Betula Pubescens Research Articles

Conservation genetics of montane willow populations in Scotland—limited natural recovery despite long-distance gene flow and high genetic diversity

Plant species around the world are negatively affected by habitat fragmentation and climate change. Montane willow populations in the UK have declined primarily due to grazing, as well as climate change and muirburn in certain areas. Only small, isolated populations remain, scattered across steep ledges where shrubs escape most grazing animals. We explored the genetic effects of habitat fragmentation on gene flow and genetic diversity in the largest remaining patches in the UK, which lie in Scotland, for two now restricted and rare montane willow species—Salix myrsinites and Salix lapponum. Using ten microsatellite loci and an almost complete genetic inventory in the central Cairngorms area (S. myrsinites n = 186, S. lapponum n = 91) we showed that genetic diversity (heterozygosity and allelic richness) is relatively high in both species, particularly high for the decaploid S. myrsinites, and clonal reproduction low. Historic gene flow between populations could be demonstrated. Significant inbreeding was detected in both species and observed seed set and numbers of juveniles in the field are low, possibly indicating signs of inbreeding depression. Both species have extremely low numbers of individuals at each site, with many being smaller than ten, and in some cases combined with skewed sex-ratios (mainly female biased). This will likely cause more severe reproductive failures in the next generations unless population numbers are increased. Reinforcing populations of both species under low grazing pressure with new, unrelated individuals, as well as creating new stepping-stone populations will be necessary to help the recovery of these species. Results from this study will inform restoration work in Scotland aiming to create continuous woodland habitats from pinewoods at lower altitudes through to higher altitude downy birch woodlands merging with montane willows.

CHEMICAL COMPOSITION AND MECHANICAL PROPERTIES OF VARIOUS PARTS OF BIRCH WOOD

The article compares mechanical parameters, group chemical compositions, iron content, lipid compositions before and after saponification, moisture, bulk density in three parts of Betula pubescens Ehrh. birch wooden parts: sapwood, false heartwood, false heartwood border. The strength properties of the false heartwood are worse than those of sapwood. The border of the false core is sometimes stronger than that of other parts. Evaluation is carried out in terms of hardness, flexural strength and compression strength. False heartwood, and even more so its border, contain more extractives extracted by ethanol, water, alkali solution, methylene chloride and less iron. The content of other components: cellulose, lignin, other polysaccharides differs, but less significantly. False heartwood border is heavier than the other wooden parts. Moisture content of the various parts decreases in the following order: false heartwood border, false heartwood, sapwood. The composition of the extractives extracted by methylene chloride is different in different parts. The composition is determined by gas-liquid chromatography-mass spectrometry before and after saponification of esters. Differences in sterols are given. An increased content of monoterpene alcohols and arylheptanoids is observed at the border. Differences in the properties of different wooden parts of a tree are explained by different amount and composition of extractives.

Recent and Past Arboreal Change: Observational and Retrospective Studies Within a Subalpine, Birch-Dominated (Betula Pubescens Ssp. Czerepanovii) Mountain Valley in the Southern Swedish Scandes-Responses to Climate Change and Land Use

Multi-scale observations and reconstructions of treeline and associated plant cover changes are reviewed in this study. The main focus is on the dynamics of the treeline ecotone within a mountain valley in the southern Swedish Scandes. This area is well-researched for more than 100 years, with a background of historical studies covering the entire Holocene epoch. Trees were present on ice-free nunataks already during the Late-Glacial, 17 000-13 000 cal. a BP. Mountain birch (Betula pubescens ssp. czerepanovii), Norway spruce (Picea abies) and Scots pine (Pinus sylvestris) then grew 400-700 m higher than their current treelines, indicative of summer temperatures 3 °C higher than present. In addition, the tree flora contained Siberian larch (Larix sibirica) and broad-leaf thermophilic and deciduous species, Quercus robur, Corylus avellana, Ulmus glabra and Alnus glutinosa. Eventually, the climate turned cooler, particularly enhanced around 5000 cal. a BP. This course of change initiated the Neoglacial period, when thermophilic species were extirpated. Concomitantly, mountain birch forest and spruce benefitted from this course of change. Pine, on the other hand was disfavored and regressed in the treeline elevation and general abundance on the landscape. These trends continued until the Mediaeval period AD 1000-1300, when temperature raised above present-day standards and the pine treeline locally shifted upslope by at least 100 m. This favourable epoch was discontinued quite abruptly by resurgence of Neoglacial cooling; the “Little Ice Age”, which prevailed until the late 19th century. Widespread glacier expansion, high-elevation arboreal decline and treeline retraction then occurred. With a gentle onset in the late 19th century or somewhat earlier, a modern and still prevailing warming period was accentuated by the late 1930s. Subsequently, slight cooling prevailed for 3-4 decades, whereupon warming was resumed with short interruptions until the present day. One distinct short-term cooling-conditioned setback occurred during the 1980s. Transient permafrost formed close to the treeline, and locally some treeline recession took place. Thereafter, warming has re-occurred and glaciers and permafrost have receded. Treeline rise and densification of the treeline ecotone are once again active processes in the mountainscape. Currently, most conspicuous is a process of pine reclamation of local ground lost during the Little Ice Age. Hereabouts, seed regeneration, still virtually without winter injuries, is taking place at an unprecedented rate and abundance. Mountain birch is gaining ground in snow rich depressions in the birch belt and is currently regressing in exposed and snow-poor sections of the local topography. Current biotic changes within the treeline ecotone are well within the ranges of inferred natural variabilty during the postglacial period.

