Search

Herbivore effects on leaf litter can have a strong impact on ecosystem nutrient cycling. Although such effects are well described for insect herbivory, research on the impacts of browsing by mammalian herbivores on leaf litter dynamics and nutrient cycling has been more limited, particularly at the level of the individual plant. Clipping treatments (66% shoot removal twice, plus unclipped) were applied to analyse the effect of browsing on the phenology (start date and pattern of leaf shedding) and leaf litter quality (nitrogen (N), soluble sugars, starch and total non-structural carbohydrate concentrations, plus C : N ratios) of Betula pubescens Ehrh. and Quercus petraea [Matt.] Liebl. saplings. Clipping decreased leaf litter biomass and delayed leaf senescence and shedding, but did not change the phenological timing of litterfall between senescence and shedding. The quality of leaf litter of both species was increased by simulated browsing, through an increase in N and carbohydrate concentrations (mainly soluble sugars) and a decreased C : N ratio. This is the first evidence we are aware of that browsing may cause changes in leaf shedding phenology, delaying the process without altering its pattern. Our results also indicate that simulated browsing increases the quality of leaf litter. However, the potential positive effect of browsing on N cycling through litter quality may be offset by its negative impact on the amount of N shed per tree.

Phenology ranks among the best ecosystem processes for fingerprinting climate change since temperature explains a high percentage of the interannual or spatial variation in phenological onset dates. However, roles of other environmental variables, such as foliar nutrient concentrations, are far from adequately understood. This observational study examined the effects of air temperature and 11 nutrients on spring phenology of Betula pendula Roth (birch) along an urban-rural gradient in Munich, Germany, during the years 2010/2011. Moreover, the influence of temperature, nutrients, and air pollutants (NO2 and O3) on the amounts of pollen and catkin biomass in 2010 was evaluated. In addition to the influence of higher temperatures advancing phenological onset dates, higher foliar concentrations of potassium, boron, zinc, and calcium were statistically significantly linked to earlier onset dates. Since flushing of leaves is a turgor-driven process and all the influential nutrients are involved in cell extension, membrane function, and stability, there might be a reasonable physiological interpretation of the observed association. The amounts of pollen were negatively correlated with temperature, atmospheric NO2, and foliar iron concentration, suggesting that these variables restrict pollen production. The results of this study suggested an influence of nutritional status on both phenology and pollen production. The interaction of urbanization and climate change should be considered in the assessment of the impact of global warming on ecosystems and human health.

Abstract: An investigation was conducted in a 2.55 hm2 plot of Pinus koraiensis-dominated broad-leaved mixed forest to study the microsite characteristics of pit and mound formed by 42 treefalls and the status of vegetation regeneration on the microsites. The soil water content, soil temperature, relative air humidity, and photosynthetically active radiation (PAR) on five microsites (mound top, mound face, pit wall, pit bottom, and intact forest floor) were measured. Among the five mirosites, mound top had the highest PAR (527.9 micromol.m-2.s-1 ) while intact forest floor had the lowest one (58.7 micromol.m-2.s-), mound top had the highest soil temperature (16.0 degrees C) but pit bottom had the lowest one (13.3 degrees C), pit bottom had the highest soil water content (34.6%) but mound face had the lowest one (0.5%), and intact forest floor had the highest relative air humidity (75.9%) but mound top had the lowest one (68.0%). The frequency of forming pit/ mound complex by the tree species was decreased in the order of Pinus koraiensis (42. 9%) >Picea asperata (31.0%) > Betula platyphylla (16.7%) > Abies fabri (7. 1%) > Prunus padus (2.4%). Among the 42 treefalls, two-thirds of them were in northwest direction. The treefalls volume had significant positive correlations with pit depth, pit length, mound height, and mound width, but negative correlation with mound thickness. The treefall mean diameter at breast height had significant positive correlations with pit width (r=0.328, P=0.017) and pit length (r=0.527, P= 0). The tree species richness at the microsites decreased in the order of intact forest floor > pit > mound, and the tree species coverage was in the sequence of intact forest floor > pit > mound.

The effects of slightly elevated temperature (+0.8 °C), ozone (O3) concentration (1.3 × ambient O3 concentration) and their combination on over-wintering buds of Betula pendula Roth were studied after two growing seasons of exposure in the field. Carbohydrate concentrations, freezing stress resistance (FSR), bud dry weight to fresh weight ratio, and transcript levels of cytochrome oxidase (COX), alternative oxidase (AOX) and dehydrin (LTI36) genes were studied in two clones (clones 12 and 25) in December. Elevated temperature increased the bud dry weight to fresh weight ratio and the ratio of raffinose family oligosaccharides to sucrose and the transcript levels of the dehydrin (LTI36) gene (in clone 12 only), but did not alter the FSR of the buds. Genotype-specific alterations in carbohydrate metabolism were found in the buds grown under elevated O3. The treatments did not significantly affect the transcript level of the COX or AOX genes. No clear pattern of an interactive effect between elevated temperature and O3 concentration was found. According to these data, the increase in autumnal temperatures and slightly increasing O3 concentrations do not increase the risk for freeze-induced damage in winter in silver birch buds, although some alterations in bud physiology occur.

1 m x 1 m fixed quadrats were parallelly arranged with a space of 2 m in each of six forest gaps in Pinus koraiensis-dominated broadleaved mixed forest, taking the gap center as the starting point and along east-west and south-north directions. In each quadrat, the coverage and abundance of herbaceous plants at different height levels were investigated by estimation method in June and September 2011, and the matrix characteristics within the quadrats were recorded. Canopy analyzer was used to take fish-eye photos in the selected overcast days in each month from June to September, 2011, and the relative light intensity was calculated by using Gap Light Analyzer 2.0 software. The differences in the relative light intensity and herbaceous plants coverage and richness between different gaps as well as the correlations between the coverage of each species and the direct light, diffuse light, and matrix were analyzed. The results showed that in opening areas and under canopy, the relative light intensity in large gaps was higher than that in small gaps, and the variation ranges of diffuse light and direct light from gap center to gap edge were bigger in large gaps than in small gaps. The direct light reaching at the ground both in large gaps and in small gaps was higher in the north than in the south direction. In the Z1, Z2, Z3, and Z4 zones, both the coverage and the richness of herbaceous plants were larger in large gaps than in small gaps, and the differences of species richness between large and small gaps reached significant level. The coverage of the majority of the herbaceous plants had significant correlations with diffuse light and matrix, and only the coverage of a few herbaceous plants was correlated with direct light.

Climate change has the potential to influence the persistence of ecological communities by altering their stability properties. One of the major drivers of community stability is species diversity, which is itself expected to be altered by climate change in many systems. The extent to which climatic effects on community stability may be buffered by the influence of species interactions on diversity is, however, poorly understood because of a paucity of studies incorporating interactions between abiotic and biotic factors. Here, I report results of a 10-year field experiment, the past 7 years of which have focused on effects of ongoing warming and herbivore removal on diversity and stability within the plant community, where competitive species interactions are mediated by exploitation through herbivory. Across the entire plant community, stability increased with diversity, but both stability and diversity were reduced by herbivore removal, warming and their interaction. Within the most species-rich functional group in the community, forbs, warming reduced species diversity, and both warming and herbivore removal reduced the strength of the relationship between diversity and stability. Species interactions, such as exploitation, may thus buffer communities against destabilizing influences of climate change, and intact populations of large herbivores, in particular, may prove important in maintaining and promoting plant community diversity and stability in a changing climate.

Concentrations of polychlorinated biphenyls (PCBs) were measured in the new-year growth of dwarf birch (Betula glandulosa) before (2001-2002), during (2003-2004), and for six years after (2005-2010) the screening and containerization of PCB-contaminated soils (>50 μg/g PCBs) at a remote Arctic radar site. During the remediation activities, ambient air PCB concentrations were measured using active air samplers for comparison to the passive samplers (dwarf birch). PCB concentrations measured by the active samplers reached a maximum of 0.037 μg/m(3) which was below the project criteria of 0.15 μg/m(3) indicating minimal source emissions. During the same time period, PCB concentrations in the dwarf birch (passive samplers) showed significant increases of 2-14 fold compared to the baseline data from previous years. The birch data also showed significant changes between monitoring events within the 2003 and 2004 sampling seasons (June to September) and decreases when ambient air concentrations were low, indicating the sensitivity of new-year growth to reflect net accumulation and ambient conditions at a temporal scale of approximately two weeks. The dwarf birch PCB concentrations remained elevated compared to baseline levels for two years after the remediation was completed. In the third year following remediation, concentrations decreased to below baseline levels reflecting the overall remediation and source removal at the site. Spatial variations observed in dwarf birch PCB concentrations are likely due to the influence of wind direction on contaminant dispersal and deposition., (Crown Copyright © 2013. Published by Elsevier B.V. All rights reserved.)

