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.     

The effect of treeshelter height on the early growth of sessile oak (Quercus petraea (Matt.) Liebl.)

Sessile oak 1+1 transplants were grown for 4 years in a weed-freeenvironment at 1 x 1 m spacing on a fertile sheltered site.Four experiment treatments were imposed: control with no treeshelterand treeshelters of heights 0.6 m, 1.2 m and 1.8 m. Treatmentshad no significant effect on tree survival. Taller sheltersproduced taller, lower diameter trees of increasingly low dryroot weight. The root:shoot ratio was 0.675 in control treesbut declined to 0.291 in 1.8-m shelters. Trees from 0.6-rn and1.2-m shelters (mean heights 152 m and 206 m respectively) supportedthemselves unaided after removal of the stake and treeshelter.The trees from 1.8-m shelters of mean height 234 cm at age fourcollapsed completely when support was removed.     

Relationships between Shoot Length, Bud Number and Branch Production in Quercus petraea (Matt.) Liebl.

Over a 3-year-period the relationships between shoot length,number of buds and branch production were investigated on theleading shoots and major crown branches on 10-year-old Quercuspetraea. The pattern of growth was similar in leading shootsand branches indicating that for some aspects of growth observationof branches can substitute for study of the leader. There weresignificant relationships between shoot length and either numberof buds or branches, and between number of buds and branches;some of the relationships differed between years. There weresignificant between tree differences in the proportion of budsforming branches. Failure of the terminal bud increased lateralbranch production. The overall shape of the crown was relatedto the average annual extension growth. Results are discussedin relation to prediction of crown development and the selectionof superior genotypes in a tree improvement programme.     

Intra- and interspecific competition differently influence growth and stem quality of young oaks (Quercus robur L. and Quercus petraea (Mattuschka) Liebl.)

Context

Cluster planting has become a conventional establishment method for oaks in Central Europe, where the spacing of seedlings within clusters varies between ‘nests’ (0.2?×?0.2 m) and ‘groups’ (1?×?1 m). Although the space between clusters is expected to fill with voluntary regeneration, its competitive effect on oak growth and quality had not been studied yet.

Aims

The aim of the study was to analyse the effects of inter- and intraspecific interactions on growth and quality of oaks grown in cluster plantings by quantifying the influence of neighbouring trees. In addition, we analysed whether the spatial position of oaks within groups (inner section or periphery) influenced their quality development.

Methods

Using Hegyi’s competition index, the influence of competition from intra- and interspecific trees from early, mid- and late-successional species, on diameter, height, slenderness and quality (length of branch-free bole) of 10- to 26-year-old oaks grown in cluster planting stands was quantified at seven sites in Baden-Württemberg and Hessen, Germany.

Results

In general, mid- and late-successional trees exerted a stronger competitive influence on growth of target oaks in clusters than the conspecific oaks and pioneer tree species. Oak quality development benefited from intraspecific competition, but self-pruning was not further promoted through additional interspecific competition. Within groups, inner oaks had a higher probability of developing into potential future crop trees than outer oaks.

Conclusion

Our study showed that intra- and interspecific competition had different effects on target oak trees and that these effect differed between nest and group plantings. The development of naturally regenerated and planted trainer trees in group plantings should be monitored carefully and if necessary be controlled through thinning or pollarding.     

Microstructural investigation of UV-laser irradiated pine (Pinus silvestris L.)

Summary Different surfaces of pre-sanded pine (Pinus silvestris L.), namely radial surfaces, tangential surfaces and cross sections, have been subjected to microstructure examination. UV-laser irradiation with a wavelength of 248 nm and an energy of 350 mJ is used to enhance the microstructure exposure. It has been shown that UV-laser irradiation is a useful and practical method for revealing microstructural details. This is more pronounced on the cross section. Sanding with emery paper finer than 800 mesh can reveal microstructure on the radial surface equivalent to that revealed by UV-laser irradiation. On the radial and tangential surfaces, more earlywood is extracted after UV-laser irradiation, resulting in an uneven surface. Some features such as loose fibres and a rack-gearing-like structure on the radial and tangential surfaces, as well as a loss of radially oriented cell walls on the cross section are observed as a result of the UV-laser treatment. The rack-gearing structure is composed mainly of a sawtooth-like pattern. The length of the sawtooth is in most cases approximately 9 and 19 m.This work was carried out in the Department of Wood Technology and Processing, Royal Institute of Technology (KTH). Financial support from KTH is gratefully acknowledged.     

