Measuring and modelling plant area index in beech stands

For some beech (Fagus sylvatica L.) stands with different stand densities the plant area index (PAI) was measured by means of a Licor LAI-2000 plant canopy analyser. The stands are located on the slopes of a valley in south-west Germany and had been treated by different types of silvicultural management (heavy shelterwood felling, light shelterwood felling, control plot). The analyser was used (a) to investigate the light conditions on plots of the same thinning regime, (b) to quantify the differences between the different treatments and (c) to obtain absolute values of PAI for interdisciplinary research. PAI was measured at three different phenological stages (leafless, leaf-unfolding and fully leafed season in 2000) and was found to be about 5.2 for the fully developed canopy on the control plots, 3.2 on the light fellings and about 2.0 for the heavy fellings. In the leafless period PAI was between 1.1 (control) and 0.4 (heavy felling). Measurements made in summer 2000 and summer 2002 were compared, and showed an increase of PAI, especially on the thinned plots. Measurements of photosynthetically active radiation (PAR) above and below the canopy in combination with measured PAI were used to apply Beers Law of radiation extinction to calculate the extinction coefficient k for different sky conditions and for the different growing seasons on the control plots. The extinction coefficient k for the beech stands was found to be between 0.99 and 1.39 in the leafless period, 0.62 to 0.91 during leaf unfolding and between 0.68 and 0.83 in the fully leafed period. Using PAR measurements and the k values obtained, the annual cycle of PAI was modelled inverting Beers Law.     

Early-stage of invasion by beech bark disease does not necessarily trigger American beech root sucker establishment in hardwood stands

Two concomitant phenomena currently affect the dynamics of sugar maple-American beech (AB) stands in northeastern North America: beech bark disease (BBD), and increased AB understory density. Many studies suggest a causal link between the two phenomena, i.e., BBD favouring beech regeneration. But this link has yet to be experimentally demonstrated. To address the question, we compared regeneration composition between recently BBD-affected and -unaffected stands. A total of 109 stands were sampled; half were affected by BBD. Seedling and sapling density were assessed, together with the origin (seedling or sprout). While BBD affects stands in the eastern part of the study region, AB was observed in the understory across the entire region. No clear difference in AB sprout density between BBD-affected and -unaffected stands was observed while AB seedling density—as well as pooled AB seedling and sprout density were higher in unaffected stands. Findings suggests that BBD, in its early stage, is not a necessary trigger of AB understory establishment. Yet, AB sapling basal area generally was higher in stands affected by BBD, likely indicating a greater rate of AB understory development due to increased light availability beneath a more open crown canopy. That development can lead to AB understory dominance. This distinction—BBD not necessarily triggering AB root sucker establishment but favoring AB advance regeneration development—also questions the generalized perception that dense AB thickets necessarily originate from root suckers.     

Carbon and nitrogen fluxes between beech and their ectomycorrhizal assemblage

To determine the exchange of nitrogen and carbon between ectomycorrhiza and host plant, young beech (Fagus sylvatica) trees from natural regeneration in intact soil cores were labelled for one growing season in a greenhouse with ¹³CO₂ and ¹⁵NO₃ ¹⁵NH₄. The specific enrichments of ¹⁵N and ¹³C were higher in ectomycorrhizas (EMs) than in any other tissue. The enrichments of ¹³C and ¹⁵N were also higher in the fine-root segments directly connected with the EM (mainly second-order roots) than that in bulk fine or coarse roots. A strict, positive correlation was found between the specific ¹⁵N enrichment in EM and the attached second-order roots. This finding indicates that strong N accumulators provide more N to their host than low N accumulators. A significant correlation was also found for the specific ¹³C enrichment in EM and the attached second-order roots. However, the specific enrichments for ¹⁵N and ¹³C in EM were unrelated showing that under long-term conditions, C and N exchange between host and EMs are uncoupled. These findings suggest that EM-mediated N flux to the plant is not the main control on carbon flux to the fungus, probably because EMs provide many different services to their hosts in addition to N provision in their natural assemblages.     

