Tsuga Canadensis Research Articles

The potential for indirect negative effects of exotic insect species on a liverwort,Bazzania trilobata(Lepidoziaceae), mediated by the decline of a foundation tree species,Tsuga canadensis(Pinaceae)1

In many ecological communities, the effects of exotic species are likely to extend beyond their direct interactions with natives, due to indirect effects. This dynamic might be particularly consequential in cases where invasive insects or other exotic herbivores target foundation plant species in the communities they invade. In this study at a site in western Massachusetts, we used experimental transplants to gauge the potential effects of a decline in the evergreen conifer Tsuga canadensis due to ongoing spread of two exotic insect pests on a liverwort, Bazzania trilobata, whose distribution is closely linked to dense stands of this conifer in the northeastern USA. After 4 years, transplanted B. trilobata samples moved to forest areas with lower abundance of T. canadensis declined significantly, particularly on sites with higher solar radiation, as determined by local slope and aspect. In addition, samples manually cleared of deciduous leaf litter were ∼ 17% larger than those exposed to natural accumulation of leaf litter, indicating a direct negative effect of deciduous trees on the liverwort that might increase as these tree species replace T. canadensis lost to invasive pests. A parallel experiment documented high mortality of B. trilobata (55%) when subjected to open canopy conditions similar to those resulting from selective “salvage” logging of hemlock in the region. These results indicate that the spread of exotic insect pests targeting T. canadensis is likely to produce strong indirect negative effects on the liverwort B. trilobata, via diminished commensal interactions with the conifer and increased amensalistic effects from the deciduous tree species that commonly replace it.

Chronic impacts of invasive herbivores on a foundational forest species: a whole‐tree perspective

Forests make up a large portion of terrestrial plant biomass, and the long-lived woody plants that dominate them possess an array of traits that deter consumption by forest pests. Although often extremely effective against native consumers, invasive species that avoid or overcome these defenses can wreak havoc on trees and surrounding ecosystems. This is especially true when multiple invasive species co-occur, since interactions between invasive herbivores may yield non-additive effects on the host. While the threat posed by invasive forest pests is well known, long-term field experiments are necessary to explore these consumer-host interactions at appropriate spatial and temporal scales. Moreover, it is important to measure multiple variables to get a "whole-plant" picture of their combined impact. We report the results of a 4-yr field experiment addressing the individual and combined impacts of two invasive herbivores, the hemlock woolly adelgid (Adelges tsugae) and elongate hemlock scale (Fiorinia externa), on native eastern hemlock (Tsuga canadensis) in southern New England. In 2011, we planted 200 hemlock saplings into a temperate forest understory and experimentally manipulated the presence/absence of both herbivore species; in 2015, we harvested the 88 remaining saplings and assessed plant physiology, growth, and resource allocation. Adelgids strongly affected hemlock growth: infested saplings had lower above/belowground biomass ratios, more needle loss, and produced fewer new needles than control saplings. Hemlock scale did not alter plant biomass allocation or growth, and its co-occurrence did not alter the impact of adelgid. While both adelgid and scale impacted the concentrations of primary metabolites, adelgid effects were more pronounced. Adelgid feeding simultaneously increased free amino acids local to feeding sites and a ~30% reduction in starch. The cumulative impact of adelgid-induced needle loss, manipulation of nitrogen pools, and the loss of stored resources likely accelerates host decline through disruption of homeostatic source-sink dynamics occurring at the whole-plant level. Our research stresses the importance of considering long-term impacts to predict how plants will cope with contemporary pressures experienced in disturbed forests.

