Tsuga Canadensis Research Articles

Tsuga canadensis (eastern hemlock)

Tsuga canadensis (eastern hemlock)

Lambdina fiscellaria (eastern hemlock looper)

Lambdina fiscellaria (eastern hemlock looper)

Land-use history impacts spatial patterns and composition of woody plant species across a 35-hectare temperate forest plot.

Land-use history is the template upon which contemporary plant and tree populations establish and interact with one another and exerts a legacy on the structure and dynamics of species assemblages and ecosystems. We use the first census (2010–2014) of a 35-ha forest-dynamics plot at the Harvard Forest in central Massachusetts to describe the composition and structure of the woody plants in this plot, assess their spatial associations within and among the dominant species using univariate and bivariate spatial point-pattern analysis, and examine the interactions between land-use history and ecological processes. The plot includes 108,632 live stems ≥ 1 cm in diameter (2,215 individuals/ha) and 7,595 standing dead stems ≥ 5 cm in diameter. Live tree basal area averaged 42.25 m2/ha, of which 84% was represented by Tsuga canadensis (14.0 m2/ ha), Quercus rubra (northern red oak; 9.6 m2/ ha), Acer rubrum (7.2 m2/ ha) and Pinus strobus (eastern white pine; 4.4 m2/ ha). These same four species also comprised 78% of the live aboveground biomass, which averaged 245.2 Mg/ ha. Across all species and size classes, the forest contains a preponderance (> 80,000) of small stems (<10-cm diameter) that exhibit a reverse-J size distribution. Significant spatial clustering of abundant overstory species was observed at all spatial scales examined. Spatial distributions of A. rubrum and Q. rubra showed negative intraspecific correlations in diameters up to at least a 150-m spatial lag, likely indicative of crowding effects in dense forest patches following intensive past land use. Bivariate marked point-pattern analysis, showed that T. canadensis and Q. rubra diameters were negatively associated with one another, indicating resource competition for light. Distribution and abundance of the common overstory species are predicted best by soil type, tree neighborhood effects, and two aspects of land-use history: when fields were abandoned in the late 19th century and the succeeding forest types recorded in 1908. In contrast, a history of intensive logging prior to 1950 and a damaging hurricane in 1938 appear to have had little effect on the distribution and abundance of present-day tree species. Our findings suggest that current day composition and structure are still being influenced by anthropogenic disturbances that occurred over a century ago.

Subterranean Survivorship and Seasonal Emergence of Laricobius spp. (Coleoptera: Derodontidae), Biological Control Agents for the Hemlock Woolly Adelgid.

Following the adventive arrival, subsequent spread, and ensuing impact of Adelges tsugae Annand (Hemiptera: Adelgidae), the hemlock woolly adelgid (HWA) in the eastern United States, a robust initiative was launched with the goal of decreasing ecosystem impacts from the loss of eastern hemlock (Pinales: Pinaceae). This initiative includes the use of biological control agents, including Laricobius spp. (Insecta: Coleoptera). Laboratory production of these agents is limited by subterranean mortality and early emergence. Therefore, the subterranean survivorship and timing of emergence of a mixture of Laricobius spp. was investigated. PVC traps internally lined with a sticky card and covered with a mesh screen were inserted into the soil to measure the percent emergence of adults based on the number of larvae placed within. The number of emerged adults in the field and laboratory-reared larval treatments was adjusted based on emergence numbers in the control and used as the response variable. Independent variables included in the final model were: treatment (field-collected vs. laboratory-reared), organic layer depth (cm), soil pH, and April-to-December mean soil moisture. No differences were found in survivorship between field-collected and laboratory-reared treatments. As pH and organic layer increased survivorship decreased, significantly. Although the majority of emergence occurred in the fall, emergence also occurred in spring and summer. The occurrence of spring and summer emergence and low survivorship (17.1 ± 0.4%) in the field across all treatments suggests that these are characteristics of Laricobius spp. field biology in their introduced range and not artifacts of the laboratory rearing process.