Although trees in polluted areas often exhibit modified growth habits, the immediate causes of changes in crown architecture and their consequences for persistence of plant populations in disturbed habitats are not well understood. We compared individuals of mountain birch, Betula pubescens ssp. czerepanovii, growing in severely disturbed habitats (industrial barrens) surrounding a nickel-copper smelter in north-western Russia, with birches growing in unpolluted habitats. They were found to have shorter heights, a shrubby growth habit, lower depth/width and surface/foliar mass ratios of the crown, higher numbers of dead branches and twisted trunks and higher branching resulting from increased numbers of long shoots and more densely spaced buds than individuals in unpolluted forests. The increased production of long shoots was enabled by their formation not only from the axillary buds of previous-year long shoots but also from the apical buds of short shoots. These latter long shoots develop in the inner part of the crown, thus increasing the crown density. Additionally, birches from industrial barrens better compensated for mechanical damage, such as trunk/shoot removal, compared to birches from unpolluted forest and mountain tundra habitats, presumably due to the larger number of buds formed annually. The specific crown architecture of these birches can be explained by the direct effects of pollution combined with changes in microclimate due to pollution-induced forest decline. The seed progenies of birches from an industrial barren reared in a benign environment produced higher numbers of long shoots than seedlings from other habitats, suggesting that adaptive changes in crown architecture are partially shaped by the selection imposed by long-term pollution impacts. Nearly spherical and compact crowns minimise the impacts of unfavourable environmental conditions on trees and are therefore adaptive. We concluded that the development of specific crown architecture allows mountain birch to dominate in habitats that are severely disturbed by pollution., (Copyright © 2012 Elsevier B.V. All rights reserved.)

Premise of the Study: Branch growth and its spatial arrangement determine crown architecture, leaf display, and, thus, the productivity of trees. Branch axes elongate by the sequential production of shoots with differing morphology and function, such as short shoots and long shoots. This study investigated ontogenetic changes in axis growth in Betula maximowicziana and quantified the role of axis reversal between the short-shoot and long-shoot habits, particularly reversal from the short-shoot to the long-shoot habit., Methods: From 8 trees with varying levels of growth vigor, 716 branch axes forming the basic crown architecture were sampled. Past growth of the branch axes was reconstructed from leaf and bud scale scars and compared between slow-growing and vigorously growing trees., Key Results: Branch axes reversed more frequently between the long- and short-shoot habits in slow-growing trees than in vigorously growing trees. Short-shoot-origin axes that reversed to the long-shoot habit lived for longer periods and grew larger than axes that remained in the short-shoot habit. Short-shoot-origin axes reversed as they grew away from branch apices, typically >6 yr after they had originated., Conclusions: Reversal of short-shoot-origin axes to the long-shoot habit is an endogenous growth process of trees with reduced vigor. Like epicormic branching, the reversal may contribute to the maintenance of productivity of large old trees by prolonging axis longevity and filling the inner part of the crown. This study presents an ontogenetic change in branch growth, which broadens our perspectives on the growth and survival of long-living trees.

By the method of space-for-time Substitution, and taking the matured (>200 years old) and over-matured (>200 years old) primary broadleaved-Pinus koraiensis forests and, their secondary forests at different succession stages (20-, 30-, 50-, 80-, and 100 years old Betula platphylla forests) in Changbai Mountains of Northeast China as test objects, this paper studied the temporal variations of soil organic carbon, soil microbial biomass, and soil enzyme activities during the secondary succession of primary broadleaved-Pinus koraiensis forests in the Mountains. Under the 20- and 80 years old B. platphylla forests, the soil organic carbon content in humus layer was the highest (154.8 and 154.3 g.kg-1, respectively); while under the matured and over-matured primary broad-leaved-Pinus koraiensis forests, this organic carbon content was relatively low, being 141. 8 and 133. 4 g.kg , respectively. The soil microbial biomass carbon and microbial quotient and the activities of soil cellulase, peroxidase, acid phosphatase, and cellobiase under the 50- and 80 years old B. platphylla forests were the highest, but the activity of soil polyphenol oxidase was the lowest, which revealed that under middle-aged and matured B. platphylla forests, soil organic carbon had a faster turnover rate, and was probably in a stronger accumulation phase. Statistical analysis showed that the soil microbial biomass carbon had significant positive correlations with the soil organic carbon, total nitrogen, and available phosphorus (r = 0.943, 0. 963, and 0.953, respectively;

Taking the 5 hm2 sampling plot in the natural secondary poplar-birch forest in Changbai Mountains as test object, and based on the two census data in 2005 and 2010, an analysis was made on the main tree species composition and quantity, size class distribution of dead individuals, and regeneration characteristics of the main tree species in different habitat types of the plot in 2005-2010. In the five years, the species number of the individuals with DBH> or = 1 cm increased from 46 to 47, among which, 3 species were newly appeared, and 2 species were disappeared. The number of the individuals changed from 16509 to 15027, among which, 2150 individuals died, accounting for 13% of the whole individuals in 2005, and 668 individuals were newly increased. The basal area of the trees increased from 28.79 m2.m-2 to 30.55 m2.m-2, with that of 41 species increased while that of 6 species decreased. The decrease of the basal area of Betula platyphylla and Populus davidiana accounted for 72.3% of the total decrease. Small individuals had higher mortality, as compared with large ones, and the mortality of the individuals with DBH<5 cm occupied 65% of the total. B. platyphylla and P. davidiana contributed most in the dead individuals with large DBH. No difference was observed in the tree mortality among different habitat types, but the mortality of the individuals with different size classes showed greater variation.

To contribute to a better understanding of the regeneration strategy of Betula albosinensis forests and the likely reasons behind either the successful recovery or failure after strip clearcutting, we compared the population structures and spatial patterns of B. albosinensis in eight B. albosinensis stands in Qinling Mountains, China. Four cut and four uncut stands were selected, and each sampled using a single large plot (0.25 ha). Results indicated that, on the one hand, B. albosinensis recruitment was scarce (average of 48 stems ha(-1)) in the uncut stands, relative to the mature population (average of 259 stems ha(-1)), suggesting a failure of recruitment. On the other hand, the subsequent regeneration approximately 50 years after the strip clearcutting showed that the density of the target species seedlings and saplings has increased significantly, and the current average density of seedlings and saplings was 156 stems ha(-1). The clumped spatial pattern of B. albosinensis suggested that their regeneration was highly dependent on canopy disturbance. However, recruitment remained poor in the uncut stands because most gaps were small in scale. The successful regeneration of sunlight-loving B. albosinensis after strip clearcutting was attributed to the exposed land and availability of more sunlight. Bamboo density did not influence B. albosinensis recruitment in the uncut stands. However, stand regeneration was impeded after strip clearcutting; thus, removing bamboo is essential in improving the competitive status of B. albosinensis at the later stage of forest regeneration after clearcutting. The moderate severity of disturbance resulting from strip clearcutting reversed the degeneration trend of primary B. albosinensis stands. This outcome can help strike a balance between forest conservation and the demand for wood products by releasing space and exposing the forested land for recruitment. Life history traits and spatiotemporal disturbance magnitude are important factors to consider in implementing effective B. albosinensis regeneration strategies.

Phytostabilization aims to reduce environmental and health risks arising from contaminated soil. To be economically attractive, plants used for phytostabilization should produce valuable biomass. This study investigated the biomass production and metal allocation to foliage and wood of willow (Salix viminalis L.), poplar (Populus monviso), birch (Betula pendula), and oak (Quercus robur) on five different soils contaminated with trace elements (TE), with varying high concentrations of Cu, Zn, Cd, and Pb as well as an uncontaminated control soil. In the treatment soils, the biomass was reduced in all species except oak. There was a significant negative correlation between biomass and foliar Cd and Zn concentrations, reaching up to 15 mg Cd kg(-1) and 2000 mg Zn kg(-1) in willow leaves. Lead was the only TE with higher wood than foliage concentrations. The highest Pb accumulation occurred in birch with up to 135 mg kg(-1) in wood and 78 mg kg(-1) in foliage. Birch could be suitable for phytostabilization of soils with high Cd and Zn but low Pb concentrations, while poplars and willows could be used to stabilise soils with high Cu and Pb and low Zn and Cd concentrations.

