Northern Forests Research Articles

Forest History Association of Wisconsin

The Enterprise Radiation Forest (ERF) study was initially introduced as a topic of discussion at the Institute of Forest Genetics, USDA, USFS, in the late 1960s. During that period, a program was endorsed for investigating the impacts of radiation on the forest ecosystem. The rationale for this was to facilitate the prediction of potential outcomes in the occurrence of a nuclear disaster. The research location was situated within the forested lands in Enterprise of Oneida County, Wisconsin, United States. The radiation source in question was a 10,000 curie source of Cesium-137, characterized by a halflife of 33 years. Furthermore, a study concerning lichens was also carried out, the data, photographs, and micrographs were meticulously gathered to illustrate the pre-irradiation activity of the species. This subject holds significant value for dissemination among peers in the scientific community, particularly considering the resilience exhibited by natural ecosystems in response to varying levels of radiation. The information is reviewed with the objective of the entire program to ascertain the potential consequences for a northern forest ecosystem in the event of a nuclear disaster, in addition to the two publications from the Atomic Energy Commission.

Seasonal and Climatic Drivers of Wet Deposition Organic Matter at the Continental Scale

AbstractDissolved organic matter (DOM) concentrations and composition within wet deposition are rarely monitored despite contributing a large input of bioavailable dissolved organic carbon (DOC) and nitrogen (DON) to the Earth's surface. Lacking from the literature are spatially comprehensive assessments of simultaneous measurements of wet deposition DOC and DON chemistry and their dependencies on metrics of climate and environmental factors. Here, we use archived precipitation samples from the US National Atmospheric Deposition Program collected in 2017 to 2018 from 17 sites across six ecoregions to investigate variability in the concentration and composition of depositional DOM. We hypothesize metrics of DOM chemistry vary with ecoregion, season, large‐scale climate drivers, and precipitation geographic source. Findings indicate differences in DOC and DON concentrations and loads among ecoregions. The highest wet deposition concentrations are from sites in the Northern Forests and lowest concentrations from sites in Marine West Coast Forests. Summer and autumn samples contained the highest DOC concentrations and DON concentrations that were consistently above detection limit, corresponding with seasonality of peak air temperatures and the phenology of the growing season in the northern hemisphere. Compositional trends suggest lighter DOM molecules in autumn and winter and heavier molecules in spring and summer. Climate drivers explain 51% of variation in DOM chemistry, revealing differing drivers on the concentrations and loads of DOC versus DON in wet deposition. This study highlights the necessity of incorporating DOC and DON measurements into national deposition monitoring networks to understand spatial and temporal feedbacks between climate change, atmospheric chemistry and landscape biogeochemistry.

Mapping the Normalized Difference Vegetation Index for the Contiguous U.S. Since 1850 Using 391 Tree-Ring Plots

The forests and grasslands in the U.S. are vulnerable to global warming and extreme weather events. Current satellites do not provide historical vegetation density images over the long term (more than 50 years), which has restricted the documentation of key ecological processes and their resultant responses over decades due to the absence of large-scale and long-term monitoring studies. We performed point-by-point regression and collected data from 391 tree-ring plots to reconstruct the annual normalized difference vegetation index (NDVI) time-series maps for the contiguous U.S. from 1850 to 2010. Among three machine learning approaches for regressions—Support Vector Machine (SVM), General Regression Neural Network (GRNN), and Random Forest (RF)—we chose GRNN regression to simulate the annual NDVI with lowest Root Mean Square Error (RMSE) and highest adjusted R2. From the Little Ice Age to the present, the NDVI increased by 6.73% across the contiguous U.S., except during some extreme events such as the Dust Bowl drought, during which the averaged NDVI decreased, particularly in New Mexico. The NDVI trend was positive in the Northern Forest, Tropical Humid Forest, Northern West Forest Mountains, Marin West Coast Forests, and Mediterranean California, while other ecoregions showed a negative trend. At the state level, Washington and Louisiana had significantly positive correlations with temperature (p < 0.05). Washington had a significantly negative correlation with precipitation (p < 0.05), whereas Oklahoma had a significantly positive correlation (p < 0.05) with precipitation. This study provides insights into the spatial distribution of paleo-vegetation and its climate drivers. This study is the first to attempt a national-scale reconstruction of the NDVI over such a long period (151 years) using tree rings and machine learning.