The Effect of Mineral Nutrients on Growth, Flushing, Apical Dominance and Branching in Quercus petraea (Matt.) Liebl

The supply of mineral nutrients had a significant effect onthe growth and form of seedling Quercus petraea. Plants receivinglarge amounts of fertilizer were more vigorous producing longershoots with more buds and branches on interwhorl sections ofshoot and in whorls than those given smaller quantities. Foreach flush there was a significant relationship between budnumber and length of shoot produced. Qualitative effects werealso apparent, high N plants flushed more frequently and producedmore branches per bud. The number of buds on interwhorl sectionsof shoot was greater than in corresponding whorls but whorlbuds had a greater tendency to form branches. Application ofNPK to 10-year-old trees in the field increased the number ofbranches produced during the lammas flush of growth. These resultsare related to growth habit and apical dominance.     

Effects of thinning on soil and tree water relations, transpiration and growth in an oak forest (Quercus petraea (Matt.) Liebl.)

To quantify the effects of crown thinning on the water balance and growth of the stand and to analyze the ecophysiological modifications induced by canopy opening on individual tree water relations, we conducted a thinning experiment in a 43-year-old Quercus petraea stand by removing trees from the upper canopy level. Soil water content, rainfall interception, sap flow, leaf water potential and stomatal conductance were monitored for two seasons following thinning. Seasonal time courses of leaf area index (LAI) and girth increment were also measured. Predawn leaf water potential was significantly higher in trees in the thinned stand than in the closed stand, as a consequence of higher relative extractable water in the soil. The improvement in water availability in the thinned stand resulted from decreases in both interception and transpiration. From Year 1 to Year 2, an increase in transpiration was observed in the thinned stand without any modification in LAI, whereas changes in transpiration in the closed stand were accompanied by variations in LAI. The different behaviors of the closed and open canopies were interpreted in terms of coupling to the atmosphere. Thinning increased inter-tree variability in sap flow density, which was closely related to a leaf area competition index. Stomatal conductance varied little inside the crown and differences in stomatal conductance between the treatments appeared only during a water shortage and affected mainly the closed stand. Thinning enhanced tree growth as a result of a longer growing period due to the absence of summer drought and higher rates of growth. Suppressed and dominant trees benefited more from thinning than trees in the codominant classes.     

Pedunculate and Sessile Oak (Quercus robur L. and Quercus petraea (Mattuschka) Liebl.): A Review of the Hybrid Controversy

Early nineteenth-century studies of variation in the genus QuercusL., particularly those relating to Pedunculate and Sessile oakby Lasch and Greville, illustrate the confused situation thatawaited the forest botanist. Attempts of that period and laterto explain this condition led to the general acceptance of atheory of unlimited hybridization and introgression betweenthe two species. Experimentation and observations between thethirties and fifties of the present century by Dengler, Høeg,Jones, and others demonstrate the weakness of this popular concept—hence the controversy. More recent investigations by Johnssonand Krahl-Urban, supported by the biometric research of Cousens,Carlisle, and Brown, have helped in the production of a moreaccurate picture of the form and extent of hybridization. Agreat deal still remains to be done to elucidate the naturalfrequency of F₁ hybrids, and backcrossea in different regions.The karyotypes of both species and hybrids have still to bedefined.     

Crookedness of pedunculate oak (Quercus robur L.) growing under a canopy of Scots pine (Pinus sylvestris L.)

Natural regeneration of pedunculate oak growing under a canopy of Scots may be used for conversion into a mixed or predominantly broadleaved forest. From an economic perspective it is desirable that the oaks have straight stems. In this paper we present a case study for analysing oak stem curvature and its causes. The study was conducted in a mature pine stand with understorey oaks of age ca. 60 years in Poland. The oaks were classified into two main groups as either straight or crooked. The following variables were measured or assessed for the oaks: (1) stem curvature (crookedness), total tree height, diameter at breast height (DBH) and some tree crown characteristics, (2) the growth of DBH and height in each year of the life of each tree and (3) the competitive pressure of surrounding trees. Durable stem curvatures were formed at the culmination of the height increment. The first 20 years of the life of the oak were crucial in terms of stem quality. The annual height increment was larger in the years when the curvature was formed than in adjacent years. The factors that caused crooked stems were the same for straight and crooked oaks, but the magnitude of the response was different. When planning the conversion of Scots pine into oak, full overhead light should be provided as early as possible, but not later than 20 years since the establishment of the regeneration.     

