and other regulatory agencies (Jacobs et al., 2013). Despite the science and technology being adequate, resolving the social and ethical questions that would arise and developing the institutional capacity to cost effectively mass produce and distribute backcross-bred and/or genetically engineered chestnuts remain significant obstacles to reintroduction. ...
... However, despite the focused and sustained efforts to make chestnut resistant to blight, research to determine optimal habitat conditions and management practices for reintroduction of blight-resistant stock is still lacking (Jacobs et al., 2013). The extirpation of American chestnut as a mature canopy tree prior to modern forest ecology and environmental science has left many questions of the species' niche unanswered (Griffin, 2000;Paillet, 2002;Jacobs, 2007;Clark et al., 2014a). Much of what we do know of chestnut ecology comes from historical, qualitative descriptions or observations of planted populations outside the native range of chestnut that were affected later or less by chestnut blight (Paillet, 1982(Paillet, , 1984Paillet and Rutter, 1989). ...
Formerly the most dominant canopy tree species throughout much of eastern North America, the American chestnut (Castanea dentata (Marsh.) Borkh.) has since been decimated by the chestnut blight (Cryphonectria parasitica (Murr.) Barr.) and relegated to scattered understory sprouts. Providing a large, reliable seed crop and high quality timber, the American chestnut was an iconic keystone species, unrivaled in its ecological influence and economic value. Since its demise, however, continued efforts have been made to develop effective chestnut blight resistance and prepare blight-resistant chestnut hybrids for reintroduction in the wild. This project is concerned with the optimal management and habitat conditions for American chestnut within the broader goal of restoration. Does American chestnut sprout regeneration benefit from fire? How does its response to fire vary according to topography? With our incomplete understanding of chestnut fire ecology and geography, this study aims to evaluate the regeneration and distribution of American chestnut sprouts in recently burned areas of a mountainous landscape in the Ridge and Valley province of the central Appalachian Mountains in Virginia. Transects divided into sections were selected in prescribed burn units and areas of wildfire to sample for chestnut response to fire. Observed chestnuts in sections were tallied, with the first in sight measured for additional response variables to gauge vitality: live height, number of live stems, blight infection, total stem diameter, average stem diameter, and shoot-to-root ratio. Characteristics of the fire regime and terrain (environmental variables) were then related to these response variables to determine how chestnut sprouts respond to fire and topography: burned/unburned, canopy cover proportion, number of burns, time since last burn, mean time between successive burns, Heat Load Index, Topographic Wetness Index, and Topographic Position Index. Response variables were averaged by environmental categories or correlated directly to environmental observational pairs. Various statistical tests were used for each comparison between response variable vs. environmental variable depending on the nature of the data involved. The results of this study suggest a complex pattern of American chestnut sprout regeneration in response to fire, with some response variables more or less important in explaining the effect of each fire regime environmental variable. Among the response variables that appear to be positively related to chestnut vitality, there was no indication that increasing fire severity, occurrence, and/or frequency was a detriment to chestnut vitality. Conversely, there was no indication that increasing fire severity, occurrence, and/or frequency reduced the prevalence of blight infection. There were few significant relationships between chestnut vitality and the DEM-derived GIS terrain variables, suggesting that chestnut is well adapted to a variety of slope positions and environmental conditions. Ultimately, American chestnut vitality in early stages of growth is strongly controlled by light availability, and fire can be an important component of restoration.
... American chestnut (Castanea dentata (Marsh.) Borkh.) is a threatened native forest tree in the eastern USA that may become an important species option for mine reclamation (Jacobs 2004(Jacobs , 2007. American chestnut once occupied up to 25% of standing volume in eastern North American forests prior to 1900 (Russell 1987). ...
... Through careful selection for blight resistance and desirable phenotype, these backcross hybrids incorporated Chinese chestnut's blight resistance while retaining the timber and nut-producing characteristics of American chestnut (Hebard 2005;Steiner et al. 2017). Although repeated breeding and additional backcross generations will be necessary (Steiner et al. 2017), initiation of chestnut restoration appears imminent and researchers have examined regeneration of pure and backcross American chestnut hybrids across varying environments (see citations in Jacobs 2007;Jacobs et al. 2013;Wang et al. 2013). ...
... A partnership established by TACF and the Appalachian Regional Reforestation Initiative (ARRI) uses reclaimed surface mines in Appalachia to facilitate re-introducing American chestnut with the FRA (OSMRE 2015). American chestnut is a fast-growing tree species with the ability to persist in shaded environments, variable soil conditions, and well-drained, dry upland sites (Latham 1992;Jacobs 2007); yet it responds favorably to increases in sunlight, soil nutrients and moisture (Wang et al. 2006). The original range of American chestnut had average annual precipitation varying from 90 to 150 cm and average annual temperatures from 5 to 15 °C (Fields-Johnson et al. 2010;Wang et al. 2013). ...
Reclamation of surface mined sites to forests is a preferred post-mining land use option, but performance of planted trees on such sites is variable. American chestnut (Castanea dentata (Marsh.) Borkh.) is a threatened forest tree in the eastern USA that may become an important species option for mine reclamation. Chestnut restoration using backcross hybrids that incorporate blight resistance may be targeted to the Appalachian coal mining region, which corresponds closely with the species’ native range. Thus, it is important to understand how chestnut hybrids perform relative to progenitors on reclamation sites to develop restoration prescriptions. Seeds of parents and three backcross generations of chestnut (100% American, 100% Chinese, and BC1F3, BC2F3, and BC3F2 hybrids) were planted into mine soils in West Virginia, USA with shelter treatments. Survival for all stock types was 44% after 8 years (American 39%, Chinese 77%, BC1F3 40%, BC2F3 28%, and BC3F2 35%). Height for all stock types was 33 cm after 8 years (American 28 cm, Chinese 67 cm, BC1F3 30 cm, BC2F3 21 cm, and BC3F2 20 cm). At another site a year later, seedlings of the chestnut stock types were planted into brown (pH 4.6) or gray sandstone (pH 6.3) mine soils and seedling survival across all stock types was 58% after 7 years. Chinese had the highest survival at 82%, while the others ranged from 38 to 66%. Height was 63 cm for all stock types after 7 years. More advanced backcross hybrids (BC2F3 and BC3F2) had the lowest vigor ratings at both sites after 7–8 years. Our results indicate that surface mines in Appalachia may provide a land base for planting blight-resistant chestnuts, although Chinese chestnut outperformed American chestnut and later generation backcross hybrids. As blight-resistant chestnuts establish and spread after planting, chestnut trees may become a component of the forest canopy again and possibly occupy its former niche, but their spread may alter future forest stand dynamics.
... The biological characteristics of American chestnut, including response to light, soil nutrients and moisture, and competition are being considered with respect to operational planting strategies ( Jacobs 2007). Knowledge of these species characteristics are necessary to select appropriate silvicultural and site preparation strategies (Clark et al. 2014). ...
... American chestnut researchers also took a critical look at their program and identified gaps, opportunities, and challenges encountered by the restoration effort. Consideration of both the social and ecological contexts of programs is also important ( Jacobs 2007, Jacobs et al. 2013. ...
... Additional gaps in the ecological context, including seed zone testing, the incorporation of different sources of resistance, and combating invasive exotic insects were identified as areas for additional study (Clark et al. 2014). The long-term impacts and dynamics of reintroduction on forest ecosystems were considered, including questions about how plantings including American chestnut would be managed over time and how the species may spread from plantings ( Jacobs 2007). Potential future challenges, including deployment strategies, were identified ( Jacobs 2007). ...
... Because American chestnut is fast-growing, long-lived, and resistant to decay (Youngs 2000, Ellison et al. 2005, De Bruijn et al. 2014a, its restoration could result in increased carbon sequestration and storage in the form of living and dead trees and durable wood products. Recent research on American chestnut ecology and silvics (i.e., growth, competitiveness, ecophysiology) in blight-free plantations has found superior growth compared to co-occurring species (Jacobs andSevereid 2004, McEwan et al. 2006). In fact, it appears that they store as much carbon in their boles as do other fast-growing species used for forestry plantations in southwest Wisconsin (Jacobs et al. 2009). ...
... On more mesic sites, production of highvalue hardwoods is a management goal. Although the effects of timber management on carbon dynamics are widely studied (Birdsey et al. 2006), it is unclear how management may impact the ability of chestnut to become abundant (Jacobs 2007, Jacobs et al. 2013. ...
... More intensive silvicultural treatments, such as burning or aggressive harvesting, may be necessary to facilitate desirable rates of spread of blight-resistant chestnut following reintroduction. However, these treatments can be expensive and controversial, and may be impractical at large scales, especially on the public lands that represent a significant portion of the original native range of chestnut (Jacobs 2007). It is possible, however, that chestnut may spread and integrate into forests more quickly than suggested by our results. ...
In the eastern United States, American chestnut (Castanea dentata) was historically a major component of forest communities, but was functionally extirpated in the early 20th century by an introduced pathogen, chestnut blight (Cryphonectria parasitica). Because chestnut is fast-growing, long-lived, and resistant to decay, restoration of American chestnut using blight-resistant stock could have the potential to increase carbon sequestration or storage in forested landscapes. However, carbon dynamics are also affected by interspecific competition, succession, natural disturbance, and forest management activities, and it is unknown how chestnut restoration might interact with these other processes. We used the PnET-Succession extension of the LANDIS-II forest landscape model to study the implications of chestnut restoration on forest composition and carbon storage in the context of other disturbances, including timber harvest and insect pest outbreaks. Our results imply that it could take a millennium or more for chestnut to fully occupy landscapes without aggressive restoration efforts. When successful, chestnut restoration activities displaced other species approximately in proportion to their abundance on the landscape, rather than replacing a single species or genus (e.g., Quercus). Insect pests increased the rate of chestnut colonization by reducing the abundance of competitors, and also had a dominant effect on carbon dynamics. Although chestnut is fast-growing, moderately shade-tolerant, and decomposes very slowly, our results suggest that it can only modestly increase the carbon storage potential of eastern forests. However, our results also demonstrate that compositional changes in forest communities can have noticeable effects on biomass accumulation, even with the large uncertainties introduced by invasive pests.
... American Chestnut (Castanea dentata) was once the foundation species for forests throughout Appalachia along the east coast of the United States. Occupying at least 50% of the basal area across 800,000 square kilometers, American Chestnut trees were once estimated to have numbered more than 4 billion in the early 1900s [1]. These trees produced a prodigious amount of chestnuts. ...
... With the introduction of chestnut blight (Cryphonectria parasitica) in the early 1900s, American Chestnut trees suffered a precipitous and rapid decline. By 1960, American Chestnut trees were almost completely absent from the canopies of eastern forests [1]. It was only in the past decades that blight resistant hybrids made the resurgence of chestnut production possible. ...
The lesser chestnut weevil, Curculio sayi (Gyllenhal), can cause irreparable damage to chestnuts through direct consumption and/or introduction of secondary pathogens. With the resurgence of blight resistant American Chestnut plantings both for commercial production and for habitat restoration, C. sayi has become a similarly resurgence pest. Here, we investigated the nature and extent of C. sayi larval damage on individual nuts and collected harvests with an eye toward the quantifying impacts. Next, we explored management options using biological control including entomopathogenic fungi and entomopathogenic nematodes. Nut damage from C. sayi can be extensive with individual nuts hosting several larvae, larvae emerging from nuts several weeks post harvest, and nut weight loss even after C. sayi have emerged from the nut. Applications of entomopathogenic fungi reduced chances of chestnut infestation, while certain strains of entomopathogenic nematodes increased the probability of C. sayi larval mortality. Understanding C. sayi damage and exploring biological control management options could be a useful tool in the effective management of this resurgent pest.
... American chestnut trees (Castanea dentata) once dominated the forests of the Eastern United States. Up until the early 1900s, an estimated four billion trees, accounting for more than 50% of the total basal area in eastern forests, grew on 800,000 km 2 [1]. A staple of early American life, chestnut trees provided tannin-rich, decay-resistant wood used in everything from furniture to housing to musical instruments [2,3]. ...
... The value of chestnut timber in Pennsylvania alone in 1912 was assessed at USD 55 million, equal to USD 1.4 billion today [3]. The introduction of chestnut blight (Cryphonectria parasitica) in the early 1900s devastated American chestnut forests [1,2,4]. Few trees survived and stump sprouts became infected well before maturation, surviving only as small, multi-stemmed shrubs. ...
With the introduction in recent years of high-yield blight-resistant chestnut varieties, the commercial chestnut industry in the United States is expanding. Accompanying this expansion is a resurgence in a primary pest of chestnut: C. sayi, the lesser chestnut weevil. This weevil damages the nut crop and infestations can surge from 0 to close to 100% in as little as two years. Understanding the dynamics of this pest has been challenging. Most work was conducted in the 1900s and only recently has this weevil garnered renewed interest. Recent work on C. sayi phenology has been completed in Missouri but conflicted with anecdotal reports from northern growers. From 2019 to 2020, we used a combination of trapping and microcosm studies to understand both C. sayi phenology and the means of monitoring this pest. C. sayi populations were univoltine and peaked in mid-October. Pyramid traps were the most effective at capturing adult C. sayi. C. sayi larvae, pupae, eclosed adults, and emerging adults were recovered from microcosm experiments. These results suggest that C. sayi emerges later in the northern US with the potential for a single generation to emerge over multiple subsequent years. Understanding C. sayi phenology along with the means of monitoring forms the basis for effective management and control in commercial chestnut orchards.
