Structural characteristics and canopy dynamics of Tsuga canadensis in forests of the southern Appalachian Mountains, USA

Tsuga canadensis (L.) Carr. forests of the southern Appalachian Mountains are currently facing imminent decline induced by a nonnative insect pest, the hemlock woolly adelgid (Adelges tsugae Annand). To effectively manage these forest systems now and in the future, land managers need baseline data on forest structure and dynamics prior to large-scale Tsuga canadensis mortality. Most of our knowledge concerning the dynamics of Tsuga canadensis forests comes from more northern locations such as the Great Lakes region and New England and, therefore, may not pertain to the ecological systems found within the southern Appalachian Mountains. We examined the structure and canopy dynamics of four Tsuga canadensis forest stands within the Cataloochee watershed, in the far eastern part of Great Smoky Mountains National Park (GSMNP). We characterized the environmental settings and vertical forest layers, as well as the diameter and age-structures of each Tsuga canadensis forest stand. These environmental and structural data showed that there were indeed differences between forest stands with and without successful Tsuga canadensis regeneration. The two forest stands exhibiting successful Tsuga canadensis regeneration were located above 1,000 m in elevation on well-drained, moderately steep slopes and had the greatest canopy openness. Structural data from these two forest stands indicated a history of more continuous Tsuga canadensis regeneration. We also constructed disturbance chronologies detailing the history of canopy response to disturbance events and related these to Tsuga canadensis regeneration within each forest stand. Student t-tests adjusted for unequal variances indicated significant differences in the number of release events per tree between forest stands with and without successful Tsuga canadensis regeneration. While forest stands with successful Tsuga canadensis regeneration were more frequently disturbed by minor to major canopy disturbances, events of moderate intensity were found to be most significant in terms of regeneration. These data will be of value to land managers maintaining stands of Tsuga canadensis where treatment for hemlock woolly adelgid infestation has been successful. In areas where treatment is impractical or unsuccessful, land managers will be able to use these data to restore Tsuga canadensis forests after the wave of hemlock woolly adelgid induced mortality has passed. As of August 2008, Joshua A. Kincaid will be a member of the Environmental Studies program at Shenandoah University in Winchester, Virginia, USA     

Stand dynamics of a yellow-poplar (Liriodendron tulipifera L.) forest in the Appalachian Mountains, Virginia, USA

Yellow-poplar (Liriodendron tulipifera L.) is a large, rapidly growing, shade-intolerant tree species common after disturbances on moist sites in the Appalachian Mountains. The species is typically scattered throughout old-growth mesophytic forests, where periodic gap formation creates conditions favorable for yellow-poplar establishment and growth. On abandoned agricultural fields, however, it is common for nearly monospecific forests of yellow-poplar to develop.This study examines stand dynamics of a yellow-poplar forest in western Virginia, USA that was established on agricultural fields abandoned in the late 1940s. Increment cores were collected from yellow-poplar trees growing on exposed ridgetops and in a more sheltered hollow. Tree-ring data show that the forest is even-aged. Tree establishment began about 5 years earlier on the ridgetops than in the hollow. Major ice storms disturbed the forest in 1978 and 1994, with two separate events in 1994. Ice storms disturb forests by depositing heavy loads of freezing rain on trees, breaking or uprooting them. The dendroecological data collected for this study provide little support for the hypothesis that ice storm disturbance promotes the establishment of new yellow-poplar cohorts. However, the data show that radial growth of some trees increased after ice storm disturbance, a pattern that reflects the increased availability of light following disturbance. Radial growth declined in some other trees as a consequence of severe injury during the storms.Radial growth responses following the 1978 ice storm were stronger on the ridgetops than in the hollow, suggesting that tree damage was more severe on the higher, more exposed sites. Growth responses were relatively mild following the storms of 1994, and did not exhibit pronounced topographic variations.     

Biotic and abiotic factors affecting the genetic structure and diversity of butternut in the southern Appalachian Mountains,USA