Phenology of Hemlock Woolly Adelgid (Hemiptera: Adelgidae) in the Central Appalachian Mountains, USA

The ability to predict key phenological stages of insect pests is of prime importance in sampling and management programs. Hemlock woolly adelgid, Adelges tsugae (Annand) (Hemiptera: Adelgidae), is a non-native invasive pest of eastern and Carolina hemlock that is currently expanding its range westward through the central Appalachian region. We conducted intensive sampling of A. tsugae across four sites in West Virginia and western Maryland from March 2013 to May 2014, and developed a degree-day model (minimum temperature threshold of 4°C) to predict the temporal distribution of progrediens eggs, progrediens egg hatch, newly hatched sistens, and settled first-instar sistens. We then linked degree-day predictions to recent weather data collected from our study region from 2012 to 2016 to provide a range of calendar days over which these key phenological events occur. The initial occurrence of progrediens eggs and progrediens egg hatch is predicted to occur at 209 (mean date of 19 April) and 346 (mean date of 8 May) degree days, respectively. The initial occurrence of newly hatched sistens and settled first-instar sistens is predicted to occur at 852 (mean date of 19 June) and 1010 (mean date of 30 June) degree days, respectively. Because our study region represents a region in which A. tsugae continues to spread, this information should be useful in optimizing sampling programs and the timing of control tactics in the central Appalachian region.

Leptoglossus occidentalis . [Distribution map

Abstract A new distribution map is provided for Leptoglossus occidentalis Heidemann. Hemiptera: Coreidae. Hosts: Pine ( Pinus spp.), Douglas fir ( Pseudotsuga menziesii ) and Eastern hemlock ( Tsuga canadensis ). Information is given on the geographical distribution in Europe (Austria, Belgium, Bosnia-Hercegovina, Bulgaria, Croatia, Czech Republic, Denmark, France, Corsica, Mainland France, Germany, Greece, Crete, Hungary, Irish Republic, Italy, Mainland Italy, Sardinia, Sicily, Luxembourg, Macedonia, Malta, Moldova, Montenegro, Netherlands, Norway, Poland, Portugal, Romania, Russia, Southern Russia, Serbia, Slovakia, Slovenia, Spain, Balearic Islands, Mainland Spain, Sweden, Switzerland, UK, Channel Islands, England and Wales, Northern Ireland, Scotland and Ukraine), Asia (Israel, Japan, Honshu, Korea Republic, Lebanon and Turkey), Africa (Morocco and Tunisia), North America (Canada, Alberta, British Columbia, New Brunswick, Nova Scotia, Ontario, Quebec, Saskatchewan, Mexico, USA, Arizona, California, Colorado, Connecticut, Idaho, Illinois, Indiana, Iowa, Kansas, Maine, Massachusetts, Michigan, Minnesota, Montana, Nebraska, New Hampshire, New Mexico, New York, North Dakota, Oregon, Pennsylvania, Rhode Island, Texas, Utah, Washington, Wisconsin and Wyoming) and South America (Chile).

Ecological risk based assessment used to restore riparian physical functions to a fresh water Creek

The purpose of this study was to determine if an interdisciplinary team using a qualitative proper functioning condition (PFC) assessment protocol could identify and reverse significant detrimental ecological alterations which occurred within Gertie's Creek watershed, Ontario, Canada. At potential, Gertie's Creek supported a woody debris glacial outwash fine gravel substrate fish spawning habitat. The anthropogenic activities on Georgina Island caused a denuded anadromous fish population since the early-to mid-1990's in the Gertie's Creek watershed. The PFC assessment indicated that anthropogenic activities on Georgina Island negatively impacted stream flows in Gertie's Creek. Reduced stream flow resulted in the natural stream (lotic) riparian habitat not advancing out of an early seral silver maple and eastern hemlock vegetated swamp (forested wetland) habitat. The Gertie's Creek interdisciplinary team PFC assessment indicated that the entire watershed is not in balance with the water and sediment being supplied along with a lack of diverse riparian vegetation. Sediment was not being transported to the wetland and lake coastal areas because of chronic reduced flows. Further qualitative assessments by the authors of other smaller lentic and lotic ecosystems on Georgina Island indicate that reduced hydrologic flow is an issue for the entire island. Ecosystem function management planning works with the ecosystem to continually respond as the ecology changes in ways that enhance remarkable natural recovery.

Influence of Imidacloprid and Horticultural Oil on Spider Abundance on Eastern Hemlock in the Southern Appalachians.