Asymmetric temperature effect on leaf senescence and its control on ecosystem productivity.

Widespread autumn cooling occurred in the northern hemisphere (NH) during the period 2004-2018, primarily due to the strengthening of the Pacific Decadal Oscillation and Siberian High. Yet, while there has been considerable focus on the warming impacts, the effects of natural cooling on autumn leaf senescence and plant productivity have been largely overlooked. This gap in knowledge hinders our understanding of how vegetation adapts and acclimates to complex climate change. In this study, we utilize over 36,000 in situ phenological time series from 11,138 European sites dating back to the 1950s, and 30 years of satellite greenness data (1989-2018), to demonstrate that leaf senescence dates (LSD) in northern forests responded more strongly to warming than to cooling in autumn. Specifically, a 1 °C increase in temperature caused 7.5 ± 0.2 days' delay in LSD, whereas a 1 °C decrease led to an advance of LSD with 3.3 ± 0.1 days (P < 0.001). This asymmetry in temperature effects on LSD is attributed to greater preoverwintering plant-resource acquisition requirements, lower frost risk, and greater water availability under warming than cooling conditions. These differential LSD responses highlight the nonlinear impact of temperature on autumn plant productivity, which current process-oriented models fail to accurately capture. Our findings emphasize the need to account for the asymmetric effects of warming and cooling on leaf senescence in model projections and in understanding vegetation-climate feedback mechanisms.

Rising forest exposure and fire severity from climate warming amplify tree cover losses from wildfire in California

Abstract Warmer temperatures and severe drought are driving increases in wildfire activity in the western United States, threatening forest ecosystems. However, identifying the influence of fire severity on tree cover loss (TCL) is challenging using commonly used categorical metrics. In this study, we quantify regional trends in wildfire-driven TCL as the product of annual burned area, average forest exposure (pre-fire tree cover), and average fire severity (relative loss of tree cover). We quantified these trends with Landsat-based 30 m resolution fire and tree cover datasets for California wildfires from 1986–2021. Rates of TCL rose faster than trends in burned area, with the magnitude of tree cover area loss per unit of area burned increasing by 70% from 0.20 ± 0.05 during 1986–1996 to 0.34 ± 0.10 during 2011–2021. Forest exposure (pre-fire tree cover) within fires increased by 41% from a decadal mean of 23.4% ± 5.5% (1986–1996) to 33.1% ± 7.8% (2011–2021). Increasing forest exposure is associated with a recent expansion of fires in dense northern forests. Concurrently, fire severity (relative TCL) rose by 30% from a decadal mean of 50.4% ± 7.2% during 1986–1996 to 65.6% ± 6.5% during 2011–2021. We developed and applied a simple conceptual framework to quantify the combined effect of wildfires affecting denser forests and burning more severely. The combined effect of these two processes contributed to nearly half (47%) of the TCL since 1986, highlighting that recent changes in burned areas alone cannot explain observed tree cover trends. Linear regression analysis revealed that warmer summers and drier winters were significant drivers of increasing forest exposure, fire severity, and burned area (R 2 from 0.54 to 0.80, p ⩽ 0.001), particularly in the northern forests. Climate extremes had a disproportionate impact on dense forests that were once more resistant to wildfire but now face risks from a shifting wildfire regime.

Boreal moss-microbe interactions are revealed through metagenome assembly of novel bacterial species

Moss-microbe interactions contribute to ecosystem processes in boreal forests. Yet, how host-specific characteristics and the environment drive the composition and metabolic potential of moss microbiomes is still poorly understood. In this study, we use shotgun metagenomics to identify the taxonomy and metabolic potential of the bacteria of four moss species of the boreal forests of Northern Québec, Canada. To characterize moss bacterial community composition and diversity, we assembled the genomes of 110 potentially novel bacterial species. Our results highlight that moss genus, species, gametophyte section, and to a lesser extent soil pH and soil temperature, drive moss-associated bacterial community composition and diversity. In the brown gametophyte section, two Stigonema spp. showed partial pathway completeness for photosynthesis and nitrogen fixation, while all brown-associated Hyphomicrobiales had complete assimilatory nitrate reduction pathways and many nearly complete carbon fixation pathways. Several brown-associated species showed partial to complete pathways for coenzyme M and F420 biosynthesis, important for methane metabolism. In addition, green-associated Hyphomicrobiales (Methylobacteria spp.) displayed potential for the anoxygenic photosystem II pathway. Overall, our findings demonstrate how host-specific characteristics and environmental factors shape the composition and metabolic potential of moss bacteria, highlighting their roles in carbon fixation, nitrogen cycling, and methane metabolism in boreal forests.