Substitution of fossil-energy intensive building materials by wood products – Does it matter? A case study from Western Norway

Forest management is an important tool for GHG mitigation by representing three carbon pools: living biomass, forest soil, and wood-based products. Additionally, increasing attention has been given to the potential for wood products to substitute fossil-intensive products as a climate mitigation strategy. The goal of this paper is to analyse the theoretical GHG effects of fully replacing four common non-wood products with wood-based products of ‘low’ and ‘high’ technology options that have a similar functionality: (1) Spruce particle board substituting polyurethane (PU) foam insulation board; (2) spruce cross-laminated timber beam (CLT) substituting steel beam; (3) birch energy wood substituting electric heating; and (4) birch plywood substituting plaster board. The analysis was based on forestry in Western Norway as a case study, where forests typically consist of naturally generated birch and expanding areas of planted Norway spruce. In this study we compare wood products derived from paired stands of Norway spruce and downy birch. The analysis showed that spruce gave a higher theoretical substitution effect relative to birch for the selected pairs of woody and non-woody products. CLT substituting steel beam gave the highest substitution effect, approximately 15% higher than particle board substituting PU foam board. The theoretical substitution effect in mass units of carbon per kg wood product for the two spruce wood products was approximately 17 times higher relative to substituting Norwegian hydro energy-based electric heating, whereas plywood substituting plaster board may in fact increase GHG emissions. As the gross emissions were relatively similar for the birch plywood and the spruce particle board, the major substitution effect was related to the avoided emission of the non-woody product rather than to the tree species per se. The paper concludes that the choice of product to be substituted was the key factor that determined the final substitution effects. Furthermore, the study showed that transportation was the single most important factor that affected the emissions between planting and delivery of the timber at production gate. The analysis enables informed decisions related to CO2-emissions at the various steps from tree planting to wood conversion, and underline the importance of informed decision related to the choice of substitution products.

Complexity of downy birch emissions revealed by Vocus proton transfer reaction time-of-flight mass spectrometer

Biogenic volatile organic compounds (BVOCs) are known to strongly influence the global climate by affecting various atmospheric constituents such as oxidants and aerosols. Among the several BVOCs that are emitted continuously into the atmosphere, studies have shown that up to 96% of the emissions have been missed out by current analytical techniques. In this study, we used a Vocus proton-transfer-reaction time-of-flight mass spectrometer (Vocus) to characterize and quantify emissions from a branch of a downy birch tree at a boreal forest site in Hyytiälä, Finland in August 2019. During the measurement period, we were able to observe real-time emissions of hydrocarbons with up to 20 carbon atoms and oxygenated compounds (OVOCs) with up to 4 oxygen atoms. OVOCs accounted for around 90% of the total observed emissions with the largest contribution from C8H8O3 (0.37 μgg–1h–1; ∼60% of total). For the first time, emissions of diterpenes (C20H32, C20H36, and C20H38) were observed from downy birch tree, although in minor quantities (0.1% of total emissions). During this late growing season, C10H16 and C10H14 contributed ∼7% in total emissions, while the sum of C5H8, C15H22, and C15H24 contributed around ∼3%. The branch experienced abiotic stress during the measurement period, which might explain the unusually high emissions of C8H8O3. Standardized emission potentials are reported for all compounds using two Guenther algorithms. While emissions of most compounds fit well with either of the two algorithms, emissions of certain compounds like C8H8O3 could not be explained by either suggesting the influence of other factors besides temperature and light. Vocus PTR-TOF-MS can help identify a diverse range of molecules even if emitted in minute quantities. The BVOCs detected from birch emissions may be important in the formation of secondary organic aerosols but their implications in the atmosphere need to be verified with further studies.