... Research related to restoration of threatened tree species generally, and American chestnut specifically, has emphasized that biotechnology is needed to overcome pests or pathogens, but understanding potential ecological barriers and responses to management are also necessary to ensure successful reintroduction (Jacobs, 2007;Jacobs et al., 2013). The majority of investigations of chestnut ecology and biology thus far reflect results of empirical studies conducted on individual field sites, yet restoration of a self-sustaining American chestnut population is a landscape problem because restoration requires a landscape-scale planting program and the population must be resilient to multiple disturbance regimes. ...
... We selected two study areas that differed in rainfall (higher vs. lower) and predominant soil types (mesic vs. xeric) to assess the generality of simulated root rot effects across ecological provinces, which functioned as a third factor with two levels (wet vs. dry). We used a clearcut-and-plant chestnut restoration strategy in all simulations, which was the most aggressive restoration strategy implemented by Gustafson et al. (2018) and has been recommended as an approach to effectively restore chestnut to the landscape (Jacobs, 2007;Jacobs et al., 2013). We simulated a generic "business as usual" timber harvest regime, and the restoration strategy planted chestnut throughout harvested stands (mean size = 9 ha) that received a silvicultural clearcut treatment, and controlled competing regeneration for 1 year. ...
American chestnut (Castanea dentata) was functionally extirpated from eastern US forests by chestnut blight, caused by a fungus from Asia. As efforts to produce blight‐resistant American chestnut germplasm advance, approaches to reintroduce chestnut throughout its former range are being developed. However, chestnut is also quite susceptible to a root disease in the southern half of its former range, and the pathogen that causes the disease (Phytophthora cinnamomi) is expected to move northward as climate warms. Genetic resistance to root rot appears to vary among individual chestnut trees, and the prevalence of resistance is highly uncertain. Because restoration of a self‐sustaining chestnut population is ultimately a landscape‐scale problem, we used a process‐based forest landscape model (LANDIS‐II) to conduct experiments to quantify the effects of root rot on the effectiveness of chestnut population restoration efforts in the center of the former range of chestnut under various climate scenarios. We developed a new LANDIS‐II extension to simulate root rot‐induced tree mortality as a function of temperature and soil moisture. We conducted a factorial simulation experiment with climate and resistance to root rot as factors and found that root rot greatly reduced chestnut biomass on the landscape, even when resistance to root rot infection was at the highest levels currently observed in published studies. Warming climate enhanced the virulence of the pathogen and resulted in a greater reduction in chestnut biomass. Results indicate that root rot has the potential to seriously hamper chestnut restoration efforts if resistance of chestnut is not enhanced through breeding and biotechnology, suggesting restoration efforts will be more successful if targeted to latitudes, elevations, and site conditions where root rot is not expected to be present well into the future, including areas north of the historical chestnut range (Canada). These results demonstrate the vital importance of incorporating root rot resistance into the larger blight resistance breeding program.
... While these factors have been considered key determinants of American chestnut distribution (Russell 1987;Stephenson et al. 1991), limitation of the species to high elevations and well-drained, xeric soils appears to reflect niche contraction in the presence of chestnut blight (Burke 2012) and P. cinnamomi (Rhoades et al. 2003). In fact, American chestnut is known to have been abundant in riparian areas in the southern Appalachians before the arrival of blight (Vandermast and Van Lear 2002), leading to the conclusion that it may be a generalist in terms of site conditions (Jacobs 2007), particularly in the absence of Phytophthora, which is most virulent in poorly-drained and compacted soils (Anagnostakis 2001;Rhoades et al. 2003). In the absence of these two pathogens or given the assisted evolution of resistance to them, other elevations and soil conditions may be suitable for American chestnut. ...
... Contemporary research has also demonstrated the sensitivity of American chestnut seeds, shoots, and leaves to frost damage in the northeastern U.S. (Gurney et al. 2011;Saielli et al. 2012;Schaberg et al. 2017). Relatively little has been published about the relationship between American chestnut distribution and precipitation (Jacobs 2007), but American chestnut growth is known to be limited in very wet and very dry soils (Russell 1987), so the importance of precipitation variables in our model may reflect sensitivity to both drought and saturation. Experimental studies have demonstrated physiological adaptation to water stress in American chestnut (Abrams et al. 1990;Bauerle et al. 2006); however, observed declines in the abundance of chestnut sprouts in both southwestern Virginia (Parker et al. 1993) and western North Carolina (Elliot and Swank 2008) have been partially attributed to severe drought conditions. ...
Given the scale and speed of contemporary environmental changes, intensive conservation interventions are increasingly being proposed that would assist the evolution of adaptive traits in threatened species. The ambition of these projects is tempered by a number of concerns, including the potential maladaptation of manipulated organisms for contemporary and future climatic conditions in their historical ranges. Following the guidelines of the International Union for the Conservation of Nature, we use a species distribution model (SDM) to consider the potential impact of climate change on the distribution and quantity of suitable habitat for American chestnut (Castanea dentata), a functionally extinct forest species that has been the focus of various restoration efforts for over 100 years. Consistent with other SDMs for North American trees, our model shows contraction of climatically suitable habitat for American chestnut within the species’ historical range and the expansion of climatically suitable habitat in regions to the north of it by 2080. These broad changes have significant implications for restoration practice. In particular, they highlight the importance of germplasm conservation, local adaptation, and addressing knowledge gaps about the interspecific interactions of American chestnut. More generally, this model demonstrates that the goals of assisted evolution projects, which often aim to maintain species in their native ranges, need to account for the uncertainty and novelty of future environmental conditions.
... Chestnut trees have been naturally replaced in forest stands by various species, but commonly by hickory (Carya spp.), yellow poplar (Liriodendron tulipifera), and oaks (Quercus spp.) (Nelson, 1955). Through a combination of backcross-breeding (Hebard, 2006) and more recent transgenic approaches (Zhang et al., 2013), the reintroduction of chestnut throughout the eastern deciduous forest is considered "imminent" (Jacobs, 2007) and engenders great public support. In the event of a successful reintroduction of the American chestnut, significant ecosystem changes in C and nutrient cycling and ecosystem water availability are expected (Ellison et al., 2005), but have yet to be understood or quantified at a landscape level. ...
... Significant work has been done involving the silvicultural prescriptions and habitat preferences of chestnut (Jacobs and Severeid, 2004;McCament and McCarthy, 2005;Jacobs, 2007;Rhoades et al., 2009), indicating that chestnut is a generalist, intermediate shade-tolerant species, adapted to a relatively broad range of site conditions. It is reported that chestnut is highly competitive and fast-growing during the juvenile phase and it is readily capable of out-competing and replacing other native species such as oak (Quercus) and hickory (Carya) species for canopy dominance. ...
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.
... Recommended strategies include planting blight resistant trees [82], creating strains of blight fungus that are less virulent [83], and crossbreeding trees [84], such as naturally resistant Asian chestnut trees and American chestnuts. Although many papers focus on gene manipulation as a restoration strategy, others suggest more large- scale strategies such as maintaining tree stand structure, maintaining healthy and resis- tant tree species, and timber extraction [85]. ...
... Invasive plant encroachment into ecosystems have unintended consequences for microbial pathogens, such as influencing the abundance and diversity of native fungal pathogens in ways that benefit their growth or harm native plants. Indeed, invasive plants alter soil fungal composition [63,67,82]. The spread of invasive pathogens by invasive species has been widely covered in agricultural research. ...
... The causal agent of chestnut blight, Cryphonectria parasitica, was first discovered in the northeastern United States in the early 1900's, after it had been brought over from Asia via infected chestnut nursery stock (Griffin, 2000). By 1960, chestnut blight had killed about 4 billion American chestnut trees, and so almost all American chestnut trees that are alive today are susceptible sprouts that originated from blight-killed trees (Jacobs, 2007). Due to the fact that it can now only persist as an understory sprout in its native range, American chestnut is regarded as functionally extinct (Paillet, 2002). ...
... American chestnut was once a widespread, dominant tree species throughout the deciduous forests of eastern North America, but is currently described as functionally extinct (Griffin, 2000). Almost all American chestnut trees that exist today are susceptible sprouts that originated from blight-infected trees (Jacobs, 2007). There have been several attempts to create a blight-resistant American chestnut tree to introduce into its native range. ...
The American chestnut (Castanea dentata) once played an integral part in forests within
Eastern North America, providing many ecological and economic benefits. The majority of these trees were eradicated by an introduced pathogenic fungus, leaving the American chestnut functionally extinct. Disease-resistant transgenic trees containing the transgene oxalate oxidase were developed to re-establish the American chestnut to its native range. In order to introduce transgenic American chestnut trees into forests, federal policies from USDA APHIS, FDA and EPA require that the ecological functions of the transgenic trees be equivalent to those of wildtype American chestnut trees. This study is aimed at determining if the rates of decomposition, elemental concentrations and contents, and diversity of colonizing fungi are significantly different among transgenic and wild-type American chestnut leaf litter in situ. Litterbags containing each type of leaf litter were placed in a shelterwood plot for 12, 18, 24, and 30 months for the decomposition experiment and five months for the fungal diversity experiment. Differences among litter types in the decomposition experiment increased over time, with more differences appearing at 30 months. No clear differences among types were found in decomposition rate, C and N content, C/N ratio, or the majority of nutrients. The only statistically significant difference among types found during nutrient release was in calcium concentration and content, and phosphorus concentration, with one of the transgenic types having higher values over time than other litter types In the fungal diversity experiment, one of the transgenic events did show a slightly lower diversity of fungal species than other litter types, but the community structures were similar among litter types; after 5 months all litter types were dominated by ectomycorrizal fungi. Taken together, these studies suggest that the process of genetic engineering using the transgene oxalate oxidase does not have any measureable effect on the mineralization of plant material. Upon future approval of federal deregulation, the American chestnut will be the first genetically modified non-orchard tree to be deregulated and environmentally released, which will make the process easier for the genetic engineering of other threatened native tree species in the future.
... Forest managers are considering large-scale reforestation and restoration plantings of putatively disease-resistant American chestnut seedlings produced through backcross hybridization with blightresistant Chinese chestnut (C. mollissima) (Steiner and Carlson 2006;Jacobs 2007). Although ongoing work holds much promise, the effectiveness and feasibility of a large-scale effort still presents challenges (Clark and others 2014, 2016; Steiner and others 2017). ...
... Although ongoing work holds much promise, the effectiveness and feasibility of a large-scale effort still presents challenges (Clark and others 2014, 2016; Steiner and others 2017). Recent research has advanced our understanding of the performance of disease-resistant chestnut genotypes (Clark and others 2012, 2016; Brown and others 2014; Knapp and others 2014;Pinchot and others 2015), although the potential impacts of these novel genotypes on ecological processes and other factors have been largely unexamined (Jacobs 2007;Jacobs and others 2013). ...
Loss of native foundation tree species to introduced pests profoundly alters the structure and function of many forest ecosystems. Recent advances to resurrect or prevent the loss of species by developing resistant hybrids hold promise, but uncertainty remains about the potential impacts of introducing a novel genotype on ecological processes, such as fire. A classic example of a non-native, pathogen-caused loss of a foundation species is American chestnut (Castanea dentata), a species now functionally extinct from the eastern US but undergoing experimental trials to resurrect the species with a putatively disease-resistant genotype. We compared the litter flammability among American chestnut, Chinese chestnut (C. mollisima), and a population of first intercross, third-generation backcrossed hybrid (BC3F2) using laboratory burning experiments. Litter flammability of American chestnut was consistently greater than Chinese chestnut, whereas the hybrid had an intermediate flammability or more closely resembled Chinese chestnut flammability by some measures. Greater flammability in American chestnut was associated with a longer leaf structure with greater curling when dry. American chestnut had flammability properties consistent with other pyrophytic species present in contemporary fire-prone ecosystems. The loss of American chestnut may have altered litter flammability of some eastern US forest ecosystems, a result more commonly associated with compositional changes in conjunction with fire exclusion and other disturbances. Resurrecting American chestnut with a hybrid genotype may mitigate this change in areas where less flammable species have replaced American chestnut. Resurrection of lost foundation species through introduction of resistant genotypes may represent a resounding ecological success story, but unanticipated changes to ecological processes, such as fire, should be considered.
... Therefore, strenuous efforts should be instituted to curb its outbreak, the infectivity of which could be aggravated by global warming. It is an urgent task to accelerate the selection and breeding of new varieties with strong resistance to the disease (Jacobs, 2007). Based on the prediction results in relation to current and future climate, we propose classifying the excellent habitats of C. ...
Castanea henryi, with edible nuts and timber value, is a key tree species playing essential roles in China's subtropical forest ecosystems. However, natural and human perturbations have nearly depleted its wild populations. The study identified the dominant environmental variables enabling and limiting its distribution and predicted its suitable habitats and distribution. The 212 occurrence records covering the whole distribution range of C. henryi in China and nine main bioclimatic variables were selected for detailed analysis. We applied the maximum entropy model (MaxEnt) and QGIS to predict potentially suitable habitats under the current and four future climate-change scenarios. The limiting factors for distribution were accessed by Jackknife, percent contribution, and permutation importance. We found that the current distribution areas were concentrated in the typical subtropical zone, mainly Central and South China provinces. The modeling results indicated temperature as the critical determinant of distribution patterns, including mean temperature of the coldest quarter, isothermality, and mean diurnal range. Winter low temperature imposed an effective constraint on its spread. Moisture served as a secondary factor in species distribution, involving precipitation seasonality and annual precipitation. Under future climate-change scenarios, excellent habitats would expand and shift northwards, whereas range contraction would occur on the southern edge. Extreme climate change could bring notable range shrinkage. This study provided a basis for protecting the species' germplasm resources. The findings could guide the management, cultivation, and conservation of C. henryi, assisted by a proposed three-domain operation framework: preservation areas, loss areas, and new areas, each to be implemented using tailor-made strategies.
