Northern Temperate Forests Research Articles

Fungal community composition and genetic potential regulate fine root decay in northern temperate forests.

Understanding how genetic differences among soil microorganisms regulate spatial patterns in litter decay remains a persistent challenge in ecology. Despite fine root litter accounting for ~50% of total litter production in forest ecosystems, far less is known about the microbial decay of fine roots relative to aboveground litter. Here, we evaluated whether fine root decay occurred more rapidly where fungal communities have a greater genetic potential for litter decay. Additionally, we tested if linkages between decay and fungal genes can be adequately captured by delineating saprotrophic and ectomycorrhizal fungal functional groups based on whether they have genes encoding certain ligninolytic class II peroxidase enzymes, which oxidize lignin and polyphenolic compounds. To address these ideas, we used a litterbag study paired with fungal DNA barcoding to characterize fine root decay rates and fungal community composition at the landscape scale in northern temperate forests, and we estimated the genetic potential of fungal communities for litter decay using publicly available genomes. Fine root decay occurred more rapidly where fungal communities had a greater genetic potential for decay, especially of cellulose and hemicellulose. Fine root decay was positively correlated with ligninolytic saprotrophic fungi and negatively correlated with ECM fungi with ligninolytic peroxidases, likely because these saprotrophic and ectomycorrhizal functional groups had the highest and lowest genetic potentials for plant cell wall degradation, respectively. These fungal variables overwhelmed direct environmental controls, suggesting fungal community composition and genetic variation are primary controls over fine root decay in temperate forests at regional scales.

Evolutionary history of theAsplenium scolopendriumcomplex (Aspleniaceae), a relictual fern with a northern pan-temperate disjunct distribution

AbstractAsplenium scolopendrium is distributed in northern temperate forests with many global biogeographic disjunctions. The species complex of A. scolopendrium has been generated by spatial segregation coupled with divergent evolution. We elucidated the biogeographic history of the A. scolopendrium complex by exploring its origin, dispersal and evolution, thus providing insights into the evolutionary history of the Tertiary floras with northern pan-temperate disjunct distributions. The results revealed that all infraspecific taxa descended from a widely distributed common ancestor in the Northern Hemisphere. This pan-temperate ancestral population formed by unidirectional westward dispersal from European origins primarily during the Early Eocene when the Earth’s climate was much warmer than today. The splitting of European, American and East Asian lineages occurred during the Early Miocene due to geo-climatic vicariances. Polyploidy events in the American ancestral populations created additional reproductive barriers. The star-shaped haplotypes in each continent indicated that local disjunctions also led to derived genotypes with potential to diverge into different taxa. This intracontinental lineage splitting is likely related to latitudinal range shift and habitat fragmentation caused by glacial cycles and climate change during the Pleistocene. The evolutionary history of the A. scolopendrium complex supported the Boreotropical hypothesis exhibiting range expansion during the Early Eocene Climatic Optimum.

Root traits and soil nutrient and carbon availability drive soil microbial diversity and composition in a northern temperate forest

Root traits and soil nutrient and carbon availability drive soil microbial diversity and composition in a northern temperate forest

Seasonal Responses of Hydraulic Function and Carbon Dynamics in Spruce Seedlings to Continuous Drought.

Drought is expected to increase in the frequency and duration associated with climate change. Although hydraulic function and carbon (C) storage have been widely recognized as key components to plant survival under a single drought, the physiological responses to continuous drought remain largely unknown, particularly for high northern temperate and boreal forests which are sensitive to water stress. In this study, we quantified the survival, growth, gas exchange, water relations, and nonstructural carbohydrates (NSCs) in 3-year-old Jezo spruce (Picea jezoensis) seedlings responding to continuous drought stress. Seedlings were maintained in drought conditions for 392 days, covering two growing and one dormant winter season. Seedlings subjected to drought showed a significant decrease in net photosynthesis rate (Anet) and stomatal conductance (gs) in both growing seasons, and biomass in the second growing season. The seedling mortality continuously increased to 35.6% at the experimental end. Notably, responses of C storage and leaf water potential to drought varied greatly depending on seasons. Living seedlings exposed to drought and control treatments had similar NSC concentrations in both growing seasons. However, seedlings with concentrations of both the soluble sugars and starch less than 1% in root died in the winter dormant season. In the second growing season, compared with the control treatment, droughted seedlings had significantly lower leaf water potential and stem wood-specific hydraulic conductivity (Kw). Meanwhile, the leaf predawn water potential did not recover overnight. These suggest that C starvation might be an important reason for seedlings that died in the winter dormant season, while in the growing season drought may limit seedling survival and growth through inducing hydraulic failure. Such seasonal dependence in hydraulic dysfunction and C depletion may lead to higher mortality in spruce forests facing extended drought duration expected in the future.