Immediate phenotypic variation and the lagged effect of evolutionary adaptation to climate change appear to be two key processes in tree responses to climate warming. This study examines these components in two types of growth models for predicting the 2010-2099 diameter growth change of four major boreal species Betula papyrifera, Pinus banksiana, Picea mariana, and Populus tremuloides along a broad latitudinal gradient in eastern Canada under future climate projections. Climate-growth response models for 34 stands over nine latitudes were calibrated and cross-validated. An adaptive response model (A-model), in which the climate-growth relationship varies over time, and a fixed response model (F-model), in which the relationship is constant over time, were constructed to predict future growth. For the former, we examined how future growth of stands in northern latitudes could be forecasted using growth-climate equations derived from stands currently growing in southern latitudes assuming that current climate in southern locations provide an analogue for future conditions in the north. For the latter, we tested if future growth of stands would be maximally predicted using the growth-climate equation obtained from the given local stand assuming a lagged response to climate due to genetic constraints. Both models predicted a large growth increase in northern stands due to more benign temperatures, whereas there was a minimal growth change in southern stands due to potentially warm-temperature induced drought-stress. The A-model demonstrates a changing environment whereas the F-model highlights a constant growth response to future warming. As time elapses we can predict a gradual transition between a response to climate associated with the current conditions (F-model) to a more adapted response to future climate (A-model). Our modeling approach provides a template to predict tree growth response to climate warming at mid-high latitudes of the Northern Hemisphere.

Based on the two successive years observation of the water content of ten representative shrub species in Maoershan Mountain region of Northeast China, this paper studied the dynamics of the water content of these shrub species during their growth period and related affecting factors, with the prediction models of the shrub water content established. For the ten shrub species, their minimal water content during growth period was higher than 100% , and most of the species had a water content higher than 200% within the period from the late phase of leaf-unfolding to early phase of leaf-falling. Euonymus verrucosus, Sorbaria sorbifolia, and Sambucus williamsii were incombustible in their whole growth period due to the extremely high water content, while Syringa reticulate, Philadelphus schrenkii, Euonymus verrucosus, Spiraea chamaedryfolia, Lonicera maackii, Lonicera ruprechtiana, and Rhamnus parvifolia were combustible only in the phases of budding and leaf-falling. Soil moisture content and daily maximum temperature had effects on the water content of most (7) of the ten shrubs, and canopy drought severity index affected the water content of 5 of the ten shrubs. The established 9 prediction models could explain more than 35% of the water content variance of the shrub species, with a mean MRE of 35.9% and a mean MRE of 13.4%.

Premise of the Study: Consequences of global climate change are detectable in the historically nitrogen- and phosphorus-limited Arctic tundra landscape and have implications for the terrestrial carbon cycle. Warmer temperatures and elevated soil nutrient availability associated with increased microbial activity may influence rates of photosynthesis and respiration. •, Methods: This study examined leaf-level gas exchange, cellular ultrastructure, and related leaf traits in two dominant tundra species, Betula nana, a woody shrub, and Eriophorum vaginatum, a tussock sedge, under a 3-yr-old treatment gradient of nitrogen (N) and phosphorus (P) fertilization in the North Slope of Alaska. •, Key Results: Respiration increased with N and P addition-the highest rates corresponding to the highest concentrations of leaf N in both species. The inhibition of respiration by light ("Kok effect") significantly reduced respiration rates in both species (P < 0.001), ranged from 12-63% (mean 34%), and generally decreased with fertilization for both species. However, in both species, observed rates of photosynthesis did not increase, and photosynthetic nitrogen use efficiency generally decreased under increasing fertilization. Chloroplast and mitochondrial size and density were highly sensitive to N and P fertilization (P < 0.001), though species interactions indicated divergent cellular organizational strategies. •, Conclusions: Results from this study demonstrate a species-specific decoupling of respiration and photosynthesis under N and P fertilization, implying an alteration of the carbon balance of the tundra ecosystem under future conditions.

Oak forests dominate much of the eastern USA, but their future is uncertain due to a number of threats and widespread failure of oak regeneration. A sudden loss of oaks (Quercus spp.) could be accompanied by major changes in forest nitrogen (N) cycles with important implications for plant nutrient uptake and tree species composition. In this study, we measured the changes in N use and growth rates of black birch trees (Betula lenta L.) following oak girdling at the Black Rock Forest in southeastern New York, USA. Data were collected from nine experimental plots composed of three treatments: 100% oaks girdled (OG), 50% oaks girdled (O50) and control (C). Foliar N concentration and foliar (15)N abundance increased significantly in the oak-girdled plots relative to the control, indicating that the loss of oaks significantly altered N cycling dynamics. As mineralization and nitrification rates increase following oak loss, black birch trees increase N absorption as indicated by higher foliar N content and increased growth rates. Foliar N concentration increased by 15.5% in the O50 and 30.6% in the OG plots relative to the control, while O50 and OG plots were enriched in (15)N by 1.08‰ and 3.33‰, respectively (P < 0.0001). A 641% increase in black birch growth rates in OG plots suggests that this species is able to respond to additional N availability and/or increased light availability. The loss of oaks and subsequent increase in black birch productivity may have a lasting impact on ecosystem form and function.

From January 2008 to January 2009, a field experiment was conducted to investigate the effects of simulated nitrogen (N) deposition (0, 5, 15, and 30 g N x m(-2) x a(-1)) on the soil enzyme activities in a Betula luminifera plantation in Rainy Area of West China. As compared with the control (0 g N x m(-2) x a(-1)), simulated N deposition stimulated the activities of soil hydrolases (beta-fructofuranosidase, cellulase, acid phosphatase, and urease) significantly, but depressed the activities of soil oxidases (polyphenol oxidase and peroxidase). These results suggested that the increased exogenous inorganic N could stimulate soil microbial activity and increase the demands of both B. luminifera and soil microbes for C and P, whereas the depress of soil polyphenol oxidase and peroxidase activities under N addition could inhibit the degradation of litter and promote its accumulation in soil, leading to the increase of soil C storage in the B. luminifera plantation ecosystem.

In the present experiment, the single and combined effects of elevated temperature and ozone (O(3)) on four silver birch genotypes (gt12, gt14, gt15 and gt25) were studied in an open-air field exposure design. Above- and below-ground biomass accumulation, stem growth and soil respiration were measured in 2008. In addition, a (13)C-labelling experiment was conducted with gt15 trees. After the second exposure season, elevated temperature increased silver birch above- and below-ground growth and soil respiration rates. However, some of these variables showed that the temperature effect was modified by tree genotype and prevailing O(3) level. For instance, in gt14 soil respiration was increased in elevated temperature alone (T) and in elevated O(3) and elevated temperature in combination (O(3) + T) treatments, but in other genotypes O(3) either partly (gt12) or totally nullified (gt25) temperature effects on soil respiration, or acted synergistically with temperature (gt15). Before leaf abscission, all genotypes had the largest leaf biomass in T and O(3) + T treatments, whereas at the end of the season temperature effects on leaf biomass depended on the prevailing O(3) level. Temperature increase thus delayed and O(3) accelerated leaf senescence, and in combination treatment O(3) reduced the temperature effect. Photosynthetic : non-photosynthetic tissue ratios (P : nP ratios) showed that elevated temperature increased foliage biomass relative to woody mass, particularly in gt14 and gt12, whereas O(3) and O(3) + T decreased it most clearly in gt25. O(3)-caused stem growth reductions were clearest in the fastest-growing gt14 and gt25, whereas mycorrhizal root growth and sporocarp production increased under O(3) in all genotypes. A labelling experiment showed that temperature increased tree total biomass and hence (13)C fixation in the foliage and roots and also label return was highest under elevated temperature. Ozone seemed to change tree (13)C allocation, as it decreased foliar (13)C excess amount, simultaneously increasing (13)C excess obtained from the soil. The present results suggest that warming has potential to increase silver birch growth and hence carbon (C) accumulation in tree biomass, but the final magnitude of this C sink strength is partly counteracted by temperature-induced increase in soil respiration rates and simultaneous O(3) stress. Silver birch populations' response to climate change will also largely depend on their genotype composition.