Impact of silvicultural practices on the genetic variations between sugar maple (Acer saccharum Marsh.) stands in the Northern Forest, U.S.A

Tree harvesting practices that enhance genetic diversity are essential for the long-term sustainability of our forests. Using eSSRs, which are markers within expressed genes and thus, potentially subjected to natural selection and reveal adaptive potential, this study examines the effects of selection (SE) and shelterwood (SW) management systems using unmanaged (UM) stands as reference on the genetic diversity of sugar maples in the Northern Forest, USA. Comparison between management types shows no difference between SE and SW, but compared to UM, both have lower allelic richness (AR) while only SE has lower expected heterozygosity (HE). Size class comparison shows that seedlings have higher AR and HE than poles and mature trees. Two-way interactions between management types, size classes, and study stands from each of the four states that comprise the Northern Forest region (Maine, New Hampshire, Vermont and New York) were also examined. Results show that seedlings in UM and SW have higher AR compared to all size classes in SE and poles and mature trees in SW, while only seedlings from SW have higher HE compared to poles and mature trees in SE and SW. Only in Maine was there a difference in AR between SW and SE stands per state. Seedlings in New Hampshire and Maine have higher HE, as well as seedlings and mature trees in New York compared to the poles in New Hampshire and mature trees in Maine. Overall, the results indicate genetic erosion in sugar maple stands in the Northern Forest region. This genetic impact may be due to several factors including the intensity of cutting associated with SE and SW systems and size of the canopy gaps created. Higher seedling genetic diversity in SW compared to SE may be due to their more open stand structure that facilitates gene flow and seedling recruitment. When using SE, longer cutting cycle paired with lower level of residual basal area is recommended. This approach allows for a more open stand structure that could facilitate pollen and seed exchanges from the stands, improving their genetic diversity. In both SE and SW systems, leaving high-quality growing stocks will enhance their genetic diversity and ensure their sustainability. This study increases our awareness of the potential genetic impacts of forest harvesting practices and guides the development of recommendations to alleviate genetic erosion in sugar maple stands.

Season-Dependent Effect of Fire-Derived Charcoal on Above- and Belowground Litter Decomposition in Boreal Forests

Fire-derived charcoal (charcoal) is a stable byproduct of forest fires that accumulates in the litter layer and soils of boreal forests. Therefore, decomposition of litter and roots, as one of the key processes in the carbon cycle, in the soils of northern forests almost everywhere go in the presence of charcoal. To date, there are extremely scarce data on the influence of charcoal on decomposition in boreal forests, and most of them do not consider the cold period, which lasts on average half a year in this zone. The purpose of this work was to determine the seasonal influence of charcoal on the decomposition of plant litter of different quality (larch needles, birch leaves, grasses, and mixtures of these species of litter) on the surface of the soil and the roots of these same species in the soil. In “litterbag” experiment it was found that charcoal accelerated decomposition of litter and that its effect was species-specific. The acceleration of mass loss in the presence of charcoal occurred for recalcitrant litter (needles) and all types of roots during the cold period. In the warm period, acceleration of decomposition in the presence of charcoal was observed only for needles and was not observed for roots. Thus, our study shows a greater influence of charcoal on intra-soil decomposition especially in the cold period. Seasonal influence of charcoal was established for the first time and should be taken into account as an important factor of humus formation and carbon dynamics in soils of boreal forests.