Nutritional and environmental factors influence small mammal seed selection in a northern temperate forest

AbstractRodents can influence the succession and assembly of plant communities by preying on and dispersing seeds. Using a seed tray experiment with three common seeds, American beech (Fagus grandifolia), red maple (Acer rubrum), and eastern hemlock (Tsuga canadensis), we assessed factors that influence seed selection and foraging time of three rodents: deer mice (Peromyscus maniculatus), white‐footed mice (Peromyscus leucopus), and southern red‐backed voles (Myodes gapperi). All three rodents preferred beech seeds, likely due to its large size and high lipid content. However, when beech availability was low, secondary seed selection differed by rodent species with P. maniculatus equally selecting hemlock and red maple, P. leucopus preferring hemlock, and M. gapperi preferring red maple. Red maple seeds contained high levels of phenolic compounds, which hinder digestion, and the elongated cecum of M. gapperi may allow for better processing of these compounds relative to Peromyscus. Beech seeds were nearly always removed from trays intact, suggesting rodents could be important dispersers compared to the small‐seeded species, which were generally processed on trays. The influence of environmental factors on seed selection was only notable when beech seed availability was low. Beech seed availability was also the primary factor influencing foraging time on trays, with individuals increasing foraging time as beech availability decreased. Consistent with predator avoidance behaviors, denser shrub cover increased foraging time for P. maniculatus, whereas moon luminosity decreased foraging for all three species. Our findings underscore that seed quality drives seed selection but that preferences are context dependent, varying with seed availability and digestive capacity.

Patterns and potential drivers of exotic plant diversity in managed northern temperate and boreal forests

Although exotic (i.e., non-native) plant species are among the main factors contributing to ecosystem change globally, investigations of northern temperate and boreal forest ecosystems in North America in the context of invasion science are scarce. Multiple hypotheses, including the ‘biotic resistance’, ‘intermediate disturbance’ and ‘disturbance-mediated’ hypotheses, can serve as a framework to assess invasibility. Here we used the NEBIE (natural disturbances and extensive, basic, intensive, and elite silviculture intensities) plot network, consisting of field sites across different forest types that originated from a range of silviculture systems to assess the role of silviculture intensity on exotic plant diversity. Botanical surveys were conducted pre- and two-, five-, and ten years post-forest harvesting. Thirty exotic plant species were observed across all studied forests, of which 20 belonged to the Asteraceae, Fabaceae, and Poaceae families. Exotic species richness was highly correlated with native species richness and peaked as a result of intermediate linked-press (i.e., climate, soils, historic disturbance regimes, and silviculture systems) stresses/disturbances and compounded pulse (i.e., harvest intensity, site preparation, and herbicide use) disturbances for all post-harvesting measurement years. Observed exotic species are considered to have traits consistent with those of ruderal species. In this context, our results support the intermediate disturbance and disturbance-mediated hypotheses, but not the biotic resistance hypothesis. To reduce the richness of exotic plant species in northern temperate and boreal forests we recommend minimizing the use of intermediate compounded pulse disturbances.

How can the forest sector mitigate climate change in a changing climate? Case studies of boreal and northern temperate forests in eastern Canada

