Productivity of mixed versus pure stands of oak (Quercus petraea (Matt.) Liebl. and Quercus robur L.) and European beech (Fagus sylvatica L.) along an ecological gradient

The mixture of beech (Fagus sylvatica L.) and oak (sessile oak, Quercus petraea (Matt.) Liebl., and pedunculate oak, Q. robur L.) is of considerable importance in Europe and will probably become even more important under climate change. Therefore, the performance of oak and beech in mixture was compared with the species’ growth in pure stands. Data from 37 long-term mixing experiments in Poland, Germany and Switzerland were pooled for analysis of mixing effects on stand productivity and possible interrelationships with mixing portions or site conditions. We found that on average, mixed stands of oak and beech exceeded biomass productivity in pure stands by 30 % or 1.7 t ha^?1 year^?1, as the growth of both species was benefitted by the mixture. However, that the interaction actually ranged from facilitation and overyielding on poor sites to underyielding on fertile sites triggered by competition. An empirically derived interaction model showed volume and dry mass growth changing in mixed stands from gains of 50 % to losses of 10 % depending on site conditions. It is concluded that the analysed mixture grows in accordance with the stress-gradient hypothesis and that our results suggest a site-specific relationship between species mixture and biomass productivity. As a consequence, an adequate species mix should result in increased productivity under steady state as well as climate change.     

Provenance-specific growth responses to drought and air warming in three European oak species (Quercus robur, Q. petraea and Q. pubescens)

Provenance-specific growth responses to experimentally applied drought and air warming were studied in saplings of three European oak species: Quercus robur, Quercus petraea and Quercus pubescens. Four provenances of each species were grown in large open-top chambers and subjected to four climates: control, periodic drought, air warming or their combination in 3 subsequent years. Overall growth responses were found among species and provenances, with drought reducing shoot height growth and stem diameter growth and air warming stimulating shoot height growth but reducing stem diameter growth and root length growth. Differential growth responses in shoots, stems and roots resulted in altered allometric growth relations. Root length growth to shoot height growth increased in response to drought but decreased in response to air warming. Stem diameter growth to shoot height growth decreased in response to air warming. The growth responses in shoots and stems were highly variable among provenances indicating provenance-specific sensitivity to drought and air warming, but this response variability did not reflect local adaptation to climate conditions of provenance origin. Shoot height growth was found to be more sensitive to drought in provenances from northern latitudes than in provenances from southern latitudes, suggesting that genetic factors related to the postglacial immigration history of European oaks might have interfered with selective pressure at provenance origins.     

Effect of flooding on C metabolism of flood-tolerant (Quercus robur) and non-tolerant (Fagus sylvatica) tree species

Flooding is assumed to cause an energy crisis in plants because-due to a lack of O(2)-mitochondrial respiration is replaced by alcoholic fermentation which yields considerably less energy equivalents. In the present study, the effect of flooding on the carbon metabolism of flooding-tolerant pedunculate oak (Quercus robur L.) and flooding-sensitive European beech (Fagus sylvatica L.) seedlings was characterized. Whereas soluble carbohydrate concentrations dropped in roots of F. sylvatica, they were constant in Q. robur during flooding. At the same time, root alcohol dehydrogenase activities were decreased in beech but not in oak, suggesting substrate limitation of alcoholic fermentation in beech roots. Surprisingly, leaf and phloem sap sugar concentrations increased in both species but to a much higher degree in beech. This finding suggests that the phloem unloading process in flooding-sensitive beech was strongly impaired. It is assumed that root-derived ethanol is transported to the leaves via the transpiration stream. This mechanism is considered an adaptation to flooding because it helps avoid the accumulation of toxic ethanol in the roots and supports the whole plant's carbon metabolism by channelling ethanol into the oxidative metabolism of the leaves. A labelling experiment demonstrated that in the leaves of flooded trees, ethanol metabolism does not differ between flooded beech and oak, indicating that processes in the roots are crucial for the trees' flooding tolerance.     