Poleward increase in feeding efficiency of leafminer Stigmella lapponica (Lepidoptera: Nepticulidae) in a latitudinal gradient crossing a boreal forest zone.

Damage to plant communities imposed by insect herbivores generally decreases from low to high latitudes. This decrease is routinely attributed to declines in herbivore abundance and/or diversity, whereas latitudinal changes in per capita food consumption remain virtually unknown. Here, we tested the hypothesis that the lifetime food consumption by a herbivore individual decreases from low to high latitudes due to a temperature-driven decrease in metabolic expenses. From 2016 to 2019, we explored latitudinal changes in multiple characteristics of linear (gallery) mines made by larvae of the pygmy moth, Stigmella lapponica, in leaves of downy birch, Betula pubescens. The mined leaves were larger than intact leaves at the southern end of our latitudinal gradient (at 60°N) but smaller than intact leaves at its northern end (at 69°N), suggesting that female oviposition preference changes with latitude. No latitudinal changes were observed in larval size, mine length or area, and in per capita food consumption, but the larval feeding efficiency (quantified as the ratio between larval size and mine size) increased with latitude. Consequently, S. lapponica larvae consumed less foliar biomass at higher latitudes than at lower latitudes to reach the same size. Based on space-for-time substitution, we suggest that climate warming will increase metabolic expenses of insect herbivores with uncertain consequences for plant-herbivore interactions.

Adventitious roots as a source of information in reconstructing the activity of modern aeolian processes in the temperate climate zone: A case study from the Kozłów sandy area (SW Poland)

This paper presents a spatial-temporal reconstruction of inland dune movements at an anthropogenic active sandy area known as the Kozłów Desert, SW Poland. This unique sandy area, with assemblages of aeolian forms typical of “true” deserts, is an inactive military training ground (decommissioned in 1992) where military activity led to the initiation of geomorphic processes. The reconstruction was carried out based on the growth reaction characteristics of Scots pine (Pinus sylvestris L.) and downy birch (Betula pubescens L.) trees. 14 increment cores were collected from 12 trees and analysed with standard dendrochronological techniques. Samples of adventitious roots from all the trees examined were collected and prepared to extend the analyses and check their usefulness in dating modern geomorphic processes. The adventitious roots of pine and birch were found to react differently to burial, in terms of both reaction time and the shape of the root system. Growth-ring widths and wood anatomy were indicative of sudden or multi-stage sand movement, thus confirming the usefulness of adventitious roots as an additional source of information about aeolian process activity. More broadly, the study shows that the dynamics of landforming processes can be assessed more accurately and reliably by using such a combination of methods, comparing data from roots to data from tree trunks.

Population structure and genetic variation of fragmented mountain birch forests in Iceland.

Betula pubescens Ehrh. (mountain birch) is the only forest-forming tree in Iceland. Since human settlement (874 AD), the continuous 25,000 to 30,000 km2 forest has shrunk to 1.200 km2 of fragmented patches, making it a good object to study population genetic consequences of habitat fragmentation and disturbance. Further, genetic studies have also shown that hybridization between the tetraploid (2n = 56) B. pubescens and the diploid (2n = 28) Betula nana L. (dwarf birch) occurs among Iceland's natural populations. This study assessed the genetic variation within and among 11 birch forests remaining across Iceland. Genotype-by-sequencing methodology provided a total of 24,585 single nucleotide polymorphisms (SNP´s), with a minor allele frequency >5% for genetic analyses. The analysis showed similar diversity within forests, suggesting that fragmentation and hybridization have had a limited effect on the genetic variation within sites. A clear genetic divergence is found among forests from the different regions of Iceland that may reflect historical isolation; the differentiation between forests increased with geographic distances reflecting isolation by distance. Information on the distribution of genetic variation of birch in Iceland is essential for its conservation and to establish genotype-phenotype associations to predict responses to new environmental conditions imposed by climate change and novel biotic/abiotic stressors.

Betula alba Bark Extract and Empetrum nigrum Fruit Juice, a Natural Alternative to Niacinamide for Skin Barrier Benefits.