Forest based climate mitigation emerged as a key component of the Paris Agreement, and thus requires robust science to reduce uncertainties related to such strategies. The aim of this study was to assess and compare the cumulative effects on carbon dynamics of forest management and climate change on boreal and northern temperate forest sector in eastern Canada for the 2020–2100 period. We used the spatially explicit forest landscape model LANDIS-II and its extension Forest Carbon Succession, in conjunction with the Carbon Budget Model for Harvested Wood Products framework. We simulated the dynamics of forest composition and carbon flows from forest ecosystems to wood products and their substitution effect on markets under increasing climate forcing, according to a tonne-year approach. Simulations were conducted for a series of forest management scenarios based on realistic practices principally by clearcut in the boreal territory and continuous-cover forestry in the northern temperate one. These scenarios included: i) a business-as-usual scenario (BaU), representing the current management strategy, ii) increased harvesting by 6.3% to 13.9%, iii) increased conservation (i.e. reduced harvesting by 11.1% to 49.8%), iiii) and a scenario representing the natural evolution of the forest landscape (i.e. without any management activity). Our study revealed that increasing harvesting levels had contrasting effects on the mitigation potential in northern temperate (enhance net sequestration) and boreal forest sector (enhance net emissions) in comparison to the BaU from 2040 onwards, regardless of the future climate. Carbon storage in wood products and the substitution effect were not sufficient to offset carbon emissions from ecosystems. Moreover, climate change had a strong impact on the capacity of both landscapes to act as carbon sinks. Northern temperate landscapes became a net source of carbon over time due to their greater vulnerability to climate change than boreal landscapes. Our study highlights the need to consider the initial landscape characteristics in simulations to maximize the mitigation potential of alternative forest management strategies. The optimal management solution can be very different according to the characteristics of forest ecosystems. This opens the possibility of optimizing management for specific forest stands, with the objective of maximizing the mitigation potential of a given landscape.

Patterns and Drivers of Exotic Plant Establishment in Managed Northern Temperate and Boreal Forests

Patterns and Drivers of Exotic Plant Establishment in Managed Northern Temperate and Boreal Forests

Climate Drives Modeled Forest Carbon Cycling Resistance and Resilience in the Upper Great Lakes Region, USA.

Forests dominate the global terrestrial carbon budget, but their ability to continue doing so in the face of a changing climate is uncertain. A key uncertainty is how forests will respond to (resistance) and recover from (resilience) rising levels of disturbance of varying intensities. This knowledge gap can optimally be addressed by integrating manipulative field experiments with ecophysiological modeling. We used the Ecosystem Demography‐2.2 (ED‐2.2) model to project carbon fluxes for a northern temperate deciduous forest subjected to a real‐world disturbance severity manipulation experiment. ED‐2.2 was run for 150 years, starting from near bare ground in 1900 (approximating the clear‐cut conditions at the time), and subjected to three disturbance treatments under an ensemble of climate conditions. Both disturbance severity and climate strongly affected carbon fluxes such as gross primary production (GPP), and interacted with one another. We then calculated resistance and resilience, two dimensions of ecosystem stability. Modeled GPP exhibited a two‐fold decrease in mean resistance across disturbance severities of 45%, 65%, and 85% mortality; conversely, resilience increased by a factor of two with increasing disturbance severity. This pattern held for net primary production and net ecosystem production, indicating a trade‐off in which greater initial declines were followed by faster recovery. Notably, however, heterotrophic respiration responded more slowly to disturbance, and it's highly variable response was affected by different drivers. This work provides insight into how future conditions might affect the functional stability of mature forests in this region under ongoing climate change and changing disturbance regimes.

Influences of climate fluctuations on northeastern North America’s burned areas largely outweigh those of European settlement since AD 1850

There is a pressing need for a better understanding of changing forest fire regimes worldwide, especially to separate the relative effects of potential drivers that control burned areas. Here we present a meta-analysis of the impacts of climate fluctuation and Euro-Canadian settlement on burned areas from 1850 to 1990 in a large zone (>100 000 km2) in northern temperate and boreal forests of eastern Canada. Using Cox regression models, we tested for potential statistical relationships between historical burned areas in 12 large landscapes (reconstructed with dendrochronological data) with climate reconstructions, changes in the Euro-Canadian population, and active suppression (all reconstructed at the decadal scale). Our results revealed a dominant impact of climate fluctuations on forest burned areas, with the driest decades showing fire hazards between 5 to 15 times higher than the average decades. Comparatively, the Euro-Canadian settlement had a much weaker effect, having increased burned areas significantly only during less fire-prone climate conditions. During periods of fire-prone climate, burned areas were maximum independent of fluctuations in Euro-Canadian populations. Moreover, the development of active fire suppression did not appear to reduce burned areas. These results suggest that a potential increase in climate moisture deficit and drought may trigger unprecedented burned areas and extreme fire events no matter the effects of anthropogenic ignition or suppression.

Plant-plant interactions change during succession on nurse logs in a northern temperate rainforest.