... The limitation of tree and tree product movement (Mabbett, 2017), the efforts associated with changes in silvicultural strategies such as the treatment of stumps where Heterobasidion spp. are emerging , severing root connections where DED or other vascular diseases are present (Campana and Stipes, 1981), or the use of disease-resistant tree genotypes and hybrids (Jacobs, 2007) also come at a cost and further require societal acceptance. While acceptance of various control strategies may be more easily granted if communities are economically impacted by a disease and thus knowledgeable about the issues (Okan et al., 2017), a longer and more involved dialogue among stakeholders may be required to reach social acceptance of certain disease control strategies and of their costs (ecological, evolutionary, and societal) (Martín et al., 2019). ...
Inexplicably, the review literature on biological invasions has often omitted those by plant pathogens. Here, we provide a review on the consequences of invasions by forest pathogens, whether non-native and introduced or native and invasive due to ecosystem-level alterations such as those caused by climate change, practices associated with forestry, and the planting of exotic hosts. Together, these two classes of invasive pathogens can be defined as emergent and can lead to the rise of novel plant diseases causing detrimental effects on affected ecosystems. This chapter will present examples of such detrimental effects with a focus that goes beyond the mortality of the main host plants, by including ecosystem-level, evolutionary, economic, and societal impacts associated with disease outbreaks caused by emergent tree pathogens.
... Because of their role in creating new crops, plant breeders play a crucial role in the development of sustainable agricultural systems for the future (Brummer et al. 2011). Some general breeding strategies have included selection for lower input requirements that may decrease fossil fuel use, water contamination, and production cost (Tilman 1999;Robertson and Swinton 2005;Dawson et al. 2008) or adaptation to stress (Araus et al. 2008;Cattivelli et al. 2008;Jacobs 2007;Santini et al. 2007). Other strategies include breeding for highly diverse cropping systems (Ceccarelli et al. 2010;Liebman 2012) and regional breeding strategies to withstand variable and or changing environments. ...
There is an increased demand for food-grade grains grown sustainably. Hard red winter wheat has comparative advantages for organic farm rotations due to fall soil cover, weed competition, and grain yields. However, limitations of currently available cultivars such as poor disease resistance, winter hardiness, and baking quality, challenges its adoption and use. Our goal was to develop a participatory hard red winter wheat breeding program for the US Upper Midwest involving farmers, millers, and bakers. Specifically, our goals include (1) an evaluation of genotype-by-environment interaction (GEI) and genotypic stability for both agronomic and quality traits, and (2) the development of on-farm trials as well as baking and sensory evaluations of genotypes to include farmers, millers, and bakers’ perspectives in the breeding process. Selection in early generations for diseases and protein content was followed by multi-environment evaluations for agronomic, disease, and quality traits in three locations during five years, on-farm evaluations, baking trials, and sensory evaluations. GEI was substantial for most traits, but no repeatable environmental conditions were significant contributors to GEI making selection for stability a critical trait. Breeding lines had similar performance in on-station and on-farm trials compared to commercial checks, but some breeding lines were more stable than the checks for agronomic, quality traits, and baking performance. These results suggest that stable lines can be developed using a participatory breeding approach under organic management. Crop improvement explicitly targeting sustainable agriculture practices for selection with farm to table participatory perspectives are critical to achieve long-term sustainable crop production.
Key message
We describe a hard red winter wheat breeding program focused on developing genotypes adapted to organic systems in the US Upper Midwest for high-end artisan baking quality using participatory approaches.
... Although genetic technologies have expedited the production of blight-resistant American chestnut germplasm, in our interviews, scientists involved in both the backcross and transgenic programs expressed concern over the imminent bottleneck in the production of blight-resistant material for restoration and uncertainty about how it might be resolved. The goal of restoring the species across its native range, which covered some 180 million acres, will require large-scale production of seeds and trees, and TACF's seed orchards are not likely sufficient to keep up with demand, either for restoration or to satisfy public interest (Jacobs, 2007). Some of the scientists we interviewed suggested that commercial nurseries may play an important role. ...
Innovations in genetics and genomics have been heavily critiqued as technologies that have widely supported the privatization and commodification of natural resources. However, emerging applications of these tools to ecological restoration challenge narratives that cast genetic technoscience as inevitably enrolled in the enactment and extension of neoliberal capitalism. In this paper, we draw on Langdon Winner’s theory of technological politics to suggest that the context in which genetic technologies are developed and deployed matters for their political outcomes. We describe how genetic approaches to the restoration of functionally extinct American chestnut trees—by non-profit organizations, for the restoration of a wild, heritage forest species, and with unconventional intellectual property protections—are challenging precedents in the political economy of plant biotechnology. Through participant observation, interviews with scientists, and historical analysis, we employ the theoretical lens provided by Karl Polanyi’s double movement to describe how the anticipations and agency of the developers of blight-resistant American chestnut trees, combined with chestnut biology and the context of restoration, have thus far resisted key forms of the genetic privatization and commodification of chestnut germplasm. Still, the politics of blight-resistant American chestnut remain incomplete and undetermined; we thus call upon scholars to use the uneven and socially constructed character of both technologies and neoliberalism to help shape this and other applications of genetic technoscience for conservation.
... Members of the Fagaceae family are susceptible to P. cinnamomi, with the Quercus genus having moderate susceptibility, and the Castanea genus being highly susceptible (Crandall et al. 1945;McConnell et al. 2015). Because C. dentata possesses no natural resistance to the pathogen and breeding of blight-resistant hybrids did not previously select for Phytophthora resistance, many hybrids are also susceptible (Anagnostakis 2001;Jacobs 2007). Although we did not test our seedling roots for Phythophthora colonization, patterns of mortality in our greenhouse experiment as well as previous samples (Clark unpublished data) from our planting sites suggest that the pathogen may be directly involved in the negative PSFs of Castanea. ...
The reintroduction of disease‐resistant hybrids is a commonly proposed solution to the introduction of pathogens and pests that weaken or eliminate native plant species. Plant interactions with soil biota result in plant–soil feedbacks (PSFs), which have consequences for individual plant growth and survival as well as broader community‐level processes, such as species diversity and coexistence. Because of their importance, species reintroduction should consider these interactions, yet little work has integrated this perspective. Here, we investigate the effects of hybrid Castanea (chestnut) reintroduction on PSFs and how these mechanisms may influence the recruitment of other species in contemporary forests. We also examine how blight‐resistant Castanea hybrids perform in the soil conditions of contemporary forests and we compare their below‐ground interactions with those of C. dentata. We conducted a reciprocal greenhouse experiment testing the effect of species‐specific soil inoculum on the growth and survival of C. dentata, Castanea hybrids and other forest dominants. Our results suggest that C. dentata and hybrids had similar belowground interactions and were regulated by negative PSFs, meaning soil microbial communities reduced conspecific growth and survival. These negative PSFs may involve the presence of the non‐native pathogen Phytophthera cinnamomi. Soil inoculum of C. dentata and Castanea hybrids had similar effects on heterospecific growth, suggesting Castanea restoration will have neutral effects on natural regeneration in restoration plantings. We conclude that Castanea hybrids may fill a similar below‐ground niche to their parent species, and that site selection, screening for soil pathogens, and site planting density will be important to restoration.
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... More recently, the development of a transgenic American chestnut that is pathogen-resistant also holds much promise for reintroducing the species (Zhang et al. 2013, Steiner et al. 2017. While more research is needed on the efficacy of larger scale reintroductions of pathogen-resistant American chestnut, studies of site suitability and silvicultural considerations have been conducted in an effort to facilitate landscape-level reintroduction (Jacobs 2007, Zhang et al. 2019, Tulowiecki 2020. As demonstrated by restoration efforts with other co-occurring species (e.g., P. rigida, P. echinata; Stambaugh et al. 2019), successful reintroduction of American chestnut may benefit from a better understanding of its disturbance ecology and the potential to incorporate fire in its recovery and management. ...
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.
... Global forests provide essential ecological, economic and cultural services, but their capacity for carbon storage and climate regulation is increasingly threatened by altered climatic conditions and increased attack by pests and pathogens [1,2]. In recent decades, devastating outbreaks of tree disease such as chestnut blight [3], Dutch elm disease [4], and ash dieback [5], have changed the global landscape, and tree pests and diseases therefore represent a major future threat to forest biomes. Such diseases often involve the activity of both insect pests and microbial pathogens, and ultimately arise from complex interactions between the host, environment, pests and pathogens [6][7][8]. ...
Forest declines caused by climate disturbance, insect pests and microbial pathogens threaten the global landscape, and tree diseases are increasingly attributed to the emergent properties of complex ecological interactions between the host, microbiota and insects. To address this hypothesis, we combined reductionist approaches (single and polyspecies bacterial cultures) with emergentist approaches (bacterial inoculations in an oak infection model with the addition of insect larvae) to unravel the gene expression landscape and symptom severity of host–microbiota–insect interactions in the acute oak decline (AOD) pathosystem. AOD is a complex decline disease characterized by predisposing abiotic factors, inner bark lesions driven by a bacterial pathobiome, and larval galleries of the bark-boring beetle Agrilus biguttatus . We identified expression of key pathogenicity genes in Brenneria goodwinii , the dominant member of the AOD pathobiome, tissue-specific gene expression profiles, cooperation with other bacterial pathobiome members in sugar catabolism, and demonstrated amplification of pathogenic gene expression in the presence of Agrilus larvae. This study highlights the emergent properties of complex host–pathobiota–insect interactions that underlie the pathology of diseases that threaten global forest biomes.
... A series of insects and pathogens have pulsed through the Eastern Deciduous Forest in the United States, causing widespread tree mortality. For example, the fungal pathogen Cryphonectria parasitica (Murrill) Barr swept through the Appalachian Mountains, devastating American chestnut (Castanea dentata (Marshall) Borkh.) and initiating what has become a flagship restoration effort [1][2][3][4][5]. A series of mortality agents have had similar effects, including the butternut canker, dogwood anthracnose, gypsy moth and hemlock wooly adelgid, among many others [6][7][8][9]. ...
In the Midwestern United States, there is a strong management impetus toward reforestation to replace trees lost to due to tree mortality and to establish forests on previously cleared properties. Here, we describe a public outreach and volunteer effort that aimed to generate positive, community-engaged restoration outcomes and report on a practical experiment involving seed handling. We obtained tree seeds that were donated by members of the community to local land managers. We evaluated the size of the seeds collected and tested the influence of common stratification media (none, sand and vermiculite) and seed size on germination success of three tree genera involved in restoration efforts: Quercus, Carya and Juglans (oak, hickory and walnut). We found a species-specific effect of media on germination, such that Carya and Quercus showed little response to their stratification media, but Juglans had higher germination rates when stratified with vermiculite. Further, all genera of seeds germinated faster when stratified with either media than without. Thus, we suggest stratifying these seeds with media to promote germination success. We also tested for seed size as a predictor of mortality during stratification, following the logic that a size-based selection criterion might save time and space during stratification. We found species-specific impacts of seed size on germination, but relationships were highly variable, and we suggest avoiding screening seeds based on their size. In addition to these scientific results, we describe the broader forest restoration project, which may be a useful model for engaging the community in restoration efforts.
... For example, American elm trees with resistance to Dutch elm disease have been planted in multiple restoration plantings with early success . Other diseases like the chestnut blight also required the reintroduction of resistant trees, where crosses of Chinese chestnut (Castanea mollissima Blume) and American chestnut were then backcrossed multiple times with American chestnut and selected for resistance characteristics (Jacobs, 2007). These resistant trees thrived in areas with slow growing species like oaks and hickories (Schlarbaum et al., 1997). ...
The invasive emerald ash borer (Agrilus planipennis Fairmaire, EAB) has destroyed ash tree (Fraxinus spp.) populations across the US, but remnant populations including many small trees and, more rarely, larger trees remain after EAB had its first major impact across the landscape. The future survival of these remnant trees is critical to the viability of the ash species. Several different management options, including biocontrol, EAB-tolerant or resistant ash trees, and silvicultural strategies exist or are under development. Here we model changes that could occur in a preserve's remnant population of green ash (Fraxinus pennsylvanica Marsh.) after EAB peak mortality to assess management strategies. We used population viability analysis (PVA) and created a stage based model with baseline conditions and a model with recurrent catastrophes, where a catastrophe was defined as a year with reduced ash survival from an EAB outbreak. The catastrophes model had an increasing probability of a catastrophe occurring over ten years and included a gradual increase in ash survival (decline in EAB impacts) over the 9 years following a catastrophic event. We explored management scenarios for the catastrophes model including, 1) the reduction of future EAB induced mortality events to mimic possible effects of biological control or other environmental constraints ; 2) addition of trees with increased survival to mimic restoration by planting ash trees with resistance to EAB, which are currently under development, or mimic clusters of trees with natural resistance to EAB created by natural selection. We also performed a sensitivity analysis to assess which size class impacted the population persistence the most over time and found that new seedlings were the most influential. There was no risk of extinction under the baseline model. The reduced catastrophe scenario was an improvement from the catastrophes model, reducing probability of extinction by 33%. Adding healthy ash improved population abundances over time and reduced the probability of extinction when there were repeated plantings. These scenarios relied on assumptions about how the population would react to management treatments, based on the scientific literature and cautious estimates. This approach provides a starting point for experiments testing individual management treatments to generate testable hypotheses, and the model may be readily updated with new data as it becomes available. Our PVA has revealed potential outcomes of alternative management practices and can increase our understanding of natural ash populations remaining after EAB introduction.