The Scandinavian region is home to a unique biome with endemic plant species. The aim of this study was to explore this natural diversity and identify plant extracts providing positive skin barrier effects. Six plant extracts were identified as starting material. Following biochemical screening, two candidates outperformed the rest: Betula alba (BA) and Empetrum nigrum (EN). Quantitative PCR analysis showed that BA and EN upregulated barrier genes, when used individually and in combination. Betula alba increased AQP3 and OCLN protein expression, something niacinamide was incapable of. Additionally, the skin barrier was strengthened, evidenced by inhibition of KLK5 and hyaluronidase and showed strong antioxidant and anti-inflammatory activity through DPPH and COX2 inhibition, respectively. A first split-face clinical study was conducted using the combination of extracts versus placebo. There was a significantly better skin restructuring effect and corneocyte cohesion on the side treated with combined extracts. A second split-face clinical study assessed the combined extracts versus 3% niacinamide. Significant variations in skin hydration and TEWL were observed in favor of the extract treated side. In conclusion, we identified a natural alternative to niacinamide for improving skin barrier health, in Scandinavian plant extracts, which yield strong performance, but at a lower concentration.

Study of Catalysts for Suberinic Acid-Based Adhesive Polymerization

Birch outer bark is a byproduct accumulated from birch tree (Betula pendula Roth. and Betula pubescens Ehrh.) processing and contains up to 50 wt% suberin. Suberin is a biopolyester built mostly from α,ω-bifunctional fatty acids (suberinic acids) which after depolymerization together with lignocarbohydrate complex is a potential adhesive for obtaining particleboard composites. These composites can be made in hot-pressing process at around 225 °C temperature. The high hot-pressing temperature for suberinic acid-based adhesive is a disadvantage compared to hot-pressing temperatures for conventional resins such as urea-formaldehyde and phenol-formaldehyde (120–130 °C and 170–180 °C respectively). In this study we looked into possible ways to improve the properties (modulus of elasticity (MOE), bending strength (MOR) of suberinic acid-based particleboards by utilization of catalysts (additives) for SA-based adhesive polymerization, thus reducing hot-pressing temperature by potentially achieving the same mechanical properties as for the catalyst-untreated boards hot-pressed at higher temperature. The suitability of potential protonic acid, Lewis acid, as well as tin-based and basic catalyst was studied with differential scanning calorimetry (DSC) by quantifying specific enthalpy of the exothermic peak with an onset temperature of ≈185 °C. Based on DSC results, six catalysts (mixtures) were chosen (sulfanilic acid, p-toluenesulfonic acid, Al2(SO4)3, SnCl2, SnCl2/p-toluenesulfonic acid, dibutyltin oxide) for further studies on the effects of mechanical properties of particleboards. Treatment with 5 wt% sulfanilic acid, 5 wt% p-toluenesulfonic acid (free suberinic acid basis) significantly improved both MOE and MOR values. 6 wt% Al2(SO4)3 significantly improved MOE value.

Establishment of mountain birch (Betula pubescens ssp. tortuosa) on a glacial outwash plain: Spatial patterns and decadal processes.

Most of the Earth's surface has now been modified by humans. In many countries, natural and semi‐natural ecosystems mostly occur as islands, isolated by land converted for agriculture and a variety of other land‐uses. In this fragmented state, long‐distance dispersal may be the only option for species to adapt their ranges in response to changing climate. The order of arrival of species may leave a lasting imprint on community assembly. Although mostly studied at and above the species level, such priority effects also apply at the intraspecific level. We suggest that this may be particularly important in subarctic and arctic ecosystems. Mountain birch (Betula pubescens ssp. tortuosa) is characterized by great intraspecific variation. We explored spatio‐temporal patterns of the first two mountain birch generations on a homogeneous, early successional glacial outwash plain in SE Iceland that was the recipient of spatially extensive long‐distance dispersal ca. 30 years ago. We evaluated the decadal progress of the young population by remeasuring in 2018, tree density and growth form, plant size, and reproductive effort on 30 transects (150 m2) established in 2008 at four sites on the plain and two adjacent sites ca. 10 km away. All measured variables showed positive increases, but contrary to our predictions of converging dynamics among sites, they had significantly diverged. Thus, two of the sites (only 500 m apart) could not be distinguished in 2008, but by 2018, one of them had much faster growth rates than the other, a higher growth form index reflecting more upright tree stature, greater reproductive effort, and much greater second‐generation seedling recruitment. We discuss two hypotheses that may explain the diverging dynamics, site‐scale environmental heterogeneity, and legacies of intraspecific priority effects.