Soil temperature is proposed to affect the photosynthetic rate and carbon allocation in boreal trees through sink limitation. The aim of this study was to investigate the effect of temperature on CO(2) exchange, biomass partitioning and ectomycorrhizal (ECM) fungi of boreal tree species. We measured carbon allocation, above- and below-ground CO(2) exchange and the species composition of associated ECM fungi in the rhizosphere of Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies K.) and silver birch (Betula pendula Roth) seedlings grown in soil maintained at 7-12, 12-15 and 16-22 °C. We found increased root biomass and photosynthetic rate at higher soil temperatures, but simultaneously with photosynthesis rate, higher temperature generally increased soil respiration as well as shoot, and root and rhizosphere respiration. The net CO(2) exchange and seedling biomass did not increase significantly with increasing temperature due to a concomitant increase in carbon assimilation and respiration rates. The 2-month-long growth period in different soil temperatures did not alter the ECM fungi species composition and the below-ground carbon sink strength did not seem to be directly related to ECM biomass and species composition in any of the tree species. Ectomycorrhizal species composition and number of mycorrhiza did not explain the CO(2) exchange results at different temperatures.

Premise of the Study: In a warming climate, boreal trees may have adjusted their growth strategy (e.g., onset and coordination of growth among different organs such as stem, shoot, and foliage, within and among species) to cope with the extended growing seasons. A detailed investigation into growth of different organs during a growing season may help us assess the potential effects of climate change on tree growth in the boreal forest., Methods: The intra-annual growth of stem xylem, shoot tips, and foliage area of Pinus banksiana, Populus tremuloides, and Betula papyrifera was monitored in a boreal forest in Quebec, Canada during the growing season of 2007. Xylem formation was measured at weekly intervals, and shoot elongation and foliage expansion were measured three times per week from May to September. Growth indices for stem, shoot, and foliage were calculated and used to identify any climate-growth dependence., Key Results: The time periods required for stem growth, branch extension, and foliage expansion differed among species. Of the three species, P. banksiana had the earliest budburst (20 May) yet the latest completion date of the foliage growth (2 August); P. tremuloides had the latest budburst (27 May) yet the earliest completion date of the foliage growth (10 July). Air temperature positively affected shoot extension growth of all three species. Precipitation positively influenced stem growth of the two broadleaf species, whereas growing season temperature positively impacted stem growth of P. banksiana., Conclusion: The results show that both the timing of growth processes and environmental dependences differ among co-occurring species, thereby leading to different adaptive capability of these boreal tree species to climate change.

Background and Aims: Altitudinal timberlines are thought to move upward by global warming, a crucial topic in ecology. Tall tree species (the conifer Abies mariesii and the deciduous broad-leaved Betula ermanii) dominate the sub-alpine zone between 1600 and 2500 m a.s.l., the timberline, on Mount Norikura in central Japan. Dwarf pine Pinus pumila dominates above the timberline to near the summit (3026 m a.s.l.). This study evaluated how the timberline formed on Mount Norikura by examining altitudinal changes in stand structure and dynamics around the timberline., Methods: One hundred and twenty-five plots of 10 m × 10 m were established around the timberline (2350-2600 m a.s.l.). Trunk diameter growth rate during 6 years was examined for A. mariesii, B. ermanii and P. pumila. Mortality during this period and mechanical damage scars on the trunks and branches due to strong wind and snow were examined for A. mariesii only., Key Results: The density, maximum trunk height and diameter of A. mariesii in plots decreased with altitude. The maximum trunk height of B. ermanii decreased with altitude, but density and maximum trunk diameter did not decrease. In contrast, the density of P. pumila abruptly increased from around the timberline. A strong negative correlation was found between the densities of P. pumila and tall tree species, indicating their interspecific competition. Trunk diameter growth rates of A. mariesii and B. ermanii did not decrease with altitude, suggesting that these two tall tree species can grow at the timberline. The ratio of trees with mechanical damage scars increased with altitude for A. mariesii, a tendency more conspicuous for larger trees. The mortality of larger A. mariesii was also greater at higher altitude. Tall tree species may not increase their trunk height and survive around the timberline because of mechanical damage., Conclusions: This study suggests that the altitudinal location of the timberline is mainly affected by mechanical damage due to strong wind and snow rather than by growth limitation due to low temperature. Therefore, the timberline would not move upward even under global warming if these growth and mortality characteristics do not change for a long time.

Interactions of Betula pendula and Picea abies with dark septate endophytes of the Phialocephala fortinii-Acephala applanata species complex (PAC) were studied. PAC are ubiquitous fungal root symbionts of many woody plant species but their ecological role is largely unknown. Sterile birch and spruce seedlings in monoculture and mixed culture were exposed to four PAC strains, added either singularly or paired in all possible combinations at 18°C and 23°C. Plant and fungal biomass was determined after 4 months. The most significant factors were strain and host combination. One of the strains significantly reduced biomass gain of spruce but not of birch. Plant biomass was negatively correlated with total endophytic fungal biomass in half of the strain - plant combinations. Endophytic PAC biomass was four times higher in spruce (≈ 40 mg g(-1) drw) than in birch (≈ 10 mg g(-1) drw). Competition between strains was strain-dependent with some strains significantly reducing colonization density of other strains, and, thus, attenuating adverse effects of 'pathogenic' strains on plant growth in some strain - plant combinations. Biomass gain of spruce but not of birch was significantly reduced at higher temperature. In conclusion, host, fungal genotype, colonization density and presence of a competing PAC strain were the main determining factors for plant growth., (© 2011 Society for Applied Microbiology and Blackwell Publishing Ltd.)

Vegis has put forward the theory that the range of growth-promoting temperatures changes during the induction and the release of dormancy. We have tested the response of buds of Betula pubescens Ehrh. and B. pendula Roth. on temperature during the induction and release of dormancy. Betula seedlings were exposed to dormancy-inducing high-temperature and short-day conditions and subsequently to dormancy-releasing chilling conditions in darkness. To monitor the dormancy status of the seedlings, subsets of them were transferred to five forcing temperatures and their budburst was observed. The results show that the expression of dormancy was temperature dependent, so that the minimum temperature for 100% budburst rose during the induction and dropped during the release of dormancy. These responses may explain previous contradictions between experimental and modelling studies, but that needs to be verified with more extensive experiments, some of which are identified in this study. The results provide further evidence for the concept of gradual change in bud dormancy. They also suggest that global change studies modelling budburst phenology should address the changing expression of bud dormancy.

Recent molecular and physiological studies have demonstrated that ultraviolet-B radiation (UV-B) can affect some of the processes involved in leaf growth, but the phases of leaf growth affected have not been clearly delimited. We used functional growth analysis to assess the effects of UV-B radiation on the time course of leaf growth in seedlings of two birch species (Betula pendula and Betula pubescens). Our aim was to identify the phase(s) of leaf development affected by UV-B radiation. In a greenhouse study, 1-year-old birch seedlings were subjected to three daily doses of supplemental UV-B radiation treatments (UV-B⁺) and no UV-B radiation controls (UV-B⁻). Leaf growth measurements every 2 days were complemented by assessment of other functional traits over a 4-week period at the start of the growing season. Using fitted curves, we were able to determine that the rate of leaf expansion was slowed by the UV-B⁺ treatment in leaves of B. pendula because of a slower maximum leaf growth rate compared with plants under the UV-B⁻ controls, but that compensation toward the end of the period of expansion negated this difference when leaves reached their final size. UV-B⁺ had little effect on the rate of B. pubescens leaf growth despite a larger reduction in leaf final size due to UV-B⁺ than occurred in B. pendula leaves. In conclusion, effective regulation ameliorated the effects of UV-B radiation on leaf and seedling growth in B. pendula, whereas in B. pubescens, reductions in leaf final size under UV-B⁺ were consistent with a slightly reduced rate of height growth., (Copyright © Physiologia Plantarum 2011.)