Community structure and assembly of myxomycetes in northern Chinese forests under geographic barriers

ABSTRACT The study of myxomycete biogeography has a long-standing history and has consistently drawn scholarly interest. Nevertheless, studies focusing specifically on the spatial and temporal distribution patterns of myxomycete diversity are relatively limited, with even fewer investigating the mechanisms driving the generation and maintenance of myxomycete diversity. Therefore, this study selected two geographically distant sampling sites within northern Chinese forests to investigate myxomycete species composition, community structure, environmental drivers, and assembly patterns under geographic barriers. We established plots in the Altai Mountains (ALE) and the Greater Khingan Mountains (GKM), gathered bark and litter, and conducted 80-day moist chamber cultures of myxomycetes. Additionally, myxomycete specimens were collected in the field simultaneously to supplement the data set. This study collected 541 myxomycete specimens belonging to 73 species from 28 genera, spanning 12 families and eight orders. The ALE and the GKM had 20 identical species, accounting for 27% of the total species. Myxomycetes from both regions exhibited abundant occurrence 18 days after cultivation, with the quantity on bark substrates notably higher than on litter. Arcyria pomiformis and Comatricha elegans were the most common species in moist chamber cultures. Mantel test outcomes revealed that environmental factors had no significant impact on myxomycete community similarity between the two areas, aligning with findings from the neutral community model analysis, indicating a predominant influence of stochastic processes on myxomycete community structure in moist chamber cultures. This study represents the first application of a quantitative framework to analyze myxomycete community assembly cultivated in moist chambers.

Review of the Current Status and Development Trend of Global Forest Carbon Storage Research Based on Bibliometrics

Forests are one of the largest terrestrial ecosystems on Earth, absorbing carbon dioxide from the atmosphere through photosynthesis and storing it as organic carbon, thereby mitigating global warming. Conducting bibliometric analysis of forest carbon storage can identify current research trends and hot issues in this field, providing data support for researchers and policy makers. This review article provides a comprehensive bibliometric analysis of global forest carbon storage research, using databases from the Web of Science Core Collection. CiteSpace software (6.2.6 version) was employed to visualize and analyze the data, focusing on key researchers, institutions, and countries, as well as major research themes and emerging trends. The main findings are as follows: (1) Since the 21st century, the publication volume in this field has been increasing, with the United States and China being the top contributors. (2) There is active collaboration among key authors, institutions, and countries, with a notable close-knit network centered around French author Philippe Ciais. This group includes nearly half of the field’s authors and many of them are crucial for advancing research in this field. (3) Cluster and citation burst analyses suggest that future research will focus more on the impact of forest management policies on carbon stocks, with particular attention to the roles of northern temperate forests and mangroves in global carbon storage. These findings provide valuable insights into the current state and future directions of forest carbon storage research. This article is instrumental in elucidating the role of forest ecosystems within the global carbon cycle, evaluating the impacts of anthropogenic activities on forest carbon stocks, and informing the development of effective climate change mitigation strategies.

Is there variation in ten woody species reproductive phenology within the Atlantic Forest biodiversity hotspot?

ABSTRACT Understanding reproductive phenology in tropical and subtropical forests is challenging. Thus, there are scarce large-scale phenological studies for those forests. Digitized herbarium collections can provide valuable information for understanding biological rhythms, e.g. timing of reproduction. Our aim was to verify the geographical variability of flowering and fruiting patterns and the effects of local climate on the reproductive phenology of woody species in the Atlantic Forest biodiversity hotspot. We used herbarium records compiled from the Global Biodiversity Information Facility – GBIF, speciesLink, JABOT, and the “Portal de Datos de Biodiversidad Argentina” as a main source of data to assess differences in reproductive phenology for 10 species with wide geographical distribution in the Atlantic Forest. Contrary to our expectations, we observed a non-seasonal reproductive phenology of all species and relations with temperature in the northern forests and to precipitation in the southern forests. When considered individually, there was no obvious relationship between phenophases and climatic factors. We expected that species occurring in a broad geographic distribution would change their biological rhythms related to local environmental factors, but it is likely that widely distributed species are abundant exactly because they are less dependent on biophysical characteristics of the environment. This is the first study comparing species located in the northern and southern regions of the Atlantic Forest using herbarium data, highlighting its importance to understand large scale ecological rhythms in tropical biomes.

Continuous mapping of forest canopy height using ICESat-2 data and a weighted kernel integration of multi-temporal multi-source remote sensing data aided by Google Earth Engine.