Sidestream materials show potential as top-dressed soil improvers for peatland forests.

The effects of top-dressing of several industrial and farming sidestream materials on the growth of downy birch (Betula pubescens Ehrh.) and Scots pine (Pinus sylvestris L.) seedlings in natural sphagnum peat soil were evaluated. Wood fly ash, industrial filter cake waste, mine tailings sand (quartz feldspar from lithium orebody), and digestate and liquid reject of cow manure from a biogas plant were studied for their physical and chemical properties, as well as for their effects as soil ameliorants on seedling growth during one growing period in a greenhouse. Each material was top-dressed on unfertilised peat in pots in quantities that corresponded to the amounts of ash used in Finnish peatland forest fertilisation (2-6tha-1). During growing, the pH of percolate water from the growing pots was below 4, and in the treatments with filter cake even below 3. However, no clear impairment of seedling growth due to acidity was observed. In all treatments, birch and pine seedlings grew at least as well as in the unfertilised peat (control treatment). Growth was strongest in the peat top-dressed with additives originating from cow manure, in which the high N and P contents promoted growth so much that foliar N was found to be diluted with respect to a high P content in the birch seedlings. No harmful concentrations of heavy metal residues were observed from the materials used. Overall, the results suggest that all the used sidestream materials show potential as soil improvers on forested peatlands.

Mercury in a birch forest in SW Europe: Deposition flux by litterfall and pools in aboveground tree biomass and soils

Atmospheric mercury (Hg) is largely assimilated by vegetation and subsequently transferred to the soil by litterfall, which highlights the role of forests as one of the largest global Hg sinks within terrestrial ecosystems. We assessed the pool of Hg in the aboveground biomass (leaves, wood, bark, branches and twigs), the Hg deposition flux through litterfall over two years (by sorting fallen biomass in leaves, twigs, reproductive structures and miscellaneous) and its accumulation in the soil profile in a deciduous forest dominated by Betula alba from SW Europe. The total Hg pool in the aboveground birch biomass was in the range 532–683 mg ha−1, showing the following distribution by plant tissues: well-developed leaves (171 mg ha−1) > twigs (160 mg ha−1) > bark (159 mg ha−1) > bole wood (145 mg ha−1) > fine branches (25 mg ha−1) > thick branches (24 mg ha−1) > newly sprouted leaves (20 mg ha−1). The total Hg deposition fluxes through litterfall were 15.4 and 11.7 μg m−2 yr−1 for the two years studied, with the greatest contribution coming from birch leaves (73 %). In the soil profile, the pool of Hg in the mineral soil (37.0 mg m−2) was an order of magnitude higher than in the organic horizons (1.0 mg m−2), mostly conditioned by parameters such as soil bulk density and thickness, total C and N contents and the presence of certain Al compounds.

Long-term spatiotemporal dynamics in a mountain birch (Betula pubescens ssp. czerepanovii) forest in south-east Norway.

Mountain birch forest covers large areas in Eurasia, and their ecological resilience provides important ecosystem services to human societies. This study describes long-term stand dynamics based on permanent plots in the upper mountain birch belt in SE Norway. We also present forest line changes over a period of 70 years. Inventories were conducted in 1931, 1953, and 2007. Overall, there were small changes from 1931 up to 1953 followed by a marked increase in biomass and dominant height of mountain birch throughout the period from 1953 to 2007. In addition, the biomass of spruce (Picea abies) and the number of plots with spruce present doubled. The high mortality rate of larger birch stems and large recruitment by sprouting since the 1960s reveal recurrent rejuvenation events after the earlier outbreak of the autumnal moth (Epirrita autumnata). Our results demonstrate both a high stem turnover in mountain birch and a great ability to recover after disturbances. This trend is interpreted as regrowth after a moth attack, but also long-term and time-lagged responses due to slightly improved growth conditions. An advance of the mountain birch forest line by 0.71 m year-1 from 1937 to 2007 was documented, resulting in a total reduction of the alpine area by 12%. Most of the changes in the forest line seem to have taken place after 1960. Regarding silviculture methods in mountain birch, a dimension cutting of larger birch trees with a cutting interval of c. 60 years seems to be a sustainable alternative for mimicking natural processes.