... Traditionally, perennial crops have not been a major focus of breed-ing programs because they generally take more time and scientific knowledge to improve, and therefore, products such as new cultivars are often not produced within the timeframe of funding cycles. Current tree breeding programs are developing elms (Ulmus spp.), chestnuts (Castanea dentata), hemlocks (Tsuga spp.), and other species which are resistant to introduced diseases and insects [109,110]. As compared with natural selection, artificial selection via plant breeding has overcome these stresses more effectively by rapidly incorporating diverse exotic genetic sources of resistance, hybridizing to include multiple, different genetic resistances into the same plant, and making use of off-season locations or artificial conditions to shorten generation cycles. ...
... Given the long generation time of trees, reduced genetic diversity could leave populations vulnerable to extinction through pathogen evolution as well as other emerging threats (e.g. emerald ash borer, Agrilus planipennis) (Jacobs, 2007). In addition, the proportion of trees tolerant to ash dieback are currently unknown but are likely to be very low, perhaps in the range of 1%-5% (McKinney et al., 2014;McMullan et al., 2018). ...
Tree pathogens are a major threat to forest ecosystems. Conservation management strategies can exploit natural mechanisms of resistance, such as tree genotype and host‐associated microbial communities. However, fungal and bacterial communities are rarely looked at in the same framework, particularly in conjunction with host genotype. Here, we explore these relationships and their influence on ash dieback disease, caused by the pathogen Hymenoscyphus fraxineus, in European common ash trees. We collected leaves from UK ash trees and used microsatellite markers to genotype trees, qPCR to quantify H. fraxineus infection load, and ITS and 16S rRNA amplicon sequencing to identify fungal and bacterial communities, respectively. There was a significant association between H. fraxineus infection intensity and ash leaf fungal and bacterial community composition. Higher infection levels were positively correlated with fungal community alpha diversity, and a number of fungal and bacterial genera were significantly associated with infection presence and intensity. Under higher infection loads, leaf microbial networks were characterised by stronger associations between fewer members than those associated with lower infection levels. Together these results suggest that H. fraxineus disrupts stable endophyte communities after a particular infection threshold is reached, and may enable proliferation of opportunistic microbes. We identified three microbial genera associated with an absence of infection, potentially indicating an antagonistic relationship with H. fraxineus that could be utilised in the development of anti‐pathogen treatments. Host genotype did not directly affect infection, but did significantly affect leaf fungal community composition. Thus, host genotype could have the potential to indirectly affect disease susceptibility through genotype x microbiome interactions, and should be considered when selectively breeding trees. Synthesis. We show the diversity, composition and network structure of ash leaf microbial communities are associated with the severity of infection from ash dieback disease, with evidence of disease‐induced dysbiosis. We also show that host genotype influences leaf fungal community composition, but does not directly influence tree infection. These findings help to elucidate relationships between host genetics, the microbiome, and a tree pathogen, highlighting potential resistance mechanisms and possible co‐infection concerns that could inform ash tree management.
... PW wrote the initial draft, and all authors commented on and discussed revisions. resource (Jacobs 2007;Jacobs et al. 2013). Native pests and pathogens can also have important sustained or periodic impacts with high levels of mortality and damage (Aukema et al. 2006). ...
Key message
To inform emerging initiatives, we explored five programmes that aimed to develop trees resistant to specific pests or pathogens. These case studies show resistant tree programmes are a medium to long-term approach requiring sustained investment, and can encounter substantial difficulties in developing and maintaining resistance. Equally, adequately resourced and well-planned programmes have resulted in operational deployment of resistant trees.
Context
Developing trees that are resistant to specific pests and pathogens is an increasingly prominent strategy for responding to this escalating threat. It is therefore important to ensure decisions to use resistant trees and approaches to development are well-informed.
Aims
We aimed to provide insights for newer or proposed resistant tree breeding programmes by identifying key lessons from earlier programmes, some of which date back several decades.
Methods
We selected five mature programmes as case studies, and in each case synthesised information from key publications and by following citations to original sources. We examined the objectives, methods, problems, successes and timescales in each programme.
Results
Resistant tree breeding is generally a medium to long-term approach requiring sustained investment and co-ordination, although culturally valued species can attract considerable support from volunteers. Deployment of resistant trees often recommends maintaining genetic variation and mixing with other tree species. Substantial costs and loss of confidence in future material can arise if resistance breaks down or resistant material is susceptible to other threats.
Conclusion
The case studies illustrate success is not guaranteed, but also provide evidence that adequately resourced and well-planned resistant tree programmes can contribute to strategies to mitigate impacts from pests and pathogens.
... Another pathogen is Cryphonectria parasitica, having a similar negative impact on this species. At the beginning of the twentieth century, chestnut was teetering on the brink of extinction caused mainly by C. parasitica (Jacobs 2007). The widespread loss of chestnut from the eastern USA ecosystem caused severe economic and ecosystem disruptions that had both short-term effects and longterm impacts (Diamond et al. 2000;Gilland et al. 2012;Clark et al. 2016). ...
Context
The American chestnut (Castanea dentata, hereafter called chestnut), a valuable tree species that was once common in the last century in the eastern USA, is currently nearly extinct due to blight. Many efforts have been made to develop blight-resilient seedlings of this species, and an associated challenge is to identify the most suitable sites for its restoration.
Objectives
Our objectives were to identify the suitable sites for planting blight-resistant chestnut seedlings and the environmental parameters associated with the suitability assessment. Furthermore, we considered land ownership due to practical planning and management implications.
Methods
Our study area is located in northeast Georgia, USA. We used global sensitivity and uncertainty analysis to select four environmental factors, as criteria in multi-criteria decision analysis, to create suitability maps for chestnut reestablishment.
Results
The results indicate that chestnut is sensitive to elevation, precipitation during the driest month (PDM), normalized difference of water index (NDWI), ground slope, and topographic aspect. Soil attributes did not play a significant role in determining the site suitability. Deciduous forests were the most suitable sites for chestnut reestablishment, while over 99% of the suitable sites fall within the federal lands. The occurrence of chestnut may be expected to increase in areas with high elevations and steep slopes.
Conclusions
This study identifies the most critical environmental variables in northern Georgia for assuring a successful reestablishment of chestnut with the new blight-resistant strains of this species. It also identifies silvicultural prescriptions that may help landowners with the reestablishment process and its success.
... Therefore, extensive mortality of American chestnut trees in the southeastern United States in the early to mid-1800s has been speculated to be from Phytophthora root rot (Crandall et al. 1945;Zentmyer 1980). Today, Phytophthora root rot has the potential to limit reintroduction of American chestnut trees with improved resistance to Cryphonectria parasitica across large areas of the native range of Castanea dentata (Anagnostakis 2001;Jacobs 2007). Whereas American chestnut resprouts from the roots after stems are killed by chestnut blight, the whole plant is killed by Phytophthora root rot. ...
Restoration of American chestnut (Castanea dentata) depends on combining resistance to both the chestnut blight fungus (Cryphonectria parasitica) and Phytophthora cinnamomi, which causes Phytophthora root rot, in a diverse population of C. dentata. Over a 14-year period (2004 to 2017), survival and root health of American chestnut backcross seedlings after inoculation with P. cinnamomi were compared among 28 BC3, 66 BC4, and 389 BC3F3 families that descended from two BC1 trees (Clapper and Graves) with different Chinese chestnut grandparents. The 5% most resistant Graves BC3F3 families survived P. cinnamomi infection at rates of 75 to 100% but had mean root health scores that were intermediate between resistant Chinese chestnut and susceptible American chestnut families. Within Graves BC3F3 families, seedling survival was greater than survival of Graves BC3 and BC4 families and was not genetically correlated with chestnut blight canker severity. Only low to intermediate resistance to P. cinnamomi was detected among backcross descendants from the Clapper tree. Results suggest that major-effect resistance alleles were inherited by descendants from the Graves tree, that intercrossing backcross trees enhances progeny resistance to P. cinnamomi, and that alleles for resistance to P. cinnamomi and C. parasitica are not linked. To combine resistance to both C. parasitica and P. cinnamomi, a diverse Graves backcross population will be screened for resistance to P. cinnamomi, survivors bred with trees selected for resistance to C. parasitica, and progeny selected for resistance to both pathogens will be intercrossed.
... Dispersal by squirrels will be important for chestnut restoration, which is the goal of the TACF breeding program. Chestnut is likely to be planted largely in reclaimed minelands, old fields, and other open sites (Jacobs, 2007). ...
Dispersal of seeds by scatter‐hoarding rodents is common among tropical and temperate tree species, including chestnuts in the genus Castanea. Backcrossed (BC) interspecific hybrid chestnuts exhibit wide variation in seed traits: as the parent species (Castanea dentata and C. mollissima) have distinct seed phenotypes and tend to be handled differently by seed dispersers, phenotypic variation in BC trees is likely due to inheritance of genes that have undergone divergent evolution in the parent species. To identify candidate genomic regions for interspecific differences in seed dispersal, we used tagged seeds to measure average dispersal distance for seeds of third‐generation BC chestnuts and sequenced pooled whole genomes of mother trees with contrasting seed dispersal: high caching rate/long distance; low caching rate/short distance; no caching. Candidate regions affecting seed dispersal were identified as loci with more C. mollissima alleles in the high caching rate/ long‐distance pool than expected by chance and observed in the other two pools. Functional annotations of candidate regions included predicted lipid metabolism, dormancy regulation, seed development, and carbohydrate metabolism genes. The results support the hypothesis that perception of seed dormancy is a predominant factor in squirrel caching decisions, and also indicate profitable directions for future work on the evolutionary genomics of trees and coevolved seed dispersers. We identified hybrid chestnut trees with variable seed traits and estimated the average seed dispersal distance (by squirrels) for each tree. By sequencing pooled genomes of trees with similar dispersal distance, we identified loci in the chestnut genome that may influence seed dispersal.
... Introduction species while providing protection from environmental extremes and limiting competition from shade-intolerant pioneer species (Nyland et al. 2002;Parker et al. 2001). Oaks are routinely grown in shelterwoods, and American chestnuts have recently been tested successfully under shelterwoods and partial canopy removal (Rhoades et al. 2009;Clark et al. 2012;Belair et al. 2014 Joesting et al. 2007;Jacobs 2007;Wang et al. 2013). ...
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.
... This prevented a similar shift from taking place in Europe, where chestnuts are still a common and economicaly important tree (Heiniger and Rigling, 1994). Attempts are now being made to breed and genetically modify blight-resistant strains of American chestnut trees to replant into the forests of eastern North America (Diskin et al., 2006;Jacobs, 2007). ...
... Future efforts should focus on selecting native elms, because backcross breeding of plants to exotic species may prove less publicly accepted in forest restoration (Jacobs 2007). Acceptance of genetically modified elms in the future is also uncertain, although cisgenic approaches, with a concept closer to traditional breeding, could offer new options for elm restoration. ...
Author had ordered for open access after the article went online in Springer link. The article was changed to open access article.
... Future efforts should focus on selecting native elms, because backcross breeding of plants to exotic species may prove less publicly accepted in forest restoration (Jacobs 2007). Acceptance of genetically modified elms in the future is also uncertain, although cisgenic approaches, with a concept closer to traditional breeding, could offer new options for elm restoration. ...
Elms (Ulmus spp.) were once dominant trees in mixed broadleaf forests of many European territories, mainly distributed near rivers and streams or on floodplains. Since ancient times they have provided important services to humans, and several selected genotypes have been massively propagated and planted. Today elm populations are severely degraded due to the negative impact of human-induced changes in riparian ecosystems and the emergence of the highly aggressive Dutch elm disease pathogens. Despite the death of most large elm specimens, there is no evidence of genetic diversity loss in elm populations, probably due to their ability to resprout after disease. The recovery of elm populations from the remaining diversity should build from genomic tools that facilitate achievement of resistant elm clones. Research works to date have discerned the genetic diversity of elms and are well on the way to deciphering the genetic clues of elm resistance and pathogen virulence, key findings for addressing recovery of elm populations. Several tolerant clones suitable for use in urban and landscape planting have been obtained through traditional species hybridization with Asian elms, and various native clones have been selected and used in pilot forest restoration projects. Successful reintroduction of elms should also rely on a deeper understanding of elm ecology, in particular their resilience to abiotic and biotic disturbances. However, all these efforts would be in vain without the final acceptance of elm reintroduction by the social actors involved, making it necessary to evaluate and publicize the ecosystem services elms can provide for today’s society.