In order to quantify the contribution of soil fauna to the decomposition of birch (Betula albosinensis) leaf litter in subalpine forests in western Sichuan of Southwest China during freeze-thaw season, a field experiment with different mesh sizes (0.02, 0.125, 1 and 3 mm) of litterbags was conducted in a representative birch-fir (Abies faxoniana) forest to investigate the mass loss rate of the birch leaf litter from 26 October, 2010 to 18 April, 2011, and the contributions of micro-, meso- and macro-fauna to the decomposition of the leaf litter. Over the freeze-thaw season, 11.8%, 13.2%, 15.4% and 19.5% of the mass loss were detected in the litterbags with 0.02, 0. 125, 1 and 3 mm mesh sizes, respectively. The total contribution of soil fauna to the litter decomposition accounted for 39.5% of the mass loss, and the taxa and individual relative density of the soil fauna in the litterbags had the similar variation trend with that of the mass loss rate. The contribution rate of soil fauna to the leaf litter mass loss showed the order of micro- < meso- < macro-fauna, with the highest contribution of micro-fauna (7.9%), meso-fauna (11.9%), and macro-fauna (22.7%) at the onset of freezing stage, deeply frozen stage, and thawing stage, respectively. The results demonstrated that soil fauna played an important role in the litter decomposition in subalpine forests of western Sichuan during freeze-thaw season.

Vessels of broad-leaved trees have been analyzed to study how trees deal with various environmental factors. Cambial injury, in particular, has been reported to induce the formation of narrower conduits. Yet, little or no effort has been devoted to the elaboration of vessel sampling strategies for retrospective injury detection based on vessel lumen size reduction. To fill this methodological gap, four wounded individuals each of grey alder (Alnus incana (L.) Moench) and downy birch (Betula pubescens Ehrh.) were harvested in an avalanche path. Earlywood vessel lumina were measured and compared for each tree between the injury ring built during the growing season following wounding and the control ring laid down the previous year. Measurements were performed along a 10 mm wide radial strip, located directly next to the injury. Specifically, this study aimed at (i) investigating the intra-annual duration and local extension of vessel narrowing close to the wound margin and (ii) identifying an adequate sample of earlywood vessels (number and intra-ring location of cells) attesting to cambial injury. Based on the results of this study, we recommend analyzing at least 30 vessels in each ring. Within the 10 mm wide segment of the injury ring, wound-induced reduction in vessel lumen size did not fade with increasing radial and tangential distances, but we nevertheless advise favoring early earlywood vessels located closest to the injury. These findings, derived from two species widespread across subarctic, mountainous, and temperate regions, will assist retrospective injury detection in Alnus, Betula, and other diffuse-porous species as well as future related research on hydraulic implications after wounding.

Pollen grains are one of the most important groups of atmospheric biological particles that originate allergic processes. Knowledge of intradiurnal variation of the atmospheric pollen may be useful for the treatment and prevention of pollen allergies. Intradiurnal fluctuation of hourly pollen counts in 24 h are related to the daily rhythm of anther opening, and modified by various interacting factors. Flowering and pollen production of individual species are influenced by genetic, phenological, ecological, meteorological and climatic factors. Estimation of the intradiurnal variability in the pollen count permits evaluation of the threat posed by allergens over a given area. Measurements performed in Szczecin over a period of 7 years (2006-2012) permitted analysis of hourly variation of the pollen count of birch (Betula) and ash (Fraxinus) in 24 h, and evaluation of the impact of weather conditions and the concentration of gas air pollutants on the intradiurnal patterns of both taxa. Aerobiological monitoring was conducted using a Hirst volumetric trap (Lanzoni VPPS 2000). Consecutive phases during the day were defined as 1, 5, 25, 50, 75, 95, 99% of annual total pollen. The analysis revealed that 50% of total daily pollen was noted at 14:00 for Betula and Fraxinus. The hourly distribution of birch pollen count skewed to the left and the majority of pollen of this taxon appears in the air in the first 12 hours of the day. However, for ash, the hourly distribution of pollen count skewed to the right. Statistically significant correlation was noted between the Betula and Fraxinus pollen concentration and the mean air temperature, relative humidity, wind speed, air pressure, total radiation and nitrogen oxides (NO(x)).

Densification of the shrub layer has been reported in many subarctic regions, raising questions about the implication for large herbivores and their resources. Shrubs can tolerate browsing and their level of tolerance could be affected by browsing and soils productivity, eventually modifying resource availability for the caribou. Our objective was to assess the compensatory growth potential of a subarctic shrub, Betula glandulosa Michx., in relation with caribou browsing and nutriment availability for the plants. We used a simulated browsing (0, 25 and 75% of available shoots) and nitrogen-fertilisation (0 and 10 g m(-2)) experiment to test two main hypotheses linking tolerance to resource availability, the Compensatory Continuum Hypothesis and the Growth Rate Hypothesis as well as the predictions from the Limiting Resource Model. We seek to explicitly integrate the relative browsing pressure in our predictions since the amount of tissues removed could affect the capacity of long-lived plants to compensate. Birches fully compensated for moderate browsing with an overall leaf biomass similar to unbrowsed birches but undercompensated under heavy browsing pressure. The main mechanism explaining compensation appears to be the conversion of short shoots into long shoots. The leaf area increased under heavy browsing pressure but only led to undercompensation. Fertilisation for two consecutive years did not influence the response of birch, thus we conclude that our results support the LRM hypothesis of equal tolerance under both high and low nitrogen availability. Our results highlight that the potential for compensatory growth in dwarf birch is surpassed under heavy browsing pressure independently of the fertilisation regime. In the context of the worldwide decline in caribou herds, the reduction in browsing pressure could act synergistically with global climate change to promote the current shrub expansion reported in subarctic regions.

Most manipulation experiments simulating global change in tundra were short-term or did not measure plant growth directly. Here, we assessed the growth of three shrubs (Cassiope tetragona, Empetrum hermaphroditum and Betula nana) at a subarctic heath in Abisko (Northern Sweden) after 22 years of warming (passive greenhouses), fertilisation (nutrients addition) and shading (hessian fabric), and compare this to observations from the first decade of treatment. We assessed the growth rate of current-year leaves and apical stem (primary growth) and cambial growth (secondary growth), and integrated growth rates with morphological measurements and species coverage. Primary- and total growth of Cassiope and Empetrum were unaffected by manipulations, whereas growth was substantially reduced under fertilisation and shading (but not warming) for Betula. Overall, shrub height and length tended to increase under fertilisation and warming, whereas branching increased mostly in shaded Cassiope. Morphological changes were coupled to increased secondary growth under fertilisation. The species coverage showed a remarkable increase in graminoids in fertilised plots. Shrub response to fertilisation was positive in the short-term but changed over time, likely because of an increased competition with graminoids. More erected postures and large, canopies (requiring enhanced secondary growth for stem reinforcement) likely compensated for the increased light competition in Empetrum and Cassiope but did not avoid growth reduction in the shade intolerant Betula. The impact of warming and shading on shrub growth was more conservative. The lack of growth enhancement under warming suggests the absence of long-term acclimation for processes limiting biomass production. The lack of negative effects of shading on Cassiope was linked to morphological changes increasing the photosynthetic surface. Overall, tundra shrubs showed developmental plasticity over the longer term. However, such plasticity was associated clearly with growth rate trends only in fertilised plots.

By using sampling plot method, an investigation was conducted on the regeneration characteristics of woody plant seedlings in five kinds of typical secondary forests (Pinus tabulaeformis, Quercus valiena var. acuteserrata, Betula albo-sinensis, Picea asperata, and Pinus armandii) in Qinling Mountains. There was an obvious species differentiation of woody plant seedlings and saplings in the forests. Except for Q. valiena var. acuteserrata and P. armandii forests, the similarity coefficient of the seedlings and saplings species in the forests was lower. The seedlings and saplings quantity, species richness index, Simpson dominance index, and evenness index were higher in P. tabulaeformis and Q. valiena var. acuteserrata forests, the lowest in B. albo-sinensis forest, and basically the same in P. asperata and P. armandii forests. The percentages of the seedlings and saplings in the five forests had significant differences (P < 0.05). Except in B. albo-sinensis forest where the percentage of the saplings was higher, the percentage of the seedlings in the other stands was larger, and in the order of P. asperata forest > P. tabulaeformis forest > Q. valiena var. acuteserrata forest > P. armandii forest, respectively. The sprouting percentage of the seedlings in different forests had significant difference (P < 0.05), and was in the sequence of P. armandii forest > P. asperata forest > B. albo-sinensis forest > Q. valiena var. acuteserrata forest > P. tabulaeformis forest. In Q. valiena var. acuteserrata and P. tabulaeformis forests, the percentage of tree seedlings was the highest, occupying 68% and 51.4% of the total number of woody seedlings, respectively, and their communities were in the medium succession period, with a stronger persistent regeneration capability; in P. asperata and P. armandii forests, the percentage of tree seedlings was 40% and 15%, respectively, and their communities were in the late succession period, with a rather poor regeneration capability; while in B. albo-sinensis forest, the seedlings were difficult to develop into saplings, and thus, its continuous persistent regeneration capability was lack.