Hemlock woolly adelgid, Adelges tsugae Annand (Hemiptera: Adelgidae), is an exotic pest of eastern hemlock, Tsuga canadensis (L.) Carrière (Pinales: Pinaceae), in the eastern United States. Two commonly used insecticides to manage adelgid are imidacloprid, a systemic neonicotinoid insecticide, and horticultural oil, a refined petroleum oil foliar spray. We have investigated the influence of imidacloprid and horticultural oil on spider abundance at different canopy strata in eastern hemlock. In total, 2,084 spiders representing 11 families were collected from the canopies of eastern hemlock. In beat-sheet and direct observation samples, the families Theridiidae, Araneidae, Salticidae, and Anyphaenidae were the most abundant. Significantly higher numbers of spiders were recorded on untreated control trees compared with trees treated with imidacloprid using soil drench and soil injection applications. Spider abundance in trees injected with imidacloprid and horticultural oil applications did not significantly differ from control trees. Spider abundance was significantly greater in the top and middle strata of the canopy than in the bottom stratum, where imidacloprid concentrations were the highest. Regression analysis showed that spider abundance was inversely associated with imidacloprid concentration. This research demonstrates that imidacloprid, when applied with selected methods, has the potential to result in reductions of spider densities at different strata. However, slight reductions in spider abundance may be an acceptable short-term ecological impact compared with the loss of an untreated hemlock and all the associated ecological benefits that it provides. Future studies should include investigations of long-term impact of imidacloprid on spiders associated with eastern hemlock.

Rhododendron maximum impacts seed bank composition and richness following Tsuga canadensis loss in riparian forests

AbstractSouthern Appalachian riparian forests have undergone changes in composition and function from invasive pathogens and pests. Castanea dentata mortality in the 1930s from chestnut blight (Cryphonectria parasitica) and Tsuga canadensis mortality in the 2000s from the hemlock woolly adelgid (Adelges tsugae) have led to the expansion and increased growth of Rhododendron maximum, an evergreen subcanopy shrub. A better understanding of seed bank characteristics and the various abiotic and biotic factors that affect the seed bank may be useful in determining the restoration potential of forest communities following invasion‐related disturbances. We compared the seed bank of two deciduous forest types: hardwood forests with a dense R. maximum subcanopy (hereafter, RR) and hardwood forests without R. maximum (hereafter, HWD). We evaluated numerous microenvironmental variables through principal component analysis (PCA) and correlated the derived PCA axes scores to seed bank density and richness across forest types. We found that seed bank density was comparable between the forests types; however, seed bank richness was much lower in RR than HWD and the species composition was dissimilar between forest types. Twenty‐eight of 64 (44%) species in the seed bank of HWD were not found in the seed bank of RR. Species that were represented in both forest types were often found in contrasting densities. Most notably, seed bank densities of several woody species were considerably higher in RR (85%) than HWD (45%), while herbaceous seed bank density was lower in RR (11%) than HWD (50%). Mineral soil pH, soil nutrient availability, and soil moisture were lower, and organic soil (Oi + Oe + Oa) depth and mass were greater in the RR than HWD forest type. PCA correlations revealed that PCA4 (represented by understory density and Oe + Oa phosphorus and carbon/nitrogen ratio) was negatively correlated with total seed bank density. PCA1 (represented by Oe + Oa cations and phosphorus, understory richness, ground‐layer cover, and mineral soil pH) and PCA4 were positively correlated with total seed bank richness. These results suggest that the soil seed bank will not be the primary mode of recruitment to establish a diverse and herbaceous‐rich community if a RR is present.

