The development of beech in monoculture and mixtures

The importance of producing good quality beech timber seems to increase even if there are periods with low demands for it. Due to relatively substantial amount of fertile abandoned agriculture soils in Southern Sweden possibilities to increase the area occupied by beech seems to be high. Former studies indicate the positive influence of shelter on a survival of seedlings and quality formation e.g. crookedness, forking. The aim of the study was to answer the question: if the shelterwood benefit to better quality of beech and which admixture species creates the most favourable conditions for beech regeneration? Furthermore, the goal was to study a possible hampering of the beech growth, due to the shelter. The thesis comprises two parts. In the first literature was reviewed, in the second field results were analyzed. Different beech traits were compared in mixed and open grown stands. The following beech traits were measured and judged on sample trees: diameter in breast height, diameter of the thickest branch, tree class, stem crookedness, quality of the stem, shape of the tree and occurrence of the spike knots. The statistical analyze was made by means of ANOVA planned comparisons. Every measured row was regarded as an independent observation. Contrast was made between three groups; NS (no shelter) - pure beech and mixture with alder (control plot), LS (low shelter) – mixtures with hornbeam, aspen and spruce, HS (high shelter) – mixtures with larch, birch, and hybrid aspen. The results showed that mixing beech with fast growing species has a positive influence on beech quality formation, especially shape of the tree and commercial quality. There was no significant decrease of diameter and volume growth of beech, due to the shelter. Finally the admixtures with fast growing species were regarded as the most favourable for artificial regeneration of beech

Monitoring of long-term tolerance of European ash to Hymenoscyphus fraxineus in clonal seed orchards in Sweden

The invasive alien pathogenic fungus Hymenoscyphus fraxineus causing ash dieback (ADB) has devastated European ash (Fraxinus excelsior) populations across Europe. Breeding for resistance is the most feasible measure to reduce future losses of ash, and the presence of resistance, albeit at low level, has been demonstrated in numerous genetic trials around Europe. This study is a continuation of the inventories tracking the vitality status of different clones, which started in 2006 at two ash seed orchards in southern Sweden. A new inventory conducted in the summer of 2021 revealed that the ten clones previously identified as the most tolerant to ADB based on periodic surveys from 2006 and onwards still remain the most tolerant, while susceptible clones continued to decline and are completely disappearing from the orchards. Browsing caused mortality in some of the most tolerant clones in one of the orchards during the last assessment period. Despite the animal damage, the stable resistance observed in tolerant clones over a 15 years period forms a solid basis for the continuation of the breeding programme where good candidates are selected for further study

Non-Destructive Evaluation of Downy and Silver Birch Wood Quality and Stem Features from a Progeny Trial in Southern Sweden

This study investigated whether improved downy birch could perform as well as improved silver birch, and whether there was sufficient genetic variation and control for non-destructive testing (NDT) values to include them as selection traits in breeding programs. NDT tools were applied to a 15-year-old downy birch family trial intermixed with improved silver birch. Average diameters, fissured bark height, and grain angle were higher for silver than downy birch. The genetic analysis for downy birch provided estimates of narrow-sense heritability (h 2 ) for acoustic velocity and Pilodyn penetration depth that were above 0.3 but had low genetic variation. Grain angle had relatively high genetic variability (18%) and an h 2 of 0.20. A subsample of 49 trees had 4 mm cores x-rayed for wood density estimates, and 34 stems had 12 mm cores macerated for cell measurements. t-tests revealed that average wood density and cell measurements were not significantly different between species. For silver and downy birch, fiber length and vessel length increased between inner and outer measurement positions, and fiber length was reasonably correlated with acoustic velocity. Silver birch tended to have denser and stiffer wood, while downy birch had less rough bark and straighter grain, and these results are in agreement with existing knowledge. The h 2 values were similar to those observed in other birch species and indicate there is potential to breed for improved wood density and grain angle in downy birch

Genetic parameters of stem and wood traits in full-sib silver birch families

This study investigated heritability of stem and wood traits to improve Swedish silver birch (Betula pendula Roth.) through breeding. Birch is 12% of Sweden’s forest area but mainly used for low value pulp or firewood. This paper applied non-destructive test (NDT) methods, and estimated traits’ heritability (h2), to help breed birch for high value solid wood products. Two trials of 22 families were assessed at age 19 for stem diameter (DBH), stem straightness, rough brown bark height (BH), grain angle (GA), Pilodyn penetration depth (Pilo) and acoustic velocity (AV). X-ray densitometry was performed on a subsample of radial cores taken at 1.3 m from the ground to get an average benchmark density. The h2 values were moderate for GA (0.20 and 0.21) and Pilo (0.53 and 0.48) at the two sites, but the h2 values for AV were low (0.05 and 0.30). There were moderate genotypic correlations between BH and DBH (0.51–0.54). There were low genotypic and phenotypic correlations between NDT measurements and other traits so including NDT in birch breeding efforts should not inadvertently reduce size, stem or wood quality. The high genetic correlations between sites suggest that GA, Pilo and AV values were determined more by genotype than by environment