... Castenea dentata (Marshall) Borkh. ;Jacobs 2007;Jacobs et al. 2013) or synthetic biology to create designer organisms with heretofore unknown capabilities (Stanturf 2015). This new material (whether species, provenances, or clones) must be adapted to current and future conditions and could be analogous, non-native species or genetically altered versions of native species (with genes from closely related or unrelated organisms, respectively, termed cisgenic or transgenic). ...
Restoring the estimated 1 billion hectares of degraded forests must consider future climate accompanied by novel ecosystems. Transformational restoration can play a key role in adaptation to climate change but it is conceptually the most divergent from contemporary approaches favoring native species and natural disturbance regimes. Here, we review concepts of novelty in ecosystems with examples of emergent/neo-native and designed novel ecosystems, with application to transformational restoration. Danish forests have a high degree of novelty and provide a realistic context for discussing assisted migration, one method of transformational adaptation. Deforestation and impacts of past land use created a highly degraded landscape dominated by heathland in western Denmark. Restoration with non-native species began 150 years ago because the native broadleaves could not establish on the heathlands. Danish forestry continues to rely extensively on non-native species. Preparing for transformational adaptation requires risky research today to prepare for events in the future and refugia from the last glaciation may provide genetic material better adapted to future climate. A new project will test whether species and provenances from the Caspian forests in Iran possess greater genetic diversity and superior resistance (physiological adaptability) and resilience (evolutionary adaptability) and possibly a gene pool for future adaptation.
... Chestnut's historical relevance and once ecological stature has inspired breeding programs that eventually led to backcrossing methodology initiated in the 1980s, which have produced American chestnut hybrids with putative resistance to chestnut blight [16,17]. Experimental plantings in forests [18][19][20][21][22] and afforestation projects on reclamation lands [23][24][25][26][27] have facilitated the introduction of backcrossed chestnut hybrids into the native range of American chestnut in North American forests [28]. ...
Plant and fungal interactions drive successional trajectories within reforestation offering both mutualisms (ectomycorrhizal fungi [ECM]) and fungal pathogens. Appalachian forest and mine reclamation projects re-introducing American chestnut and chestnut hybrids will inevitably document the return of chestnut blight, resulting in cankers causing branch dieback and loss of photosynthetic tissue. Similar to herbivory, the loss of photosynthetic tissue may reduce ECM root colonization and cause changes in fungal species composition. To test this, 75 six-year-old established chestnut trees were selected to represent the following: (1) Healthy trees free of chestnut blight; (2) trees with cankers and 50% branch dieback; (3) trees that died prior to the fifth growing season. Each tree had a chestnut seed planted 24 cm from the base. ECM colonization of both the established parent trees (n = 50) and five-month-old seedlings (n = 64) were quantified and genera determined by fungal DNA sequencing of the internal transcribed (ITS) region. Healthier seven-year-old chestnuts trees had significantly more ECM roots than those trees infected with chestnut blight cankers. However, disease die-back on chestnut did not have an influence on community composition among the parent trees or the neighboring five month seedlings. Results also demonstrated that five-month-old seedlings neighboring healthy parent trees had greater ECM on roots (P = 0.002), were larger in size (P = 0.04), and had greater survival (P = 0.01). ECM genera such as Cortinarius, Russula and Scleroderma provided tree to seedling inoculation. ECM colonization by Cortinarius spp. resulted in larger chestnut plants and increased nitrogen foliar concentrations on the five month seedlings. It can be hypothesized that blight will aid in diversifying forest stand composition and these early ECM networks will help facilitate the survival of other native hardwoods that recruit into these sites over time.
... An organism's phenotype can be quite useful because it may reflect desired attributes, i.e. it embodies or represents something in a faithful or appropriate way. In forestry, a tree's phenotype has often been used in breeding programs aimed at favouring specific attributes, such as survival, growth, and form (Beineke 1989;Jacobs 2007;Ross-Davis et al. 2008). In ecology, bark phenotype has been used to help determine fire resistance (e.g. ...
We carried out a study to determine if bark type could reflect the growth potential of yellow birch (Betula alleghaniensis Britt.) and sugar maple (Acer saccharum Marsh.) at the northern limit of their range in Québec, Canada (47°N, 75°W). We measured a large sample of 266 trees that ranged in size from 95 to 712 mm in diameter at breast height, on two independent study sites. Our results suggest that trees with smooth bark type had mean 5-year diameter increment 8 and 11 mm higher than trees with rough bark type, depending upon the study site. Differences in growth of 8 and 11 mm represented 85% of the overall rough bark type increment in the first site and 78% of the overall rough bark type increment in the second site. The rapid identification of a tree’s growth potential using bark type could be of great use to practitioners because it avoids the need to bore trees to collect increment cores, which injures trees and may serve as an entry point for disease. Moreover, the proposed method helps protect or release the smallest trees with high growth potential and remove trees with low growth potential. While the proposed method is valuable to practitioners operating in uneven-aged forests, its applicability still needs to be tested in even-aged forests.
... Provided the susceptible species has not suffered a major population crash, hybridization can use a genetically diverse base of parent trees, and some programmes also aim to incorporate resistance against multiple pests and pathogens (Clark et al., 2014). However, because hybrids also retain less desirable traits from the resistant parent, backcrossing with susceptible species may be needed to recover the characteristics of the susceptible species (Jacobs, 2007). ...
Pests and pathogens are an increasing threat to trees and forests, and the associated biodiversity and ecosystem services. Producing trees that are resistant to such threats is frequently emphasized by policymakers across Europe and North America. However, there are several approaches for developing and deploying resistant trees, and the process can be time-consuming and potentially complex and controversial. Here, we provide a framework to inform the selection of the most suitable approaches in different contexts, highlighting important constraints and considerations associated with using resistant trees. We identify six common steps within resistant tree programmes, and for each step discuss a range of options. Our proposed framework emphasizes inter-dependencies amongst these steps, and can inform decisions and approaches in proposed and ongoing resistance programmes. We also highlight potential pitfalls in the use of resistant trees, including: low durability of resistance, low viability against other threats, lack of acceptability/demand from forest owners and the public, and negative ecological impacts. Lastly, we emphasize the need to evaluate resistant trees alongside complementary strategies for mitigating the impacts of pests and pathogens (e.g. biosecurity, maintenance of adaptive capacity), and in the context of the other anthropogenic pressures faced by trees and forests.
... Furthermore, in recent years, the number of tree diseases and their rate of spread appear to have increased across the globe, due to several factors including climate change and global trade (Woodward and Boa, 2013). For example, in North America, chestnut blight Cryphonectria parasitica has caused near complete loss of chestnuts Castanea dentata (Jacobs, 2007). Dutch elm disease Ophiostoma spp. ...
Trees along linear features are important landscape features, and their loss threatens ecological connectivity. Until recently, trees outside of woodlands (TOWs) were largely unmapped however; the development of innovation mapping techniques provides opportunities to understand the distribution of such trees and to apply spatially explicit models to explore the importance of trees for connectivity. In this study, we demonstrate the utility of models when investigating tree loss and impacts on connectivity. Specifically, we investigated the consequences of tree loss due to the removal of roadside trees, a common management response for diseased or damaged trees, on wider landscape functional connectivity. We simulated the loss of roadside trees within six focal areas of the south east of the UK. We used a spatially explicit individual-based modelling platform, RangeShifter, to model the movement of 81 hypothetical actively dispersing woodland breeding species across these agriculturally fragmented landscapes. We investigated the extent to which removal of trees, from roadsides within the wider landscape, affected the total number of successful dispersers in any given year and the number of breeding woodlands that became isolated through time. On average roadside trees accounted for < 2% of land cover, but removing 60% of them (~ 1.2% of land cover) nevertheless decreased the number of successful dispersers by up to 17%. The impact was greatest when roadside trees represented a greater proportion of canopy cover. The study therefore demonstrates that models such as RangeShifter can provide valuable tools for assessing the consequences of losing trees outside of woodlands.
... Researchers have captured the natural resistance inherent in lingering American chestnut (Griffin 2000), have backcrossed C. mollissima resistance genes into C. dentata genotypes (Hebard 2006, Diskin et al. 2006, and have successfully developed techniques to genetically modify C. dentata (Zhang et al. 2013). These efforts are coming to fruition, and resistant 'American' chestnut are being deployed (Jacobs 2007, Jacobs et al. 2013). In addition, Asian and European chestnuts, and their hybrids, are increasingly cultivated for nut production (Fulbright et al. 2009). ...
American chestnut was once a crucial component of North American forests, but it was functionally eliminated by the introduction of the chestnut blight fungus. Chestnut is recently experiencing resurgence, but the introduced Asian chestnut gall wasp, a specialist herbivore, threatens chestnut recovery. I characterized this invasion and the interactions developing with host associates as the gall wasp spread in North America. Gall wasp dispersal is attributable to host plant distribution, effects of prevailing winds during adult insect emergence, and to topography. This knowledge may be useful to more accurately predict locations of future gall wasp infestations. Gall wasp invasiveness is also affected by its ability to modulate reproduction and reallocate nutritive resources for body maintenance and egg quality. The gall wasp can form galls of different shape and structure based on population levels and parasitism pressure, in order to optimize fitness. Simple, uni-lobed galls are formed when population pressure is low, and complex, multi- lobed galls are formed when gall wasp populations are high. A fungal plant pathogen, identified as Colletotrichum sp., infects galls and acts as an opportunistic entomopathogen, causing gall wasp mortality while sparing the parasitoid. A non-native torymid parasitic wasp has been deployed for biological control. Using a Y-olfactometer I demonstrated that a combination of olfactory and visual cues from chestnut galls and chestnut foliage is required for parasitoid adults to locate hosts. In addition, I evaluated interactions between the gall wasp and stem cankers on chestnut. Using potted Chinese chestnut seedlings with or without gall wasp or a native Nectria cankering pathogen, I found that the gall wasp has a negative impact on plant fitness, and a positive impact on fungal fitness. My work helps elucidate ecological mechanisms underlying the success of the exotic Asian chestnut gall wasp in North America, and adds to our knowledge base characterizing evolving ecological interactions between native and introduced species.
... However, TACF will continue increasing blight resistance in the chestnut seedlings that it is distributing for planting. Research has found that mine reclamation sites can be planted to establish founder populations of blight-resistant chestnuts that could then spread by 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; research is ongoing. ...
Appalachian forests are among the most productive and diverse in the world. The land underlying them is also rich in coal, and surface mines operated on more than 2.4 million acres in the region from 1977, when the federal Surface Mining Control and Reclamation Act was passed, through 2015. Many efforts to reclaim mined lands most often resulted in the establishment of grasses, shrubs, and nonnative plants. Research showed that forests could be returned to these mined lands, also restoring the potential for the land to provide forest ecosystem services and goods. Scientists and practitioners developed a set of science-based best management practices for mine reforestation called the Forestry Reclamation Approach (FRA). To help practitioners implement the 5 steps of the FRA and achieve other restoration goals (such as wildlife enhancement), 13 Forest Reclamation Advisories have been written since 2005 and others are underway. The 12 Advisories that are most directly relevant to the Appalachian region are being published here in a single volume for the first time.
These Advisories were originally posted on the Web site of the Appalachian Regional Reforestation Initiative (ARRI), an organization created in 2004 by the U.S. Department of the Interior’s Office of Surface Mining Reclamation and Enforcement along with State mining regulatory authorities in the Appalachian region. Members of ARRI come from the coal mining industry, government agencies, and research institutions. The goal of this initiative is to promote forest reclamation and restoration on mine lands through planting of high-value hardwood trees, increasing those trees’ survival rates and growth, and speeding the establishment of forest habitat through natural succession. To accomplish these goals, ARRI promotes and encourages use of the FRA by reclamation specialists. The Advisories are intended to serve as easy-to-understand guides to implementing the FRA; they provide specific recommendations as well as illustrations and photos to demonstrate tasks. The reformatted Advisories in this volume contain updated information and the latest additional resources to guide reclamation practitioners and other stakeholders in the reestablishment of healthy, productive forests in the Appalachian region.
... The rate of spread of tree diseases and the number of different diseases causing serve impacts appears to have been increasing in recent years due, in part, to climate change and global trade (Woodward and Boa 2013). In North America, chestnut blight has caused near complete loss of Castanea dentata chestnuts ( Jacobs 2007), Dutch elm disease has caused a similar loss of Ulmus spp. elms in Europe and North America ( Potter et al. 2011) and several species of Pinus pine around the world are now threatened with the fungus Gibberella circinata which causes pine pitch canker ( Wingfield et al. 2008). ...
Forests worldwide are currently threatened by a number of non-native tree diseases. Widespread death of a tree species will have ecological impacts on species that in some way depend on that tree species to complete their life-cycle. One measure to mitigate these impacts is to establish alternative tree species to replace the threatened tree species. These alternative tree species should be as similar as possible to the threatened tree species in terms of species supported, tree traits and the environmental conditions under which the tree will grow. This study assesses the availability and quality of data to assess the ecological impact of Hymenoscyphus fraxineus on Fraxinus excelsior and the suitability of 48 alternative trees to replace F. excelsior in the UK. To make this assessment data were collected on 1) species use (whether the 955 ash-associated species will use the alternative tree species), 2) traits (bark pH, deciduous, floral reward, fruit type, height, leaf dry matter content, leaf shape, length of flowering time, mycorrhizal association, pollen vector and specific leaf area) and 3) site requirements (occurrence within northern/southern and upland/lowland Britain, detailed climatic and soil nutrient requirements). For all three assessment methods there was lower confidence in the suitability of non-native tree species to replace F. excelsior due to lack of data. Different alternative tree species
were ranked most suitable depending on the methods used. We conclude that no one species is suited to all the site types associated with F. excelsior, nor will any one tree species support a high percentage of the ash-associated species while also matching many of the traits of F. excelsior. Our work provides broad guidance on the suitability of the 48 alternatives but site specific information is required to refine this selection at each site. The study highlights a lack of information to make a full assessment of the suitability of many species, particularly non-native species and calls for the collation of biological records so that rapid assessments
of the potential ecological impacts of the loss of any given tree species and the suitability of their alternative tree species can be made.