Boron (B) is an essential micronutrient whose deficiency is common both in agriculture and in silviculture. Boron deficiency impairs the growth of plants and affects many metabolic processes like carbohydrate metabolism. Boron deficiency and also excess B may decrease the sink demand by decreasing the growth and sugar transport which may lead to the accumulation of carbohydrates and down-regulation of photosynthesis. In this study, we investigated the effects of B nutrition on the soluble and storage carbohydrate concentrations of summer leaves and autumn buds in a deciduous tree species, Betula pendula Roth. In addition, we investigated the changes in the pools of condensed tannins between summer and autumn harvests. One-year-old birch seedlings were fertilized with a complete nutrient solution containing three different levels of B: 0, 30 and 100% of the standard level for complete nutrient solution. Half of the seedlings were harvested after summer period and another half when leaves abscised. The highest B fertilization level (B100) caused an accumulation of starch and a decrease in the concentrations of hexoses (glucose and fructose) in summer leaves, whereas in the B0 seedlings, hexoses (mainly glucose) accumulated and starch decreased. These changes in carbohydrate concentrations might be related to the changes in the sink demand since the autumn growth was the smallest for the B100 seedlings and largest for the B30 seedlings that did not accumulate carbohydrates. The autumn buds of B30 seedlings contained the lowest levels of glucose, glycerol, raffinose and total polyols, which was probably due to the dilution effect of the deposition of other substances like phenols. Condensed tannins accumulated in high amounts in the birch stems during the hardening of seedlings and the largest accumulation was detected in the B30 treatment. Our results suggest that B nutrition of birch seedlings affects the carbohydrate and phenol metabolism and may play an important role in the hardening process of the seedlings.

This paper analyzed the spatial structural characteristics of natural Populus davidiana - Betula platyphylla secondary forest in a 4 hm2 plot of Mulan Paddock, based on the diameter distribution and the spatial structure parameters mingling degree, neighborhood comparison, and angle index. In the forest, the diameter distribution of the stands presented as an inverse 'J' curve, the average mingling degree was 0.4, with the individuals at weak and zero mingling degree reached 51.6%, and the average mingling degree of P. davidiana and B. platyphylla was 0.25 and 0.39, respectively. The neighborhood comparison based on the diameter at breast height (DBH) and tree height was almost the same, suggesting that the P. davidiana and B. platyphylla were in the transition state from subdominant to middle. The horizontal distribution pattern had a close relation to the minimum measured DBH, being clustered when the DBH was > or = 1 cm and < 6 cm, and random when the DBH was > or = 6 cm.

An investigation was conducted on the species composition and population diameter-class structure of a typical secondary Betula albo-sinensis forest in Xiaolongshan of west Qinling Mountains, and the spatial distribution pattern and interspecific correlations of the main populations were analyzed at multiple scales by the O-ring functions of single variable and double variables. In the test forest, B. albo-sinensis was obviously dominant, but from the analysis of DBH class distribution, the B. albo-sinensis seedlings were short of, and the natural regeneration was very poor. O the contrary, the regeneration of Abies fargesii and Populus davidianas was fine. B. albo-sinensis and Salix matsudana had a random distribution at almost all scales, while A. fargesii and P. davidianas were significantly clumped at small scale. B. albo-sinensis had positive correlations with A. fargesii and P. davidianas at medium scale, whereas S. matsudana had negative correlations with B. albo-sinensis, A. fargesii, and P. davidianas at small scale. No significant correlations were observed between other species. The findings suggested that the spatial distribution patterns of the tree species depended on their biological characteristics at small scale, but on the environmental heterogeneity at larger scales. In a period of future time, B. albo-sinensis would still be dominant, but from a long-term view, it was necessary to take some artificial measures to improve the regeneratio of B. albo-sinensis.

Background and Aims: The ability to simulate plant competition accurately is essential for plant functional type (PFT)-based models used in climate-change studies, yet gaps and uncertainties remain in our understanding of the details of the competition mechanisms and in ecosystem responses at a landscape level. This study examines secondary succession in a temperate deciduous forest in eastern China with the aim of determining if competition between tree types can be explained by differences in leaf ecophysiological traits and growth allometry, and whether ecophysiological traits and habitat spatial configurations among PFTs differentiate their responses to climate change., Methods: A temperate deciduous broadleaved forest in eastern China was studied, containing two major vegetation types dominated by Quercus liaotungensis (OAK) and by birch/poplar (Betula platyphylla and Populus davidiana; BIP), respectively. The Terrestrial Ecosystem Simulator (TESim) suite of models was used to examine carbon and water dynamics using parameters measured at the site, and the model was evaluated against long-term data collected at the site., Key Results: Simulations indicated that a higher assimilation rate for the BIP vegetation than OAK led to the former's dominance during early successional stages with relatively low competition. In middle/late succession with intensive competition for below-ground resources, BIP, with its lower drought tolerance/resistance and smaller allocation to leaves/roots, gave way to OAK. At landscape scale, predictions with increased temperature extrapolated from existing weather records resulted in increased average net primary productivity (NPP; +19 %), heterotrophic respiration (+23 %) and net ecosystem carbon balance (+17 %). The BIP vegetation in higher and cooler habitats showed 14 % greater sensitivity to increased temperature than the OAK at lower and warmer locations., Conclusions: Drought tolerance/resistance and morphology-related allocation strategy (i.e. more allocation to leaves/roots) played key roles in the competition between the vegetation types. The overall site-average impacts of increased temperature on NPP and carbon stored in plants were found to be positive, despite negative effects of increased respiration and soil water stress, with such impacts being more significant for BIP located in higher and cooler habitats.

With rising concentrations of both atmospheric carbon dioxide (CO(2)) and tropospheric ozone (O(3)), it is important to better understand the interacting effects of these two trace gases on plant physiology affecting land-atmosphere gas exchange. We investigated the effect of growth under elevated CO(2) and O(3), singly and in combination, on the primary short-term stomatal response to CO(2) concentration in paper birch at the Aspen FACE experiment. Leaves from trees grown in elevated CO(2) and/or O(3) exhibited weaker short-term responses of stomatal conductance to both an increase and a decrease in CO(2) concentration from current ambient level. The impairement of the stomatal CO(2) response by O(3) most likely developed progressively over the growing season as assessed by sap flux measurements. Our results suggest that expectations of plant water-savings and reduced stomatal air pollution uptake under rising atmospheric CO(2) may not hold for northern hardwood forests under concurrently rising tropospheric O(3)., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

By the methods of field survey and laboratory soaking extraction, an investigation was conducted on the accumulation amount, water-holding capacity, water-holding rate, and water-absorption rate of the litters under six main forests (Picea wilsonii forest, P. wilsonii - Betula platyphlla forest, Populus davidiana - B. platyphlla forest, Cotonester multiglorus - Rosa xanthina shrubs, Pinus tabulaeformis forest, and Larix principis-rupprechtii forest) in Xinglong Mountain of Gansu. The accumulation amount of the litters under the forests was 13.40-46.32 t hm(-2), and in the order of P. tabulaeformis forest > P. wilsonii - B. platyphlla forest > L. principis-rupprechtii forest > P. wilsonii forest > C. multiglorus-R. xanthina shrubs > P. davidiana - B. platyphlla forest. The litter storage of coniferous forests was greater than that of broadleaved forests, and the storage percentage of semi-decomposed litters was all higher than that of un-decomposed litters. The maximum water-holding rate of the litters was 185.5%-303.6%, being the highest for L. principis-rupprechtii forest and the lowest for P. tabulaeformis forest. The litters' water-holding capacity changed logarithmically with their soaking time. For coniferous forests, un-decomposed litters had a lower water-holding rate than semi-decomposed litters; whereas for broadleaved forests, it was in adverse. The maximum water-holding capacity of the litters varied from 3.94 mm to 8.59 mm, and was in the order of P. tabulaeformis forest > L. principis-rupprechtii forest > P. wilsonii - B. platyphlla forest > P. wilsonii forest > C. multiglorus - R. xanthina shrubs > P. davidiana - B. platyphlla forest. The litters' water-holding capacity also changed logarithmically with immersing time, and the half-decomposed litters had a larger water-holding capacity than un-decomposed litters. The water-absorption rate of the litters presented a power function with immersing time. Within the first one hour of immersed in water, the water-absorption rate of the litters declined linearly; after the first one hour, the litters' water-absorption rate became smaller, and changed slowly at different immersed stages. Semi-decomposed litters had a higher water-absorption rate than un-decomposed litters. The effective retaining amount (depth) of the litters was in the order of P. wilsonii - B. platyphlla forest (5.97 mm) > P. tabulaeformis forest (5.59 mm) > L. principis-rupprechtii forest (5.46 mm) >P. wilsonii forest (4.30 mm) > C. multiglorus - R. xanthina shrubs (3.03 mm)>P. davidiana - B. platyphlla forest (2.13 mm).

