Tsuga Canadensis Research Articles

Investigating Surficial Geologic Controls on Soil Properties, Inorganic Nutrient Uptake, and Northern Hardwood Growth in Western Massachusetts, USA

The influence of glacial geologic materials on soil properties, tree nutrient acquisition, and tree growth rates in New England is not well-constrained. Here, our research investigates the effect of two dominant surficial deposits, glacial till and glaciofluvial deposits, on soils and northern hardwood trees in western Massachusetts. We investigated sixteen paired glaciofluvial and glacial till sites located on the perimeters of glacial lake Hitchcock sediments, which drained 12,400 years ago. At each site, a 12.2-m-radius circular plot was selected, a soil pit was excavated, and all trees within the plot were sampled for foliage and cored with an increment borer. Our analyses found glaciofluvial soils to have significantly higher pH, clay fraction, and water field capacity than glacial till soils. Glaciofluvial soils also had less rock fragments and lower sand content than glacial till soils. We observed significantly higher pseudo-total K, Ca, Mg, and Mn concentrations in glacial till soils, but found similar foliar concentrations for five of the six tree species. Tree cores showed Black Birch, Red Maple, and Red Oak grew 1.3 to 2.1 times faster on glaciofluvial soils. Our study found that glaciofluvial soils, which exhibit greater water retention, less rocks, more fine particles, and higher soil pH than glacial till soils, promote faster growth of Black Birch, Red Maple, and Red Oak. However, the growth of American Beech, White Oak, and Eastern Hemlock was not impacted by surficial deposits, implying adaptation to nutrient limitations, coarser rocky soils, and potential water stress. Thus, the growth of some common tree species is affected by geologic materials, but others are not affected.

Simulation and statistical modelling approaches to investigate hydrologic regime transformations following Eastern hemlock decline

AbstractEcohydrological processes occurring at or near the Earth's surface are strongly influenced by Eastern hemlock [EH; Tsuga canadensis (L.) Carrière], a foundation tree species of eastern North American forests. EH populations are currently threatened by the invasive hemlock woolly adelgid (HWA; Adelges tsugae Annand). HWA HWA populations have been expanding rapidly throughout the EH's range. Catchment‐scale research examining the hydrological consequences of HWA infestation is lacking, and plot‐scale studies remain conflicted in their findings. Given the complex relationships between canopy interception, unsaturated and saturated groundwater storage, and root water uptake, it is not immediately clear how EH loss will affect the hydrologic cycle. We investigated the impact of EH mortality on stream discharge characteristics across a regional sample of catchments utilizing both simulation and statistical modelling approaches. We first examined the relationship between various catchment characteristics, including EH health, and three hydrological variables through regression analysis. We then employed a non‐parametric statistical test to evaluate differences in hydrologic regime trends between non‐infested and infested catchments. Finally, we calibrated a physically based hydrologic model and considered differences in optimal model parameter values and simulated overland runoff between non‐infested and infested catchments. HWA presence modified several ecohydrological characteristics and precipitation partitioning between groundwater flows and surface runoff, potentially driving higher stream flashiness and overland flow, lower baseflow contributions and catchment storage, shorter flow‐path lengths, and variable source area dilation at infested sites. Our results suggest that EH decline will augment flooding potential associated with the increasing frequency and intensity of Atlantic Basin tropical cyclone events. Further, our physically based simulation provides more determinate results than regression analysis, indicating that a purely statistical methodology, commonly utilized in studying the relationship between landcover characteristics and hydrologic regime, neglects dynamic physical ecohydrologic relationships.