Available online at https://www.slu.se/globalassets/ew/org/inst/mykopat/forskning/stenlid/advances-in-ash-dieback-research.pdf
... Management includes silvicultural treatments such as thinning and prescribed fire to increase resistance to threats (Jacobs 2007), and the use of assisted colonization to increase genetic diversity by establishing populations adapted to future climates within or adjacent to reserves (St Clair and Howe 2011). Other innovative management strategies may be applied, including using in situ conservation of seedling banks to maintain a large number of young plants in a relatively small area, especially for species with recalcitrant seeds (Pritchard et al. 2014). ...
Genetic diversity provides the essential basis for the adaptation and resilience of tree species to environmental stress and change. The genetic conservation of tree species is an urgent global necessity as forest conversion and fragmentation continue apace, damaging insects and pathogens are transported between continents, and climate change alters local habitat suitability. Effective and efficient genetic conservation of tree species presents a substantial challenge because of the lack of basic information about many species, inadequate resources, and a historical lack of coordination within and between conservation sectors. Several cooperative efforts are already under way and are achieving conservation success, but much work remains. The Gene Conservation of Tree Species—Banking on the Future workshop in 2016 enabled the exchange of information and the creation of collaborations among tree conservation stakeholders. Several key themes emerged during the meeting’s presentations and dialogue, which are further explored in this paper. In situ conservation of species is the long-term goal and is often the most efficient approach for preserving the genetic diversity of many forest tree species. Whether existing reserves adequately protect species and are sufficient for future conservation needs is uncertain. Ex situ conservation is an important complement to in situ efforts, acting as an insurance measure against extinction, providing material for restoration, enabling additional research opportunities, and educating the public. Networks of botanic gardens, government agencies, and non-governmental organizations must continue to coordinate ex situ and in situ efforts to improve the efficiency and effectiveness of tree conservation efforts. Assessing and prioritizing which species and populations require genetic conservation and prioritizing among them is a critical need. Two key tree restoration needs are for wider dissemination of planting stock, particularly stock with resistance to insects and pathogens, and for specific silvicultural prescriptions that facilitate restoration efforts. Effective genetic conservation of forest trees will require ongoing cooperation among widely diverse groups of scientists, managers, and policymakers from the public and private sectors.
The unintentional introduction and rapid spread of chestnut blight (caused by Cryphonectria parasitica (Murr.) Barr) in the early 20th century resulted in the demise of American chestnut (Castanea dentata (Marsh.) Borkh.; Fagaceae) as a major component of forest canopies resulting in negative impacts on eastern forest communities. Research efforts over the last century have documented the persistence of occasional trees and root crown/ stump sprouts throughout much of the species' historic range, providing the basis for ongoing breeding of blight-resistant trees and restoration efforts. Here we use environmental niche modeling to investigate whether environmentally suitable habitat remains for remnant trees throughout the southwestern historical range, and to evaluate the reintroduction potential of this relatively understudied part of the historical distribution. We also use stage-structured matrix projection models to investigate the potential demographic future of C. dentata near the historical southwestern range limit based on observations of American chestnut in these areas over the last several decades. We found suitable upland habitat with areas of high forest canopy cover occurs throughout much of the southwestern portion of the historical range and that populations of American chestnut in these areas are predicted to drastically decline over the coming decades. These results highlight the continued presence of suitable C. dentata habitat throughout the southwestern extent of its historical distribution, which should be incorporated into evaluations for future reintroduction, and emphasize the need for efforts to locate, conserve, and introduce genetic material from individuals with locally adapted genotypes into active restoration programs.
American chestnut (Castanea dentata (Marsh) Borkh.), once a co-dominant canopy species in eastern U.S. forests, has been functionally extinct for almost a century. Hybrid American-Chinese chestnuts, with the potential to be blight-resistant, present an opportunity to study its functional niche. The objective of this research was to identify silvicultural strategies related to light, herbivory, and competition for increasing the success of hybrid chestnut (BC3F3 generation) plantings in an Appalachian cove forest ecosystem in West Virginia (WV). Large and small circular canopy gaps were created to manipulate light with the prediction that seedlings would perform best in larger gaps. Within these gaps, landscape fabric was added to half of the seedlings to decrease vegetative competition and 30.5 cm tall tree shelters were placed around half of the seedlings to help mitigate rodent predation. After five years, results show an interaction between landscape fabric and gap size whereby landscape fabric had a positive effect on seedling height in large gaps but not in small gaps (p < 0.05). Survival was dependent on interactions between treatments with the highest seedling survival (80%) in small gaps with tree shelters and landscape fabric. Differences between treatments were less pronounced in large gaps where survival was much lower (45%). In conclusion, seedlings are likely to have the greatest long-term survival if they are planted in smaller gaps protected from vegetative competition and rodent predation.
The primary factor limiting the distribution and growth of American chestnut (Castanea dentata (Marsh.) Borkh.) in eastern North America is tolerance to chestnut blight that is caused by the introduced fungal pathogen Cryphonectria parasitica (Murr.) Barr. However, a better understanding of how genetics and the environment influence American chestnut physiology and growth will also be needed to guide restoration as blight-tolerant growing stock becomes available. Here we describe patterns of phenology, cold injury and radial growth for American chestnut from 13 seed sources that represent three temperature zones (warm, moderate and cold) grown together in a unique provenance test in Vermont, USA. Temperature zones were established using data on the mean minimum winter temperatures over 10–30 years for weather stations nearest seed source locations; these averages were −5 °C and above for the warm temperature zone, −5 to −10 °C for the moderate temperature zone, and below −10 °C for the cold temperature zone. There was a consistent trend for trees from the warm temperature zone to break bud and leaf out earlier, and experience greater spring leaf frost damage and shoot winter injury than trees from other temperature zones. After initial establishment, woody growth (approximately 6 years of ring counts) was robust and tended to be greatest among moderate temperature zone sources and lowest for cold zone sources. Especially for trees from the warm zone, earlier budbreak was associated with greater growth. Foliar frost injury was not associated with altered growth, whereas winter shoot damage was associated with lower growth – especially following significant shoot loss. Even though warm temperature zone sources experienced more winter injury than trees from cold temperature zones, the growth of cold temperature zone sources tended to underperform that for warm and moderate zone sources – this suggests that, at least for the limited time that we evaluated growth, greater protection from the cold may come at the cost of greater growth potential. Although American chestnut is considered to be a relatively drought-tolerant species and growth was assessed during a period of historically high precipitation, higher moisture availability the year before, and occasionally during, the year of ring formation was broadly associated with greater growth across the temperature zones. Despite the negative influences of winter shoot injury on growth, the overall productivity of trees was exceptional, even at the northern edge of the species’ range provided that moisture availability was adequate.
Non-structural carbohydrates (NSCs) are critical for the survival of trees, but the ability to accurately predict NSC levels for a given forest tree species is lacking. We evaluated NSC dynamics in American chestnut (Castanea dentata), a species of high restoration interest, to test the conventional model of seasonal and inter-organ dynamics and to facilitate informed conservation efforts. Chestnut trees were sampled over the course of one year at different phenological stages. Then, organ-specific NSC concentration data were paired with biomass estimates from a custom-built allometric model to generate NSC pool sizes. Organ-level NSC concentrations and pools generally peaked at leaf fall (October) and were lowest during shoot expansion (June), although interactions between organ type and collection period drove variation in pool sizes. Whole-tree NSC pools increased from 2.47 ± 0.42 kg at shoot expansion to 4.29 ± 0.65 kg at leaf fall. Coarse roots were the most important NSC reservoir, accounting for 46.5% − 56.6% of the total whole-tree NSC reserves, depending on the time of year. Coarse root NSC pools were larger and more dynamic than in previous studies with other temperate deciduous trees, and they were the primary supplier of NSCs to support spring leaf-out. Preferential belowground NSC allocation and the ability to mobilize root NSCs to fuel growth and metabolism suggest that chestnut could thrive under disturbance-based management.
Mit der Zunahme des weltweiten Handels steigt auch die Anzahl der mitverschleppten Pilzarten (Neomyceten) stark an. Mittlerweile sind etwa 300 Neomyceten allein in der Schweiz bekannt, von denen bislang aber nur wenige als invasiv gelten. Diese invasiven Pilze, meist handelt es sich um Baumschädlinge, können aber für den Fortbestand gewisser Baumarten und die mit ihnen vergesellschafteten heimischen Organismen eine Gefahr darstellen. Haben sich die invasiven Arten erst einmal angesiedelt, ist eine Bekämpfung äusserst schwierig oder gar unmöglich. Deshalb sollte die Einschleppung weiterer Neomyceten in die Schweiz verhindert werden, was eine verstärkte Kontrolle des Pflanzenhandels bedingt.
Exotic forest insects and pathogens (EFIP) have become regular features of temperate forest ecosystems, yet we lack a long-term perspective on their net impacts on tree mortality, carbon sequestration, and tree species diversity. Here, we analyze 3 decades (1987–2019) of forest monitoring data from the Blue Ridge Mountains ecoregion in eastern North America, including 67 plots totaling 29.4 ha, along with a historical survey from 1939. Over the past century, EFIP substantially affected at least eight tree genera. Tree host taxa had anomalously high mortality rates (≥ 6% year−1 from 2008 to 2019 vs 1.4% year−1 for less-impacted taxa). Following the arrival of EFIP, affected taxa declined in abundance (− 25 to − 100%) and live aboveground biomass (AGB; − 13 to − 100%) within our monitoring plots. We estimate that EFIP were responsible for 21–29% of ecosystem AGB loss through mortality (− 87 g m−2 year−1) from 1991 to 2013 across 66 sites. Over a century, net AGB loss among affected species totaled roughly 6.6–10 kg m−2. The affected host taxa accounted for 23–29% of genera losses at the plot scale, with mixed net effects on α-diversity. Several taxa were lost from our monitoring plots but not completely extirpated from the region. Despite these losses, both total AGB and α-diversity were largely recovered through increases in sympatric genera. These results indicate that EFIP have been an important force shaping forest composition, carbon cycling, and diversity. At the same time, less-affected taxa in these relatively diverse temperate forests have conferred substantial resilience with regard to biomass and α-diversity.
Phytophthora cinnamomi Rands causes root rot in a number of important forest tree species around the world, including American chestnut (Castanea dentata) and shortleaf pine (Pinus echinata). Conventionalmethods for detecting P. cinnamomi in forest soils may require too much time and space to permit widescale and long-term screening of the large sample numbers required for landscape-scale distribution analysis. This project compared conventional detection methods (baiting with full rhododendron leaves or leaf discs and subsequent culturing on selective media) with amolecular detection method using DNA extracted from leaf baits. These methods were comparable, and the DNA-based method was correlated with culture-based methods. In a field-validation screening using the leaf bait polymerase chain reaction method, P. cinnamomi was found across a range of topographic conditions, including dry ridge-top sites and moist lowland sites. Soil texture analysis supports the traditional association of P. cinnamomi with finer-textured soils. Further largescale surveys are necessary to elucidate landscape-scale distribution patterns in eastern U.S. forests.
There has been an increased interest in tree breeding for resistance to exotic pests and pathogens, however relatively little research has focused on the reintroduction of these tree species. Understanding the durability of resistance in field settings and the field performance of improved trees is critical for successful species reintroduction. To evaluate methods for reintroducing American chestnut [Castanea dentata (Marsh.) Borkh] to managed forests on the Cumberland Plateau, we quantified four-year survival and growth and three-year competitive ability of chestnut seedlings planted on the Daniel Boone National Forest in southeastern Kentucky, USA. We used a split-plot design to compare chestnut response among three silvicultural treatments spanning a gradient of light levels; midstory removal, thinning, and shelterwood with reserves (2, 24, and 65% available photosynthetically active radiation, respectively) and three chestnut breeding types; American, Chinese (C. mollissima Blume.), and BC2F3 hybrid. One of two hybrid families planted had similar survival to American chestnuts, 21 and 27% survival, respectively, while the other had better survival, 57%. Chinese chestnut survival was better than the other breeding generations (90%). High mortality among American and hybrid chestnut seedlings was likely caused by infection from Phytophthora cinnamomi Rands. Incidence of blight infection was low. While chestnut seedling growth was greatest in the high-light treatment, competitive ability of chestnut, evaluated by comparing planted seedling height to height of understory competitors, was maximized in the intermediate light treatment. These results demonstrate the importance of evaluating competition pressure from co-occurring vegetation and field performance of resistant genotypes when assessing methods for reintroducing tree species to forested settings.