Variation in the maximum stand density index and its linkage to climate in mixed species forests of the North American Acadian Region

Maximum stand density index (SDImax) is an important factor controlling stand dynamics that varies by species and region, but less is understood how it differs within a region for a given species. In this analysis, linear quantile mixed modeling (LQMM) and an extensive network of permanent plots were utilized to examine regional variation in the SDImax of 15 species (7 softwoods and 8 hardwoods) across the complex forests of the Acadian Region in North America. Observed plot-level SDImax was then linked to various stand, plant trait, site, and climatic factors and the spatial patterns throughout the region examined. Results indicated high variability of SDImax for a given species with northern hardwood species like yellow birch (Betula alleghaniensis Britt.), sugar maple (Acer saccharum Marsh.), and American beech (Fagus grandifolia Ehrh.) having the lowest values (555 – 627), while softwood species such as northern white cedar (Thuja occidentalis L.; 1014), eastern hemlock (Tsuga canadensis (L.) Carr.; 1026), and white pine (Pinus strobus L.; 967) had the highest values. Compared to the other stand and site factors examined, climate showed the strongest relationship with SDImax with R2 ranging from 82 to 98%. Of the climatic variables examined, those representing growing season length and the timing of precipitation were most influential. For the majority of the species examined, reductions in SDImax were forecasted due to changing climatic conditions. Across species, mean SDImax was found to linearly decline with wood specific gravity and increase with leaf longevity, but showed limited relationships with other species-level functional traits. Overall, the analysis highlights the strong variability of SDImax within and between species as well as the important role that climate has on this attribute within a region.

Identifying foundation species in North American forests using long‐term data on ant assemblage structure

AbstractFoundation species are locally abundant and uniquely control associated biodiversity, whereas dominant species are locally abundant but are thought to be replaceable in ecological systems. It is important to distinguish foundation from dominant species to direct conservation efforts. Long‐term studies that remove abundant species while measuring community dynamics have the potential to (1) aid in the identification of foundation vs. dominant species and, (2) once a foundation species is identified, determine how long its effects persist within a community after its loss. Long‐term data on ant assemblages within two canopy‐manipulation experiments—the Harvard Forest Hemlock Removal Experiment (HF‐HeRE) and the Black Rock Future of Oak Forests Experiment (BRF‐FOFE)—provide insights into how ant assemblages change and reassemble following the loss of Tsuga canadensis or Quercus spp. Previous research documented foundation species effects on ants in the HF‐HeRE for up to four years after T. canadensis loss. Six additional years of data at HF‐HeRE presented for the first time here show that removal of T. canadensis resulted in taxonomic and some measures of functional shifts in ant assemblages that persisted for ten years, further supporting the hypothesis that T. canadensis is a foundation species at Harvard Forest. In contrast, ant assemblages at BRF‐FOFE varied little regardless of whether oaks or other tree species were removed from the canopy, suggesting that Quercus species do not act as foundation species at Black Rock Forest. Deer and moose exclosures within each experiment also allowed for comparisons between effects on ants of foundation or dominant tree species relative to effects of large herbivores. At HF‐HeRE, effects of T. canadensis were stronger than effects of large herbivores on taxonomic and functional diversity of ant assemblages. At BRF‐FOFE, in contrast, effects of Quercus species were weaker than effects of large herbivores on ant taxonomic diversity and some measures of ant functional diversity. These findings illustrate the importance of distinguishing between the roles of irreplaceable foundation species and replaceable dominant ones in forested ecosystems along with other drivers of biodiversity (e.g., herbivory).

The potential to characterize ecological data with terrestrial laser scanning in Harvard Forest, MA.

Contemporary terrestrial laser scanning (TLS) is being used widely in forest ecology applications to examine ecosystem properties at increasing spatial and temporal scales. Harvard Forest (HF) in Petersham, MA, USA, is a long-term ecological research (LTER) site, a National Ecological Observatory Network (NEON) location and contains a 35 ha plot which is part of Smithsonian Institution's Forest Global Earth Observatory (ForestGEO). The combination of long-term field plots, eddy flux towers and the detailed past historical records has made HF very appealing for a variety of remote sensing studies. Terrestrial laser scanners, including three pioneering research instruments: the Echidna Validation Instrument, the Dual-Wavelength Echidna Lidar and the Compact Biomass Lidar, have already been used both independently and in conjunction with airborne laser scanning data and forest census data to characterize forest dynamics. TLS approaches include three-dimensional reconstructions of a plot over time, establishing the impact of ice storm damage on forest canopy structure, and characterizing eastern hemlock (Tsuga canadensis) canopy health affected by an invasive insect, the hemlock woolly adelgid (Adelges tsugae). Efforts such as those deployed at HF are demonstrating the power of TLS as a tool for monitoring ecological dynamics, identifying emerging forest health issues, measuring forest biomass and capturing ecological data relevant to other disciplines. This paper highlights various aspects of the ForestGEO plot that are important to current TLS work, the potential for exchange between forest ecology and TLS, and emphasizes the strength of combining TLS data with long-term ecological field data to create emerging opportunities for scientific study.