Forest Canopy Height (FCH) is a crucial parameter that offers valuable insights into forest structure. Spaceborne LiDAR missions provide accurate FCH measurements, but a significant challenge is their point-based measurements lacking spatial continuity. This study integrated ICESat-2's ATL08-derived FCH values with multi-temporal and multi-source remote sensing (RS) datasets to generate continuous FCH maps for northern forests in Iran. Sentinel-1/2, ALOS-2 PALSAR-2, and FABDEM datasets were prepared in Google Earth Engine (GEE) for FCH mapping, each possessing unique spatial and geometrical characteristics that differ from those of the ATL08 product. Given the importance of accurately representing the geometrical characteristics of the ATL08 segments in modeling FCH, a novel Weighted Kernel (WK) approach was proposed in this paper. The WK approach could better represent the RS datasets within the ATL08 ground segments compared to other commonly used resampling approaches. The correlation between all RS data features improved by approximately 6% compared to previously employed approaches, indicating that the RS data features derived after convolving the WK approach are more predictive of FCH values. Furthermore, the WK approach demonstrated superior performance among machine learning models, with random forests outperforming other models, achieving a coefficient of determination (R2) of 0.71, root mean square error (RMSE) of 4.92m, and mean absolute percentage error (MAPE) of 29.95%. Furthermore, in contrast to previous studies using only summer datasets, this study included spring and autumn data from Sentinel-1/2, resulting in a 6% increase in R2 and a 0.5-m decrease in RMSE. The proposed methodology filled the research gaps and improved the accuracy of FCH estimations.

Persistence, changes and robustness of nest webs along a latitudinal gradient in the Canadian boreal forest

IntroductionIn eastern Canada, the boreal forest is associated with an important latitudinal shift in forest composition and structure, which occurs in the transition between the mixed southern boreal forest and the coniferous northern boreal forest. Along this transition, upland mixedwood stands with large deciduous trees (important for cavity-dependent vertebrate species) are gradually replaced by forests with smaller conifer trees, primarily black spruce (Picea mariana). Concomitantly, the availability of lowland forests flooded by the American beaver (Castor canadensis), which can provide adequate conditions for tree-cavity users, is also decreasing.MethodsWe hypothesized that this latitudinal gradient would bring important changes in the functional diversity and network structure of vertebrate cavity-using communities. Along this latitudinal gradient we used a nest web approach to analyze the structure and robustness of networks of cavity users in upland forests and in lowland forests flooded by beavers.ResultsDespite their low availability in the northern forest region, we found that mixedwood stands persisted throughout the boreal forest in being the main drivers of nest webs network structure of upland forests whereas old black spruce stands contribution was low. In lowland forests, beaver ponds harbored nest webs with a rich and complex structure in both forest regions. Species removal simulations revealed that across our latitudinal gradient upland and lowland forest nest webs responded differently. In upland forests, the removal of trembling aspen and the Pileated Woodpecker (Dryocopus pileatus) caused the highest proportions of secondary extinctions, showing low robustness of nest webs given that these two species were highly connected to the other species. Contrastingly, nest webs in beaver ponds were more robust mainly because excavator species used a higher diversity of tree species despite the removal of the Northern Flicker (Colaptes auratus) which induced numerous secondary extinctions. The Pileated Woodpecker remained the pivotal species across the two forest regions in upland forests whereas the Northern Flicker became the main large cavity provider in beaver ponds across the latitudinal gradient.DiscussionWe discuss how mixedwood forests and beaver ponds, which are key habitat types for the cavity-using vertebrate community across our latitudinal gradient, should be maintained and protected in landscapes under industrial timber harvesting.