Use of thermal imaging to determine leaf conductance along a canopy gradient in European beech (Fagus sylvatica)

Using an infrared camera, we measured the leaf temperature across different canopy positions of a 23-m-tall deciduous forest tree (Fagus sylvatica L.) including typical sun and shade leaves as well as intermediate leaf forms, which differed significantly in specific leaf area (SLA). We calculated a temperature index (I(G)) and a crop water stress index (CWSI) using the surface temperatures of wet and dry reference leaves. Additional indices were computed using air temperature plus 5 °C (I(G)?+?5, CWSI?+?5) as dry references. The minimum temperature of the wet leaf and the maximum temperature of the dry leaf proved to be most suitable as reference values. We correlated the temperature indices with leaf area-related conductance to water vapor (g(L)) using porometry at the leaf level and using xylem sap flow at the branch level. At the leaf and at the branch level, I(G) and CWSI were equally well suited as proxies of g(L), whereas the relationships of I(G)?+?5 and CWSI?+?5 with g(L) were only weak or even insignificant. At the leaf level, the correlations of I(G) and CWSI with g(L) were significant in all parts of the crown. The slopes of g(L) vs. I(G) and CWSI did not differ significantly among the crown parts; this indicates that they were not influenced by SLA or irradiance. At the branch level, close correlations (r?>?0.8) were found between temperature indices and g(L) across the crown. These results demonstrate that satisfactory relationships between temperature indices and g(L) can be established in tall trees even in those canopy parts that are exposed to relatively low levels of irradiance and exhibit relatively low values of g(L).     

Genetic control of wood colour, density and heartwood ellagitannin concentration in European oak (Quercus petraea and Q. robur)

Pressler cores of young clones of Quercus petraea and Q. roburwere analysed from two sites in Germany. Variation of wood colour(defined by the CIELAB system), density and heartwood ellagitanninswas examined between clones, species and sites. Similar studieswere made of cores from another trial of 20 half-sib familiesof parent trees deriving from five German forests. The resultsfrom both the clonal and progeny trials indicate that heartwoodellagitannin content and wood density are under strong geneticcontrol, while sapwood and heartwood colour are less so. A largeproportion of between-clone variation in wood density and ellagitanninlevels occurred between the two species, while these propertiesvaried little among ramets of the same clone grown on two contrastingsites, despite a difference in growth rates. A large proportionof the total variation among progeny was attributed to forestorigins and could not be attributed clearly to either geneticor environmental causes because of limitations of the samplingdesign     

Exploratory study on the impregnation of Scots pine sapwood (Pinus sylvestris L.) and European beech (Fagus sylvatica L.) with different hot melting waxes

Scots pine sapwood (Pinus sylvestris L.) and beech (Fagus sylvatica L.) were impregnated with five waxes. The experiments indicate deep penetration into pine sapwood. Besides the viscosity, an influence of the wax polarity is presumed. Wax penetrates pine wood deeply via the cross-section, but not sufficiently enough to impregnate longer construction elements. However, the radial wax uptake exceeds the uptake via the tangential orientation and guarantees complete soaking of the sapwood tissue. The lateral wax penetration within beech is quite low and irregular. In addition to the temperature, a prolonged process procedure is decisive for an increasing wax uptake. As such, beech wood vessel elements seem to be fully impregnable via the longitudinal surface after a longer process procedure.     

Persisting soil drought reduces leaf specific conductivity in Scots pine (Pinus sylvestris) and pubescent oak (Quercus pubescens)

Leaf specific conductivity (LSC; the ratio of stem conductivity (K(P)) to leaf area (A(L))), a measure of the hydraulic capacity of the stem to supply leaves with water, varies with soil water content. Empirical evidence for LSC responses to drought is ambiguous, because previously published results were subject to many confounding factors. We tested how LSC of similar-sized trees of the same population, under similar climatic conditions, responds to persistently wet or dry soil. Scots pine (Pinus sylvestris L.) and pubescent oak (Quercus pubescens Willd.) trees were compared between a dry site and a wet site in the Valais, an inner alpine valley in Switzerland. Soil water strongly influenced A(L) and K(P) and the plant components affecting K(P), such as conduit radius, conduit density and functional sapwood area. Trees at the dry site had lower LSC than trees with the same stem diameter at the wet site. Low LSC in trees at the dry site was associated with a smaller functional sapwood area and narrower conduits, resulting in a stronger reduction in K(P) than in A(L). These observations support the hypothesis that trees maintain a homeostatic water pressure gradient. An alternative hypothesis is that relatively high investments in leaves compared with sapwood contribute to carbon gain over an entire season by enabling rapid whole-plant photosynthesis during periods of high water availability (e.g., in spring, after rain events and during morning hours when leaf-to-air vapor pressure deficit is small). Dynamic data and a hydraulic plant growth model are needed to test how investments in leaves versus sapwood and roots contribute to transpiration and to maximizing carbon gain throughout entire growth seasons.     