Plant–plant interactions change through succession from facilitative to competitive. At early stages of succession, early‐colonizing plants can increase the survival and reproductive output of other plants by ameliorating disturbance and stressful conditions. At later stages of succession, plant interactions are more competitive as plants put more energy toward growth and reproduction. In northern temperate rainforests, gap dynamics result in tree falls that facilitate tree regeneration (nurse logs) and bryophyte succession. How bryophyte‐tree seedling interactions vary through log succession remains unclear. We examined the relationships of tree seedlings, bryophyte community composition, bryophyte depth, and percent canopy cover in 166 1.0 m2 plots on nurse logs and the forest floor in the Hoh rainforest in Washington, USA, to test the hypothesis that bryophyte‐tree seedling interactions change from facilitative to competitive as the log decays. Tree seedling density was highest on young logs with early‐colonizing bryophyte species (e.g., Rhizomnium glabrescens) and lowest on decayed logs with Hylocomium splendens, a long‐lived moss that reaches depths >20 cm. As a result, bryophyte depth increased with nurse log decay and was negatively associated with tree seedling density. Tree seedling density was 4.6× higher on nurse logs than on the forest floor, which was likely due to competitive exclusion by forest floor plants, such as H. splendens. Nurse logs had 17 species of bryophytes while the forest floor had six, indicating that nurse logs contribute to maintaining bryophyte diversity. Nurse logs enable both tree seedlings and smaller bryophyte species to avoid competition with forest floor plants, including the dominant bryophyte, H. splendens. H. splendens is likely a widespread driver of plant community structure given its dominance in northern temperate forests. Our findings indicate that plant–plant interactions shift with succession on nurse logs from facilitative to competitive and, thus, influence forest community structure and dynamics.

Within-gap position shapes fifty years of forest dynamics in a temperate hardwood forest in Connecticut, USA

Predictions of forest succession have a tremendous influence on forest management decisions, strategies, and policies. Although generalized forest succession models are intensively studied, there is a distinct lack of long-term studies confirming these models due to the logistical constraints of tracking a forest as it develops over decades or centuries. Here we use a long-term dataset spanning >50 years of third-growth forest development in experimental forest gaps within a second-growth northern temperate hardwood forest to examine the influence of gap position on the structure and composition of regeneration and confirm past models of forest succession. We document key stand development patterns in even-aged mixed-species stands, including vertical stratification and shifts in diameter distributions. While the stands have shifted into a classic inverse-J diameter distribution, these shifts are due to a combination of unimodal distributions of the shade-intolerant and intermediate guilds that grow in mean diameter over time with consistently high densities of small individuals from the shade-tolerant guild. The greatest vertical stratification between the shade-intolerant and intermediate guilds occurred 30 years after clearing but then disappeared as the intermediate guild increased in height. In contrast, the separation in strata between the shade-tolerant species and the more intolerant guilds only increased over time. Finally, we found that gap position had a significant effect on productivity. The basal area, height, and species richness (in this case, an indicator of canopy stratification) were best modeled with negative quadratic regressions with highest values in gap centers and lower values towards the edges of gaps. This pattern aligns more with expected moisture and nutrient availability within gaps than expected solar radiation in the northern hemisphere, suggesting that moisture and nutrient availability may play a greater role than is often acknowledged in temperate forest types. Furthermore, these relationships were readily apparent only after 30 years yet became more accentuated with time, highlighting the importance of long-term research on successional dynamics for management. Ultimately our results document a clear successional trajectory in these gaps that follow expectations for even-aged mixed-species stand development where a full suite of species leads to rolling periods of dominance based on species functional guilds, with early successional species replaced by late-successional species in the progression of succession.

Phylogenomic and ecological analyses reveal the spatiotemporal evolution of global pines

How coniferous forests evolved in the Northern Hemisphere remains largely unknown. Unlike most groups of organisms that generally follow a latitudinal diversity gradient, most conifer species in the Northern Hemisphere are distributed in mountainous areas at middle latitudes. It is of great interest to know whether the midlatitude region has been an evolutionary cradle or museum for conifers and how evolutionary and ecological factors have driven their spatiotemporal evolution. Here, we investigated the macroevolution of Pinus, the largest conifer genus and characteristic of northern temperate coniferous forests, based on nearly complete species sampling. Using 1,662 genes from transcriptome sequences, we reconstructed a robust species phylogeny and reestimated divergence times of global pines. We found that ∼90% of extant pine species originated in the Miocene in sharp contrast to the ancient origin of Pinus, indicating a Neogene rediversification. Surprisingly, species at middle latitudes are much older than those at other latitudes. This finding, coupled with net diversification rate analysis, indicates that the midlatitude region has provided an evolutionary museum for global pines. Analyses of 31 environmental variables, together with a comparison of evolutionary rates of niche and phenotypic traits with a net diversification rate, found that topography played a primary role in pine diversification, and the aridity index was decisive for the niche rate shift. Moreover, fire has forced diversification and adaptive evolution of Pinus Our study highlights the importance of integrating phylogenomic and ecological approaches to address evolution of biological groups at the global scale.