High Rainfall May Induce Fungal Attack of Hemlock Woolly Adelgid (Hemiptera: Adelgidae) Leading to Regional Decline.

Hemlock woolly adelgid (HWA; Adelges tsugae Annand (Hemiptera: Adelgidae)) is the cause of widespread mortality of Carolina and eastern hemlock (Tsuga caroliniana Engelmann and T. canadensis (L.) Carrière) throughout the eastern United States (U.S.). Since its arrival in the northeastern U.S., HWA has steadily invaded and established throughout eastern hemlock stands. However, in 2018, anecdotal evidence suggested a sharp, widespread HWA decline in the northeastern U.S. following above-average summer and autumn rainfall. To quantify this decline in HWA density and investigate its cause, we surveyed HWA density in hemlock stands from northern Massachusetts to southern Connecticut and analyzed HWA density and summer mortality in Pennsylvania. As native fungal entomopathogens are known to infect HWA in the northeastern U.S. and rainfall facilitates propagation and spread of fungi, we hypothesized high rainfall facilitates fungal infection of aestivating nymphs, leading to a decline in HWA density. We tested this hypothesis by applying a rain-simulation treatment to hemlock branches with existing HWA infestations in western MA. Our results indicate a regional-scale decline and subsequent rebound in HWA density that correlates with 2018 rainfall at each site. Experimental rain treatments resulted in higher proportions of aestivating nymphs with signs of mortality compared to controls. In conjunction with no evidence of increased mortality from extreme winter or summer temperatures, our results demonstrate an indirect relationship between high rainfall and regional HWA decline. This knowledge may lead to better prediction of HWA population dynamics.

Does forest tree species composition impact modelled soil recovery from acidic deposition?

Acidic deposition depleted soil base cation pools throughout central Ontario, particularly during the second half of the 20th century. While sulfur (S) and nitrogen (N) deposition have declined in recent decades, forest harvesting may continue to remove base cations from soils, highlighting the need for reliable soil chemistry forecasts. This study investigated whether differences in soil chemistry among forest plots dominated by different tree species affected predictions using a dynamic biogeochemical model, the Very Simple Dynamic model. Soil base saturation was modelled from 1850 to 2100 in plots dominated by balsam fir (Abies balsamea (L.) Mill.), eastern hemlock (Tsuga canadensis (L.) Carr.), white pine (Pinus strobus L.), sugar maple (Acer saccharum Marsh.), or yellow birch (Betula alleghaniensis Britt.). Three scenarios that manipulated future atmospheric S and N deposition and forest harvesting (2020–2100) were applied. When future atmospheric S and N deposition remained at 2020 levels and harvesting continued, base saturation increased marginally (2.0%–4.5%) in all plots. Further increases in base saturation were minor (∼1%) by 2100 when deposition reductions were implemented. When future forest harvesting was excluded, soil base saturation increased 3.4%–8.5% from 2020 to 2100. These results suggest that tree species composition has minimal influence on modelled soil chemistry forecasts in response to changes in acidic deposition, and such models can be broadly applied for regional predictions.

White-tailed deer herbivory impacts on tree seedling and sapling abundance in the Lake States Region of the USA

White-tailed deer (Odocoileus virginiana Zimmermann) browsing reduces seedling and sapling abundance of more palatable winter woody browse such as Tsuga canadensis L. Carrière, Thuja occidentalis L., Betula alleghaniensis Britton, and Pinus strobus L. across the Lake States Region of the USA. White-tailed deer consume buds and twigs of tree seedlings and saplings as forage. Deer populations in the Lake States Region of the USA have increased over recent decades due to a decrease in predators and an increase in habitat fragmentation. Higher deer population densities present challenges to regeneration of tree species. The objective of this work was to quantify the effects of deer browsing on tree seedling and sapling abundance and species richness of woody tree species which vary in deer browse palatability. Deer browsing impact measurements from the tree regeneration indicator from the US Department of Agriculture Forest Service’s Forest Inventory and Analysis program were used to predict seedling and sapling abundance from overstory basal area and a deer browsing index in the Lake States Region. Overstory basal area was important in predicting seedling and sapling abundance for all species (p < 0.05). Deer browsing affected seedling and sapling abundance differently across species, with the most palatable species showing lower stocking or negligible effects with browse. Results support the importance of quantifying impacts of deer browsing for use in determining the survival and abundance of palatable species in the smallest size cohorts.