The loss of American chestnut (Castanea dentata) due to the fungal pathogen Cryphonectria parasitica had a considerable effect on the ecology of eastern forests. Because of its historical importance, researchers have worked to develop a blight-resistant variety of American chestnut for establishment into its former range. Chestnut breeders now predict that such varieties will be available within a decade. Information on forest communities in which chestnut was abundant prior to the blight should provide historical legitimacy to restoration efforts and increase the likelihood of success. We analyzed "witness" trees from settlement-era land deeds in order to guide site selection for chestnut restoration at Mammoth Cave National Park, Kentucky. Chestnut was the ninth most important species in our sample and was positively associated with white oak (Quercus alba) and black oak (Quercus velutina) and negatively associated with post oak (Quercus stellata) and blackjack oak (Quercus marilandica). Non-metric multidimensional scaling indicated that chestnut was associated with chestnut oak (Quercus prinus), black gum (Nyssa sylvatica), and white oak in the overstory of pre-blight forests, and with serviceberry (Amelanchier arborea) and sourwood (Oxydendrum arboreum) in sub-canopy layers. We suggest targeting restoration sites which contain these species and avoiding sites where post oak or blackjack oak are currently dominant. Witness tree analysis allows for the identification of vegetation associations that historically had a chestnut component, increasing the potential for restoration success. Even so, silvicultural considerations and the introductions of pests and pathogens other than the blight fungus may inhibit chestnut restoration.
Field and laboratory studies were used to evaluate net photosynthesis and plant and tissue water relations in saplings of co-occurring xeric (Quercus prinus and Q. ilicifolia) versus mesic (Q. rubra and Castanea dentata) hardwood species during a droughty summer. Mean daily net photosynthesis, leaf conductance, leaf water potential, and water use efficiency were reduced in all four species during the peak drought period. Throughout the study, net photosynthesis and leaf conductance were on average high in Q. ilicifolia and Q. prinus, intermediate in Q. rubra, and low in C. dentata. Leaf water potential was generally highest in C. dentata and not significantly different among the Quercus species. There were few consistent patterns in the tissue water relations data, including a lack of osmotic adjustment during peak drought, a lack of correlation between osmotic potentials and gas exchange rates, decreases in osmotic potentials and tissue elasticity after the peak drought period ended, and bulk leaf water potential values below the osmotic potential at zero turgor, despite relatively high gas exchange in those plants. Thus, the tissue water relations data provided little insight to mechanisms of drought tolerance in these species and suggest some methodology problems using standard pressure-volume procedures. For. Sci. 36(4):970-981.
Ambrosia beetles can be important pests of nursery production. The beetles are difficult to control with insecticides, requiring that pesticides be closely timed before tree attack, applied repeatedly, or have long residual activity. The goal of this project was to improve management decisions for ambrosia beetle control in nurseries. This study used ethanol-baited traps, field observations of tree attacks, and emergence cages over beetle galleries to determine the following: (1) composition of ambrosia beetle fauna in middle Tennessee, (2) species responsible for attacks on chestnut (Castanea mollissima Blume), a susceptible tree species, (3) timing of tree attacks and progeny emergence, and (4) the relationship between tree attacks, progeny emergence, and beetle collections in ethanol-baited traps. Ambrosia beetles were surveyed using ethanol-baited Lindgren traps at the Tennessee State University Nursery Crop Research Station in McMinnville, TN, and at two commercial nurseries near Dibrell and Tarlton, TN, during 1998 and 1999. At the Nursery Station, species composition of ambrosia beetles attacking chestnut trees was determined in 1999. Xyleborinus saxeseni Ratzeburg, Xylosandrus crassiusculus Motschulsky, and Monarthrum fasciatum Say were the dominant ambrosia beetle species collected in traps. Xyleborinus saxeseni was the dominant species at all three locations when both 1998 and 1999 collections were totaled. Other commonly trapped species included Monarthrum mali Fitch, Xyleborus atratus Eichhoff, and Xyleborus pelliculosus Eichhoff. Tree attacks began on 2 April before trees broke dormancy. The majority of chestnut attacks occurred in April and May. Progeny emerged from 48% of the caged galleries, including 35.9, 10.3, 3.3, and 1.1% X. germanus, X. crassiusculus, Hypothenemus spp., and X. saxeseni, respectively. Beetles exhibited several unusual behaviors during this study, including emergence of female X. germanus from trees the following spring, emergence of live male X. germanus and X. crassiusculus, a staggered chronology of progeny emergence, and presence of multiple beetle species emerging from the same gallery. Xylosandrus crassiusculus and X. germanus were the dominant species attacking chestnut, but total trap collections of X. germanus were small (≤1.7%). Several findings from this study have significance to the nursery industry. The timing of peak trap collections during April (particularly collections of X. crassiusculus and X. saxeseni) coincided with peak tree attacks. The factors responsible for chestnut susceptibility to attack were not measured in this study, but since the majority of trees were attacked before dormancy break, tree phenological state probably is an important determinant of tree vulnerability. The collection of some species like X. germanus in trap collections may be a more important indicator of tree attack than abundance in the trap. Progeny emergence from chestnut trees during June and July did not coincide with increased trap collections or renewed attacks on chestnut. Therefore, traps may not always indicate ambrosia beetle abundance. Several new state records were collected during this study, including X. crassiusculus, a species capable of serious economic damage to nursery stock.
We investigated herbivore suitability, foliar chemistry, and seedling growth of blight-susceptible pure American chestnut, Castanea dentata (Marsh.) Borkh., and a blight-resistant Chinese chestnut, Castanea mollisima Blume × American chestnut hybrid, using supplemental fertilizer and ectomycorrhizal inoculation to affect nutrient availability and nutrient uptake, and the gypsy moth, Lymantria dispar (L.), to measure herbivore suitability. Gypsy moth performance was best on fertilized hybrid seedlings, and was lowest on untreated American chestnut seedlings. Foliar carbohydrates were greatest, and tannin levels were lowest, in mycorrhizae-inoculated American chestnut. Foliar nitrogen was also high in mycorrhizal American chestnut, and was equivalent to that found in fertilized seedlings of both species. American chestnut seedlings had greater height and diameter growth than hybrids, regardless of soil amendments. Our results suggest that blight resistance may exact a cost in plant growth and productivity for this chestnut hybrid, and may enhance plant suitability for a generalist herbivore. Additionally, enhanced gypsy moth performance on blight-resistant chestnut hybrids has implications with respect to the restoration of chestnut to eastern deciduous forests, because intense herbivore pressure could compromise seedling growth and survival, and play a role in sustaining potentially damaging gypsy moth populations. The implications of this work within the context of current theories addressing herbivore-plant relations are discussed.
While a number of studies have investigated the objectives and characteristics of nonindus-trial private forestland (NIPF) owners as they relate to afforestation and reforestation decisions, very few studies have addressed these among NIPF owners in the Central Hardwood Forest Region of the United States, and even fewer have linked these to plantation establishment success. This article reports on such an examination in Indiana. Landowners were found to value their land for the privacy it provides, as a place of residence, and as a legacy for future generations. They afforested primarily to provide for future generations, to supply food and habitat for wildlife, and to conserve the natural environment. Seedling survival was lowest on sites owned by individuals who did not value their land as a legacy for future generations. Many NIPF owners are engaging in requisite behaviors to ensure plantation establishment success. The results of this study are discussed in terms of their importance as indicators of the influence of cost-share programs and the insight they provide into potential target areas for future programs.
American chestnut (Castanea dentata (Marsh.) Borkh.) was once a dominant tree in eastern deciduous forests of North America and is now endangered in Canada, primarily because of the introduction of a fungal pathogen (Cryphonectria parasitica (Murrill) Barr) causing chestnut blight. A recovery plan is being developed, and more accurate information on the status of this species in its native range in southern Ontario is needed to assist in the restoration and management of this species. We conducted a 2-year inventory of the distribution and size of trees throughout southern Ontario, and characterized the habitat and incidence of blight. In total, 682 trees were sampled, 601 of which were not planted. Individuals were statistically most likely to occur in deciduous forest habitats with high canopy cover (>50%), gentle slopes (0degrees-10degrees), and acidic (pH 4-6), sandy (>75%) soils. Most trees were small (80% were <20 cm diameter at breast height (DBH)) and nonreproductive (86%). Blight cankers were visible on only 25% of trees. Of six habitat variables measured, canopy cover was positively related to tree size (height, DBH) and incidence of blight. Litter depth was also a good predictor of cankers and virulent cankers in particular, but not healing and (or) healed cankers. The presence of Acer and Quercus spp. in the canopy was associated with reduced incidence and number of cankers per tree but increased frequencies of healing and (or) healed cankers, while Carya was correlated with increased incidence and number of cankers per tree. The abundance of American chestnut and the number of blight-free trees in southern Ontario is higher than previously known. The importance of canopy density and associated species in the habitat for tree health will contribute to the development of further research programs and management strategies for the restoration of this endangered species.
Abstract Aim The character and distribution of American chestnut (Castanea dentata) populations in New England are analysed to identify the extent to which the introduced chestnut blight and historic land use practices have affected chestnut distribution and life history.Location The study focuses on chestnut in Connecticut and Massachusetts but includes analysis of data related to other Castanea species in North America and Europe.Methods The ecology and palaeoecology of chestnut is investigated using a range of techniques, including examination of the growth form of chestnut trees in plantations located away from blight, mapping of chestnut sprouts and blight-killed trees at various locations, anatomical examination of chestnut stems, analysis of early forestry practices, identification of changes in the relative abundance of chestnut pollen in Holocene lake sediments and comparison of American chestnut with other Castanea species.Results Examination of chestnut sprouts surviving in the former range of that species shows that most sprouts originated from suppressed seedlings and that environmental factors severely limited the survival of sprouts from large blight-killed trees. Palynological data show that chestnut was either present in very low populations or entirely absent from New England and only became abundant after about 2500 years ago. All factors suggest that chestnut abundance is related to the natural disturbance cycle, while human-induced transformations of the landscape and the introduction of chestnut blight have further transformed the character of chestnut in New England.Main conclusions Most surviving chestnut sprouts in New England forests represent old seedlings that have continued to re-sprout since establishment before the introduction of blight nearly 100 years ago. The growth form of these sprouts ensures a minimal substrate of bark tissue for blight establishment so that blight has a relatively minor effect on seedling–sprout survival. The identification of modern chestnut sprouts as old seedlings indicates that the observed distribution of sprouts in New England woodlands is strongly influenced by land use conditions and especially field abandonment at the time when chestnut blight arrived from its point of introduction.
In the Central Hardwood Forest region of the United States, the variable and somewhat unpredictable establishment success of hardwood tree plantations has traditionally been attributed to competing vegetation and damage due to animal browse. We examined operational plantation establishment success (1–5 years following planting) as it relates to use of particular silvicultural practices. Silvicultural histories were obtained for 87 randomly selected plantations throughout Indiana and field data were collected from each to determine tree survival, tree vigor, and abundance of surrounding vegetation. Survival was highest at sites that were treated with herbicide prior to planting and that had been mechanically planted (as opposed to hand planted). The percentage of trees with evidence of dieback was highest on sites at which browse protection measures had been used, likely reflecting a combination of damage due to inherently high white-tailed deer (Odocoileus virginianus Zimmermann) populations at such sites and ineffectiveness of current browse protection measures. Sites planted by a professional forester and those with herbicide applied subsequent to planting had a higher percentage of trees deemed free-to-grow. Subsequent herbicide application did not reduce cover or height of competing vegetation; however, when used in conjunction with mechanical site preparation techniques, overall cover and height of herbaceous vegetation was reduced.
Parallel hypotheses are advanced: (1) the distribution of resources in mesic upland temperate forests is patchy at a scale that is fine grained for adult trees and coarse grained for seedlings and (2) co-occurring tree species differ in abilities to exploit resources, resulting in differences in species rank order, by absolute growth rates of seedlings, among different resource combinations. Spatial variation in growth rate ranking among species may translate, through competition, into patterns of relative species abundances of seedlings that could persist in the community composition of adult trees. Here I report the results of factorial greenhouse experiments that address the second hypothesis. Seedlings of six co-occurring tree species of temperate eastern North American upland forests showed strong interspecific differences in growth rates and patterns of biomass allocation in response to variation in light and mineral nutrients. The ranks of four species in growth measures associated with competitive ability, absolute rates of change in stem height, total leaf area, and root biomass, varied significantly among nutrient treatments. Seedlings of American chestnut, Castanea dentata, ranked highest in traits associated with competitive ability over the broadest range of combinations of resource levels.
Efforts to restore the American chestnut focus on natural blight resistance found in a few surviving trees of the species in the natural range, strains of the blight fungus with reduced virulence (hypovirulence), and introduction of Asian chestnut blight resistance into American chestnut. These approaches may be used alone or in combination. Also critical are site selection and other forest management practices.