The diversification of the northern temperate woody flora – A case study of the Elm family (Ulmaceae) based on phylogenomic and paleobotanical evidence

AbstractUlmaceae is a woody family widespread in northern temperate forests. Despite the ecological importance of this family, its phylogeny and biogeographic history are poorly understood. In this study, we reconstruct phylogenetic relationships within the family and infer spatio‐temporal diversification patterns based on chloroplast genome (complete cpDNA) and nuclear ribosomal DNA sequences (nrDNA). The seven Ulmaceae genera are resolved in two main clades (temperate vs. tropical) by both cpDNA and nrDNA sequences. The temperate clade includes four genera, Hemiptelea, Zelkova, Planera, and Ulmus. The relationships among Planera and other genera are controversial because of inconsistent topologies between plastid and nuclear data. The tropical clade includes three genera ((Ampelocera, Phyllostylon), Holoptelea). Molecular dating and diversification analyses show that Ulmaceae originated in the Early Cretaceous (ca. 110–125 Ma) with the main lineages establishing from the Late Cretaceous to the early Eocene. The diversification rate slowed during the middle to the late Paleogene (ca. 23–45 Ma), followed by a rapid diversification of the East Asian temperate group in the Neogene, congruent with a global cooling event. The ancestral state optimization analysis suggests an East Asian origin of the temperate Ulmaceae clade during the Paleocene, which is consistent with the fossil record. Both phylogenomic and fossil evidence support East Asia as a center of origin and diversification for the temperate woody lineages.

Reconstructed high-resolution forest dynamics and human impacts of the past 2300 years of theParc national de Mont-Orford, southeastern Québec, Canada

We used a high-resolution lacustrine pollen record from Étang Fer-de-Lance (45°21′21.9′N, 72°13′35.3′W), southeastern Québec, Canada, together with microcharcoal, to infer forest dynamics and human impacts over the past 2300 years. The lake is located in the eastern sugar maple-basswood forest domain of the Northern Temperate Forest of eastern North America. We found that the pollen percentages and influxes of Fagus grandifolia (American beech) and Tsuga canadensis (eastern hemlock) significantly declined over the past 700 years. Over the last millennium, the pollen percentages and influxes of the Picea species ( P. glauca, P. mariana, P. rubens) (white, black, and red spruce), and Pinus strobus (eastern white pine) significantly increased. We showed that these shifts in forest composition are being driven by changes in regional climate. In addition to the pollen percentage changes, the Medieval Climate Anomaly (AD 800–1300) appeared as increased pollen influxes and the Dark Ages Cold Period (AD 400–700) and Little Ice Age (AD 1400–1800) appeared as decreased pollen influxes. The signal for human modification of the landscape first appeared at ~AD 1550–1650 as increases in Ambrosia (ragweed) and Poaceae (grasses) from possible Indigenous agriculture. The signal of European settler landscape modification appeared at ~AD 1770 as the beginning of a steep, “classic” Ambrosia rise. It intensified over the subsequent 250 years as further increases in non-arboreal pollen taxa and early successional Acer (maple) species. Microcharcoal analysis showed that fire was a re-occurring event in the sugar maple-basswood domain, but had little impact on forest composition.