Water fluxes in nerve fiber

Summary Van der Waals energies of interaction between model cell surfaces are calculated for various distances of separation, layer thicknesses and compositions of cell surfaces and intercellular media. In these calculations the cell peripheries are considered to consist of two layers: (1) A phospholipid-cholesterol-protein plasma membrane and (2) a surface coat, which consists of protein, sugar and water. The required Van der Waals parameters of sugars, phospholipids and cholesterol are derived from refractive indices of their solutions in the visible and ultraviolet regions. Polarizabilities and Van der Waals parameters of these substances are determined and shown to be almost independent of concentration of solutions. Resulting isotropic polarizabilities differ by less than five percent from values obtained by the addition of bond polarizabilities.The magnitude of Van der Waals interactions between cell surfaces has been found to vary with composition according to the following sequence: water–15 ergs and 6×10^–14 ergs at 50 Å distance of separation, which corresponds to free energies per unit area of 210-1600kT/ ²     

Changes in the decomposer community when converting spruce monocultures to mixed spruce/beech stands

The impact of the admixture of beech in spruce monocultures on structure and function of the decomposer community was studies in the Ore mountains (Saxony, Germany) on Dystric Cambisols between 2000 and 2002. The study sites represented four stages of forest conversion from a mature spruce stand to a mature spruce/beech stand. There, the functional profile of the nematodes, enchytraeids, lumbricids, and dipterans was analysed on the basis of ecological guilds, and their metabolic equivalences were calculated to characterize the decomposition potential of the invertebrate decomposer community. Because of the acidic parent soil the coenoses at all study sites were dominated by the enchytraeids with increasing importance of lumbricids and dipterans in progress of forest conversion. Gradual changes with rising coverage of beech culminated in intense differences of entire biomasses and metabolic equivalences between the mature stands, indicating a higher decomposition potential of the invertebrate decomposer community by the admixture of beeches in spruce forests. The quality of the beech litter is likely to be the important factors for these changes. To prove this assumption further investigations of the saprovore food chain are necessary, taking microbial parameters into account.     

European beech in its northeasternmost stands in Europe: Varying climate-growth relationships among generations and diameter classes

Age, genetics and social status of trees affect their sensitivity to environmental factors, and information about such effects is needed for comprehensive assessment of growth potential. Climatic sensitivity of radial increment (i.e., tree-ring width) of introduced European beech (Fagus sylvatica L.) of different generations and social status, growing in its northeasternmost stands in Europe, was studied by dendroclimatological methods. At present, the studied stands occur outside of the natural distribution area of the species, providing opportunity to study adaptability and potential growth of beech in novel environments under changing climate. The sensitivity of radial growth to climatic factors was modulated by the generation and social status (size) of trees. The first generation trees, which were propagated from the material transferred from the northern Germany, were highly sensitive to climatic factors and showed wide spectrum of responses. The dominant trees were particularly sensitive to June precipitation, indicating sensitivity to water deficit in summer. The suppressed trees were mainly sensitive to temperature in the dormant period. Tree-ring width of the second generation trees, which were propagated from the first generation stands, was mainly affected by water deficit in summer, yet the local factors, modulated the mechanisms of response. In one stand, tree-ring width was affected by conditions during the formation of tree-ring, indicating direct influence of weather conditions on xylogenesis. In the other stand, tree-ring width was correlated to weather conditions in the preceding year, suggesting influence via carbohydrate reserves. The effect of social status on climatic sensitivity in the second generation stands was considerably weaker, likely due to the natural and anthropogenic selection of the material best adapted for local conditions. The effect of climatic factors on radial growth of beech has shifted during the 20th century. The effect of autumn temperature has weakened, likely due to warming; the effect of factors related to water deficit in summer has intensified that could be related to both, changes in climate and ageing. The observed climate-growth relationships suggested that conditions in winter have become suitable for beech, yet careful selection of sites/regions with appropriate hydrological conditions appear necessary to counteract the increasing effect of water deficit, hence to ensure productivity of future beech sites in Latvia.     