Litter Flammability of 50 Southeastern North American Tree Species: Evidence for Mesophication Gradients Across Multiple Ecosystems

Widespread fire exclusion and land-use activities across many southeastern United States forested ecosystems have resulted in altered species composition and structure. These changes in composition and structure have been implicated in positive fire-vegetation feedbacks termed “mesophication” where fire spread and intensity are diminished. In forests and woodlands, inherent flammability of different species is the mechanistic driver of mesophication. To date, there has been limited work on documenting the high diversity of flammability among species in the region, limiting the ability to differentiate among species to restore fuels that sustain fire regimes. Here, we coalesce disparate flammability data and add missing species across the spectrum from species that facilitate fire (so called “pyrophytes”) to those that dampen fire (so called “mesophytes”). We present data on 50 important tree species from across the southeast, all burned using identical laboratory methods. We divide our results for four dominant ecosystems: Coastal Plain uplands, oak-hickory woodlands, Appalachian forests, and bottomland forests. Across ecosystems, the most flammable species were American chestnut (Castanea dentata), a suite of pines (Pinus palustris, P. elliottii, P. serotina, and P. rigida), several oaks (Q. laevis, Q. falcata, Q. margaretta, and Q. alba), and sourwood (Oxydendrum arboreum). At the mesophytic end, the least flammable species were Tsuga canadensis, Acer rubrum, and several other hardwoods previously implicated in mesophication. Each of the four ecosystems we studied contained species that spanned the pyrophytic to mesophytic gradient. These data fill in some key holes in our understanding of southeastern fire adaptations, but also provide context for restoration decisions and fire management prioritization efforts to restore and sustain fire-prone ecosystems of the region.

Detecting growth releases of mature retention trees in response to small-scale gap disturbances of known dates in natural-disturbance-based silvicultural systems in Maine

Disturbances play a fundamental role in shaping forest communities. It is therefore important to accurately quantify their frequency and magnitude in forest ecosystems. Tree-ring series are commonly used for relatively accurate detection of past disturbances. Currently, several dendroecological techniques exist that enable the detection of disturbances in tree-ring series. In this study, increment cores (n = 312) were collected from trees that were deliberately retained in harvested gaps of two natural-disturbance-based silvicultural systems in the Acadian Forest of Maine, USA. These systems were designed to approximate the gap-based natural disturbance regime of the region. Since the specific harvest dates and severities were known, we compared the efficacy of three predominant disturbance detection techniques in accurately detecting disturbance within two years of the harvest date across five common, yet ecologically distinct species -- Acer rubrum, Picea rubens, Pinus strobus, Thuja occidentalis, and Tsuga canadensis -- and the length of elapsed time prior to when maximum growth responses were experienced. We tested the growth-averaging method, the boundary-line method, and the combination of the growth-averaging and boundary-line methods (Splechtna method) using the TRADER R package. We found little variation among detection techniques in their -- relatively high success -- rate of detecting disturbance within two years of the harvest date (growth-averaging method: 69.9%, Splechtna method: 68.6%, and boundary-line method: 64.1%). We most frequently found negative correlations with pre-treatment growth rates and detection rates among detection techniques. Our estimates of disturbance severity did not influence the probability of detecting the year-of-harvest. Of the species tested, Tsuga canadensis (73.7% − 85.5%) and Thuja occidentalis (78.4% − 83.7%) had the greatest detection rates across the techniques while Pinus strobus was consistently the lowest (51%). Time-lags – defined as the number of years post-harvest before a tree reaches its peak growth rate – were also analyzed. Pre-disturbance basal area increment and crown ratio were marginally negatively correlated with the length of time-lags in response to harvest and Thuja occidentalis (7.2 ± 0.4) and Tsuga canadensis (6.8 ± 0.3) had significantly longer time-lags than Acer rubrum (5.4 ± 0.3). Overall, all techniques demonstrated relatively high detection rates (>60%), given the range of sizes and ages of the species tested and reduced two-year time window for detection. Absent from all models were variables that measured disturbance severity, which suggests tree responses to disturbance were more sensitive to tree-level attributes and local changes to the growing environment.