Antioxidant Capacity and Tentative Identification of Polyphenolic Compounds of Cones of Selected Coniferous Species

The cones of coniferous species are a waste biomass byproduct that can be potentially utilized for a variety of purposes. One of the many application fields is the extraction of bioactive materials, particularly antioxidant polyphenols. Scientific literature on the antioxidant content of coniferous cones at different ripening stages is limited. In this study, we conducted a comparative analysis of the antioxidant content of selected taxa that are either common in Hungary or that have not yet been investigated in the scientific literature in any great detail (Cedrus atlantica, Larix decidua, Picea abies, Pinus mugo, Pinus nigra, Pinus sylvestris, Pinus wallichiana, Tsuga canadensis, Tsuga heterophylla, Chamaecyparis lawsoniana, Taxodium distichum, Thuja occidentalis, Metasequoia glyptostroboides, Thuja orientalis, Cryptomeria japonica, Cunninghamia lanceolata). A comparison of green, mature and opened cones was performed for the assigned taxa. Folin-Ciocâlteu total polyphenol content (TPC), ferric reducing antioxidant power (FRAP) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) assays were used to assess the antioxidant contents. Overall antioxidant power was determined by a scoring system that combined the three assay results. In general, best values were found for green cones, followed by mature, and opened cones for each taxon. Tsuga canadensis, Metasequoia glyptostroboides, Chamaecyparis lawsoniana, Cryptomeria japonica, Thuja orientalis and Picea abies all contained high amounts of antioxidants in both green and mature cones and attained the highest scores. High-performance liquid chromatographic/tandem mass spectrometric profiling of the cone polyphenols was also completed for selected samples. Results provide a basis for future bioactivity testing of these samples.

Impacts of the Hemlock Woolly Adelgid (Adelges tsugae) on Headwater Stream Large Woody Debris Loads in the Southern Appalachian Mountains

The hemlock woolly adelgid (HWA; Adelges tsugae) is responsible for widespread mortality of eastern hemlock (Tsuga canadensis) throughout its range. Models suggest that HWA-induced mortality could serve as a disturbance event that will increase large woody debris (LWD) loads in head-water streams. The objective of this research was to investigate the extent to which HWA infestation has impacted in-channel LWD loads in southern Appalachian headwater river systems. We surveyed 26 sites within the Blue Ridge Mountains with varying degrees of eastern hemlock composition, and HWA-induced decline. We combined these into a Hemlock Decline Index (HDI) that served as an explanatory variable for analyses. Results revealed that high HDI values were associated with higher LWD loads, higher frequency of LWD jams, and larger diameter LWD. These findings indicate that the HWA is significantly impacting LWD loads in streams, and subsequently impacting stream ecology. Additionally, the HDI developed here could be a useful tool for making regional comparisons of the impacts of the HWA on forest ecosystems.

Editors' Introduction

Editors' Introduction Selima Sultana and Paul Knapp We are grateful for the excellent contributions that comprise the Spring issue of Volume 60 of the Southeastern Geographer. The four articles in this issue nicely illustrate the eclectic and diverse nature of geography yet are synchronized by their focus within the American South. Foglietti et al. examine US tornado outbreak activity during 1975–2014 and find that following exclusion of individual tornadoes, a tornado "outbreak alley" is located in the "US Midsouth" that includes southern Arkansas, northern Mississippi and northern Alabama—an area several hundred miles away from what is considered "Tornado Alley." Their work demonstrates how evaluating spatial patterns of singular tornadoes versus tornado outbreaks produces different outcomes as well as the challenges of mapping tornado outbreaks when no formal definition exists. That said, even when using a variety of tornado outbreak definitions, a similar spatial pattern emerges indicating that tornadic activity in the American South exhibits a distinct geographic character. Sherman-Morris et al. provide a novel analysis of the parasocial relationship between broadcast meteorologists and members of the public in the context of a real-world weather event. Specifically, Sherman-Morris et al. strive to provide insight on this relationship and determine whether it has any impact or effect on an individual's hurricane risk perception or protective behaviors (i.e., evacuation decisions). Their work discovers that there is no statistical relationship between an individual's parasocial relationship with their broadcast meteorologist and their hurricane risk perception or hurricane protective behavior. Their article explores the reasons for this surprising result—including changes in the media landscape, and weathercasters' different roles in different extreme weather events. Curtis et al. integrate a variety of methodologies to identify the best locations in North Carolina to convert agricultural land into sites with utility-scale photovoltaic panels, hence the term "solar farms." Using a food-water-energy approach, the authors show that the conversion of cultivated landscapes with solar farms results in both the production of a renewable energy source and improvements in water quality because of the removal of cropping. Curtis et al.'s innovative approach identifies locations where all three criteria favorable for solar farms exist. Thus, sites with an abundance of agricultural land, engaging in cropping practices most likely to result in water-quality degradation, and near transmission lines are considered the most viable for conversion. McDade et al. address the consequences of eastern hemlock mortality on large woody debris (LWD) loads in headwater stream environments of the southern Appalachians. [End Page 3] Since the introduction of the non-native hemlock woolly adelgid in 1954, eastern hemlock forests of the American South that prefer riparian zones have significantly declined and woody debris from the trees have impacted stream geomorphology. McDade et al. address this emerging issue by focusing on three headwater watersheds in North Carolina and found that greater hemlock mortality was associated with higher LWD loads but the effects of this decline on streamflow has not yet peaked. meet the team Volume 60 Issue 1 marks the beginning of our four-year term as co-editors of the Southeastern Geographer. As long-time members of SEDAAG and graduates of the University of Georgia, our appreciation of the importance of the journal is deep-rooted and we hope to continue the high standards of the journal. We are grateful for the help from the outgoing editorial team of Hilda Kurtz, Deepak Mishra, Nancy O'Hare, Christian Petterson, and Andy Walter, each whom was generous with their time assisting us through the transition. We also thank them for their numerous contributions to the journal, including implementing ScholarOne, which has substantially facilitated the review process. As they noted at the beginning of their term four years ago, serving as editors is an honor—a sentiment we share. Our role as editors will be to encourage submission of high-quality articles focusing on geographical aspects of the American South that includes both events and conditions. Likewise, we wish to continue to elevate readership and publish articles that will be cited often. In reviewing past issues of the Southeastern Geographer, we remarked on the number excellent articles on a wide variety of topics and the...