Trap catch data are poor predictors of damage caused by pine weevil (Hylobius abietis) to conifer seedlings

Damage to planted conifer seedlings caused by the pine weevil Hylobius abietis (L.) is a severe and persistent threat to successful forest regeneration in Europe. Various countermeasures are available, which vary in effectiveness, costs and environmental impact, but none are ideal for all situations. Therefore, there is strong interest in robust assessments of damage risks, as they would enable more cost-effective and environmentally friendly forest pest management. It has been suggested that numbers of adult pine weevils caught in host-odour baited traps placed in regeneration sites may be valuable in such risk assessments. However, published studies provide at most weak support for the hypothesis that trap catch data provide adequate predictions of damage. Therefore, we conducted a two-year field study, designed to determine the relationship between weevil trap catch and subsequent damage at 10 regeneration sites in central Sweden. Site factors that might influence pine weevil feeding on seedlings were recorded and used as explanatory variables in the analysis. Stoniness was the only site factor identified as having a significant effect; damage mainly increased with increases in stoniness. No significant correlation was detected between damage to planted conifer seedlings and numbers of pine weevils trapped in the same locations. We suggest that this lack of correlation between weevil numbers and damage is due to planted seedlings only constituting a minor part of the weevils food intake and considerable between-site variation in availability of food sources other than seedlings. Therefore, assessment of pine weevil numbers appears unlikely to be useful for predicting damage risk at specific regeneration sites

Multivariate mixed-effects models for stand characteristics of hybrid aspen plantations in southern Finland and southern Sweden

Hybrid aspen, a hybrid between the European aspen and North American trembling aspen (Populus tremula L. × P. tremuloides Michx.), is a promising species because of its fast-growth and its suitability for multi-purpose use. However, models for predicting the age-dependent development of stand characteristics are still missing. The main objectives of this study were therefore to develop the models for predicting stand characteristics of hybrid aspen plantations and to validate the model applicability. The target response variables were stand basal area (BA), basal area-weighted mean diameter (DG) and basal area-weighted mean height (HG). Data were obtained from clonal hybrid aspen trials in southern Finland and southern Sweden. Multivariate mixed-effects modelling was used to estimate the parameters of seemingly unrelated regression for BA, DG, and HG. Model fit provided the following predictor variables: stand age (AGE), the number of trees per hectare (TPH), site index (SI), growing degree-days (GDD5), soil and site type, and thinning treatment. The chosen predictors differed slightly by response variable, but all parameters were highly significant (P < 0.0001), and model goodness-of-fit statistics presented high accuracy: RMSE of 2.59 m2 ha−1 for BA, 1.21 cm for DG, 1.05 m for HG in arithmetic scale. The applied simulations illustrated clear differences in the predicted development of stand characteristics when input variables SI, TPH or GDD5 changed. The developed models were assessed to be easily applicable and useful for predicting the stand and tree characteristics of clonal hybrid aspen plantations, especially for the stands with AGE ≤ 30 years and TPH ≤ 2000 trees ha−1

Production of genetically improved silver birch plantations in southern and central Sweden

Investing in planting genetically unproved silver birch (Betula pendula Roth) in Swedish plantations requires understanding how birch stands will develop over their entire rotation. Previous studies have indicated relatively low production of birch compared to Norway spruce (Picea abies (L.) Karst.) and Scots pine (Pinus sylvestris L.). This could result from using unrepresentative basic data, collected from unimproved, naturally-regenerated birch (Betula spp.) growing on inventory plots often located in coniferous stands. The objective of this study was to develop a basal area development function of improved silver birch and evaluate production over a full rotation period. We used data from 52 experiments including planted silver birch of different genetic breeding levels in southern and central Sweden. The experimental plots were established on fertile forest sites and on former agricultural lands, and were managed with different numbers of thinnings and basal area removal regimes. The model best describing total stand basal area development was a dynamic equation derived from the Korf base model. The analysis of the realized gain trial for birch showed a good stability of the early calculated relative differences in basal area between tested genotypes over time. Thus, the relative difference in basal area might be with cautious used as representation of the realized genetic gain. On average forest sites in southern Sweden, improved and planted silver birch could produce between 6-10.5 m(3) ha(-1) year(-1), while on fertile agriculture land the average productivity might be higher, especially with material coming from the improvement program. The performed analysis provided a first step toward predicting the effects of genetic improvement on total volume production and profitability of silver birch. However, more experiments arc needed to set up the relative differences between different improved material