Long-term development of transition hardwood and Pinus strobus - Quercus mixedwood forests with implications for future adaptation and mitigation potential

Uncertainty about global environmental change has led to increased emphasis on the climate adaptation and mitigation potential of forests. Given the linkages between adaptive capacity and ecosystem complexity, this increased emphasis has motivated evaluations of the compositional, functional, and structural conditions characterizing a given forest ecosystem in the context of future stressors; however, less is known about how these conditions develop over time or vary between secondary forests shaped by a history of land use. To address this need, we capitalize on a 69-year field experiment to examine the long-term structural and compositional dynamics of transition ecotone hardwood (forests containing species from both southern and northern communities) and Pinus strobus-Quercus mixedwood (stands characterized by hardwood and softwood species mixtures) forests, communities which are commonly found in the Northeastern US. As expected, we observed a general increase in biomass over time and increasing density and structural complexity, with live aboveground biomass greatest in structurally complex mixedwood systems dominated by large diameter P. strobus. While all forests trended toward greater shade tolerance with increasing stand age, the functional identities of hardwood stands were stable over time compared to mixedwoods, which were more transient and ultimately generated trait profiles resembling hardwood-dominated stands. Ingrowth on all sites favored shade-tolerant Fagus grandifolia and Tsuga canadensis, which have lower future climate compatibility and adaptability compared to overstory trees, with a noticeable absence of P. strobus and Quercus spp. regeneration. Although all forest types exhibited some conditions that foster adaptation potential, the compositional stability of hardwood-dominated systems highlight the capacity of these stands to maintain comparable levels of adaptive capacity into the future. Conversely, given that P. strobus-Quercus mixedwoods examined are largely an artifact of land use, the natural successional patterns of these forests may lead to a reduction in these mixed species communities and a depreciation of associated climate benefits without silvicultural intervention to favor recruitment of these constituent species.

Love It or Leaf It: Site Selection of Breeding Treefrogs Based on Leaf Litter Subsidies

Breeding organisms rely on numerous environmental cues to determine optimal sites for oviposition. Site selection is often associated with factors that increase fitness, and the identification of these factors can help conservation efforts. For amphibians that breed in wetlands, the quality of terrestrial subsidies (e.g., leaf litter) can strongly influence larval survival and development by altering water chemistry and available nutrients. In this study, we examined the preference of breeding Gray Treefrogs (Hyla versicolor) for wetlands containing litter species of varying chemical quality. Based on previous studies of larval survival, we hypothesized that treefrogs would oviposit more eggs into wetland mesocosms containing litter with high nutrient concentrations and low phenolic concentrations. To test our hypothesis, we counted the number of eggs oviposited by treefrogs in artificial wetland mesocosms containing either Red Maple (Acer rubrum), Black Oak (Quercus velutina), or Eastern Hemlock (Tsuga canadensis) litter. We conducted this study over two breeding seasons. Counter to our hypothesis, we found that treefrogs preferred to oviposit in mesocosms containing maple litter, which contains high levels of both nutrients and phenolic acids. We discuss possible explanations for this result, including the possible anti-parasitic effects of phenolic acids. This is the first study demonstrating that breeding amphibians can differentiate between wetlands containing leaf litter species of differing chemistry. Given global declines in amphibian species concurrent with widespread changes in forest composition, our results emphasize the importance of considering leaf litter quality in wetland management and conservation efforts.