Partly decoupled tree-ring width and leaf phenology response to 20th century temperature change in Sweden

The recent warming trend, and associated shifts in growing season length, challenge the principle of uniformitarianism, i.e., that current relations are persistent over time, and complicates the uncritical inferences of past climate from tree-ring data. Here we conduct a comparison between tree-ring width chronologies of Pinus sylvestris L. (Scots pine), Picea abies (L.) Karst. (Norway spruce) and Betula pubescens Ehrh. (Downy birch) and phenological observations (budburst and leaf senescence) of Fagus sylvatica L. (European beech), Quercus robur L. (European oak), Betula sp. (Birch), Norway spruce and Scots pine) in Sweden to assess to what extent the tree-ring width–temperature relationship and the timing of phenological phases are affected by increased temperature. Daily meteorological observations confirm a prolongation of the thermal growing season, most consistently observed as an earlier onset of around 1–2 weeks since the beginning of the 20th century. Observations of budburst closely mimic this pattern, with budburst of the deciduous trees occurring 1–2.5 weeks earlier. In contrast to the changes seen in phenology and observational temperature data, the tree-ring width–temperature relationships remain surprisingly stable throughout the 20th century. Norway spruce, Scots pine and Downy birch all show consistently significant correlations with at least one 30 day-long window of temperature starting in late June–early July season. Norway spruce displays the largest degree of stability, with a consistent 60 day-long temperature window with significant correlation starting around Julian calendar day 150. Thus, our results suggest that the principle of uniformitarianism is not violated during the period covered by modern meteorological observations. Further research is needed to determine at what thresholds the temperature sensitivity of these species may alter or deteriorate as a consequence of the ongoing climate change.

Litterfall dynamics in Scots pine (Pinus sylvestris), Norway spruce (Picea abies) and birch (Betula) stands in Estonia

Canopy litterfall represents an essential aboveground flux in every forest ecosystem, affecting soil carbon and nutrient dynamics as well as soil fertility. However, despite the important role of the canopy litter flux in ecosysteḿs functioning and carbon sequestration, litterfall dynamics is still poorly studied in hemiboreal forests. The main aim of the current study was to estimate average annual litter fluxes in Scots pine, Norway spruce and birch (Betula pendula and Betula pubescens) stands, as well as to compile regional litter models for estimating the annual litter flux. The annual litter flux from a total of 33 pine, 15 spruce and 21 birch stands, with 85, 43 and 53 datapoints, respectively, was included in the study.Although the annual litter flux depended on site quality index and stand age, no significant relationship was established between stand basal area and litter flux. Average annual canopy litterfall was similar for the studied tree species, being 3.24 ± 0.14 for pine, 3.62 ± 0.16 for spruce and 3.22 ± 0.07 t ha−1 yr−1 for birch across the stands of different ages. For all studied tree species, the relative proportion of needles or leaves in the total annual litter flux declined with stand age, due to the increased share of twigs and other fractions in the litter of older stands. The developed models of the litter flux allow to estimate the annual litter production of the canopy for the studied tree species on the basis of site quality index and stand age.

Partitioning of Space Among Trees in an Old-Growth Spruce Forest in Subarctic Fennoscandia

The distribution of space among forest trees is linked to the availability of resources, among-tree competition, and hence forest dynamics. We studied partitioning of horizontal space among trees and related spatial structures in an old-growth Picea abies (L.) Karst -dominated forest in northeastern subarctic Fennoscandia, where Betula pubescens (Ehrh.) is an important co-dominant. Specifically, we asked (1) how does growing space occupied by trees vary by tree species and size in an old-growth forest with open canopy structure, and (2) at what scales does the variation in tree growing space occur? We mapped an 8.8 ha forest plot with 4,884 live trees. We used Voronoi polygons to quantify the horizontal space potentially available to each tree. We modeled the Voronoi polygon area as a function of tree size and species by using generalized additive models (GAM). We used i-to-any L-functions to study the scale-dependence of tree densities around focal trees, and mark correlation functions to study the relative sizes of trees close to each other. The GAM models showed that tree growing space increased non-linearly with tree size before saturating, and that overall growing space was larger for B. pubescens than for P. abies. Mean space occupied by trees roughly doubled from the smallest diameter class (0–5 cm) to the largest (>25 cm), from 13.7 to 26.7 m2. Depending on diameter class, shade-intolerant B. pubescens occupied on average 5–10 m2 more space than shade-tolerant P. abies. Trees close to each other were smaller than average. Size- and species-dependent differences in local tree densities accumulated mostly at the scale of a few meters but showed also broader-scale variation possibly related to edaphic variation within the study plot. The tree species- and size-related variation in the trees’ growing space suggests that among-tree competition, together with clustering of trees, shape the spatial assembly of the forest.