Six-year time course of light-use efficiency, carbon gain and growth of beech saplings (Fagus sylvatica) planted under a Scots pine (Pinus sylvestris) shelterwood

Two-year-old Fagus sylvatica L. saplings were planted under the cover of a Pinus sylvestris L. stand in the French Massif Central. The stand was differentially thinned to obtain a gradient of transmitted photosynthetically active radiation (PAR(t); 0-0.35). Eighteen Fagus saplings were sampled in this gradient, and their growth (basal stem diameter increment) was recorded over six years. Over the same period, morphological parameters (leaf area, number and arrangement in space) were monitored by 3D-digitization. Photosynthetic parameters were estimated with a portable gas-exchange analyzer. Photosynthesis was mainly related to light availability, whereas sapling morphology was mainly driven by sapling size. Annual stem diameter increment was related to the amount of light-intercepting foliage (silhouette to total leaf area ratio (STAR) x total sapling leaf area (LA)) and light availability above the saplings (PAR(t)). However, light-use efficiency, i.e., the slope of the relationship between STAR x LA x PAR(t) and stem diameter increment, decreased over time as a result of a relative decrease in the proportion of photosynthetic tissues to total sapling biomass.     

Volatile composition analysis by solid-phase microextraction applied to oak wood used in cooperage (Quercus pyrenaica and Quercus petraea): effect of botanical species and toasting process

The purpose of this study was to investigate the sorption of selected volatile substances from oak wood-chip samples (Quercus pyrenaica Willd. and Quercus petraea L.) subjected to different toasting levels, namely, without toasting, with medium toasting, and with strong toasting, through the use of solid-phase microextraction (SPME). The main volatile compounds identified as a function of the toasting level and botanical species were furfural, hexanal, α-pinene, d-limonene, decanal, vitispirane, ethyl hexanoate, cis-3-methyl-γ-octalactone (“oak lactone” or “whisky lactone”), α-terpineol, p-xylene, and nonanal. Considering the data obtained from the toasted woods (medium and strong intensity) in comparison with those of nontoasted woods, it can be pointed out that the average peak area and the number of compounds identified in the gas chromatogram decreased during the toasting process. In general, regarding the compounds analyzed, quantitative differences were found between the two oak wood species under study. High values of volatile compounds were found in Quercus pyrenaica oak wood chips. In addition, for the number of compounds identified in oak wood extracts and directly extracted from solid oak wood chips by SPME, it is concluded that the best extraction process for volatile compounds from oak wood is the use of oak wood-chip liquid extracts.     

High-pruning of European beech (Fagus sylvatica L.) and pedunculate oak (Quercus robur L.): work efficiency for target pruning as a function of tree species,pruning height,branch characteristics,pole saw type and operator

The objective of this study was to establish an operational model of productive work time per tree (work efficiency) for high-pruning of young European beech and pedunculate oak depending on tree species, pruning height, branch characteristics, pole saw type and operator. The final model included all of these independent variables with branch characteristics specified in terms of number of live branches and cross-sectional area of the thickest branch at the cut. Work time increased with increasing values of each of the three numeric variables. For a given pruning height the size of the largest branch was for all practical purposes more influential than the number of live branches. Beech took 28% longer to prune than oak. The German Ergo-Schnitt saw was 21% slower than the Japanese Silky Hayauchi saw. The variation in worker performance within our study was larger than that attributed to tree species and pruning equipment.     

Responses of two closely related oak species, Quercus robur and Q. petraea, to excess manganese concentrations in the rooting medium

