Jonathan L. Horton

The American chestnut (Castanea dentata (Marsh.) Borkh.) was a foundation species whose loss reshaped eastern North American forests. Ongoing breeding with blight-resistant Chinese chestnut (Castanea mollissima Blume) represents the leading strategy for its restoration. However, breeding programs have focused almost exclusively on pathogen resistance, leaving susceptibility to native seed predators unexamined—a critical gap, because nut production underpins the ecological function that restoration seeks to recover. Here, we investigate how hybridization level affects infestation by the lesser chestnut weevil (Curculio sayi (Gyllenhal, 1836)), monitoring 25 genetic lines across four genetic categories (Chinese, F₁, backcross, and American) for larval emergence, weight loss, damage, and emergence timing over eight weeks. Hybridization dramatically altered susceptibility: F₁ hybrids were the most susceptible category. No larval emergence was observed from American chestnuts, and backcross hybrids remained substantially susceptible despite three–four generations of backcrossing. These results expose a fundamental trade-off for restoration: blight resistance derives from the Chinese genome, whereas weevil resistance appears to be associated with the American genome. Backcross lines bred for blight resistance retain weevil susceptibility, and F₁ hybrids risk functioning as pest sinks that amplify local weevil populations. Incorporating weevil resistance screening into breeding programs could help us to ensure that restored chestnuts can fulfill their historical role as mast-producing foundation trees.

American chestnut (Castanea dentata), once a dominant canopy species in eastern North America, succumbed to invasive pathogens in the early 20th century. The American Chestnut Foundation attempts to breed pathogen resistance using backcrossed hybrids with Chinese chestnut (Castanea mollissima ). We compared steady-state photosynthetic characteristics among backcrossed chestnut hybrids (BC1F1 with 3/4 American genotype and BC3F3 with 15/16 American genotype) and pure American chestnut. Photosynthetic capacity was compared among these three chestnut classes with steady-state light response curves. Dark respiration rates, quantum yield, and maximum photosynthetic rates differed among these chestnut types, but light compensation point, a measure of shade tolerance, did not. In July and August, we measured plant water potential (at predawn, morning and afternoon) and leaf gas exchange (morning and afternoon) under ambient conditions between the 15/16 and 3/4 AC hybrids. Trees in the pure American chestnut population suffered blight-induced dieback resulting in shrubby plants that differed in size and light environment, so these were not used in diurnal comparisons. Despite similarities in soil moisture and pre-dawn water potential, there were significant differences in daily gas exchange and water potential. Trees in the 15/16 American chestnut population generally had higher gas exchange rates in the afternoon, while also experiencing lower plant water potential and a greater diurnal change in water potential. These results suggest that these trees may be better able to perform under moderate atmospherically-induced water stress than trees in the 3/4 American chestnut population. Quantifying relationships between water relations, gas exchange, and environmental factors allow evaluation of long-term performance and may better inform site selection and management practices.

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

Virginia spiraea (Spiraea virginiana Britton, Rosaceae) is a putative shade-intolerant, disturbance-adapted, riparian shrub species native to the southern Appalachian Mountains. This species was listed as threatened in 1990, and a federal recovery plan was developed in 1992. Current reassessment of the recovery plan includes proposals for propagation and out-planting to supplement and restore wild populations. Genotypes with greater shade acclimation would likely have higher survival in natural populations, would require less frequent shade-reduction management, and could be integrated into populations that need restoration. In summer 2022, we examined steady-state (maximum light-saturated photosynthetic, dark respiration rates, quantum yield, light compensation point) and dynamic (photosynthetic induction and loss patterns) photosynthetic characteristics, pigment concentrations, and specific leaf mass of cloned propagules from five elements of occurrence along the South Fork of the New River in Ashe County, North Carolina, along an artificial light gradient (100%, 75%, 50%, and 20% of full sun) in a common garden. Data were compared among light treatments using ANOVA or non-parametric tests. Light treatment had significant effects on maximum photosynthesis, dark respiration, specific leaf mass, and light compensation, but not quantum yield, pigment concentrations, or induction and loss times. Some parameters had plasticity similar to that seen in other woody shrubs, while others were less plastic. A surprising finding was that plants performed better under 75% full sunlight suggesting an ability to tolerate, and maybe even a preference for, partial shade in this species. Future studies should examine photosynthetic characteristics of individuals from genetically contrasting source populations.

Within the Roan Mountain massif in the southern Appalachian Mountains, grassy balds are important, yet threatened ecosystems dominated by native graminoids with many endemic and endangered species. Restoration efforts have been conducted for 30 years by several agencies. In 1987–1988 a vegetation analysis was conducted on these balds to characterize plant communities before intensive management began. In summer 2020, we resurveyed the vegetation using similar methodologies on Round, Jane, and part of Grassy Ridge Balds to assess the impact of management activities. Percent coverage of vegetation type was recorded in 226 one m2 plots along 11 transects. Management history was compiled for individual plots. Percent cover data were subjected to cluster analysis, principal components analysis (PCA), non-metric multidimensional scaling (NMS), and regression. Cluster analysis of sampled plots revealed 12 plant community groups. PCA revealed plots separating along a gradient of blackberry and grass cover, as well as blackberry, grass, and fern cover. Results from NMS showed less separation of plots compared to PCA with most plots clustering in the center, except those with high bare ground coverage. A significant positive relationship was seen between graminoid cover and management frequency and a negative relationship with the amount of time since management activity. All of the relationships had low explanatory power suggesting that other factors might influence the plant populations. Our research shows there is a positive association with graminoid cover and increased management frequency, but more research involving other biotic and abiotic factors and management history should be explored.