Limited decadal growth of mountain birch saplings has minor impact on surrounding tundra vegetation.

Temperatures over the Arctic region are increasing at three times the rate of the global average. Consequently, Arctic vegetation is changing and trees are encroaching into the tundra. In this study, we examine the establishment and growth of mountain birch (Betula pubescens ssp. tortuosa), which forms the treeline in subarctic Europe, and its impact on community composition across the treeline ecotone nearby Abisko, Sweden. Birch advancement along elevational gradients was studied by comparing data collected in 2016 with data collected 10 and 15 years previously. Species identity, cover, and phylogenetic relatedness were used to assess the impact of birch encroachment on community composition. Our results show that birch occurrence above the treeline did not affect plant community composition, probably owing to the observed lack of significant growth due to herbivore browsing, nitrogen limitation, or a reduction in snow cover. Independent of birch performance, the tundra community structure shifted toward a novel community dissimilar from the forest plant community found below the treeline. Taken together, our findings are explained by species‐specific responses to climate change, rather than by a linear forest advance. Future treeline advancements are likely more restricted than previously expected.

Plant-Soil-Climate Interaction in Observed and Simulated Tree-Radial Growth Dynamics of Downy Birch in Permafrost.

Climate change projections forecast most significant impacts on high-latitude forest ecosystems. Particularly, climate warming in boreal regions should increase fire severity and shorten its return interval. These processes can change the dynamics of boreal forests as younger stands become more dominating with a shift from gymnosperm to angiosperm. However, despite angiosperm’s phenological and physiological traits have a high potential for ecophysiological and dendroclimatological studies in Siberia, they have been rarely investigated due to their short-term lifespan in comparison with gymnosperm. Modeling tree growth is a common way to understand tree growth responses to environmental changes since it allows using available experiment or field data to interpret observed climate–growth relationships based on the biological principles. In our study, we applied the process-based Vaganov–Shashkin (VS) model of tree-ring growth via a parameterization approach VS-oscilloscope for the first time to an angiosperm tree species (Betula pubescens Ehrh.) from continuous permafrost terrain to understand its tree-radial growth dynamic. The parameterization of the VS model provided highly significant positive correlations (p < 0.05) between the simulated growth curve and initial tree-ring chronologies for the period 1971–2011 and displayed the average duration of the growing season and intra-seasonal key limiting factors for xylem formation. Modeled result can be valid at the regional scale for remote birch stands, whereas, justification of the local non-climatic input data of the model provided precise site-specific tree growth dynamic and their substantiated responses to driving factors.

Soil-tree-atmosphere CH4 flux dynamics of boreal birch and spruce trees during spring leaf-out

AimsStudies on tree CH4 exchange in boreal forests regarding seasonality and role of tree canopies are rare. We aimed to quantify the contribution of boreal trees to the forest CH4 budget during spring leaf-out and to reveal the role of microbes in the CH4 exchange.MethodsMethane fluxes of downy birch and Norway spruce (Betula pubescens and Picea abies) growing on fen and upland sites were measured together with soil CH4 flux, environmental variables and microbial abundances involved in the CH4 cycle. Tree CH4 fluxes were studied from three stem heights and from shoots.ResultsThe trees emitted CH4 with higher stem emissions detected from birch and higher shoot emissions from spruce. The stem CH4 emissions from birches at the fen were high (mean 45 µg m−2 h−1), decreasing with stem height. Their dynamics followed soil temperature, suggesting the emitted CH4 originated from methanogenic activity, manifested in high mcrA gene copy numbers, in the peat soil. Methanogens were below the quantification limit in the tree tissues. Upscaled tree CH4 emissions accounted for 22% of the total CH4 emissions at the fen.ConclusionsThe variation in stem CH4 flux between the trees and habitats is high, and the emissions from high-emitting birches increase as the spring proceeds. The lack of detection of methanogens or methanotrophs in the aboveground plant tissues suggests that these microbes did not have a significant role in the observed tree-derived fluxes. The stem-emitted CH4 from birches at the fen is presumably produced microbially in the soil.