Quercus robur (L.) and Q. petraea (Matt.) Liebl. are European oak species that often grow in forest soils with high soluble manganese (Mn2+) concentrations. We tested the effects of Mn2+ at concentrations of 0.0024 mM (control), 0.24 mM (typical of acidic forest soils) and 1.2 mM (typical of forest soils under strongly reducing conditions) on the growth, tissue anatomy, foliar element concentrations, subcellular element distribution and gas exchange of solution-cultured seedlings. At the highest Mn2+ concentration, seedlings were grown with and without an elevated concentration (1.2 mM) of magnesium (Mg2+). At 0.24 mM Mn2+, foliar Mn concentrations were higher than observed in the field. Vacuoles of the leaf epidermis and mesophyll were the main sites of manganese accumulation. High nutrient solution Mn2+ concentration significantly lowered foliar iron (Fe) and Mg concentrations. Elevated Mg2+ concentration raised the foliar Mg concentrations to control values, but Fe concentrations and gas exchange remained depressed. In seedlings grown in the 1.2 mM Mn2+ treatment without elevated Mg2+ damage to the phloem of the petioles and a reduction in root mass were observed in both species. The effects on shoot and root growth were greatest in Q. petraea. Alleviation of manganese toxicity symptoms by Mg2+ in Q. petraea was less effective than in Q. robur. Our results suggest that the soil solution Mn2+ concentrations that occur in European oak forests are unlikely to affect the distribution and performance of Q. robur and Q. petraea in the field.     

Differences in soil organic matter, extractable nutrients, and acidity in European beech (Fagus sylvatica L.) forest soils related to the presence of ground flora

Differences in soil organic matter (SOM) content, soil acidity, and soil exchangeable nutrients (NH₄–N, NO₃–N, Ca, K, Na, Mg) related to the presence of ground flora were studied. The study was carried out for a growing season in two different Fagus sylvatica L. forests in southern Sweden, and the differences in soil characteristics below naturally occurring patches of Deschampsia flexuosa (L.) Trin. or Anemone nemorosa L. were compared with those with no ground flora. Patches of D. flexuosa led to higher soil pH, but lower SOM, water content, base saturation, and NH₄–N concentration compared with adjacent zones without D. flexuosa. The lower SOM content suggested an increased rate of decomposition which caused soil pH to increase because of release of basic cations. In the presence of A. nemorosa, pH was higher and the exchangeable acidity lower than for patches without the herb. In early spring, when A. nemorosa emerged and flowered, the NH₄–N concentration was somewhat lower in the presence of the herb than when it was absent. For the evergreen grass D. flexuosa NH₄–N concentrations were lower in patches with the grass later in the summer season (July). This work indicates the presence of spatial and temporal differences in nutrient circulation and decomposition on the small ground flora scale, which should be considered when studying nutrient and carbon cycles of temperate forests.     

Light-mediated influence of three understorey species (Calluna vulgaris, Pteridium aquilinum, Molinia caerulea) on the growth of Pinus sylvestris seedlings

Depending on its developmental and morphological characteristics, shrubby or herbaceous understorey vegetation interacts differently with tree seedlings during the regeneration process. In acidic temperate forests, three common understorey plant species??Calluna vulgaris (L.) Hull, Pteridium aquilinum (L.) Kuhn in Kersten, Molinia caerulea (L.) Moench??are known to rapidly colonize forest gaps. Therefore, they often develop at the expense of light-demanding Scots pine (Pinus sylvestris L.) seedlings. An experiment was set up in a nursery in central France to mimic early competition occurring in a newly created gap between Scots pine seedlings and these three common understorey species (young forest-harvested individuals planted at 5 densities from 0 to 57 plants m^?2). Pine seedling survival and growth (height, diameter, shoot and root biomass) and a functional trait (leaf mass on an area basis, LMA) were measured for 2 years, and cross-analysed against plant density, plant cover and available light. When understorey plant density increased, pine seedling diameter growth and biomass were negatively affected by all three plant species; height growth only slowed beneath Pteridium. These negative effects were closely linked to competition for light beneath Pteridium and Molinia. The application of the Beer?CLambert law gave an extinction coefficient k that was high for Pteridium, intermediate for Molinia and much lower for Calluna. LMA was confirmed as an effective foliar trait to reflect the degree of stress undergone by pine seedlings.     

Mineral nutrients, carbohydrates and phenolic compounds in leaves of beech (Fagus sylvatica L.) in southern Sweden as related to environmental factors

Concentrations of major elements, trace elements, starch, total sugars and phenols were measured in leaves of beech (Fagus sylvatica L.) trees located at 89 sites in the province of Scania, southern Sweden. Concentrations of elements had only a weak relationship to soil variables, but leaf N increased with distance from sources of industrial air pollution. Within-site variation in concentrations of most elements was smaller than variation among sites and was lowest for N, P, K and Cu and highest for Mn. Most trees had optimal or superoptimal concentrations of leaf N, whereas leaf concentrations of K, Mg and P were near or below the concentrations needed for normal growth. Several nutrients were negatively correlated with leaf color, total sugars and phenols, whereas insect damage was not related to any of the measured parameters.     