The present distribution of chestnut sprout clones in Andover, Massachusetts, includes areas with abundant stumps from canopy trees killed by blight before 1922, and former abandoned pastures adjacent to woodlots that once contained mature chestnut trees Sprout densities range from less than 1 to more than 200 living clones per hectare Greatest densities occur in areas with abundant logs and stumps from preblight chestnut tress, but some areas with abundant chestnut wood have very few living sprouts Limited numbers of chestnut sprouts were found with living stems growing from small knobs of cambium on the root collars of otherwise completely dead stumps of former canopy trees More than 95 per cent of all observed chestnut sprouts show no connection with remains of preblight trees, and almost all appear to have been through several cycles of blight infection The distribution pattern of these sprouts indicates that they originated as suppressed seedlings established before 1922 and not as sprouts from the roots of canopy dominants No signs of recent seedling establishment or vegetative reproduction by sprouting from roots away from the root collar on either small live sprouts or long dead chestnut stumps were found Vegetative reproduction is now occurring by relatively rare instances of layering, and by slow expansion and division of root crowns at a rate which probably more than offsets the low mortality of entire clones Chestnut sprouts that have escaped blight for many years indicate that the natural growth condition of suppressed chestnut seedlings is a single stem with controlled release of individual basal buds This process involves a complex mechanism for apical control of the entire clone that appears to be part of a definite reproductive strategy
This study was initiated in 1939 on the SW slope of Beanfield Mountain, Giles Co., Virginia, and was repeated in 1970. Prior to the chestnut blight [Endothia parasitica (Murr.) A. and A.], which reached a peak about 1920, the study area was covered by an oak-chestnut forest except for low-elevation cove forests. Dominant oak species included chestnut oak (Quercus prinus L.), northern red oak (Q. rubra L. var. borealis) (Michx. f.) and white oak (Q. alba L.). Following the blight these oak species partially filled canopy openings and persisted as codominants for a quarter century. In 1939, at elevations above 850 m, the mountain was covered by an oak complex dominated by northern red oak. On the basis of trends observed in 1953, Catherine Keever speculated that, eventually, oak-hickory forests would replace chestnut-oak forests in the region. Results of our 1970 study support Keever's predictions. By 1970, pignut hickory (Carya glabra, Mill.) had replaced chestnut, red maple (Acer rubrum L.) invaded clearings and sugar maple (A. saccharum Marsh.) became a dominant species in mixed mesophytic forests at low elevations. A half century following the chestnut blight, the oak-chestnut forest has been replaced by an oak-hickory forest.
The components of hardwood forest regeneration on a southern Appalachian watershed were assessed during the 1st yr following clear-cutting. First-year net primary production (NPP) on the clear-cut was 1955 kg/ha, representing 22% of the NPP of a nearby undisturbed hardwood forest. First-year nutrient pools in NPP for N, P, K, Mg, and Ca were estimated at 29-44% of those in the NPP of the control. The greatest NPP and nutrient pools were represented in descending order by hardwood sprouts, herbs, vines, and seedlings. Woody successional species (Robinia pseudo-acacia, Liriodendron tulipifera, and Vitis aestivalis var. argentifolia) and herbs (Aster spp., Solidago spp., and Erechtites hieracifolia) were important in revegetation due to competitive advantages in growth rates, growth forms, and propagative capacities. The woody successional species had higher tissue concentrations of N and P than most other woody species. Herbs as a group had significantly higher foliar concentrations of K than woody species. Woody successional and herbaceous species collectively had higher biomass and elemental pools than other woody species. Following forest disturbance, these fast-growing species conserve substantial pools of nutrients in their biomass and initiate a rapid recovery of forest elemental cycling processes.
Sprouts from the root systems of American Chestnut (Castanea dentata (Marsh) Borkh) have been increasing in numbers and size in the successional forests of Connecticut in spite of the chestnut blight Chestnut stems are especially impressive in defoliation-induced canopy gaps where they sometimes attain a diameter greater than 15 cm and appear to reach canopy level only a few years after release Five sites containing natural openings of various sizes and one site subjected to selective logging were investigated by coring chestnut stems and surrounding canopy trees All chestnut sprouts subjected to strong release under natural canopy openings exhibited cores with one to three decades of slow growth followed by very rapid diameter increase The relatively good form of these chestnut stems therefore resulted from rapid changes in stem form and not by resprouting from root systems It is proposed that initial suppression in shrublike form was a natural step in canopy emplacement for the chestnut This reproductive strategy appears especially effective under severe competition with shrubs on poor sites. Modern study of chestnut ecology is important because an increase in the proportion of chestnut pollen is a characteristic indicator of the most recent climate zone inferred from pollen profiles in New England The role of chestnut as a climatic indicator is explained best by a complex process of soil impoverishment and organic litter build-up analogous to a widely accepted theory for the late Holocene development of blanket bogs in western Europe
Castanea dentata (Marsh.) Borkh. was a major forest tree in the eastern United States before an introduced blight killed the chestnut trees in the early 20th century. Its post-glacial migration, especially north of the Wisconsin terminal moraine, was apparently slower than other genera found in association with it in the 20th century. Analysis of historical documents indicates that chestnut trees were restricted to moist but well-drained, acid loam soils. Chestnut had little success on the coastal plain or where drainage was poor. In areas of its greatest dominance, many trees were of rootcrown sprout origin and seedling establishment was not common. This suggests that its slow migration, as indicated by the palynological record, may have been caused by a paucity of appropriate sites for seedling establishment north of the Wisconsin terminal moraine, before adequate leaching of lime and establishment of good drainage, especially near sites of pollen accumulation. The apparent anomaly in its migration rate may also arise from comparing the migration of this species north of the terminal moraine with that of other associated genera. The palatability of its fruits and the coincidence of its migration with the development of agriculture also suggest that its spread into New England may have been associated with cultural changes in native American populations.
The present distribution of American chestnut (Castanea dentata [Marsh.] Borkh.) as a component of upland forest communities in the mid-Appalachians was investigated in three different areas of western Virginia. Two of these (Alleghany County and the Mountain Lake area of Giles County) are within the Ridge and Valley physiographic province and the third (Shenandoah National Park) is in the Blue Ridge province. Quantitative data on composition and structure of the vegetation and various topographic variables were analyzed using correlation analysis and DCA ordination. The results of these analyses indicate that the present distribution of chestnut is strongly correlated with elevation and site moisture conditions. In general, chestnut was much less abundant (only 192 stems/ha) in Alleghany County (mean elevation of 39 stands = 645 m) than in either Shenandoah National Park (532 stems/ha) or Giles County (770 stems/ha), where sampled stands occur at mean elevations of 882 m (20 stands) and 1079 m (43 stands), respectively. Maximum density of chestnut (> 2500 stems/ha for some stands) occurred on subxeric sites, particularly mid- to upper slope positions on southern exposures. In all three areas, chestnut was conspicuously absent from most mesic sites.
Morphological features of leaves and twigs of American chestnut, Chinese chestnut, their F1 hybrid, and three successive generations of backcrosses between hybrid populations and American chestnut were examined to determine rate of recovery of the American chestnut morphology after hybridization to capture Chinese chestnut genes for blight resistance. In aggregate morphology, as measured by a composite index of species identity (ISI), 96% of trees in the third backcross generation (BC3) resembled American chestnut and were distinctly different from Chinese chestnut. The majority of BC3 trees also differed from Chinese chestnut in every individual characteristic measured for this study. Thus, recovery of American chestnut characteristics is largely achieved after three generations of backcrossing. If progeny of the BC3 hybrids can be made homozygous for blight-resistance alleles, as expected, and if the trees equally resemble American chestnut in important ecological attributes, then backcross breeding appears to be a workable strategy for restoring this species as a important component of eastern U.S. forests.
The American chestnut ( Castanea dentata ( Marsh.) Borkh.) was once an important tree species in the eastern United States prior to its devastation by the chestnut blight. The American Chestnut Foundation will soon release seeds that are blight resistant. However, the necessary site requirements for restoration efforts have not yet been explored. The goal of this study was to evaluate the survival and growth of chestnut seedlings within a diverse forest management regime. Seedlings were experimentally grown for 2 years in three mixed-oak forests subjected to thinning, burning, thinning followed by burning, and an untreated control. Seedling biomass parameters were most influenced by treatments that increased light availability. Soil chemistry and texture parameters were also correlated ( p < 0.05) with chestnut biomass. Thus, site fertility should also be considered in reintroduction efforts. While site quality may influence growth, light conditions appear to be overwhelmingly important. Therefore, we recommend that American chestnut seeds be planted in areas with moderate to high light conditions ( recently disturbed), with low surrounding competing vegetation ( possibly after a burn) for optimal growth benefits.
This study analyzed witness-tree data recorded from 1765 to 1798 with respect to landform in four major physiographic provinces represented through north central Pennsylvania. These data were also compared with present-day forest composition to evaluate broad changes that occurred 200 years after European settlement. In the Allegheny High Plateau, Tsuga canadensis (L.) Carr. represented 40-47% of witness trees in mountain coves and stream valleys, but only 9% on plateau tops, which comprised 45% Fagus grandifolia Ehrh. Pinus strobus L. represented less than or equal to 4% frequency across all landforms. The original forests of the Allegheny Mountains were dominated by mixed Quercus, Acer, Castanea dentata (Marsh.) Borkh., and Pinus and had significant T. canadensis only in stream valleys. The presettlement forests of the Allegheny Front and the Ridge and Valley provinces had a similar mix of Quercus, Pinus, Castanea, and Carya, with increased P. strobus on the more mesic sites and Pinus rigida Mill. on the xeric ridges. Comparisons of presettlement with present-day forest composition indicate a dramatic reduction of T. canadensis (32% to 4%) and F. grandifolia (33% to 12%) in the High Plateau and increases in Acer (11% to 37%), Quercus rubra L. (0% to 10%), Prunus serotina Ehrh. (1% to 6%), and Betula (5% to 10%). Other units exhibited reductions in P. strobus, P. rigida, Quercus alba L., and Carya spp. and increases in Quercus prinus L., Q. rubra, Acer rubrum L., and P. serotina. Castanea dentata had its greatest abundance on higher elevation sites in each physiographic unit, and the elimination of this species this century apparently facilitated the increase in Q. prinus and Q. rubra on ridge sites. South of the Allegheny Plateau, increases in A. rubrum, P. serotina, and other mixed-mesophytic species may be in response to fire exclusion this century. The results of this study indicate the importance of landform and physiography on presettlement forest composition as well as the dramatic changes that have occurred as a result of altered disturbance regimes following European settlement.
Formerly numerous understory stems of American chestnut (Castanea dentata (Marsh.) Borkh.) showed a precipitous decline in a 3-ha stem-mapped permanent plot in southwestern Virginia, United States. More than 64% of the understory chestnut stems died between 1982 and 1988; recruitment of new stems was less than 3% of initial stem numbers. Per capita mortality of chestnut was nearly three times that of all other species combined; the growth rate of surviving chestnut was slightly less than that of similarly sized stems of other species. Basal area increase of surviving stems did not compensate for a nearly 13% decline in basal area from dying stems. On a small spatial scale, chestnut stems were distributed in clusters generally 1 m in extent, having as many as five live individuals. Over 53% of these clusters disappeared, and only a few (1.2%) new clusters appeared in the intercensus interval. The probability of stem death appears to have been random in space. Chestnut mortality was probably not related to the ingrowth of potential competitors. Rather, the decline is likely to have been promoted by an interaction between the continuing action of the chestnut blight (Cryphonectria parasitica (Murr.) Barr) and severe drought in the growing seasons between censuses.
In 1985 and 1987, chestnut blight incidence and survival of American chestnut sprout clusters (groups of stems sprouting from a single stump) were assessed in Virginia and west Virginia forest clearcut sites, 13-19 yr after clearcutting, and in understory sites. Overall, sprout cluster blight incidence averaged 96.3% in 17 clearcuts and 37.1% in 13 understory sites; chestnut sprout cluster survival averaged 55.7 and 94.2% in clearcut and understory sites, respectively. In the 1987 survey. (…)
Carbon sequestration has been well recognized as a viable option to slow the rise in atmospheric greenhouse gas concentration. The main goals of this study were to assess the carbon sequestration potential (CSP) by afforestation of marginal agricultural land (MagLand) and to identify hotspots for potential afforestation activities in the U.S. Midwest region (Michigan (MI), Indiana (IN), Ohio, Kentucky (KY), West Virginia, Pennsylvania (PA) and Maryland (MD)). The 1992 USGS National Land Cover Dataset and the State Soil Geographic (STATSGO) database were used to determine MagLand. Two forest types (coniferous and deciduous) and two management practices (short-rotation versus permanent forest) were combined to form four afforestation scenarios. Simulation models were employed to predict changes in four carbon pools: aboveground biomass, roots, forest floor, and soil organic carbon (SOC). A scenario-generating tool was developed to detect the hotspots. We estimated that there was a total of 6.5 million hectares (Mha) MagLand available in the U.S. Midwest region, which accounts for approximately 24% of the regional total agricultural land. The CSP capacity was predicted to be 508–540TgC (1 Tg=1012g) over 20 years and 1018–1080TgC over 50 years. The results indicate that afforestation of MagLand could offset 6–8% of current CO2 emissions by combustion of fossil fuel in the region. This analysis showed only slight differences in carbon sequestration between forest types or between short-rotation and permanent forest scenarios. Note that this calculation assumed that all suitable MagLand in the U.S. Midwest region was converted to forest and that “best carbon management” was adopted. The actual CSP could be less if the economical and social factors are taken into account. The most preferred locations for implementing the afforestation strategy were found to be concentrated along a west-east axis across the southern parts of Indiana, Ohio, and Pennsylvania, as well as in an area covering southern Michigan and northern parts of Indiana and Ohio. Overall, we conclude that afforestation of MagLand in the Midwest U.S. region offers great potential for carbon sequestration. Future studies are needed to evaluate its economic feasibility, social acceptability, and operation capability.