Variation in carbon concentration and basic density along stems of sessile oak (Quercus petraea (Matt.) Liebl.) and Pyrenean oak (Quercus pyrenaica Willd.) in the Cantabrian Range (NW Spain)

Context

Information about variations in basic density (BD) and carbon content (%C) along tree stems is key to assessing forest carbon sinks.

Aims

The aim of the study was to determine any differences in %C and BD between different woody tissues (bark, sapwood and heartwood) in two widespread European oak species (Quercus pyrenaica and Quercus petraea).

Methods

Twenty trees were felled in northern Spain, and 317 discs cut from the trees were dried and analysed to determine %C and BD.

Results

There were significant differences in %C between bark, heartwood and sapwood, and between species. There were also significant differences in BD between the tissues (heartwood?>?sapwood?>?bark), and the BD was higher in Q. petraea than in Q. pyrenaica. Both %C and BD varied along the stem.

Conclusion

More accurate estimates of carbon contents were obtained by using specific values for different heights and anatomical parts, than by using single values.     

Effects of severe dehydration on leaf photosynthesis in Quercus petraea (Matt.) Liebl.: photosystem II efficiency, photochemical and nonphotochemical fluorescence quenching and electrolyte leakage

Leaf disks of oak (Quercus petraea (Matt.) Liebl.) trees were subjected to rapid dehydration in air in the dark. Optimal photochemical efficiency of PS II (F(v)/F(M)), photochemical (q(P)) and nonphotochemical (q(NP)) quenchings of chlorophyll a fluorescence, and relative conductivity (C(r)) of leaf disk diffusate were measured in leaf disks with different water deficits (D). No effect of dehydration was detected before D reached values above 0.30. When D increased from 0.30 to 0.50, q(NP) increased without any change in q(P), which may indicate that thermal deexcitation of PS II increased, allowing reduced photochemical activity and maintenance of a large pool of oxidized primary acceptors (QA), although carbon reduction was impaired. Large changes in electron transport chain activity, leading to decreases in both q(P) and q(NP), appeared only in leaf disks subjected to severe water deficits (D > 0.60) and were correlated with a modification of membrane structure. However, stability of F(v)/F(M) indicated that the functional integrity of PS II was not altered until D reached values above 0.75. We conclude that the photosynthetic apparatus of Q. petraea is rather insensitive to leaf dehydration per se during drought under natural conditions.     

Correlations between needle and shoot growth characteristics in Scots pine (Pinus sylvestris L.) stands

Shoot, needle and bud growth in three stands of different ages(9, 20, and 60 years) of Scots pine were studied in order toreveal relations between these variables. Within the growingseason the sizes of buds and needles developed in parallel.Significant regressions between number of short shoots and eitheraverage needle length or total needle length of the parent shootwere found. The strongest regressions were found in the twoyoungest stands as well as in the top of the canopy.     

Determination of elements removal in different harvesting scenarios of Scots pine (Pinus sylvestris L.) stands

Increasing demand for renewable energy and limiting CO₂ emissions have stimulated much interest in wood-based biofuels. Unfortunately, expanding the utilization of forest biomass may cause nutrient depletion in forested environments. This study investigates the element content from various parts of the tree. Comparisons were made between different harvesting scenarios and their impact on the amount of nutrients removed from the forest environment. The harvesting scenarios were: stem-only harvesting (SOH), branch and stem harvesting (BSH), and two variants of whole-tree harvesting (WTH). The elements taken into account were: carbon (C), nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sodium (Na), sulphur (S), copper (Cu), iron (Fe), nickel (Ni), manganese (Mn), zinc (Zn), cadmium (Cd), chromium (Cr) and lead (Pb). To make the results comparable, the same amount of removed biomass was taken into calculation. The differences between harvesting scenarios were significant. The amounts of removed elements formed similar pattern: the lowest level was found in SOH, average in BSH, and highest in both variants of WTH. This confirms that the application of WTH is connected with increased risk of nutrient depletion, even when the volume of harvest would be equal to other variants.     