The abundance of butternut (Juglans cinerea L.) trees has severely declined rangewide over the past 50 years. An important factor in the decline is butternut canker, a disease caused by the fungus Ophiognomonia clavigigenti-juglandacearum, which has left the remaining butternuts isolated and sparsely distributed. To manage the remaining populations effectively, information regarding how butternut’s population genetic structure is affected by environmental and historical factors is needed. In this study, we assessed genetic structure and diversity of 161 butternut trees from 19 adjacent watersheds in the southern portion of butternut’s range using 12 microsatellite markers. We assessed the genetic diversity and genetic differentiation among trees grouped at various spatial scales. Our goal was to use historical abundance and land use data for these watersheds, which are now all a part of the Great Smoky Mountains National Park (GSMNP), to understand the ecological and evolutionary forces that challenge the conservation and management of butternut. In general, butternuts within the 19 neighboring watersheds were all part of one continuous population, with gene flow throughout. Significant genetic differentiation was detected between some groups of trees, but the differentiation was quite small and may not represent an ecologically significant distinction. The mean heterozygosity in all watersheds remained high, despite extensive mortality. Overall, genetic diversity and rare alleles were evenly distributed across all watersheds, with some variability in subpopulations containing butternut-Japanese walnut hybrids (Juglans x bixbyi or buarts). These results indicate that management of this species should focus on protection from future hybridization with Japanese walnut, promotion of regeneration, and persistence of all remaining butternut trees, which still retain high levels of genetic diversity.     

Forest soil carbon inventories and dynamics along an elevation gradient in the southern Appalachian Mountains

Soil organic carbon (SOC) was partitioned between unprotected and protected pools in six forests along an elevation gradient in the southern Appalachian Mountains using two physical methods: flotation in aqueous CaCl2 (1.4 g/mL) and wet sieving through a 0.053 mm sieve. Both methods produced results that were qualitatively and quantitatively similar. Along the elevation gradient, 28 to 53% of the SOC was associated with an unprotected pool that included forest floor O-layers and other labile soil organic matter (SOM) in various stages of decomposition. Most (71 to 83%) of the C in the mineral soil at the six forest sites was identified as protected because of its association with a heavy soil fraction (> 1.4 g/mL) or a silt-clay soil fraction. Total inventories of SOC in the forests (to a depth of 30 cm) ranged from 384 to 1244 mg C/cm2.The turnover time of the unprotected SOC was negatively correlated (r = –0.95, p < 0.05) with mean annual air temperature (MAT) across the elevation gradient. Measured SOC inventories, annual C returns to the forest floor, and estimates of C turnover associated with the protected soil pool were used to parameterize a simple model of SOC dynamics. Steady-state predictions with the model indicated that, with no change in C inputs, the low- (235–335 m), mid- (940–1000 m), and high- (1650–1670 m) elevation forests under study might surrender 40 to 45% of their current SOC inventory following a 4°C increase in MAT. Substantial losses of unprotected SOM as a result of a warmer climate could have long-term impacts on hydrology, soil quality, and plant nutrition in forest ecosystems throughout the southern Appalachian Mountains.     

Decomposition of standing dead trees in the southern Appalachian Mountains

Summary Decomposition of standing dead trees that were killed by fire was examined for 10 species in the Great Smoky Mountains National Park. The decrease in wood density as fire age increased was used to estimate decomposition rates. Quercus prinus had the fastest decay rate (11% yr^-1) while Pinus virginiana had the slowest decay rate (3.6% yr^-1) for standing dead wood. Decay rates were intermediate between those reported in western USA and tropics for wood.     

A new apameine genus and species from the southern Appalachian Mountains,USA (Lepidoptera,Noctuidae, Noctuinae)

Cherokeeagen. n. is proposed for a rarely collected apameine moth species from the southern Appalachian Mountains, C. attakullakullasp. n. It is recorded from foothills and lower montane habitats of North Carolina and Georgia where hill cane, Arundinaria appalachiana Triplett, Weakley & L.G. Clark is found. Adults and their genitalia are figured and a mtDNA barcode sequence is given.     

Aliphatic nitro-compounds in Astragalus canadensis

A reinvestigation of the alphatic nitro-compounds in Astragalus canadensis resulted in the identification of two new esters of glucose with 3-nitropropanoic acid and 5-oxotetrahydrofuran-3-acetic acid, together with six known conjugates of 3-nitropropanoic acid. ¹H and ¹³CNMR data are reported for the new compounds.     

Microhabitat selection by small mammals in a southern Appalachian fen in the USA

Little ecological information is available on small mammals inhabiting wetlands in the southern Appalachian mountains of the USA. These wetland systems are becoming rare features in southern landscapes due to human activities. We investigated the small mammal fauna and examined the microhabitat associations of the two most abundant species in a southern Appalachian fen. Four species of small mammals were captured: the meadow jumping mouse (Zapus hudsonius), short-tailed shrew ( Blarina brevicauda), white-footed mouse ( Peromyscus leucopus), and golden mouse ( Ochrotomys nuttalli). Peromyscus and Ochrotomys, which were caught in the largest numbers, preferred sites characterized by moderate herbaceous cover and substantial canopy closure. Peromyscus, however, selected areas with greater canopy closure and higher tree densities, suggesting that they are greater habitat specialists than Ochrotomys in this wetland community.     