Methanol and other VOC fluxes from a Danish beech forest during late springtime

In-canopy mixing ratio gradients and above-canopy fluxes of several volatile organic compounds (VOCs) were measured using a commercial proton transfer reaction mass spectrometer (PTR-MS) in a European beech (Fagus sylvatica) forest in Denmark. Fluxes of methanol were bidirectional: Emission occurred during both day and night with highest fluxes (0.2 mg C m⁻² h⁻¹) during a warm period; deposition occurred dominantly at daytime. Confirming previous branch-level measurements on beech, the forest’s monoterpene emissions (0–0.5 mg C m⁻² h⁻¹), and in-canopy mixing ratios showed a diurnal cycle consistent with light-dependent emissions; a result contrasting temperature-only driven emissions of most conifer species. Also emitted was acetone, but only at ambient temperatures exceeding 20°C. Slow deposition dominated at lower temperatures. Our in-canopy gradient measurements contrast with earlier results from tropical and pine forest ecosystems in that they did not show this beech ecosystem to be a strong sink for oxygenated VOCs (OVOCs). Instead, their gradients were flat and only small deposition velocities (<0.2 cm s⁻¹) were observed to the onsite soil. However, as methanol soil uptake was consistent and possibly related to soil moisture, more measurements are needed to evaluate its soil sink strength. In turn, as canopy scale fluxes are net fluxes with stomatal emissions from photosynthesizing leaves potentially affecting non-stomatal oxygenated VOC uptake, only independent, controlled laboratory experiments may be successful in separating gross fluxes.     

Spatial pattern and process in forest stands within the Virginia piedmont

Abstract. Question: Underlying ecological processes have often been inferred from the analysis of spatial patterns in ecosystems. Using an individual‐based model, we evaluate whether basic assumptions of species’life‐history, drought‐susceptibility, and shade tolerance generate dynamics that replicate patterns between and within forest stands. Location: Virginia piedmont, USA. Method: Model verification examines the transition in forest composition and stand structure between mesic, intermediate and xeric sites. At each site, tree location, diameter, and status were recorded in square plots ranging from 0.25 to 1.0 ha. Model validation examines the simulated spatial pattern of individual trees at scales of 1–25 m within each forest site using a univariate Ripley's K function. Results: 7512 live and dead trees were surveyed across all sites. All sites exhibit a consistent, significant shift in pattern for live trees by size, progressing from a clumped understorey (trees ± 0.1 m in diameter) to a uniform overstorey (trees > 0.25 m). Simulation results reflect not only the general shift in pattern of trees at appropriate scales within sites, but also the general transition in species composition and stand structure between sites. Conclusions: This shift has been observed in other forest ecosystems and interpreted as a result of competition; however, this hypothesis has seldom been evaluated using simulation models. These results support the hypothesis that forest pattern in the Virginia piedmont results from competition involving species’life‐history attributes driven by soil moisture availability between sites and light availability within sites.     

Microclimatic conditions determined by stem density influence leaf anatomy and leaf physiology of beech (Fagus sylvatica L.) growing within stands that naturally regenerate from clear-cutting

Beech forests naturally regenerating from clear-cutting can exhibit different microclimates depending on size of saplings and stem density. When beech trees are young and stem density is low, the level of radiation inside the ecosystem reaching the soil surface is high; consequently, air and soil temperatures rise and the soil water content may decrease. These microclimatic parameters presumably will affect the anatomy, photosynthesis, and carbon metabolism of beech leaves. We studied the morphology and physiology of sun and shade leaves of beech trees differing in age and growing within clear-cut areas with distinct microclimate. Results were compared with those of adult trees in an unmanaged forest. We selected a stand clear-cut in 2001 (14,000 trees ha⁻¹), another clear-cut in 1996 (44,000 trees ha⁻¹) and an unmanaged forest (1,000 trees ha⁻¹). Photosynthetic photon flux density (PPFD) incident on sun leaves, air temperature, soil moisture, and soil temperature within the forests affected water status and carbohydrate storage in all trees. As trees became older, PPFD also influenced pigment composition and Rubisco activity in sun leaves. On the other hand, shade leaves from the oldest trees were the most sensitive to PPFD, air temperature, and soil moisture and temperature inside the forest. Contrariwise, microclimatic parameters slightly affected the physiology of shade leaves of the beech in the stand with the highest light attenuation. Air and soil temperatures were the parameters that most affected the photosynthetic pigments and carbohydrate storage in shade leaves of the youngest trees.     