Response and resilience to drought in northern forests revealed by Sentinel-2

ABSTRACT Enhancing forest drought resilience is important for preserving ecosystem services in the face of climate change, but operational management methods for boreal forests aiming to preserve ecosystem services under drought are still largely missing. This study explores the use of satellite remote sensing to monitor vegetation stress phases related to drought progression and to quantify both short- and long-term impacts on forest growth. Data from the Sentinel-2 satellite mission were used to calculate the response of vegetation indices across six forest types, using the time period from 2015 to 2017 as a reference dataset. The percentual difference between the drought year of 2018 and the reference period was used to represent disturbance intensity and the system’s capability to resist it. Additionally, the recovery time was taken into consideration. Breakpoint detection with daily temporal resolution was used to quantify the response time of each forest type in relation to the onset date of meteorological drought. Results indicate that Sentinel-2 data can be used to monitor vegetation stress associated with drought progression and estimate the characteristics of forest resilience. High temporal resolution observations should be prioritized over annual maximum vegetation index values to determine the intensity of disturbance. Consistent severe impacts were observed in areas with limited soil moisture availability. The recovery time of forests took up to 4 years. Drought exposure during consecutive years could be especially damaging for species requiring a longer recovery time than a single growing season. Sentinel-2-based monitoring approach could benefit decision-support systems for forest management aiming to enhance drought resilience.

Seasonal variations in soil microbial community co-occurrence network complexity respond differently to field-simulated warming experiments in a northern subtropical forest

Global warming may reshape seasonal changes in microbial community diversity and co-occurrence network patterns, with significant implications for terrestrial ecosystem function. We conducted a 2-year in situ field simulation of the effects of warming on the seasonal dynamics of soil microbial communities in a northern subtropical Quercus acutissima forest. Our study revealed that warming had no significant effect on the richness or diversity of soil bacteria or fungi in the growing season, whereas different warming gradients had different effects on their diversity in the nongrowing season. Warming also changed the microbial community structure, increasing the abundance of some thermophilic microbial species and decreasing the abundance of some symbiotrophic microorganisms. The co-occurrence network analysis of the microbial community showed that warming decreased the complexity of the intradomain network in the soil bacterial community in the growing and nongrowing seasons but increased it in the fungal community. Moreover, increasing warming temperatures increased the complexity of the interdomain network between bacteria and fungi in the growing season but decreased it in the nongrowing season, and the keystone species in the interdomain network changed with warming. Warming also reduced the proportion of positive microbial community interactions, indicating that warming reduced the mutualism, commensalism, and neutralism of microorganisms as they adapted to soil environmental stress. The factors affecting the fungal community varied considerably across warming gradients, with the bacterial community being significantly affected by soil temperature, MBC, NO3−-N and NH4+-N, moreover, SOC and TN significantly affected fungal communities in the 4 °C warming treatment. These results suggest that warming increases seasonal differences in the diversity and complexity of soil microbial communities in the northern subtropical region, significantly influencing soil dynamic processes regulating forest ecosystems under global warming.

Long-term effects of the impact of forest machinery propellers on the soils of northern forests

Long-term effects of the impact of forest machinery propellers on the soils of northern forests

Urban green spaces of İstanbul: from ‘beautifying’ efforts to ‘mega-projects’

ABSTRACT This study discusses the transformation of urban green spaces in İstanbul, focusing specifically on gardens, groves, parks, and the Northern Forests. Recent research has underscored a significant loss of green space during the 2000s, posing a threat to biodiversity and essential ecosystem services. Despite maintaining a socio-natural continuum, it is evident that the twenty-first century represents a significant departure from the past. This study identifies two pivotal periods: the ‘beautification’ efforts undertaken the young republican period and the ‘mega-projects’ of the 2000s. These periods exhibit both similarities and substantial differences in politics and spatial organization concerning the urbanization of nature. The concept of urban political ecology is incorporated here, which advocates for equal socio-natural solutions and highlights the interconnectedness between urban areas and nature. The study concludes by emphasizing the need to continue examining the winners and losers in transformation of urban green spaces and move beyond project-driven development. It contributes modestly to the growing literature by shedding light on how historically and spatially organized ecologies of urban green spaces in the context of İstanbul can help us understand the socio-spatial changes we are witnessing today, characterized by the extended urbanization of nature worldwide.