Seasonal dynamics of ectomycorrhizal fungus assemblages on oak seedlings in the southeastern Appalachian Mountains

The potential for seasonal dynamics in ectomycorrhizal (EM) fungal assemblages has important implications for the ecology of both the host trees and the fungal associates. We compared EM fungus distributions on root systems of out-planted oak seedlings at two sites in mixed southeastern Appalachian Mountain forests at the Coweeta Hydrologic Laboratory in North Carolina, from samples taken in mid-July and early September. Species level EM fungus type specificity, and identification in some cases, was enabled by direct sequencing of the mycobionts from the seedling roots. Seventy-four EM fungal ITS types were documented, most of which occurred only in the midsummer or early-fall samples, respectively. Cenococcum geophilum (morphotyped) was ubiquitously present and accounted for the majority of root tips sampled. Abundance and relative frequency of types other than C. geophilum were significantly higher in the July samples, while C. geophilum was significantly more frequent and abundant in September. Several generalistic dominants were found fairly equally at both sites and on both sample dates. Other taxa with relatively high frequency were recovered from both sites and tree seedling species, but were reliable indicators occurring primarily in the July sample (e.g., Laccaria cf laccata). Notable shifts in mycobiont dominance were apparent in relation to sample date, including increases in Cortinarius spp. richness, decreases in Thelephoraceae richness, and the disappearance of Amanita spp. types in the early fall compared to midsummer samples. However, diversity and rarity were high and differences in overall community composition (other than C. geophilum) by season were not significant based on multi-response permutation procedures. Although these results based on a single growing season are preliminary, changes in abundance and frequency, detection of significant indicator species, and the apparent systematic affinities of shifting EM types support the potential for seasonal variability in EM associations in this system.     

Reproductive biology in an invasive plant Solidago canadensis

Solidago canadensis, a perennial Compositae plant originating from North America, was introduced into China as a horticultural plant in 1935. Under natural conditions, S. canadensis allocates large amounts of energy to sexual reproduction and produces many seeds, which reflects an r-strategy with high seed number and small seed size. In addition, naturalized populations have a great capacity to grow clonally with underground stems. S. canadensis has become an invasive weed in eastern China, and has caused serious damages to agricultural production and ecosystems in several provinces in China. In order to understand the reproductive characteristics of S. canadensis and effectively control its spread, we examined soil conditions, seed characteristics, seed germination and the capacity for asexual reproduction in different plant parts. We investigated the population dispersion of S. canadensis in fixed sites for three years, and analyzed the seasonal dynamics of the morphological parameters of the underground parts and the caloric values of different organs of S. canadensis. We also compared differences in the root systems of S. canadensis and composite exotic weeds. The following results were obtained:

Predicting Microstegium vimineum invasion in natural plant communities of the southern Blue Ridge Mountains, USA

Shade-tolerant non-native invasive plant species may make deep incursions into natural plant communities, but detecting such species is challenging because occurrences are often sparse. We developed Bayesian models of the distribution of Microstegium vimineum in natural plant communities of the southern Blue Ridge Mountains, USA to address three objectives: (1) to assess local and landscape factors that influence the probability of presence of M. vimineum; (2) to quantify the spatial covariance error structure in occurrence that was not accounted for by the environmental variables; and (3) to synthesize our results with previous findings to make inference on the spatial attributes of the invasion process. Natural plant communities surrounded by areas with high human activity and low forest cover were at highest risk of M. vimineum invasion. The probability of M. vimineum presence also increased with increasing native species richness and soil pH, and decreasing basal area of ericaceous shrubs. After accounting for environmental covariates, evaluation of the spatial covariance error structure revealed that M. vimineum is invading the landscape by a hierarchical process. Infrequent long-distance dispersal events result in new nascent sub-populations that then spread via intermediate- and short-distance dispersal, resulting in 3-km spatial aggregation pattern of sub-populations. Containment or minimisation of its impact on native plant communities will be contingent on understanding how M. vimineum can be prevented from colonizing new suitable habitats. The hierarchical invasion process proposed here provides a framework to organise and focus research and management efforts.     

Water source utilization under differing surface flow regimes in the riparian species Liquidambar styraciflua,in the southern Appalachian foothills,USA

Plant Ecology - Studies across the United States and globally have revealed that mature riparian trees often utilize little streamwater, relying on soil moisture and groundwater instead....     