Leaf litter decomposition in temperate deciduous forest stands with a decreasing fraction of beech (Fagus sylvatica)

We hypothesised that the decomposition rates of leaf litter will increase along a gradient of decreasing fraction of the European beech (Fagus sylvatica) and increasing tree species diversity in the generally beech-dominated Central European temperate deciduous forests due to an increase in litter quality. We studied the decomposition of leaf litter including its lignin fraction in monospecific (pure beech) stands and in stands with up to five tree genera (Acer spp., Carpinus betulus, Fagus sylvatica, Fraxinus excelsior, Tilia spp.) using a litterbag approach. Litter and lignin decomposition was more rapid in stand-representative litter from multispecific stands than in litter from pure beech stands. Except for beech litter, the decomposition rates of species-specific tree litter did not differ significantly among the stand types, but were most rapid in Fraxinus excelsior and slowest in beech in an interspecific comparison. Pairwise comparisons of the decomposition of beech litter with litter of the other tree species (except for Acer platanoides) revealed a “home field advantage” of up to 20% (more rapid litter decomposition in stands with a high fraction of its own species than in stands with a different tree species composition). Decomposition of stand-representative litter mixtures displayed additive characteristics, not significantly more rapid than predicted by the decomposition of litter from the individual tree species. Leaf litter decomposition rates were positively correlated with the initial N and Ca concentrations of the litter, and negatively with the initial C:N, C:P and lignin:N ratios. The results support our hypothesis that the overall decomposition rates are mainly influenced by the chemical composition of the individual litter species. Thus, the fraction of individual tree species in the species composition seems to be more important for the litter decomposition rates than tree species diversity itself.     

Changes of vascular plant diversity along a chronosequence of beech coppice stands,central Apennines,Italy

Abstract

This research sought to understand the patterns of vegetation recovery after disturbances because of coppice management in beech forests. Eighty sampling units from the mountain belt of the Marche region (Apennines, Italy) were collected according to a stratified sampling based on their geological setting (limestone, sandstone), elevation classes and age after last coppicing (to represent a chronosequence, from 1 to 90 years). The expected successional trend of decreasing species richness was confirmed, together with some stabilisation processes for older stand ages. However, more complex diversity patterns were found when total species richness was decomposed into the species richness of five social behaviour types (SBTs), defined based on the species' habitat preference. On both bedrocks, temporal gradients explained the observed diversity changes at the stand level: forest specialists increased whereas non-forest species decreased. A relatively long time after coppicing (40–60 years), the contribution of the beech specialist species doubled, whereas non-forest and species from anthropogenic habitats decreased by about 50%. On sandstone, the contribution of gap species also decreased over a long-period, and the beech stands experienced stronger changes over time. We conclude that the decomposition of total species richness in terms of SBT affords the opportunity to identify temporal references for thresholds which can be used to assess plant diversity status in relation to management schedules and conservation policy decisions.     

Individual biomass factors for beech, oak and pine in Slovakia: a comparative study in young naturally regenerated stands

Biomass conversion and expansion factors (BCEF) which convert tree stem volume to whole tree biomass and biomass allocation patterns in young trees were studied in order to estimate tree and stand biomass in naturally regenerated forests. European beech (Fagus sylvatica L.), Sessile oak (Quercus petraea (Mattuschka) Liebl.) and Scots pine (Pinus sylvestris L.) stands were compared. Seven forest stands of each species were chosen to cover their natural distribution in Slovakia. Species-specific BCEF are presented, generally showing a steep decrease in all species in the smallest trees, with the only exception in the case of branch BCEF in beech which grows with increasing tree size. The values of BCEF for all tree compartments stabilise in all species once trees reach about 60–70-mm diameter at base. As they grow larger, all species increase their allocation to stem and branches, while decreasing the relative growth of roots and foliage. There are, however, clear differences between species and also between broadleaves and conifers in biomass allocation. This research shows that species-specific coefficients must be used if we are to reduce uncertainties in estimates of carbon stock changes by afforestation and reforestation activities.     