Competition, Climate, and Size Effects on Radial Growth in an Old-Growth Hemlock Forest

Research Highlights: We applied neighborhood and dendro-ecological methods in a stand with a 33-year record of forest dynamics, finding that growth will decrease for several species under predicted climate trends. Background and Objectives: Conventional tree-ring analysis removes the influence of competition and size on growth, precluding assessment of the relative influence of these factors. An old-growth eastern hemlock forest in east–central New York was mapped in 1978 and was measured at eight-year intervals since then. Our objective was to use these data to examine the influence of climate, neighborhood, and tree size on radial growth. Materials and Methods: We evaluated an array of climatic indices to find which ones had the strongest influence on radial growth from increment cores of eastern hemlock (Tsuga canadensis L.), yellow birch (Betula alleghaniensis Britton), and sugar maple (Acer saccharum Marsh.). We used the strongest climatic indices in combination with neighborhood and target-tree size information to create growth models for the three tree species. Results: Size accounted for 2% to 21% of observed growth; the shade-tolerant sugar maple and eastern hemlock grew fastest when large, but the mid-tolerant yellow birch grew fastest when small. Competition accounted for 9% to 21% of growth; conifers had a weaker competitive effect than deciduous trees, and eastern hemlock was less sensitive to competition than sugar maple and yellow birch. Climate accounted for only 2% of growth variation; eastern hemlock showed a positive response to warming climate trends, but yellow birch and sugar maple showed negative responses. Conclusions: Predicted climate trends are likely to result in decreased growth of sugar maple and yellow birch, and the sensitivity of these species to competition suggests the effect will be exacerbated when they grow in crowded conditions.

Selection of softwood species for structural and non-structural timber construction by using the analytic hierarchy process (AHP) and the multi-objective optimization on the basis of ratio analysis (MOORA)

In this study, the hybrid approach of the analytic hierarchy process (AHP) and the multi-objective optimization on the basis of ratio analysis (MOORA) was used in order to select the most suitable softwood timber for constraction. Douglas fir (Pseudotsuga menziesii), Lodgepole pine (Pinus concorta), Red pine (Pinus resinosa), Redwood (Sequoia sempervirens), Engelmann spruce (Picea engelmannii), Eastern hemlock (Tsuga canadensis), Western larch (Larix occidentalis) and Western redcedar (Thuja plicata) were evaluated in terms of economic, physical, mechanical, thermal and durability properties. According to the results, the most suitable timbers for structural and non-structural applications were determined western larch and redwood, respectively.