Cloud immersion: an important water source for spruce and fir saplings in the southern Appalachian Mountains

Cloud immersion can provide a potentially important moisture subsidy to plants in areas of frequent fog including the threatened spruce-fir communities of the southern Appalachian Mountains (USA). These mountaintop communities grow only above ~1,500 m elevation, harbor the endemic Abies fraseri, and have been proposed to exist because of frequent cloud immersion. While several studies have demonstrated the importance of cloud immersion to plant water balance, no study has evaluated the proportion of plant water derived from cloud moisture in this ecosystem. Using the isotopic mixing model, IsoSource, we analyzed the isotopic composition of hydrogen and oxygen for water extracted from ground water, deep soil, shallow soil, fog, and plant xylem at the upper and lower elevational limits both in May (beginning of the growing season) and October (end of the growing season). Cloud-immersion water contributed up to 31 % of plant water at the upper elevation sites in May. High-elevation plants of both species also experienced greater cloud immersion and had greater cloud water absorption (14–31 %) compared to low-elevation plants (4–17 %). Greater cloud water uptake occurred in May compared to October, despite similar rainfall and cloud-immersion frequencies. These results demonstrate the important water subsidy that cloud-immersion water can provide. With a warming climate leading potentially to increases in the ceiling of the cloud base and, thus, less frequent cloud immersion, persistence of these relic mountaintop forests may depend on the magnitude of these changes and the compensating capabilities of other water sources.     

Seasonal occupancy of sympatric larger carnivores in the southern San Andres Mountains,south-central New Mexico,USA

We investigated factors facilitating coexistence of pumas (Puma concolor), coyotes (Canis latrans), and bobcats (Lynx rufus) in the arid San Andres Mountains of south-central New Mexico, during the season (winter and spring, prior to the annual monsoon) of greatest resource stress. We established a camera-trapping grid in the San Andres, 2007–2011, and modeled occupancy of the three carnivores as a function of habitat, prey, and presence of the other carnivore species. Species interaction factors were >1.3 for each pair of carnivores, and the presence of the other carnivore species never significantly influenced occupancy of any other carnivore. Similarly, occupancy of the San Andres landscape was positively correlated among all carnivores. Occupancy of pumas was most influenced by proximity of water; coyote occupancy was influenced by terrain ruggedness and presence of medium (primarily lagomorph) prey, and bobcat occupancy was influence primarily small prey and proximity to water. The three carnivores also did not show temporal partitioning in use of habitats. Rather than segregation driven by competition, predation, or despotism, our results appeared to reflect preferences for differing habitat characteristics between ambush and cursorial predators and preferred habitats for travel.     

Induction of antifreeze protein production by juvenile hormone in larvae of the beetle,Dendroides canadensis

Summary Larvae of the beetleDendroides canadensis accumulate protein antifreezes during the winter.D. canadensis which were collected in the early fall, prior to the initiation of cold hardening processes, were treated with either 3.3 or 6.6 g juvenile hormone I topically in acetone and maintained for 21 days under normally non-inductive acclimation conditions (16 light/8 dark, 20 °C). Hormone treated animals significantly elevated the levels of antifreeze protein in their hemolymph compared to those of acetone treated and untreated controls or animals measured on the day of collection. D. canadensis treated with the anti-JH compound precocene II (P2) in acetone for 24 h at a concentration of 20 g/cm² (a dose below LD₅₀ for behavioral survival) and then maintained under acclimation conditions conducive to antifreeze protein production (8 light/16 dark, 20 °C) for 2 weeks failed to elevate levels of antifreeze. Acetone treated control animals accumulated a significant concentration of antifreeze protein.D. canadensis were also treated with 20 and 150 g/cm² P2 (a dose below the LD₅₀ for gross survival) followed by acclimation to short (8 h) photoperiod at 10 °C. All animals receiving the higher P2 dosage failed to elevate antifreezes while only 42.9% of the individuals treated with the lower dosage initiated antifreeze protein production. In contrast, over 80% of untreated and 70% of acetone treated controls responded to these inductive acclimation conditions by elevating antifreeze concentrations.These results indicate that juvenile hormone participates in the seasonal control of antifreeze protein production inDendroides canadensis. Since this species does not enter a diapause state prior to or throughout the winter this is the first evidence establishing a direct hormonal mechanism involved with insect cold hardiness.     