Microsites Supporting Endemic Populations of Mountain Stewartia (Stewartia ovata) in East Tennessee

Mountain stewartia (Stewartia ovata) is the only member of the family Theaceae endemic to Tennessee. Apart from its physical description and rarity, little is known about this woody understory species. Accounts of stewartia populations and range descriptions are longstanding, but microsite descriptions are limited in detail. We quantified microsites supporting populations of stewartia across East Tennessee as a first step in determining whether stewartia is rare because of rare or altered habitat, limited sexual reproduction, poor dispersal, or a combination of these factors. Five populations of stewartia averaging 7.40 ± 1.08 stems per population were inventoried across four East Tennessee counties. Soils on all sites were strongly acidic, highly permeable, well-drained, cobbly loams associated with steep slopes and higher elevations and were low in phosphorus, potassium, calcium, and magnesium. A dense overstory comprised of sourwood (Oxydendrum arboreum), eastern hemlock (Tsuga canadensis), white oak (Quercus alba), eastern white pine (Pinus strobus), red maple (Acer rubrum), and mockernut hickory (Carya tomentosa) resulted in 7.05% ± 1.41% of full photosynthetically active radiation (PAR). The midstory and understory were dominated by eastern white pine, red maple, and eastern hemlock. Quantification of stand-level conditions in extant stewartia populations suggested similarities in soil pH, nutrient levels, drainage, overstory composition and structure, and PAR levels. Certain conditions in stewartia sites were unique in the region, suggesting that habitat may limit populations along with other factors. Further investigations of stewartia reproductive ecology, dispersal, and habitat requirements will be key to conserving this species.

The genetic diversity of disjunct populations of Eastern hemlock (Tsuga canadensis) in Minnesota

Tree conservation efforts have increasingly focused on intraspecific genetic diversity to help identify trees and populations for conservation. Disjunct populations and populations on the periphery of a species' range may be useful genetic resources. Eastern hemlock (Tsuga canadensis (L.) Carriere), a common native conifer in the eastern United States, exists on the northwestern edge of its range in Minnesota. Eastern hemlock has occurred in Minnesota in smaller disjunct populations for at least 1,200 years, but is now listed in the state as an endangered species. The number of trees has decreased significantly from over 5,000 in the early 1900s to less than 40 known mature trees, which are restricted to native stands in the northeastern region of the state. This decrease was due to logging, fire, herbivorous predation, and poor regeneration. There are additional trees of native provenance cultivated at the Minnesota Landscape Arboretum in Chanhassen, MN and trees of unknown provenance at various municipal and state parks and on private property across the state. We are using previously described microsatellite markers derived from Tsuga canadensis and T. caroliniana to investigate the genetic diversity of native disjunct populations and naturalized and cultivated trees in Minnesota. We collected foliage samples for DNA extraction from native provenance trees, trees of unknown provenance in naturalized and cultivated areas in Minnesota, trees in the Great Lakes region and trees from the center of species diversity in North Carolina. Additionally, over the course of two years we collected seed and grew seedlings from six native trees in Minnesota, four trees of native provenance from the Minnesota Landscape Arboretum, and 12 trees of unknown provenance. We are using these genetic resources to infer the relationships within and among populations and to unearth the origin of trees of unknown provenance. Results from this research can be used to understand the population genetics of Eastern hemlock in Minnesota and to inform decisions about the conservation and management of remaining native and cultivated trees.