Spatial structure of semi-natural and plantation stands of Scots pine (Pinus sylvestris L.) in northern Scotland

The success of current initiatives to maintain and enhance thearea of and the special habitats provided by the remnant semi-naturalpinewoods of northern Scotland will depend upon foresters' abilityto foster more natural structures in even-aged plantations throughstand manipulation. However, there is little information onthe structures and spatial patterns that can be found in Scottishpinewoods; such knowledge could be used to design appropriatesilvicultural regimes. A study was carried out to compare spatialstructure in three 0.8–1.0 ha plots in the CairngormsNational Park; one plot was a 78-year-old plantation stand,the other two were semi-natural stands with trees up to 300years old. Basic mensurational data showed that the semi-naturalstands were characterized by a wider range of tree sizes andmore large (>50 cm d.b.h.) trees. Spatial structure was evaluatedwith a range of different indices: the aggregation index ofClark–Evans (CE), the uniform angle and diameter differentiationindices, Ripley's L function of tree spatial distribution, pairand mark correlation functions and experimental variograms oftree diameter. The CE revealed a regular distribution in theplantation with the semi-natural stands having a random pattern.Further analysis of the latter stands indicated that, in eachcase, the older trees in the stand were regularly distributedwhile the younger ones were clustered. There was little differencein uniform angle values between the stands while the diameterdifferentiation distributions suggested greater variety in diameterwithin the semi-natural stands than in the plantation. The Ripley'sL function showed that trees in the plantation were regularlydistributed at close distances but clustered over wider distances.There were differences in pattern between the semi-natural stands;in one, trees were clustered because the positions of the youngertrees were influenced by past regeneration trials, whereas inthe other stand a random pattern was observed. Similarly, thevariogram indicated widespread homogeneity in diameter withinthe plantation, while the semi-natural stands showed high variationat close spacing because of competition followed by spatialautocorrelation up to 20 m distance. Thereafter, one of thesestands had a very different pattern because of a more intensiveregeneration history. All the indices, apart from uniform angle,were able to discriminate between the plantation and the twosemi-natural stands, but only the more detailed spatial indiceswere capable of identifying differences within the latter. Theimplications of these results for management strategies in plantationsare discussed.     

Thinning increases cone production of stone pine (Pinus pinea L.) stands in the Northern Plateau (Spain)

Context

Edible stone pine (Pinus pinea L.) nut is a forest product which provides the highest incomes to the owners of stone pine forests.

Aim

The objective of this work is to evaluate the effect of first thinning on growth and cone production in an artificially regenerated stand in order to determine optimum intensity.

Methods

A thinning trial was installed in 2004 to compare two thinning regimes (heavy and moderate) and a control treatment. From 2004 to 2012, six inventories of forest attributes were carried out, and the cone crop was harvested annually. We evaluated the effect of thinnings on growth using repeated measures analysis of variance with a mixed model approach. With regards to cone production, we first estimated the probability of finding cones in a tree by applying a generalized mixed model and then estimated cone production by using a mixed model, including climatic variables.

Results

We found that thinning had a positive influence on tree diameter increment. Thinning increased the probability of finding cones and cone production. However, significant differences between heavy and moderate thinnings were not found.

Conclusion

We recommend early silvicultural treatments in stone pine stands to favor the development of trees and larger edible pine nut production.     

Response of Scots pine (Pinus sylvestris L.) and pubescent oak (Quercus pubescens Willd.) to soil and atmospheric water deficits under Mediterranean mountain climate

The physiological responses to water deficits of Scots pine (Pinus sylvestris L.) and pubescent oak (Quercus pubescens Willd.) were studied under Mediterranean mountain climate. Minimum leaf water potentials were ?3.2 MPa for oak and ?2.1 MPa for pine, with higher predawn values for pubescent oak. Relative sap flow declined in both species when vapour pressure deficit (D) went above ca. 1.2 kPa, but stomatal control was stronger for pine during the 2003 summer drought. P. sylvestris plant hydraulic conductance on a half-total leaf area basis (k _L,s?1) was 1.2–2.6 times higher than the values shown by Q. pubescens, and it showed a considerably steeper decrease during summer. Leaf-level gas exchange was positively related to k _L,s?1 in both species. Scots pine was more vulnerable to xylem embolism and closed stomata to prevent substantial conductivity losses. The results of this study confirm that pubescent oak is more resistant to extreme drought events.     