Interactive effects of disturbance and nitrogen availability on phosphorus dynamics of southern Appalachian forests

Understanding the main and interactive effects of chronically altered resource availability and disturbance on phosphorus (P) availability is increasingly important in light of the rapid pace at which human activities are altering these processes and potentially introducing P limitation. We measured P pools and fluxes in eighteen mixed forest stands at three elevations (low, mid, high) subjected to increasing atmospheric N deposition, where hemlock (Tsuga canadensis) was absent or declining due to infestation by the exotic hemlock woolly adelgid (Adelges tsugae). While total soil P was similar across the study area, phosphorus fractionation revealed distinct differences in the distribution of soil P fractions as elevation and N availability increased. Soils from high elevation plots where N availability was greatest had 139 % larger organic P pools and 55 % smaller residual and refractory P pools than soils from low elevation plots with less N availability, suggesting that increased N availability has driven the depletion of recalcitrant P pools by stimulating biotic demand and sequestration. These differences in P distribution among fractions influenced how tree mortality affected P dynamics. At high elevations, plots containing declining hemlocks had significantly greater foliar P concentrations and fluxes of P from the forest floor than reference plots at similar elevations, whereas at low and mid-elevations there were no consistent differences between plots. Across all elevation classes, hardwood foliar N:P ratios were lower in plots with declining hemlocks. Collectively, these results suggest that increased N availability enhances bioavailable P, which is sequestered in vegetation until disturbances liberate it.     

Pleistocene glacial refugia across the Appalachian Mountains and coastal plain in the millipede genus Narceus : Evidence from population genetic, phylogeographic, and paleoclimatic data

Background  

Species that are widespread throughout historically glaciated and currently non-glaciated areas provide excellent opportunities to investigate the role of Pleistocene climatic change on the distribution of North American biodiversity. Many studies indicate that northern animal populations exhibit low levels of genetic diversity over geographically widespread areas whereas southern populations exhibit relatively high levels. Recently, paleoclimatic data have been combined with niche-based distribution modeling to locate possible refugia during the Last Glacial Maximum. Using phylogeographic, population, and paleoclimatic data, we show that the distribution and mitochondrial data for the millipede genus Narceus are consistent with classical examples of Pleistocene refugia and subsequent post-glacial population expansion seen in other organismal groups.     

High-elevation rock outcrop vegetation of the Southern Appalachian Mountains

Abstract. Species composition patterns and vegetation-environment relationships were quantified for high-elevation rock outcrops of the Southern Appalachian Mountains, an infrequent and insular habitat in a forested landscape. Outcrops occur over a wide geographic range encompassing extensive variation in both geology and climate. Geographic-scale factors interact with site-scale factors to produce variation in vegetation among outcrops. Similarly, site-scale factors interact with micro-scale factors to produce variation in vegetation within outcrops. To provide a quantitatively-based classification of outcrop vegetation we used a TWINSPAN analysis of 154 100-m² plots. We recognized nine communities that primarily correspond to different combinations of elevation, bedrock type, geography, and moisture. Within outcrops of a single bedrock type, vegetation composition of 100-m² plots was consistently correlated with elevation and solar radiation, but relationships to soil nutrients varied with bedrock type. Both site-scale (100 m²) factors (e.g. elevation, slope, aspect, and bedrock type) and plot-scale (1-m²) microsite factors (e.g. soil depth, vegetation height, soil nutrients) were strongly correlated with species composition at the 1-m² level. Environment can be used to predict composition more effectively for 100-m² plots on a single bedrock type than either across bedrock types or at a 1-m² scale. Composition-environment relationships resemble those described for outcrop systems from other regions with pronounced topographic relief more than they do those described for the nearby but flatter and lower-elevation outcrops of the Southeastern Piedmont. There is strong spatial autocorrelation in this community, perhaps owing to dispersal limitation. Consequently, a comprehensive conservation strategy must include reservation of both a range of geologic types and a range of geographic locations.     

Interactive effects of ozone and climate on water use, soil moisture content and streamflow in a southern Appalachian forest in the USA

* Documentation of the degree and direction of effects of ozone on transpiration of canopies of mature forest trees is critically needed to model ozone effects on forest water use and growth in a warmer future climate. * Patterns of sap flow in stems and soil moisture in the rooting zones of mature trees, coupled with late-season streamflow in three forested watersheds in east Tennessee, USA, were analyzed to determine relative influences of ozone and other climatic variables on canopy physiology and streamflow patterns. * Statistically significant increases in whole-tree canopy conductance, depletion of soil moisture in the rooting zone, and reduced late-season streamflow in forested watersheds were detected in response to increasing ambient ozone levels. * Short-term changes in canopy water use and empirically modeled streamflow patterns over a 23-yr observation period suggest that current ambient ozone exposures may exacerbate the frequency and level of negative effects of drought on forest growth and stream health.