Nutrient content and ionic pattern in beech (Fagus sylvatica L.) from natural stands in Eastern Austria and ecological implications

Macro and Micro cation content, concentration of water soluble cations and anions, as well as nitrogen content in beech leaves from a variety of forest stands in the eastern part of Austria have been determined. Special attention has been focused on the highly air polluted Vienna Woods. A broad natural variability in total content of minerals, as well as in nitrogen content could be observed. In general, cation nourishment has been found to be adequate on all stands. The pattern of water soluble i.e. physiologically active cations, especially with regard to divalent cations, varies broadly among beeches from different provenances: Mg/Mn ratios differ within three orders of magnitude between dolomite and highly acidic, nutrient poor stands over silicate rock. The term mineral deficiency limit should, therefore, be used very carefully with respect to single nutrients. Organic anions (quinate, malate, citrate) clearly dominate over inorganic anions. The relative amount of the latter increased from NO₃, Cl, inorganic phosphate to SO₄. A concentration of SO₄ is markedly in leaves within the direct reach of SO₂ sources, its level, however, remaining well below the organic anions. Slight evidence of an antagonistic behavior between SO₄ and organic acids could be found. Total nitrogen as well as the ratio insoluble:soluble nitrogen were tendencially higher in Vienna Wood beeches, indicating an additional use of the airborne nitrogen. The high flexibility of beech with respect to mineral content and ionic balance is discussed with regard to the ecological distribution of beech and the susceptibility to air pollution.     

施肥对板栗林地土壤N2O通量动态变化的影响

2011年6月—2012年6月期间,在浙江省临安市典型板栗林地进行施肥对土壤N2O通量变化影响的试验研究。目的在于探明不同施肥处理下板栗林地土壤N2O通量的动态变化规律,并探讨土壤N2O通量和土壤环境因子之间的关系。试验设置4个处理:对照(不施肥)、无机肥、有机肥、有机无机混合肥。采用静态箱-气相色谱法测定了板栗林地土壤N2O通量,并测定了土壤温度、水分、水溶性有机碳(WSOC)和微生物量碳(MBC)含量。结果表明:板栗林土壤N2O通量呈显著季节性变化,最大值出现在夏季,最小值出现在冬季;而且,施肥处理显著提高土壤N2O年均通量和年累积量;在整个试验期间,无机肥、有机肥和有机无机混合肥处理下土壤N2O的排放系数分别达到0.96%、1.45%和1.29%。此外,施肥也显著增加了土壤WSOC和MBC的含量(P<0.05)。不同施肥处理条件下,土壤N2O通量与土壤5 cm处温度、WSOC含量间均呈极显著正相关(P<0.01),但与MBC含量之间的相关性不显著。土壤N2O排放与土壤含水量间除对照处理外均没有显著相关性。综上所述,施肥引起土壤WSOC含量的增加可能是施肥增加板栗林地土壤N2O排放速率的主要原因之一。     

Belowground drought response of European beech: fine root biomass and carbon partitioning in 14 mature stands across a precipitation gradient

How tree root systems will respond to increased drought stress, as predicted for parts of Central Europe, is not well understood. According to the optimal partitioning theory, plants should enhance root growth relative to aboveground growth in order to reduce water limitations. We tested this prediction in a transect study with 14 mature forest stands of European beech (Fagus sylvatica L.) by analysing the response of the fine root system to a large decrease in annual precipitation (970–520 mm yr⁻¹). In 3 years with contrasting precipitation regimes, we investigated leaf area and leaf biomass, fine root biomass and necromass (organic layer and mineral soil to 40 cm) and fine root productivity (ingrowth core approach), and analysed the dependence on precipitation, temperature, soil nutrient availability and stand structure. In contrast to the optimal partitioning theory, fine root biomass decreased by about a third from stands with >950 mm yr⁻¹ to those with <550 mm yr⁻¹, while leaf biomass remained constant, resulting in a significant decrease, and not an increase, in the fine root/leaf biomass ratio towards drier sites. Average fine root diameter decreased towards the drier stands, thereby partly compensating for the loss in root biomass and surface area. Both δ¹³C‐signature of fine root mass and the ingrowth core data indicated a higher fine root turnover in the drier stands. Principal components analyses (PCA) and regression analyses revealed a positive influence of precipitation on the profile total of fine root biomass in the 14 stands and a negative one of temperature and plant‐available soil phosphorus. We hypothesize that summer droughts lead to increased fine root mortality, thereby reducing root biomass, but they also stimulate compensatory fine root production in the drier stands. We conclude that the optimal partitioning theory fails to explain the observed decrease in the fine root/leaf biomass ratio, but is supported by the data if carbon allocation to roots is considered, which would account for enhanced root turnover in drier environments.