Facilitation between invasive herbivores: hemlock woolly adelgid increases gypsy moth preference for and performance on eastern hemlock

1. Interactions between invertebrate herbivores with different feeding modes are common on long‐lived woody plants. In cases where one herbivore facilitates the success of another, the consequences for their shared host plant may be severe. Eastern hemlock (Tsuga canadensis), a canopy‐dominant conifer native to the eastern U.S., is currently threatened with extirpation by the invasive stylet‐feeding hemlock woolly adelgid (Adelges tsugae). The effect of adelgid on invasive hemlock‐feeding folivores remains unknown.2. This study evaluated the impact of feeding by hemlock woolly adelgid on gypsy moth (Lymantria dispar) larval preference for, and performance on, eastern hemlock. To assess preference, 245 field‐grown hemlocks were surveyed for gypsy moth herbivory damage and laboratory paired‐choice bioassays were conducted. To assess performance, gypsy moth larvae were reared to pupation on adelgid‐infested or uninfested hemlock foliage, and pupal weight, proportional weight gain, and larval period were analysed.3. Adelgid‐infested hemlocks experienced more gypsy moth herbivory than did uninfested control trees, and laboratory tests confirmed that gypsy moth larvae preferentially feed on adelgid‐infested hemlock foliage. Gypsy moth larvae reared to pupation on adelgid‐infested foliage gained more weight than larvae reared on uninfested control foliage.4. These results suggest that the synergistic effect of adelgid and gypsy moth poses an additional threat to eastern hemlock that may increase extirpation risk and ecological impact throughout most of its range.

Influence of field technique, density, and sex on home range and overlap of the southern red-backed vole (Myodes gapperi)

Home range is shaped by an individual’s interactions with the environment and conspecifics, and both size and placement may vary in response to population fluctuations. The method used to collect locational data may also affect home-range estimates. We examined the effect of density, sex, and field method on home range of southern red-backed voles (Myodes gapperi (Vigors, 1830)) inhabiting eastern hemlock (Tsuga canadensis (L.) Carrière) forests. Twelve mark–recapture grids were used to census M. gapperi from 2014 to 2017. In 2017, individuals were radio-collared. Home-range size, core-area size, and shared space were calculated using kernel density estimators from both mark–recapture and radiotelemetry data. Density effects on home range and core area were analyzed and differences between sex and field method were compared. We found (i) density did not affect home-range size, (ii) male home range was larger than female home range, (iii) females shared space more frequently and to a greater extent with males than other females, and (iv) home-range estimates were not significantly different between mark–recapture and radiotelemetry. Male home range, however, was larger under radiotelemetry and may reflect a truncation effect when mark–recapture grid size is smaller than male home range.

Antioxidant properties assessment of the cones of conifers through the combined evaluation of multiple antioxidant assays

Wood logging generates considerable amounts of waste biomass (e.g. cones, bark, leaves, and roots), worthwile to use, as a potential source of antioxidants. Polyphenols represent an important type of non-enzymatic antioxidants in plants. Current data in scientific literature regarding the antioxidant content of coniferous cones and the antioxidant concentrations at different ripening stages is limited and have not been investigated in detail yet. Our investigation aimed to implement an ultrasonic extraction method for the assessment and comparison of the antioxidant polyphenol content of conifer cones: six arbitrarily selected taxa (Cedrus atlantica, Larix decidua, Picea abies, Pinus nigra, Pseudotsuga menziesii, Tsuga canadensis) commonly found in Hungary were investigated in the present study, which provides methodology for future investigations. The comparison of green, mature, and opened cones were carried out for each taxon. Folin-Ciocâlteu total phenol content, ferric reducing ability of plasma (FRAP) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) assays were used to assess the antioxidant properties. The 30 min ultrasonic extraction using acetone:water 80:20 v/v solution resulted in the optimum yield on total polyphenols, FRAP, and DPPH. Best values were found for green cones, followed by mature, and opened cones for each species. Overall antioxidant power was determined by a scoring system that combined the three assay results. Taxa with the highest scores were Picea abies and Tsuga Canadensis, which contained high amounts of antioxidants in both green and mature cones and, surprisingly, also in opened cones (P. abies). Results provide a basis for future investigation and comparison involving a large number of taxa.