Influence of deer herbivory on regeneration dynamics and gap capture in experimental gaps, 18 years post-harvest

Declines in species diversity have been linked to shifting disturbance regimes and increases in ungulate herbivory. Successful forest regeneration depends on silvicultural methods that can address stand-specific recruitment limitations. This study revisits a long-term experimental gap study in a hemlock-hardwood forest. Our objective was to determine if the treatment effects of deer exclosures and gap size would alter regeneration trajectories. We examined cohort development using permanent plots and gap-wide surveys of likely gap-capture trees. After 18 years, deer herbivory was a strong filter for tree regeneration and appeared to pose an insurmountable bottleneck to the recruitment of some species. Overall, 90% of unprotected stems >0.5 to ≤2 m showed evidence of being browsed by white-tailed deer (Odocoileus virginianus Zimmerman). Our results indicate that browse sensitive species were unable to recruit even in resource-rich gap environments. Eastern hemlock (Tsuga canadensis L.) and yellow birch (Betula alleghaniensis Britton) were particularly sensitive to herbivory and absent in heights >1 m outside exclosures. However, inside exclosures in larger gaps, yellow birch saplings often co-dominated the tallest cohorts and eastern hemlock was well established at heights >1 m. Sugar maple (Acer saccharum Marsh.) was the dominant tree species across all treatments and ironwood (Ostrya virginiana Mill.) was frequently among the tallest trees in gaps outside of deer exclosures. Gap size only impacted unprotected seedlings which suggests regeneration is more sensitive to gap size when deer are present. The installation of relatively small (∼3.5% of total gap area) deer exclosures, at year two post-harvest, provided opportunities for the recruitment of browse-sensitive species. Collectively, our results highlight the pervasive role of ungulates in structuring forest composition.

Antioxidant and Antibacterial Properties of Norway Spruce (Picea abies H. Karst.) and Eastern Hemlock (Tsuga canadensis (L.) Carrière) Cone Extracts

According to recent studies, Norway spruce cones and eastern hemlock cones possess exceptionally high antioxidant capacities; however, the antioxidant efficiency of extractives and their bioactive effects have yet to be investigated in detail. The present article utilizes state-of-the art analytical chemical methodology and chemometric evaluation to reveal cone extractives with the highest antioxidant potential, accounting for possible bioactive effects. Antioxidant properties were determined by the Ferric reducing antioxidant power (FRAP) assay and the Folin–Ciocalteu’s total phenol content (TPC) assay. Structure and relative polyphenol concentrations were determined using liquid chromatography/diode array detection/tandem mass spectrometry. The antibacterial testing was conducted using Staphylococcus aureus and Escherichia coli strains. Using correlation analysis and factor analysis, a scoring evaluation was implemented to determine and compare the antioxidant efficiency of extractives. In Norway spruce, piceatannol-O-hexoside and coumaric acid derivatives were found to be the most powerful antioxidants, while in eastern hemlock, kaempferol glycosides were the most powerful. The antibacterial test did not show any promising antimicrobial activity against E. coli, although a visible inhibitory effect on S. aureus strain was observed.

Characterization of a Disjunct Population of Eastern Hemlock (Tsuga canadensis) and Surrounding Plant Communities in the North Carolina Piedmont after 65 Years of Forest Change

Hemlock Bluffs Nature Preserve is a 57-ha preserve in the piedmont of North Carolina. A small disjunct Tsuga canadensis (Eastern Hemlock) population exists in the preserve, primarily within a microclimate on a north-facing bluff. A study published in 1956 included a 1952–1953 inventory of the hemlock population as well as records of the local flora and climate. We re-inventoried the Eastern Hemlock population, conducted a new floristic survey, and recorded new climate data in the preserve in 2018–2019. Our new data reveal a notable change in both the Eastern Hemlock population and preserve-wide stand structure. Only 2% average light transmittance through the canopy was recorded in the preserve in the 2019 growing season, compared to 11% in the 1953 growing season (P = 0.02). At least 7 plant taxa underwent notable shifts in distribution, mostly moving down-slope on the bluff face. Average ambient air temperatures on the bluff were 1.62 °C higher in 2018–2019 than in 1952–1953. Canopy closure, inbreeding depression, increased temperatures, erosion, and browsing by Odocoileus virginianus (White-tailed Deer) all likely contribute to low Eastern Hemlock seed germination and high seedling mortality within the preserve. These factors may also partially account for observed shifts in floristic distribution. In addition to mortality caused by Adelges tsugae (Hemlock Woolly Adelgid), these environmental changes endanger the future viability of this Eastern Hemlock population.