This study was conducted in the Swedish subArctic, near Abisko, in order to assess the direction and scale of possible vegetation changes in the alpine-birch forest ecotone. We have re-surveyed shrub, tree and vegetation data at 549 plots grouped into 61 clusters. The plots were originally surveyed in 1997 and re-surveyed in 2010. Our study is unique for the area as we have quantitatively estimated a 19% increase in tree biomass mainly within the existing birch forest. We also found significant increases in the cover of two vegetation types--"birch forest-heath with mosses" and "meadow with low herbs", while the cover of snowbed vegetation decreased significantly. The vegetation changes might be caused by climate, herbivory and past human impact but irrespective of the causes, the observed transition of the vegetation will have substantial effects on the mountain ecosystems.

Taking Betula ermanii forests distributed at the altitudes 1800-2050 m on the northern slope of Changbai Mountains as test objects, and using leaf carbon isotope content (813 C) as an indicator of B. ermanii water use efficiency (WUE), this paper studied the effects of altitudinal gradient on the WUE of B. ermanji forests in the area. With the increase of altitude, the soil volumetric water content (VMC) and the leaf mass per area (LMA) of B. ermanji increased significantly, while the leaf water content (LWC) and soil temperature were in adverse. There was a significant positive correlation between leaf delta13 C and altitude, with the increment of leaf delta13 C being 1.013 % per hundred x (100 m)(-1), and the leaf delta13C was positively correlated with soil VWC and LMA but negatively correlated with soil temperature and LWC. Temperature was not the sole limiting factor for the distribution of treeline in Changbai Mountains, whereas the physiological drought of B. ermanii during its growing season caused by the different water and heat conditions and their interactions along the altitudinal gradient could be the other limiting factors.

Shrubs and trees are expected to expand in the sub-Arctic due to global warming. Our study was conducted in Abisko, sub-arctic Sweden. We recorded the change in coverage of shrub and tree species over a 32- to 34-year period, in three 50 x 50 m plots; in the alpine-tree-line ecotone. The cover of shrubs and trees (<3.5 cm diameter at breast height) were estimated during 2009-2010 and compared with historical documentation from 1976 to 1977. Similarly, all tree stems (> or =3.5 cm) were noted and positions determined. There has been a substantial increase of cover of shrubs and trees, particularly dwarf birch (Betula nana), and mountain birch (Betula pubescens ssp. czerepanovii), and an establishment of aspen (Populus tremula). The other species willows (Salix spp.), juniper (Juniperus communis), and rowan (Sorbus aucuparia) revealed inconsistent changes among the plots. Although this study was unable to identify the causes for the change in shrubs and small trees, they are consistent with anticipated changes due to climate change and reduced herbivory.

One-year-old birch (Betula platyphylla) and larch (Larix olgensis) seedlings were respectively planted in pots with the soils taken from 35-year-old pure birch and larch plantations, and the seedlings growth, biomass increment, foliar nutrient content, and soil nutrient status were monitored, aimed to evaluate the fertility levels of the two soils and the possible interspecific interaction in mixed larch-birch forest. Birch soil had significantly higher contents of total N and available N than larch soil, while larch soil had significantly higher contents of total P, available P, and total K than birch soil (P < 0.05). In the first growth season, the height and collar diameter growth and the biomass accumulation of birch seedlings growing on birch soil were 69%, 52%, and 65% (P < 0.05) higher than those growing on larch soil, and the larch seedlings also had 12%, 8%, and 37% gains of the indices, respectively. The foliar N concentration of both larch and birch seedlings growing on birch soil was higher than that on larch soil, while the foliar P concentration was higher when the seedlings were growing on larch soil than on birch soil. The birch soil had higher content of available N because of the higher litterfall, while the larch soil had greater available P because of the higher P mobilizing effect. It was predicted that in mixed birch-larch forest, the complementary interaction of soil N and P could benefit the growth of the two tree species.

Rising temperature and tropospheric ozone (O(3)) concentrations are likely to affect carbon assimilation processes and thus the carbon sink strength of trees. In this study, we investigated the joint action of elevated ozone and temperature on silver birch (Betula pendula) and European aspen (Populus tremula) saplings in field conditions by combining free-air ozone exposure (1.2 × ambient) and infrared heaters (ambient +1.2&emsp14;°C). At leaf level measurements, elevated ozone decreased leaf net photosynthesis (P(n)), while the response to elevated temperature was dependent on leaf position within the foliage. This indicates that leaf position has to be taken into account when leaf level data are collected and applied. The ozone effect on P(n) was partly compensated for at elevated temperature, showing an interactive effect of the treatments. In addition, the ratio of photosynthesis to stomatal conductance (P(n)/g(s) ratio) was decreased by ozone, which suggests decreasing water use efficiency. At the plant level, the increasing leaf area at elevated temperature resulted in a considerable increase in photosynthesis and growth in both species.

Background and Aims: A meta-analysis of global change experiments in arctic tundra sites suggests that plant productivity and the cover of shrubs, grasses and dead plant material (i.e. litter) will increase and the cover of bryophytes will decrease in response to higher air temperatures. However, little is known about which effects these changes in vegetation structure will have on seedling recruitment of species and invasibility of arctic ecosystems., Methods: A field experiment was done in a bryophyte-dominated, species-rich subarctic heath by manipulating the cover of bryophytes and litter in a factorial design. Three phases of seedling recruitment (seedling emergence, summer seedling survival, first-year recruitment) of the grass Anthoxanthum alpinum and the shrub Betula nana were analysed after they were sown into the experimental plots., Key Results: Bryophyte and litter removal significantly increased seedling emergence of both species but the effects of manipulations of vegetation structure varied strongly for the later phases of recruitment. Summer survival and first-year recruitment were significantly higher in Anthoxanthum. Although bryophyte removal generally increased summer survival and recruitment, seedlings of Betula showed high mortality in early August on plots where bryophytes had been removed., Conclusions: Large species-specific variation and significant effects of experimental manipulations on seedling recruitment suggest that changes in vegetation structure as a consequence of global warming will affect the abundance of grasses and shrubs, the species composition and the susceptibility to invasion of subarctic heath vegetation.

Taking the 4 hm2 fixed sampling plot in the Beigou forest farm of Weichang County in Hebei Province as test object, and by adopting the parameters (point pattern distribution, mingling, and size differentiation), this paper analyzed the community structure and distribution pattern of a natural secondary forest in the farm. There were eleven populations in the arbor layer of the forest, among which, Populus davidiana and Betula platyphylla had the obvious advantage in population density and basal area, being the dominant and constructive species of the arbor layer. Spatially, these two species all presented cluster modes remarkably, and competed each other greatly. The main accompanying species Larix principis-rupprechti and Acer truncatum also presented cluster modes, but the density and volume were significantly lower than the two dominant species', not able to compete with the dominate species. Affected by the low mingling of dominant species, the average mingling of the whole stand was only 0.40, while the mingling of accompanying species generally presented moderate or high. The mean size differentiation of the whole stand was 0.49, and P. davidiana, B. platyphylla, L. principis-rupprechti, and Quercus mongolica were of dominance or sub-dominance in the spatial structural units, while the other accompanying species had no obvious dominance.