Importance of rainfall partitioning in a northern mixed forest canopy for soil water isotopic signatures in ecohydrological studies

AbstractThe forest canopy can play a significant role in modifying the amount and isotopic composition of water during its passage throughout the near‐surface critical zone. Here, partitioning of gross rainfall into interception, throughfall, and stemflow and its implications for the amount and isotopic composition of soil water was studied for red oak, eastern white pine, and eastern hemlock trees in a northern hardwood‐conifer forest in south central Ontario, Canada. Stemflow production was greatest for red oak as a result of its upward‐projecting branches and least for eastern white pine due to its horizontal branches and rougher bark. These stemflow contributions to the near‐bole soil surface failed to produce consistently wetter soils relative to distal locations from the bole for all tree species. There was also no consistent evidence of isotopic enrichment of throughfall and stemflow relative to gross rainfall or of stemflow relative to throughfall for red oak or eastern hemlock. However, there was isotopic enrichment of both throughfall and stemflow for eastern white pine with increasing maximum atmospheric vapour pressure deficit, which may reflect the potential for evaporative fractionation as a result of retention and detention of water moving through the canopy by the rougher bark of this species. Dry soil conditions limited sampling of mobile soil water during the study, and there was no consistent evidence that either throughfall or stemflow fluxes controlled temporal changes in the isotopic signature of soil water beneath the tree. Thus, the potential for throughfall and stemflow fluxes in northern hardwood‐conifer forests to modify the isotopic composition of water taken up by the tree via transpiration remains an open question.

Loss of foundation species revisited: conceptual framework with lessons learned from eastern hemlock and whitebark pine

AbstractEcologists and conservation biologists often prioritize the study of species that are declining, threatened, or endangered over species that are abundant and ecologically important, such as foundation species (FS). Because entire ecosystems and their biodiversity depend on FS, we argue that they have high conservation priority. A citation analysis reveals that FS are studied, but often are characterized ambiguously. More effort is needed to identify FS before they, and the ecosystems they define, are at risk of decline or loss. We suggest a new conceptual framework that includes: informed identification of FS in ecosystems; documentation of ecosystem services provided by FS; a long‐term monitoring strategy to detect threats to FS within specified ecosystems; and, if threats are identified, a comprehensive conservation and adaptive management strategy for FS. We use two widely distributed, rapidly declining North American foundation tree species (Tsuga canadensis [eastern hemlock] and Pinus albicaulis [whitebark pine]) to illustrate this framework. These species exemplify the importance of identifying FS early and conserving or restoring them when they are threatened.

A 20-year experiment on the effects of deer and hare on eastern hemlock regeneration

Eastern hemlock (Tsuga canadensis (L.) Carrière) is a shade-tolerant, slow-growing tree once common in forests across the Great Lakes region. It was heavily exploited in the late 19th and early 20th centuries and now experiences limited regeneration across much of its range. This failure to regenerate has been ascribed to poor seedbed conditions, insufficient canopy openings, warmer climate, and browsing by white-tailed deer (Odocoileus virginianus (Zimmermann, 1780)) or snowshoe hare (Lepus americanus Erxleben, 1777). To test whether deer or hare limit hemlock regeneration, we studied >2000 hemlock seedlings inside and adjacent to experimental deer exclosures at 59 sites randomly distributed across hemlock and hemlock-component stands in northern Wisconsin and the western Upper Peninsula of Michigan in the United States. We monitored local deer and hare abundance, seedling growth, and seedling survival for 20 years. Two First Nations reservations showed lower deer density and greater survival and growth of unprotected seedlings than three national forests of the United States. Cohorts of hemlock seedlings protected from deer survived at a rate four times higher than those exposed to deer (59.3% vs. 15.0%) and shared a combined height 5.2 times greater. Hare densities significantly affected seedling survival only within exclosures. This extensive, long-term study identifies deer as the primary factor constraining hemlock regeneration in the region.