A Microhistological Investigation of Winter Diets of White-Tailed Deer in Relict Eastern Hemlock Stands, Upper Peninsula of Michigan

To better understand winter foraging patterns of Odocoileus virginianus (White-tailed Deer) in the context of global change, we assessed foraging trends using microhistological analysis of fecal pellets from 2006–2018 across a network of monitoring plots in 39 relict Tsuga canadensis (Eastern Hemlock) stands in the western Upper Peninsula of Michigan. We found that deciduous browse comprised the majority of the diet, but conifer species were also eaten. During severe winters, Eastern Hemlock and Abies balsamea (Balsam Fir) were more prevalent in the diet, whereas in mild winters, Thuja occidentalis (Northern White Cedar) was more prevalent. Because Northern White Cedar comprises only a small amount of the forest community in these stands, deer were likely traveling beyond these winter yarding areas to forage. The relationship between conifer consumption and winter severity highlights the importance of energy conservation for winter survival of White-tailed Deer. More extreme winter weather is predicted with climate change, potentially prolonging confinement and limited forage availability, which is liable to alter energy budgets of deer, thus potentially altering population dynamics.

Eastern white pine and eastern hemlock growth: possible tradeoffs in response of canopy trees to climate

A warming climate and extended growing season may confer competitive advantages to temperate conifers that can photosynthesize across seasons. Whether this potential translates into increased growth is unclear, as is whether pollution could constrain growth. We examined two temperate conifers — eastern white pine (Pinus strobus L.) and eastern hemlock (Tsuga canadensis (L.) Carrière) — and analyzed associations between growth (476 trees in 23 plots) and numerous factors, including climate and pollutant deposition variables. Both species exhibited increasing growth over time and eastern white pine showed greater maximum growth. Higher spring temperatures were associated with greater growth for both species, as were higher autumnal temperatures for eastern hemlock. Negative correlations were observed with previous year (eastern hemlock) and current year (eastern white pine) summer temperatures. Spring and summer moisture availability were positively correlated with growth for eastern white pine throughout its chronology, whereas for hemlock, correlations with moisture shifted from being significant with current year’s growth to previous year’s growth over time. The growth of these temperate conifers might benefit from higher spring (both species) and fall (eastern hemlock) temperatures, though this could be offset by reductions in growth associated with hotter, drier summers.

Assessing the Effect of Eastern Hemlock (Tsuga canadensis) Decline from Hemlock Woolly Adelgid (Adelges tsugae) Infestation on Ectomycorrhizal Colonization and Growth of Red Oak (Quercus rubra) Seedlings

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.

Residual Stand Damage under Different Harvesting Methods and Mitigation Strategies

A major component of sustainable forest management are the stands left behind after the logging operation. Large mechanized harvesting equipment involved in current forest management can inflict damage on residual trees; and can pose a risk of mortality from diseases, natural calamities, and/or degrade future economic value. The primary objective of this study was to evaluate the residual stand damage under different harvesting methods and silvicultural prescriptions i.e., crop tree release (CTR), diameter limit cut (DLC), and overstory removal (OSR). The second objective was to evaluate the intensity and frequency of damage occurring on the bole, canopy, and root at tree and stand level. The third objective was to document strategies adopted globally to minimize stand damage due to timber harvesting. Five harvest blocks implementing three silvicultural prescriptions, were selected as the treatments across two different industrial timberlands in central and northern Maine (Study Site (SS) I and II, respectively). A hybrid cut-to-length (Hyb CTL) and whole-tree (WT) harvesting method were employed for conducting the harvest in SS I and II, respectively. Systematic transect sampling was employed to collect information on type, frequency, and intensity of damages. The inventory captured 41 and 8 damaged trees per hectare with 62 and 22 damages per hectare from SS I and SS II respectively. Bole damage was the most frequent damage across all treatments. The Hyb CTL had lower damage density (damage per ha) and severity compared to WT. The average number of trees damaged per ha was higher for CTR prescriptions compared to DLC. There were no significant differences in the height of the damages from the ground level between treatments within each study site; however, there was a significant difference between the study sites. Species damaged was directly related to the residual trees left behind and was dominated by American beech, yellow birch, sugar maple, and eastern hemlock. Finally, the study provides strategies that can be adopted at different forest managerial phases to mitigate residual stand damage.