Earthworm cast microbiomes differ across soil types in northern forests

Earthworms influence soil properties and element cycling, notably through the formation of casts. These biogenic structures are hotspots of microbial activity and play a role in soil carbon and nutrient dynamics. Previous research revealed that earthworm casts harbour distinct microbiomes from mineral soils under controlled laboratory conditions. But field studies are scarce, especially in northern forests currently undergoing earthworm invasion. Identifying drivers of earthworm cast microbiomes in the field and their potential differences with mineral soils and forest floors is therefore crucial to advance our understanding of their impact on soil functioning and nutrient cycling. Using a combined PLFA and DNA (ITS and 16S) approach, we characterized the fungal and bacterial communities of field-collected earthworm casts from three soil types: Luvisols, Brunisols (WRB: Cambisols), and Podzols. We compared them with those of surrounding mineral soils and forest floors. We did not find evidence of community filtering effects following gut transit and mixing of mineral soil and forest floor, as α- diversity and species richness were not reduced in casts. Cast microbiomes were dominated by taxa also found in forest floors and mineral soils. Yet they presented key differences in that they were systematically enriched in saprotrophic fungi and Bacteroidota and depleted in ectomycorrhizal fungi. Further, they were more similar to forest floor than mineral soil microbiomes. We also found that, although cast microbiomes were dominated by taxa common to casts of all sites, they differed across soil types. This finding highlights the prevailing role of pedogenesis in explaining the microbiome composition of field-aged casts. Our results also underscore the importance of sampling both forest floors and mineral soils when investigating the effects of earthworms on carbon and microbial dynamics in forest ecosystems.

Boom and bust: the effects of masting on seed predator range dynamics and trophic cascades

AbstractAimSpatiotemporal variation in resource availability is a strong driver of animal distributions. In the northern hardwood and boreal forests of the northeastern United States, tree mast events provide resource pulses that drive the population dynamics of small mammals, including the American red squirrel (Tamiasciurus hudsonicus), a primary songbird nest predator. This study sought to determine whether mast availability ameliorates their abiotic limits, enabling red squirrel elevational distributions to temporarily expand and negatively impact high‐elevation songbirds.LocationNortheastern United States.MethodsWe used two independent datasets to evaluate our hypotheses. First, we fit a dynamic occupancy model using data from camera trap surveys to evaluate red squirrel distributional responses to pulses in the tree mast. We also assessed population responses using systematic auditory surveys analysed with an open‐population binomial mixture model. Further, we used modelled red squirrel abundance in nest‐survival models to evaluate whether their abundance is correlated with the daily nest survival of three songbird species.ResultsThe tree mast provided a critical resource pulse that resulted in a two‐fold increase in the annual elevational distribution of red squirrels. The elevational distribution of red squirrels ranged from a minimum of ~450 m (range: 663–1145 m asl) following two consecutive years without a masting event to a maximum of over 1000 m (range: 443–1545 m asl) after a large mast event. The daily nest survival of three songbird species tended to decline with an increase in the abundance of red squirrels.Main ConclusionsTree mast is a central biological phenomenon in many temperate and boreal forests. This study reveals how this resource pulse results in range changes in a small mammal that is both a seed and bird predator, as well as prey for many carnivores. Thus, understanding this phenomenon can inform the conservation and management of northern forests, including breeding songbirds.

Soil carbon stabilization of mining-degraded, reforested lands in southern Ontario

We took advantage of the northern forest near Sudbury, Ontario, Canada where logging and metal-mining pollution had degraded the landscape prior to it being restored and reforested to investigate how soil organic matter is stabilized with stand age in highly ‘eroded’ sites with minimal residual soil and in ‘stable’ sites with residual soil. Soil organic matter in sandy, acidic soils of the northern forest is thought to be stabilized in organo-mineral particles (<20 μm in size); however, forest disturbance and soil erosion might help to promote less-decomposed plant detritus being stabilized within aggregate structures (53 μm in size). We use a combination of physical fractionation (size) and chemical analysis (carbon to nitrogen ratio, natural abundance of stable isotopes of carbon and nitrogen) of the fractions. The composition of bulk soils with young trees (15-yr old) was 25% microaggregates (53 to 250 μm in size) and 47% in a smaller silt + clay fraction (<53-μm in size). Bulk soil with older trees (28- and 30- to 32-yr old) had equal proportions of macroaggregates (>250 μm in size), microaggregates, and silt + clay fraction. The C density was much greater and less decomposed for macroaggregates than for the silt + clay fraction. Untreated sites, with trees but not restored with added lime, had a smaller proportion of macroaggregates in bulk soil. Even though aggregate structures typically are not associated with sandy, acidic forest soils, the results for these Regosols in the northern forest of the Greater Sudbury region show that stabilized soil C involves formation of macroaggregates along with microaggregates, both of which help to stabilize particulate organic matter.