Determinants of temperature sensitivity of soil respiration with the decline of a foundation species.

The eastern hemlock (Tsuga canadensis) is an important foundation species that is currently declining throughout eastern U.S. forests due to the exotic pests hemlock woolly adelgid (Adelges tsugae) and elongate hemlock scale (Fiorinia externa). Hemlock is often replaced by deciduous tree species, such as black birch (Betula lenta), and has been shown to have large consequences for carbon dynamics due to a substantial loss of soil organic layer carbon storage in hemlock forests when replaced by birch and higher decomposition found in black birch stands. Soil carbon is one of the most important components of the global carbon cycle and has high potential to feedback to climate change when large portions of stored carbon are lost to the atmosphere. There is a general consensus that soil respiration increases with temperature, but there has yet to be a consensus on how temperature sensitivity of soil respiration is affected by various biotic and abiotic factors, such as soil moisture and substrate quality. In this study, the effects of soil temperature and soil moisture on soil respiration (Rs), the temperature sensitivity of soil respiration (Q10), and soil basal respiration (R10) were investigated for hemlock, young birch, and mature birch forest types annually for three years. The Rs values of the three forest types were primarily driven by soil temperature rather than by soil moisture across all years. Soil respiration data collected from hemlock, young birch, and mature birch stands were used to determine annual Q10 and R10 values. The Q10 and R10 values were not significantly different between forest stands, but they were significantly different over the three years. Determinants of Q10 and R10 differed between forest type, with soil moisture primarily influencing Q10 in hemlock and mature birch stands and soil temperature primarily influencing R10 in mature birch stands. The results suggest a complex interaction of soil moisture and soil temperature, and potentially substrate quality and quantity, as determinants of temperature sensitivities in eastern U.S. forests that have transitioned from hemlock-dominated to black birch-dominated forests.

Quantifying trends and uncertainty in prehistoric forest composition in the upper Midwestern United States.

Forest ecosystems in eastern North America have been in flux for the last several thousand years, well before Euro‐American land clearance and the 20th‐century onset of anthropogenic climate change. However, the magnitude and uncertainty of prehistoric vegetation change have been difficult to quantify because of the multiple ecological, dispersal, and sedimentary processes that govern the relationship between forest composition and fossil pollen assemblages. Here we extend STEPPS, a Bayesian hierarchical spatiotemporal pollen–vegetation model, to estimate changes in forest composition in the upper Midwestern United States from about 2,100 to 300 yr ago. Using this approach, we find evidence for large changes in the relative abundance of some species, and significant changes in community composition. However, these changes took place against a regional background of changes that were small in magnitude or not statistically significant, suggesting complexity in the spatiotemporal patterns of forest dynamics. The single largest change is the infilling of Tsuga canadensis in northern Wisconsin over the past 2,000 yr. Despite range infilling, the range limit of T. canadensis was largely stable, with modest expansion westward. The regional ecotone between temperate hardwood forests and northern mixed hardwood/conifer forests shifted southwestward by 15–20 km in Minnesota and northwestern Wisconsin. Fraxinus, Ulmus, and other mesic hardwoods expanded in the Big Woods region of southern Minnesota. The increasing density of paleoecological data networks and advances in statistical modeling approaches now enables the confident detection of subtle but significant changes in forest composition over the last 2,000 yr.

Soil Warming Accelerates Biogeochemical Silica Cycling in a Temperate Forest.