Overyielding in young tree communities does not support the stress‐gradient hypothesis and is favoured by functional diversity and higher water availability

Abstract Biodiversity effects on productivity and other ecosystem functions are strongly dependent on climate and resource availability. Based on the stress‐gradient hypothesis, under conditions of greater abiotic stress, diversity effects on plant performance are intensified due to the increased relative importance of positive plant interactions. However, whether this hypothesis is consistently applicable in forest systems remains unclear. A field trial was established to test the stress‐gradient hypothesis and examine diversity effects on above‐ground biomass production of young trees in mixtures exposed to different water availability. Six native tree species of northern temperate forests (Acer saccharum, Betula papyrifera, Larix laricina, Picea glauca, Pinus strobus and Quercus rubra) were planted as monocultures and as mixtures of two, four and six species. For five growing seasons, four replicates of each community were exposed to conditions of either low‐ or high‐water availability created by rainfall exclusion and weekly irrigation, respectively. Growth‐years 4 and 5 were significantly different when the climatic water balance of the growing seasons was compared. We tested the effects of functional diversity on: (a) total growth of mixtures under low‐ and high‐water availability, and (b) annual growth in years 4 (higher water availability, 2017) and 5 (lower water availability, 2018). Annual growth of most species in both years was greater under high‐ versus low‐water availability. Functional diversity had a significant positive effect on total biomass production and annual growth, and this effect was more strongly expressed under high‐water availability. Functional diversity effects on annual growth did not differ between years 4 and 5 regardless of their climatic water balance. Functional and species identity were key to understanding productivity responses to mixture and treatment effects. Synthesis. Contrary to the stress‐gradient hypothesis, the positive effects of functional diversity on productivity were enhanced by high‐water availability and were independent of seasonal water balance.

Temperate forests respond in a non-linear way to a population gradient of wild deer

Abstract Wild deer exert strong top–down control on forest composition by browsing on palatable trees, and these effects are exacerbated as red, fallow, and roe deer populations increase in northern temperate forests. However, the relationship between deer abundance and plant recruitment remains poorly documented. Here, we combined camera trap and vegetation plot data to quantify the shape of the relationship between habitat utilization by deer (red, fallow and roe deer) with different components of the forest understory in ten sites distributed across a temperate mixed forest in the Veluwe, the Netherlands. The list of forest attributes included the density, richness and diversity of saplings, the proportion of conifers to broadleaves, the number of browsed broadleaves and conifers, the forest basal area, the understory cover of shrubs, moss and bare soil and the depth of the litter layer. When applying General Linear Mixed Models to those camera trap data, six of the eleven forest variables were related to the utilization level (UL) by deer. With increasing UL by fallow deer, there was a decrease in sapling species richness (β = −0.26). With increasing UL by red deer, there was a decrease in litter depth (β = −0.14) and an increase in browsed broadleaf stems (β = 0.40). With increasing UL by roe deer, there was a decrease in species richness of sapling plants (β = −0.26), Shannon diversity (β = −0.11) and shrub cover (β = −0.36), whereas there was an increase in stem density (β = 0.06). When combining all deer species into one guild, a negative relation was found between UL by deer and sapling richness (β = −0.21), diversity (β = −0.09) and litter depth (β = −0.14) and a positive relation with sampling density (β = 0.04). The relationship between UL by deer and different forest attributes followed a linear log10 shape. When back transforming, the response was curvilinear with large changes at a low UL and small changes when the UL was high. Yet, the exact shape of the curve varied according to (a) biotic factors specific to each study location. The conservation of temperate forests can benefit from limiting the size of deer populations and the time deer spend browsing in forest patches with high biodiversity value.

Impacts of simulated nitrogen deposition on soil enzyme activity in a northern temperate forest ecosystem depend on the form and level of added nitrogen

Extracellular enzymes in the soil are pivotal to nutrient cycling in the ecosystem. Simulated nitrogen (N) deposition has resulted in positive, negative, and neutral effects of added N on soil extracellular enzyme activity (EEA).A field experiment involving two levels (50 and 150 kg ha−1 yr−1) and three forms (NaNO3, NH4NO3, (NH4)2SO4) of added N was conducted in a northern temperate forest. Over 8 years beginning in 2011, we measured the extracellular enzyme activity of six soil-based enzymes involved in C- (β-glucosidase, BG; polyphenol oxidase, PPO; catalase, CAT), N- (urease, UR) and P- (acid phosphatase, ACP; alkaline phosphatase, AKP) cycling during the growing season (March to September).High-level N addition produced a more obvious effect in promoting the activity of C-cycling enzymes and ACP, while the activities of UR and AKP under high-level N addition decreased significantly at rates of 10.0 and 26.8%, respectively. NH4+-N had a stronger effect on soil EEAs than NO3−-N, except UR activity. Furthermore, N addition induced a time-lag effect on the activity of BG, PPO, and ACP. BG activity achieved a maximum value in 2016 after increasing at an average rate of 21.2%. Furthermore, additional N produced nonlinear effects in the inter-annual variation of BG and CAT activity, which emphasized the importance of long-term monitoring.The effects of N addition on soil EEAs depended on the forms and levels of N added. The stimulatory effects of N addition on the activity of C-cycling enzymes may lead to instability in the soil C pool.