Assessing an integrated biological and chemical control strategy for managing hemlock woolly adelgid in southern Appalachian forests

Abstract In the eastern United States, hemlock woolly adelgid (HWA), Adelges tsugae Annand (Hemiptera: Adelgidae) is considered an invasive pest of eastern hemlocks; an ecologically foundational tree species. Current management of HWA focuses on chemical and biological controls, with recent research suggesting that these two tactics could be integrated successfully. The approach is to protect a subset of hemlocks with systemic insecticides while releasing predatory insects onto adjacent, unprotected trees. The goal of this study was to assess the effects of chemical and biological control tactics, alone and in combination, on hemlock health and HWA densities at three southern Appalachian sites (KY, WV, and TN) from 2010 to 2016. Although insecticide applications were effective at protecting individual trees, none of the overall treatments (chemical, biological, or combined) had a significant effect on tree health or HWA population index values relative to untreated plots. Tree health generally declined at all sites over time. HWA populations were highly variable over time and were likely more strongly influenced by extremely low, winter temperatures than by the treatments. Cross-correlation analysis of tree health and HWA population indicated a time-lag effect. At two of the three sites, recovery of tree health lagged 0 – 3 years behind decline in HWA population, and decline in HWA populations lagged approximately 0 – 1 years behind decline in tree health. The predatory beetle, Laricobius nigrinus, was recovered two-years, post-release at the KY and WV sites in 2012 and 2013, but was not recovered from the TN site. The lack of sustained recovery of L. nigrinus may be attributable to the occurrence of extremely low, winter temperatures in 2014 and 2015, which produced subsequent crashes in the HWA populations. In TN, the L. nigrinus population may have been unrecoverable due to a decline in the HWA population shortly after initial release.

Two invasive herbivores on a shared host: patterns and consequences of phytohormone induction.

Herbivore-induced changes in host quality mediate indirect interactions between herbivores. The nature of these indirect interactions can vary depending on the identity of herbivores involved, species-specific induction of defense-signaling pathways, and sequence of attack. However, our understanding of the role of these signaling pathways in the success of multiple exotic herbivores is less known. Eastern hemlock (Tsuga canadensis) is attacked by two invasive herbivores [elongate hemlock scale (EHS; Fiorinia externa) and hemlock woolly adelgid (HWA; Adelges tsugae)] throughout much of its range, but prior attack by EHS is known to deter HWA. The potential role of phytohormones in this interaction is poorly understood. We measured endogenous levels of phytohormones in eastern hemlock in response to attack by these invasive herbivores. We also used exogenous application of methyl jasmonate (MJ) and acibenzolar-S-methyl (ASM), a salicylic acid (SA) pathway elicitor, to test the hypothesis that defense-signaling phytohormones typically induced by herbivores could deter HWA. Resistance to adelgid attack was assessed using a behavioral assay. Adelgid feeding significantly elevated both abscisic acid (ABA) and SA in local tissues, while EHS feeding had no detectable effect on either phytohormone. HWA progrediens and sistens crawlers preferred to settle on ASM-treated foliage. In contrast, HWA crawlers actively avoided settlement on MJ-treated foliage. We suggest that induction of ABA- and SA-signaling pathways, in concert with defense-signaling interference, may aid HWA invasion success, and that defense-signaling interference, induced by exotic competitors, may mediate resistance of native hosts.

Hemlock Woolly Adelgid (Hemiptera: Adelgidae): A Non-Native Pest of Hemlocks in Eastern North America

Hemlock woolly adelgid, Adelges tsugae Annand, is an invasive insect species in eastern North America that was accidentally introduced from southern Japan. It is the single most important pest of hemlocks in eastern North America and has a severe impact on the two susceptible species: eastern hemlock, Tsuga canadensis (L.) Carriere (Pinales: Pinaceae) and Carolina hemlock, Tsuga caroliniana Engelmann (Pinales: Pinaceae). Since the first report of hemlock woolly adelgid in Virginia in 1951, it has been slowly but steadily increasing its range. Recent establishments outside the contiguous range in Michigan and Nova Scotia have also occurred. At the stand level, hemlock trees are being replaced by hardwood trees in eastern North America, impacting some critical ecosystem processes. Several institutions are actively researching ways to protect the existing hemlock stands from further damage and to restore the ecosystems impacted by their loss. Although several control options for hemlock woolly adelgid have been developed, none are completely effective on their own, so a combination of all available control strategies is being used in an effort to save the existing hemlock stands. High-value hemlocks are being protected using chemicals, while a suite of predators is being released in forested areas. However, biological control has not provided immediate protection for heavily infested trees, so options for restoring hemlocks (hybrids with Asian species and punitively resistant stock) and finding viable replacements are being evaluated.