Biological cycling of silica plays an important role in terrestrial primary production. Soil warming stemming from climate change can alter the cycling of elements, such as carbon and nitrogen, in forested ecosystems. However, the effects of soil warming on the biogeochemical cycle of silica in forested ecosystems remain unexplored. Here we examine long-term forest silica cycling under ambient and warmed conditions over a 15-year period of experimental soil warming at Harvard Forest (Petersham, MA). Specifically, we measured silica concentrations in organic and mineral soils, and in the foliage and litter of two dominant species (Acer rubrum and Quercus rubra), in a large (30 × 30 m) heated plot and an adjacent control plot (30 × 30 m). In 2016, we also examined effects of heating on dissolved silica in the soil solution, and conducted a litter decomposition experiment using four tree species (Acer rubrum, Quercus rubra, Betula lenta, Tsuga canadensis) to examine effects of warming on the release of biogenic silica (BSi) from plants to soils. We find that tree foliage maintained constant silica concentrations in the control and warmed plots, which, coupled with productivity enhancements under warming, led to an increase in total plant silica uptake. We also find that warming drove an acceleration in the release of silica from decaying litter in three of the four species we examined, and a substantial increase in the silica dissolved in soil solution. However, we observe no changes in soil BSi stocks with warming. Together, our data indicate that warming increases the magnitude of silica uptake by vegetation and accelerates the internal cycling of silica in in temperate forests, with possible, and yet unresolved, effects on the delivery of silica from terrestrial to marine systems.

Loss of a Foundation Species, Eastern Hemlock (Tsuga canadensis), May Lead to Biotic Homogenization of Fungal Communities and Altered Bacterial Abundance in the Forest Floor

Tsuga canadensis (Eastern Hemlock) is a key forest foundation species that is currently declining across the eastern US due to attack by exotic insect species, primarily Adelges tsugae (Hemlock Woolly Adelgid). In the northeastern US, declining Eastern Hemlock stands are typically replaced by fast-growing deciduous Betula lenta (Black Birch) trees, altering ecosystem processes and ecological communities. In this study, we used an approach that substituted space for time to explore how the forest floor's soil organic horizon, macrofungal communities, and bacterial abundance might be altered following Eastern Hemlock replacement by Black Birch. We compared intact, mature Eastern Hemlock forest plots at 2 sites in western Massachusetts to adjacent areas of vigorous regeneration of young Black Birch triggered by logging activity at the sites ∼25–30 years ago. Forest-floor soil organic horizons were significantly thicker under Eastern Hemlock forests and exhibited a higher carbon:nitrogen (C:N) ratio, suggesting slower decomposition and greater accumulation of organic material under Eastern Hemlock compared to deciduous Black Birch canopies. Macrofungal communities emerging from the forest floor did not differ strongly in morphospecies richness between Eastern Hemlock and Black Birch plots. However, a greater number of rare fungi taxa, defined in this study as those represented by a single observation, were detected in Eastern Hemlock plots, and the composition of Black Birch plots was more homogenized and less variable. The abundance of bacterial colony forming units (CFUs) in the soil organic horizon appeared to follow a seasonal pattern of variation between mature Eastern Hemlock versus young Black Birch plots; CFUs were most abundant in Black Birch soils in the fall, potentially tracking input of new deciduous leaf litter, whereas Eastern Hemlock plots had higher CFU counts in the summer. The results of this study suggest that forest-floor characteristics will be substantially altered by the impending loss of Eastern Hemlock, associated macrofungal communities may become simplified and homogenized, and the timing of peak bacterial abundance in the forest floor might be shifted to the fall.

Woody Regeneration Response to Overstory Mortality Caused by the Hemlock Woolly Adelgid (Adelges tsugae) in the Southern Appalachian Mountains

Adelges tsugae Annand (hemlock woolly adelgid, HWA, an invasive insect native to Japan), which causes defoliation and death of Tsuga canadensis (L.) Carrière (eastern hemlock), was introduced to the United States in the early 1950s and has spread throughout much of the range of T. canadensis causing widespread mortality. In 2016 and 2017, we resampled long-term vegetation monitoring plots across five forest types (ecogroups) within Great Smoky Mountains National Park that contained T. canadensis in 2003 (prior to the spread of HWA within the park) to examine changes in the species composition and diversity of the regeneration layer. We hypothesized that compositional changes in the seedling and sapling strata would be driven primarily by the pre-HWA importance value of T. canadensis and relative dominance of Rhododendron maximum L. (rosebay rhododendron), and that species diversity metrics would differ across year depending on ecogroup and the relative dominance of R. maximum. Non-metric multi-dimensional scaling (NMDS) revealed that the seedling and sapling strata of plots with greater pre-HWA importance of T. canadensis and lower basal area of R. maximum generally exhibited greater compositional change between 2003 and 2017. Topo-edaphic variables were also significant in both NMDS ordinations and were associated with the distribution of multiple hardwood species. Species richness, evenness, and Shannon-Wiener diversity varied with strata following the loss of T. canadensis, with the degree and direction of change varying with the dominance of R. maximum.