The role of common mycorrhizal networks (CMNs) in postfire boreal forest successional trajectories is unknown. We investigated this issue by sampling a 50-m by 40-m area of naturally regenerating black spruce (Picea mariana), trembling aspen (Populus tremuloides), and paper birch (Betula papyrifera) seedlings at various distances from alder (Alnus viridis subsp. crispa), a nitrogen-fixing shrub, 5 years after wildfire in an Alaskan interior boreal forest. Shoot biomasses and stem diameters of 4-year-old seedlings were recorded, and the fungal community associated with ectomycorrhizal (ECM) root tips from each seedling was profiled using molecular techniques. We found distinct assemblages of fungi associated with alder compared with those associated with the other tree species, making the formation of CMNs between them unlikely. However, among the spruce, aspen, and birch seedlings, there were many shared fungi (including members of the Pezoloma ericae [Hymenoscyphus ericae] species aggregate, Thelephora terrestris, and Russula spp.), raising the possibility that these regenerating seedlings may form interspecies CMNs. Distance between samples did not influence how similar ECM root tip-associated fungal communities were, and of the fungal groups identified, only one of them was more likely to be shared between seedlings that were closer together, suggesting that the majority of fungi surveyed did not have a clumped distribution across the small scale of this study. The presence of some fungal ribotypes was associated with larger or smaller seedlings, suggesting that these fungi may play a role in the promotion or inhibition of seedling growth. The fungal ribotypes associated with larger seedlings were different between spruce, aspen, and birch, suggesting differential impacts of some host-fungus combinations. One may speculate that wildfire-induced shifts in a given soil fungal community could result in variation in the growth response of different plant species after fire and a shift in regenerating vegetation.

Boron (B) deficiency is a common micronutrient deficiency that has been reported to affect the phenolic metabolism of plants. Thus, it may play a role in defense against herbivorous animals. However, the role of B in a plant's resistance to herbivores has not received any particular attention from researchers. In this study, we tested the effects of B nutrition 1) on the biochemical and mechanical defenses of birches and the growth of seedlings, and 2) the resistance of seedlings to larvae of the autumnal moth, Epirrita autumnata. Boron fertilization improved the resistance of birch, which was shown as reduced pupal weight of the herbivore. However, B fertilized trees suffered from heavier defoliation than unfertilized ones due to compensation feeding of larvae. The growth of the seedlings was diminished, and several biochemical changes occurred in leaves of herbivore seedlings, and B also played a role in these changes. Polyphenoloxidases (PPOs) and peroxidases (PODs) and their substrates, chlorogenic acids, were induced by herbivory in B fertilized seedlings but not in unfertilized seedlings. The lower pupal weights and increased consumption of the herbivores were probably linked to the plants' phenoloxidase-mediated production of reactive quinones, which decrease the nutritive value. Herbivory upon new stems led to an increase in the number of resin glands that provide defense against mammalian herbivores. Herbivory also had a substantially negative effect on B concentration in leaves of B fertilized seedlings. We postulate that B nutrition of trees may play a significant role in the induced defense of birches.

Late soil-thawing period is a critical stage connecting winter and growth season. The significant temperature fluctuation at this stage might have strong effects on soil ecological processes. In order to understand the soil biochemical processes at this stage in the subalpine/alpine forests of west Sichuan, soil samples were collected from the representative forests including primary fir forest, fir and birch mixed forest, and secondary fir forest in March 5-April 25, 2009, with the activities of soil invertase, urease, and phosphatase (neutral, acid and alkaline phosphatases) measured. In soil frozen period, the activities of the three enzymes in test forests still kept relatively higher. With the increase of soil temperature, the activities of hydrolases at the early stage of soil-thawing decreased rapidly after a sharp increase, except for neutral phosphatease. Thereafter, there was an increase in the activities of urease and phosphatase. Relative to soil mineral layer, soil organic layer had higher hydrolase activity in late soil-thawing period, and showed more obvious responses to the variation of soil temperature.

Soil particle size and land management practices are known to have considerable influence on carbon (C) storage in soils, but such information is lacking for silvopastoral systems in Spain. This study quantified the amounts of soil C stored at various depths to 100 cm under silvopastoral plots of radiata pine ( D. Don) and birch ( Roth) in comparison to treeless pasture in Galicia, Spain. Soils were fractionated into three size classes (<53, 53-250, and 250-2000 μm), and C stored in them and in the whole (nonfractionated) soil was determined. Overall, the C stock to 1 m ranged from 80.9 to 176.9 Mg ha in these soils. Up to 1 m depth, 78.82% of C was found in the 0- to 25-cm soil depth, with 12.9, 4.92, and 3.36% in the 25- to 50-, 50- to 75-, and 75- to 100-cm depths, respectively. Soils under birch at 0 to 25 cm stored more C in the 250- to 2000-μm size class as compared with those under radiata pine; at that depth, pasture had more C than pine silvopasture in the smaller soil fractions (<53 and 53-250 μm). In the 75- to 100-cm depth, there was significantly more storage of C in the 250- to 2000-μm fraction in both silvopastures as compared with the pasture. The higher storage of soil C in larger fraction size in lower soil depths of silvopasture suggests that planting of trees into traditional agricultural landscapes will promote longer-term storage of C in the soil., (American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America.)

By the methods of static chamber and gas chromatography, this paper studied the effects of fire disturbance on the seasonal dynamics and source/sink functions of CH4, CO2 and N2O emissions from Betula platyphylla-forested wetland as well as their relations with environmental factors in Xiaoxing' an Mountains of China. In growth season, slight fire disturbance on the wetland induced an increase of air temperature and ground surface temperature by 1.8-3.9 degrees C and a decrease of water table by 6.3 cm; while heavy fire disturbance led to an increase of air temperature and 0-40 cm soil temperature by 1.4-3.8 degrees C and a decrease of water table by 33.9 cm. Under slight or no fire disturbance, the CH4 was absorbed by the wetland soil in spring but emitted in summer and autumn; under heavy fire disturbance, the CH4 was absorbed in spring and summer but emitted in autumn. The CO2 flux had a seasonal variation of summer > spring = autumn under no fire disturbance, but of summer > autumn > spring under fire disturbance; and the N2O flux varied in the order of spring > summer > autumn under no fire disturbance, but of autumn > spring > summer under slight fire disturbance, and of summer > spring = autumn under heavy fire disturbance. At unburned site, the CO2 flux was significantly positively correlated with air temperature and ground surface temperature; at slightly burned site, the CO2 flux had significant positive correlations with air temperature, 5-10 cm soil temperature, and water table; at heavily burned sites, there was a significant positive correlation between CO2 flux and 5-40 cm soil temperature. Fire disturbance made the CH4 emission increased by 169.5% at lightly burned site or turned into weak CH4 sink at heavily burned site, and made the CO2 and N2O emissions and the global warming potential (GWP) at burned sites decreased by 21.2% -34.7%, 65.6% -95.8%, and 22.9% -36.6% respectively, compared with those at unburned site. Therefore, fire disturbance could decrease the greenhouse gases emission from Betula platyphylla-forested wetland, and planned firing could be properly implemented in wetland management.

A process-based ecosystem model was used to assess the impacts of changing climate on net photosynthesis and total stem wood growth in relation to water availability in two unmanaged Norway spruce (Picea abies) dominant stands with a mixture of Scots pine (Pinus sylvestris) and birch (Betula sp.). The mixed stands were grown over a 100-year rotation (2000-99) in southern and northern Finland with initial species shares of 50, 25 and 25% for Norway spruce, Scots pine and birch, respectively. In addition, pure Norway spruce, Scots pine and birch stands were used as a comparison to identify whether species' response is different in mixed and pure stands. Soil type and moisture conditions (moderate drought) were expected to be the same at the beginning of the simulations irrespective of site location. Regardless of tree species, both annual net canopy photosynthesis (P(nc)) and total stem wood growth (V(s)) were, on average, lower on the southern site under the changing climate compared with the current climate (difference increasing toward the end of the rotation); the opposite was the case for the northern site. Regarding the stand water budget, evapotranspiration (E(T)) was higher under the changing climate regardless of site location. Transpiration and evaporation from the canopy affected water depletion the most. Norway spruce and birch accounted for most of the water depletion in mixed stands on both sites regardless of climatic condition. The annual soil water deficit (W(d)) was higher on the southern site under the changing climate. On the northern site, the situation was the opposite. According to our results, the growth of pure Norway spruce stands in southern Finland could be even lower than the growth of Norway spruce in mixed stands under the changing climate. The opposite was found for pure Scots pine and birch stands due to lower water depletion. This indicates that in the future the management should be properly adapted to climate change in order to sustain the productivity of mixed stands dominated by Norway spruce.