Pinus sylvestris L. and other conifers as natural sources of ascorbic acid

Context: There is a widespread opinion that needles of conifers are a good source of ascorbic acid and may help to cure and prevent scurvy. Aims: To determine the content of ascorbic acid in needles and shoots of Pinus sylvestris, Picea abies, Juniperus communis and several other conifers. Methods: Ascorbic acid content was analyzed by HPLC: aminocolumn 250 mm x 4.6 mm, 5 µm; mobile phase acetonitrile and 0.05 M KH2PO4 (75:25), flow rate 1.0 mL/min, detection at 266 nm. Results: The fresh needles contained more (10.8 x 10-3%) of ascorbic acid than the fresh shoots (5.4 x 10-3%) of the same P. sylvestris tree. In needles collected during one year with monthly intervals from the same pine tree the content of vitamin C varied from 0.5 x 10-3% to 15.7 x 10-3%. The needles gathered in winter from November to March contained much more of ascorbic acid (5.2-15.7 x 10-3%) than needles collected during warmer season (0.5-2.8 x 10-3%). The fresh needles of compared conifers (n=11) contained ascorbic acid from 0% (Tuja occidentalis) to 15.0 x 10-3% (Tsuga canadensis), needles of J. communis contained ascorbic acid a little more (13.3 x 10-3%) than needles of P. sylvestris, P. abies and Microbiota decussata (9.0-10.8 x 10-3%). Conclusions: The concentration of ascorbic acid in needles and shoots of studied conifers is rather low if compared to other natural sources of vitamin C. Fresh plant material of P. sylvestris, P. abies and J. communis contained more ascorbic acid than frozen material. The concentration of ascorbic acid in needles of these three trees was higher than in shoots.

Northeastern United States species treated with copper-based preservatives: Durability in mississippi stake tests

This paper reports on the ground-contact durability of lesser-used wood species of the northeastern United States after treatment with copper-based preservatives. Stakes (19 by 19 by 457 mm) cut from balsam-fir (Abies balsamea), eastern hemlock (Tsuga canadensis), eastern spruce (mixture of Picea glauca, Picea mariana and Picea rubens), red maple (Acer rubrum) or eastern white pine (Pinus strobus) were treated with one of four concentrations of chromated copper arsenate type C (CCA-C), copper citrate (CC), alkaline copper quat type C (ACQ-C) or copper azole type A (CBA-A) and placed into the ground at a test site in southern Mississippi. Similarly treated southern pine (Pinus spp.) stakes were included for comparison. The stakes were rated for decay and termite attack after 1, 2, 3, 4, 5, 8, 10 and 12 years. Eastern white pine and incised eastern hemlock and balsam-fir had durability similar to southern pine when treated with CCA or the other copper-based preservatives. Eastern spruce was less durable than the other softwood species, apparently because of low preservative uptake. Red maple had the least durability at all retentions and for all preservatives. This study indicates that several northeastern softwoods can be adequately durable when pressure-treated with CCA-C or copper-based preservatives.

Impact of hemlock woolly adelgid (Adelges tsugae) infestation on xylem structure and function and leaf physiology in eastern hemlock (Tsuga canadensis).