Using U-Net-Like Deep Convolutional Neural Networks for Precise Tree Recognition in Very High Resolution RGB (Red, Green, Blue) Satellite Images

Very high resolution satellite imageries provide an excellent foundation for precise mapping of plant communities and even single plants. We aim to perform individual tree recognition on the basis of very high resolution RGB (red, green, blue) satellite images using deep learning approaches for northern temperate mixed forests in the Primorsky Region of the Russian Far East. We used a pansharpened satellite RGB image by GeoEye-1 with a spatial resolution of 0.46 m/pixel, obtained in late April 2019. We parametrized the standard U-Net convolutional neural network (CNN) and trained it in manually delineated satellite images to solve the satellite image segmentation problem. For comparison purposes, we also applied standard pixel-based classification algorithms, such as random forest, k-nearest neighbor classifier, naive Bayes classifier, and quadratic discrimination. Pattern-specific features based on grey level co-occurrence matrices (GLCM) were computed to improve the recognition ability of standard machine learning methods. The U-Net-like CNN allowed us to obtain precise recognition of Mongolian poplar (Populus suaveolens Fisch. ex Loudon s.l.) and evergreen coniferous trees (Abies holophylla Maxim., Pinus koraiensis Siebold & Zucc.). We were able to distinguish species belonging to either poplar or coniferous groups but were unable to separate species within the same group (i.e. A. holophylla and P. koraiensis were not distinguishable). The accuracy of recognition was estimated by several metrics and exceeded values obtained for standard machine learning approaches. In contrast to pixel-based recognition algorithms, the U-Net-like CNN does not lead to an increase in false-positive decisions when facing green-colored objects that are similar to trees. By means of U-Net-like CNN, we obtained a mean accuracy score of up to 0.96 in our computational experiments. The U-Net-like CNN recognizes tree crowns not as a set of pixels with known RGB intensities but as spatial objects with a specific geometry and pattern. This CNN’s specific feature excludes misclassifications related to objects of similar colors as objects of interest. We highlight that utilization of satellite images obtained within the suitable phenological season is of high importance for successful tree recognition. The suitability of the phenological season is conceptualized as a group of conditions providing highlighting objects of interest over other components of vegetation cover. In our case, the use of satellite images captured in mid-spring allowed us to recognize evergreen fir and pine trees as the first class of objects (“conifers”) and poplars as the second class, which were in a leafless state among other deciduous tree species.

Surveying for Batrachochytrium dendrobatidis and B. salamandrivorans in wild and captive amphibian populations in Estonia and Latvia.

The pathogenic chytrid fungi Batrachochytrium dendrobatidis (Bd) and B. salamandrivorans (Bsal) cause infections that have become primary drivers of amphibian biodiversity loss. While globally widespread, the distribution margins of Bd and Bsal have not been determined, and the presence of these pathogens has probably gone unnoticed in many areas, especially in northern Eurasia. To better understand the presence and distribution of both pathogens in the northern temperate and boreal forest biomes, 243 individuals were sampled from 8 native amphibian species across Estonia. Additionally, 68 amphibians were sampled from captive collections in Estonia and Latvia. Pathogen infection was assessed using metabarcoding of the ITS2 marker. No positive matches for Bsal infection were found. Bd was detected in 13 specimens, 3 of which were sampled at the Riga Zoo (with a prevalence of 5.2%) and 10 in natural environments in Estonia (3.3%). The infected wild individuals belonged to 6 amphibian species and were detected throughout the mainland of Estonia, but not on islands. Prevalence of infection with Bd ranged between 3.1 and 12.5% among native species. In addition, we found molecular evidence for a potentially new sister species to Bd in nature. Although outbreaks of chytridiomycosis have never been observed in Estonia, it cannot be excluded that the dynamics of local amphibian populations are affected by Bd infections. Therefore, further work, including capture-mark-recapture studies and long-term monitoring, are required to clarify the impact of Bd on amphibians in Northern Europe.