Seasonal and Topographic Variations in Ecohydrological Separation Within a Small, Temperate, Snow‐Influenced Catchment

AbstractThe hypothesis of ecohydrological separation (ES) proposes that the water contained in surface soils is not uniformly extracted by root water uptake nor uniformly displaced by infiltration. Rather vegetation selectively removes water held under tension, and water infiltrating wet soil will bypass much of the water‐filled pore space. Methodological differences across previous studies have contributed to disagreement concerning the prevalence of ES. We measured stable isotopes of O and H in precipitation, snowpack, canopy throughfall, and stream water over a period of 18 months in a temperate catchment. At six locations across a wetness gradient, we sampled bulk soil water isotopes weekly and xylem water of Eastern hemlock and American beech stems seasonally. We used these observations in a soil column model including StorAge Selection functions to estimate the isotopic composition and ages of groundwater recharge and ET. Our findings suggest ES may exist with spatial and temporal heterogeneity. Root water uptake ages possibly vary between Eastern hemlock and American beech, suggesting functional strategies for water uptake may control the presence of ES. Newly infiltrated water bypassing the shallow soil was the most likely explanation for bulk soil isotopic measurements made at upslope locations during the winter and summer seasons, whereas rapid displacement of stored soil water by infiltrated waters was the most likely during the spring and fall seasons. Future research incorporating high temporal frequency soil and plant xylem water isotopic measurements applied to StorAge Selection functions may provide a useful framework for understanding rooting zone isotope dynamics.

Small mammal tree seed selection in mixed forests of the Eastern United States

Small mammals play a critical role in forest ecosystems as both seed predators and dispersers; they have been shown to affect tree species composition within forests and may significantly reduce recruitment rates of certain tree species, many of which are commercially valuable. Thus, understanding small mammal seed preference is essential for both animal ecologists and foresters. Although extensive research on small mammal seed choice has been conducted both in North America and Europe, limited knowledge is available on: (1) the effects of silvicultural practices on seed choice; (2) seed selection – as most studies focus on seed use; and (3) certain understudied seed-small mammals interactions – e.g. few studies have concurrently examined both coniferous and deciduous seeds from North American mixed forests, and the seed selection of some small mammal species is not well-known (e.g. Napaeozapus). To contribute to filling these gaps, our study focused on the following objectives: (1) to quantify seed selection of seven forest seed species by small mammal species within the mixed forests of the eastern US; (2) to evaluate the influence of silvicultural practices on seed choice; (3) to explore relationships between seed choice and environmental factors such as weather and microhabitat.We conducted a series of cafeteria-style experiments in the field and in the laboratory; 2459 seed choice events, mostly by four small mammal species (Peromyscus maniculatus, Myodes gapperi, Napaeozapus insignis, and Tamiasciurus hudsonicus) were analyzed using multinomial mixed-effect models, allowing us to determine the probability of selection for each seed species. We identified a consistently high-preference seed (Pinus strobus) and one low-preference seed (Betula papyrifera). All other species (Acer rubrum, Picea rubens, Tsuga canadensis, Quercus rubra, and to some extent, Abies balsamea) had intermediate preference levels. Indeed, selection varied also by small mammal species (e.g. Acer rubrum was the top choice for Myodes gapperi in the field).Further, we found that the silvicultural practices examined here (even-aged management, two-stage shelterwood, and unmanaged) did not directly influence seed choice, whereas illumination (night- and day-time light levels), rain, and temperature did, and the magnitude of the effects varied by small mammal species. Our results show that in mixed forests, small mammals may impact seeds of economically valuable trees (e.g. Pinus strobus and Acer rubrum), whereas they may ignore seeds of less valuable trees (e.g. Betula papyrifera and Abies balsamea). We recommend that forest managers consider small mammal communities when developing forest regeneration plans.