Estimating seed quantity and quality in shortleaf pine (Pinus echinata Mill.) cones from natural stands

The quantity and quality of seeds were studied in 886 shortleaf pine cones collected from 48 trees in each of two 15-ha natural stands in western Arkansas, USA. The number of seeds per cone ranged from 0 to 102, and averaged 34.6 and 38.0 in the two stands. Between 30 and 50 percent of the seeds were sound. Overall mean values for total number and total sound seeds compare with previous work. However, the wide variation between individual trees in a stand needs to be considered when evaluating cone abundance and estimating potential seed yields. For the stands observed in this study, a sample of 65 to 85 cones would be needed to estimate the number of sound seeds per cone (within ±3 seeds) with 95 percent probability. Sampling 1 or 2 cones from each of about 3 trees per ha would provide a reliable estimate of sound seed contents.     

Comparative mast seed production in unmanaged and shelterwood white pine (Pinus strobus L.) stands in central Ontario

The effect of the seed cut of the uniform shelterwood silvicultural system on white pine seed production, seed characteristics, and seed viability during 2 mast seeding events was examined in operationally harvested second growth, white pine-dominated forest stands in central Ontario. Seed traps placed along transects in unmanaged and shelterwood stands in each of 3 blocks were used to monitor seed production in 2000 and 2006 (4 and 10 years after harvesting). During these 2 mast seed years between 386,000 and 2,730,600 seed ha^?1 were produced among study stands. Total seed production expressed on a per hectare and unit pine basal area basis did not differ by harvest treatment or among blocks in either year. Variability in seed production among stands was primarily due to differences in stand structure, with seed production positively related to white pine basal area. Seed characteristics were largely similar between harvested and unmanaged stands and between seed years. Seed viability was relatively high in both years, with seed from shelterwoods germinating slightly slower than those from unmanaged stands. Seed quality, as estimated by laboratory germination performance, was higher in 2006 than 2000, likely due to improved seed development and maturation in the warmer, wetter growing season of 2006. Our results suggest that the seed cut of the uniform shelterwood system applied to second growth white pine stands is unlikely to adversely affect white pine seed production, seed quality, or potential for natural regeneration during mast seeding events.     

Development and transferability of two multiplexes nSSR in Scots pine (Pinus sylvestris L.)

Single sequence repeat(SSR) multiplexing is a semi high-throughput PCR methodology for the analysis of multiple SSRs.We developed two SSR multiplexes selected from SSR loci previously reported in the pine literature and tested the transferability of both SSR multiplexes in nine other pine species.We tested 234 nuclear SSR loci(n SSRs) previously described in the pine literature and selected ten n SSRs following the simple criteria of interpretability and reproducibility.Selected nuclear loci were divided into two n SSRs multiplex sets and their amplification was optimized for three different multiplex PCR methods based on:(a) a custom PCR protocol,(b) a custom protocol with hotstart taq polymerase,and(c) a commercially available kit for SSR multiplexing.To validate their performance,the level of genetic diversity was assessed in three Scots pine natural populations(Hungary,northern Sweden and southern Sweden).In addition,we also tested the transferability of these multiplexes in nine other pine species.We have developed two n SSRs multiplexes of five loci each that will contribute to reduce the costs of n SSR scoring,while increasing the capacity of n SSR loci analysis.Amplification was successful in all three populations(94 % success) and the level of polymorphism(7.1 alleles/marker) was similar to that previously reported for other Scots pine natural populations.Transferability of both multiplexes was successful for those pine species closely related to Scots pine.     

Effects of moist chilling and solid matrix priming on germination of loblolly pine (Pinus taeda L.) seeds

Loblolly pine (Pinus taeda L.) seeds from sources with a mild climate under maritime influence (North Carolina) required shorter moist chilling to achieve maximum germination vigor than seeds from sources with a harsher continental climate (Oklahoma). Solid matrix priming (SMP) for 6 d achieved as much as 60 d of moist chilling to improve rapidity, synchrony and completeness of germination for three of the four families studied. SMP after moist chilling increased the rapidity, synchrony and completeness of germination. The benefit of SMP was greatest for non-stratified seeds and the benefit decreased with length of moist chilling. In general, delaying planting for one week after SMP had minor effects on germination when seeds were kept in the SMP matrix at 4°C. Delayed planting after SMP can increase germination rapidity and synchrony of seeds that have received long moist chilling and reduce the benefit of SMP in non-moist-chilled seeds.