Conditional inference trees in the assessment of tree mortality rates in the transitional mixed forests of Atlantic Canada.

Long-term predictions of forest dynamics, including forecasts of tree growth and mortality, are central to sustainable forest-management planning. Although often difficult to evaluate, tree mortality rates under different abiotic and biotic conditions are vital in defining the long-term dynamics of forest ecosystems. In this study, we have modeled tree mortality rates using conditional inference trees (CTREE) and multi-year permanent sample plot data sourced from an inventory with coverage of New Brunswick (NB), Canada. The final CTREE mortality model was based on four tree- and three stand-level terms together with two climatic terms. The correlation coefficient (R2) between observed and predicted mortality rates was 0.67. High cumulative annual growing degree-days (GDD) was found to lead to increased mortality in 18 tree species, including Betula papyrifera, Picea mariana, Acer saccharum, and Larix laricina. In another ten species, including Abies balsamea, Tsuga canadensis, Fraxinus americana, and Fagus grandifolia, mortality rates tended to be higher in areas with high incident solar radiation. High amounts of precipitation in NB’s humid maritime climate were also found to contribute to heightened tree mortality. The relationship between high GDD, solar radiation, and high mortality rates was particularly strong when precipitation was also low. This would suggest that although excessive soil water can contribute to heightened tree mortality by reducing the supply of air to the roots, occasional drought in NB can also contribute to increased mortality events. These results would have significant implications when considered alongside regional climate projections which generally entail both components of warming and increased precipitation.

Effects of Rhododendron removal on soil bacterial and fungal communities in southern Appalachian forests

Rhododendron maximum, a native ericaceous evergreen shrub, is expanding in forests of the southern Appalachian region following eastern hemlock (Tsuga canadensis) mortality due to hemlock woolly adelgid (Adelges tsugae) infestations. The goal of our study was to examine soil microbial community responses to experimental R. maximum removal treatments. The experiment was implemented as a 2 × 2 factorial design, including two R. maximum canopy removal levels (cut vs. not cut) combined with two forest floor removal levels (burned vs. not burned). These treatments were designed as potential management strategies to facilitate hardwood tree establishment in forests that have experienced T. canadensis declines. We sampled soils after removals and characterized bacterial and fungal communities using amplicon sequencing. Shrub removal did not affect bacterial or fungal α diversity but did affect both bacterial and fungal community composition. Relative abundances of bacterial phyla and fungal classes exhibited no differences among R. maximum removal treatments. However, specific bacterial and fungal taxa that were responsive to R. maximum removal (i.e., differentially abundant sequences) did exhibit clear patterns at high taxonomic levels. Specifically, taxa that responded negatively to R. maximum removal were found primarily in two bacterial phyla (Proteobacteria and Bacteroidetes) and one fungal class (Archaeorhizomycetes) while positive responders were clustered in several other bacterial phyla (e.g., Actinobacteria, Planctomycetes, Cyanobacteria). Fungal functional guilds also responded to R. maximum removal, including negative responses of ericoid mycorrhizae and positive responses of arbuscular mycorrhizae and wood saprotrophs. Effects of R. maximum removal on soil microbial communities were minor overall, but clear effects on some key functional groups were evident (i.e., mycorrhizal fungi), suggesting that microbial responses to R. maximum removal may influence recovery of forests in the southern Appalachian region.