Hemlock woolly adelgid (Adelges tsugae Annand) (HWA) is an invasive insect that feeds upon the foliage of eastern hemlock (Tsuga canadensis (L.) Carrière) trees, leading to a decline in health and often mortality. The exact mechanism leading to the demise of eastern hemlocks remains uncertain because little is known about how HWA infestation directly alters the host's physiology. To evaluate the physiological responses of eastern hemlock during early infestation of HWA, we measured needle loss, xylem hydraulic conductivity, vulnerability to cavitation, tracheid anatomy, leaf-level gas exchange, leaf water potential and foliar cation and nutrient levels on HWA-infested and noninfested even-aged trees in an experimental garden. HWA infestation resulted in higher xylem hydraulic conductivity correlated with an increase in average tracheid lumen area and no difference in vulnerability to cavitation, indicating that needle loss associated with HWA infestation could not be attributed to reduced xylem transport capacity. HWA-infested trees exhibited higher rates of net photosynthesis and significant changes in foliar nutrient partitioning, but showed no differences in branch increment growth rates compared with noninfested trees. This study suggests that HWA-induced decline in the health of eastern hemlock trees is not initially caused by compromised water relations or needle loss.

Mortality and Recovery of Hemlock Woolly Adelgid (Adelges tsugae) in Response to Winter Temperatures and Predictions for the Future

Eastern (Tsuga canadensis) and Carolina hemlocks (T. caroliniana) of eastern North America have been attacked by the non-native hemlock woolly adelgid (Adelges tsugae Annand) (HWA) since the first half of the 20th century. Unlike most insects, HWA develops through one generation from fall to late winter, exposing this insect to the lethal effects of winter temperatures. The mortality inflicted by winter temperatures on HWA determines the surviving population density as well as its ability to spread to uninfested areas. With the ongoing changes in climate, knowledge of this species’ ability to survive and spread in the future can help land managers prepare for its management. This study began during the winter of 2014 and ended in the spring of 2017. During this period, winter mortality of HWA was recorded at 100 sites from Maine to Georgia (n = 209). Changes in population density from the sistens to the succeeding progrediens generation were recorded at 24 sites (n = 35). Models were developed to predict HWA mortality using the lowest minimum temperature prior to the mortality assessment date, the number of days with mean temperature <−1 °C, and the mean daily temperature of the three days preceding that minimum. Models were also developed to predict population density changes from the overwintering sistens generation to the following progrediens generation. Future projections under climate change showed increases in winter survival and population growth rates over time. Especially towards the northeastern edge of T. canadensis’ distribution as minimum temperatures are predicted to increase at a greater rate. This will result in an increase in density throughout its current distribution and expansion northward causing an increase in its impact on eastern Tsuga spp.

Transplanting boreal soils to a warmer region increases soil heterotrophic respiration as well as its temperature sensitivity

Under a warming climate, the boreal forest could become one of the largest terrestrial net CO2 sources, as increasing disturbances and soil organic matter decomposition rates (heterotrophic respiration, Rh) could offset net primary production. Since soil represents the boreal forest's largest C pool, it is critical of correctly predicting future changes in Rh, as well as its sensitivity to temperature (Q10 of Rh). We simulated a soil warming by transplanting soil cores from boreal balsam fir (Abies balsamea, BF) and black spruce (Picea mariana, BS) stands to a more southern Eastern hemlock stand (Tsuga canadensis, EH). We measured Rh and soil properties over 3 years, from June to October. Over three snow-free seasons, soil temperature (first 10 cm, including the FH organic layers) and Rh increased for BF (+3.2 °C, +60% of Rh) and BS cores (+2.3 °C, +27% of Rh). Microbial C concentration decreased by 54–73% in the FH layers of warmed and control cores relative to initial values, despite unchanged chemically labile C, probably due to excised roots and mycorrhizal hyphae. This suggests a possible underestimation of Rh during the experiment. In BF soils only, the increase in Rh was accompanied by an increase in its sensitivity to temperature. Under a +5 °C soil warming, mean predicted Rh of BF soils would increase by 83% rather than by 56%. Relative to BS soils, such increase in sensitivity could be partly due to a higher fraction of chemically labile C (+52%) in the FH layers and a higher mean warming effect. It suggests that for BF forest soils, predicting decomposition rates for a warmer climate based on current temperature sensitivities could be inadequate. However, longer-term studies are needed to see if this increase in Q10 of Rh for BF soils would be maintained for longer periods.