Needle and stem wood production in Scots pine (Pinus sylvestris) trees of different age,size and competitive status

We studied effects of tree age, size and competitive status on foliage and stem production of 43 Scots pine (Pinus sylvestris L.) trees in southern Finland. The tree attributes related to competition included foliage density, crown ratio and height/diameter ratio. Needle mass was considered to be the primary cause of growth through photosynthesis. Both stem growth and foliage growth were strongly correlated with foliage mass. Consequently, differences in growth allocation between needles and stem wood in trees of different age, size, or position were small. However, increasing relative height increased the sum of stem growth and foliage growth per unit foliage mass, indicating an effect of available light. Suppressed trees seemed to allocate more growth to stem wood than dominant trees, and their stem growth per unit foliage mass was larger. Similarly, trees in dense stands allocated more growth to stem wood than trees in sparse stands. The results conformed to the pipe model theory but seemed to contradict the priority principle of allocation.     

Intra- and interspecific diversity in the response to waterlogging of two co-occurring white oak species (Quercus robur and Q. petraea)

Quercus robur L. and Quercus petraea (Matt.) Liebl. are sympatric oak species with different ecological requirements. Quercus robur is more tolerant to waterlogging than Q. petraea. This ecological divergence may play a role in the maintenance of the two species despite the absence of an insurmountable reproductive barrier between them. We predicted that the genetic architecture of traits related to waterlogging tolerance differs between the species. To gain insight into this architecture in the absence of genetic markers for waterlogging tolerance, we compared populations of seedlings of each species for diversity in the expression of quantitative phenotypic traits induced by severe hypoxia. To determine the capacity for hypertrophied lenticel formation, we applied gas-impermeable mastic to stems of seedlings. Two months after application, the mastic treatment had induced the formation of 3 (+/- 2) cm(-2) hypertrophied lenticels in the absence of root hypoxia. Leaf epinasty during root hypoxia was an early predictor of seedling mortality. Four weeks of waterlogging resulted in greater epinasty in Q. petraea than in Q. robur, but fewer hypertrophied lenticels (16 +/- 6 versus 21 +/- 9 cm(-2)) and adventitious roots (2.7 +/- 4.7 versus 5.2 +/- 5.9). Differences between species in these traits were associated with differences in the frequencies of extreme phenotypes rather than with a generally higher tolerance to waterlogging in Q. robur seedlings.     

Pathogenicity of canadian isolates of the Bursaphelenchus xylophilus (pinewood nematode) to provenances of Pinus sylvestris and Pinus contorta as grown in Finland: A greenhouse study

Seedlings of Scots pine (Pinus sylvestris L.) and lodgepole pine (P. contorta Dougl.) provenances, as grown in Finland, were inoculated with “m”; and “r”; “forms”; of the pinewood nematode (Bursaphelenchus xylophilus) from Canada, an m form isolate from France and an r form isolate from Missouri, USA. Scots pine was highly susceptible to an Alberta r form and a British Columbia m form isolate and moderately susceptible to two Quebec m form isolates. Lodgepole pine was higly susceptible to the two r form (Alberta and Missouri) isolates and moderately susceptible to the British Columbia m form and the two Quebec m form isolates. Mortality of both pines after inoculation with the French isolate was inconsistent. Mortality of both pines occurred more rapidly following inoculation with r form than with m form nematodes. Large numbers of nematodes were generally found in the tissues of both pines. Our results with seedlings need to be corroborated by inoculating larger field‐grown trees.     

EuMIXFOR empirical forest mensuration and ring width data from pure and mixed stands of Scots pine (<Emphasis Type="Italic">Pinus sylvestris L.</Emphasis>) and European beech (<Emphasis Type="Italic">Fagus sylvatica L.</Emphasis>) through Europe

Key message

This data set provides unique empirical data from triplets of Scots pine ( Pinus sylvestris L.) and European beech ( Fagus sylvatica L.) across Europe. Dendrometric variables are provided for 32 triplets, 96 plots, 7555 trees and 4695 core samples. These data contribute to our understanding of mixed stand dynamics. Dataset access at   http://dx.doi.org/10.5061/dryad.8v04m . Associated metadata available at https://metadata-afs.nancy.inra.fr/geonetwork/apps/georchestra/?uuid=b3e098ca-e681-4910-9099-0e25d3b4cd52&hl=eng .