Eastern hemlock (Tsuga canadensis (L.) Carrière) is a foundation species in eastern North American forests, providing critical habitats for a number of species. These trees are experiencing widespread decline due to the spread of hemlock woolly adelgid (HWA: Adelges tsugae Annand Order Hemiptera) into their range, potentially resulting in the disappearance of hemlocks from eastern forests. Hemlock dieback can lead to cascading effects on associated ecosystems, including belowground, mycorrhizal fungal communities. Ectomycorrhizal fungi (EM), which are mutualistic with many tree species and provide nutrients to plant hosts, are known to colonize hemlock as well as neighboring tree species at lower levels following HWA infection. This study investigated the effect of hemlock decline from HWA infestation on mycorrhizal communities, as inferred from colonization on northern red oak (Quercus rubra L.) “bait” seedlings grown near “host” hemlock trees. Hemlock health surveys were conducted in healthy (Carl Sandburg Home National Historic Site – CARL) and declining (Warren Wilson College – WWC) stands in western North Carolina, and host trees were paired between stands based on diameter. In each stand, northern red oak seedlings were planted within a meter of host hemlocks in early summer and allowed to grow for 8 w, when they were harvested. Seedling growth and dry biomass were recorded at harvest and roots were sampled for mycorrhizal colonization frequencies. Different mycorrhizal morphotypes were collected from seedling roots for subsequent DNA barcoding analyses to characterize EM taxonomic richness to compare mycorrhizal community assemblages between the two stands. Mycorrhizal colonization frequencies (percentage of the total number of EM-colonized root tips per seedling) and growth in seedling height were significantly greater at CARL than WWC, suggesting healthy hemlock stands are more favorable for oak seedling growth than declining stands. Moreover, a greater proportion of seedlings grown in the healthy stand were colonized by EM, indicating EM assemblages differ between a healthy and a declining hemlock stand. Differences between EM communities corresponded with altered seedling growth allocation, as seedlings in the declining stand had higher root to shoot ratios with reduced stem height, but showed greater investment in root biomass and stem diameter growth. We conclude EM communities differ between a healthy and declining hemlock stands, and changes in EM communities following hemlock dieback may affect the growth of replacement species.

American ginseng (Panax quinquefolius) roots have long been harvested for use in herbal medicine. Overharvesting has threatened long-term viability of wild American ginseng populations. Research has been ongoing to determine factors affecting the variation of ginsenosides in roots. Given the conservation concerns regarding wild American ginseng, we began experimenting with a partial-root harvest method in 2014 for extracting tissue for ginsenoside analysis without killing individual plants or causing long-term declines in wild populations. We took partial-root harvest samples from 57 plants in four wild populations throughout western North Carolina and monitored morphological attributes of these and 56 paired, unharvested plants of similar size for four years after harvest. Partial-root samples were taken from an additional 162 plants from 16 new populations in 2015 and 2016. Morphological attributes of these plants were monitored annually or biannually. In the paired plant study, annual reemergence did not differ between harvested and unharvested plants in any year after harvest. Leaf area was significantly lower in harvested plants than unharvested controls in the first year postharvest, but these differences did not persist after the first year. In the unpaired study, preharvest-postharvest comparisons were more variable, likely due to different harvest years and interannual variation in weather. Our results demonstrate that partial-root harvest could be an effective way for ginsenoside researchers to reduce their impact on wild and cultivated American ginseng populations and it may represent a non-destructive harvest protocol for root tissue phytochemical analysis.

High-elevation species in some Southern Appalachian communities have been shown to be dependent on frequent cloud immersion. However, little is known about the influence of clouds on rare and endemic species native to high-elevation rock outcrops. These outcrops are characterized by shallow soil and high insolation, exposing species to frequent water stress, which might be partially ameliorated by cloud immersion. We compared leaf gas-exchange characteristics of two rock outcrop specialists (Hydatica petiolaris and Sibbaldiopsis tridentata) and two forest-edge herb generalists (Potentilla simplex and Solidago flexicaulis) growing at a high-elevation outcrop in the Craggy Mountains in North Carolina. At least 1 hr of cloud immersion occurred on 67% of days, mostly in the morning hours, whereas most (54%) daylight hours were cloudy. Temperature was lower and humidity higher on cloudy days. Light response curves did not reveal differences among species. Diurnal gas-exchange curves revealed that leaf-to-air vapor-pressure deficits were lower on cloudy days, and on those days, outcrop specialists had higher stomatal conductance and internal CO₂ concentration, but there was no effect on net photosynthetic rates, suggesting little stomatal limitation to photosynthesis on clear days. Water-use efficiency varied among species but was not consistently higher for outcrop specialists. More research is needed to further elucidate the influence of clouds and cloud immersion on rock outcrop communities.

We studied the habitat characteristics of Spiraea virginiana Britton (Virginia spiraea), a federally threatened riparian shrub, along eight rivers in western North Carolina. Comparisons between plots with and without S. virginiana revealed that S. virginiana plots were on steep, south-facing slopes and had a higher percentage of large substrate, lower herbaceous and vine cover, higher non–S. virginiana shrub density, lower tree influence, and higher visible sky than control plots. When relating these habitat attributes to the presence/absence of S. virginiana using conditional logistic regression, only substrate size and non–S. virginiana shrub density had significant effects on S. virginiana presence. Principal components analysis (PCA) of all plots (S. virginiana and control) found S. virginiana plots separating from controls that had higher vine and herb cover and lower non–S. virginiana shrub density and slope. Spiraea virginiana plots at the Cheoah River separated from other sites by having...