Influence of spacing and thinning on wood properties in conifer plantations

As reported in four appended papers (I-IV), effects of genotype (half-sib family) and initial spacing (I) or initial spacing (II) and various thinning methods (III & IV) on stands and properties of sawn-products were investigated in Scots pine (I & IV), lodgepole pine (II) and Norway spruce (III) stands in southern Sweden. Most of the analysed growth parameters were found to be affected by interaction between genotype and initial spacing, but the treatments had no significant interactive effects on most quality parameters (I). Very wide initial spacing (4x4 m, 625 trees/ha⁻¹) was found to negatively affect most growth and quality properties of lodgepole pine. Differences in effects of the density currently used in forestry (2500 trees/ha⁻¹) and a tested density (1100 trees/ha⁻¹, 3x3 m), were quite small, but increasing the spacing decreased frequencies of potential high quality trees. The results indicate that Scots pine and lodgepole pine have similar volume production rates and external quality traits (II). External properties of trees in the stands, particularly stem straightness and frequencies of quality defects (e.g. spike knots), were affected by the selection strategies applied in the thinning treatments. Thus, selection in thinnings should focus on these traits as they affect both the quality and grades of logs (III). The applied thinning treatments did not significantly influence board properties, such as basic density, Modulus of Elasticity and Knot Area Ratio. However, differences in these variables between outer and inner boards indicate that quality improvement might be connected to improvement in the growth of individual trees (IV). In summary, use of improved planting material and wider than currently applied 2x2 m spacing in combination with selection of high quality trees might lead to production of higher quality timber. However, the scope for selection decreases with time and since the Scots pine boards from thinned stands and unthinned stands did not significantly differ the target traits and both objectives and market conditions must be carefully considered

Growth response of Pinus sylvestris L. and Picea abies [L.] H. Karst to climate conditions across a latitudinal gradient in Sweden

11 Pág.Pinus sylvestris L. (Scots pine) and Picea abies [L.] H. Karst. (Norway spruce) are the most important economic tree species in Sweden. However, like every other tree species, they are affected by climate change, especially drought conditions. In this study, we analysed the effect of climate variability on the radial growth of Scots pine and Norway spruce in Sweden. Sixteen sites of pairwise monospecific stands of Scots pine and Norway spruce distributed across latitudinal gradients in Sweden (55 – 67 ° N) were used. In each site, we sampled at least 15 dominant/codominant Scots pine and Norway spruce trees without any defect in the sampled plots’ buffer zone (3 – 5 m wide). We performed a correlation analysis between climate variables and the radial growth of the species using different timescales; and regressed the coefficients with latitudes. Thereafter, important climate variables for both species were identified. Our results showed that temperature is the main climate factor affecting the radial growth of Scots pine while Norway spruce is more sensitive to early summer precipitation. The impact of summer precipitation on the radial growth of both species transitioned from a positive to a negative trend across a latitudinal gradient. Conversely, a contrasting pattern was noted in the relationship with summer temperature. The radial growth of both species responded positively to spring temperature, particularly at lower latitudes. The resistance of pine and spruce to drought showed a clear linear increase with latitude (p < 0.001). Compared to spruce, pine showed a better capacity to attain pre-drought growth levels (i.e., resilience) and was independent of latitude. Our findings contribute to the understanding of the spatial patterns of the growth-climate relationship of Scots pine and Norway spruce in Sweden; and could offer useful guidance on adaptive forest management in the face of climate change.This research was funded by the SLU strategic funding Trees for Future (T4F) and the Stiftelsen Seydlitz MP Foundation. It also received support from the Instituto de Ciencias Forestales (ICIFOR-INIA), Madrid. Jorge Aldea's work was supported by the grant RYC2021–033031-I, funded by MCIN/AEI/10.13039/501,100,011,033 and by the European Union "NextGenerationEU"/PRTR".Peer reviewe

Nondestructive wood density testing in downy birch and silver birch genetics field trial, southern Sweden

Non-destructive testing of wood density, as is already done for Eucalyptus, can allow for earlyselection of birch trees for breeding programmes and stands for harvesting. In this work, external stemquality traits were visually assessed in a family trial of downy (Betula pendula) and silver (B.pubescens) birch in southern Sweden. A subsample of trees was measured for wood density using thePilodyn resistometer portable NDT tool. An X-ray microdensitometric analysis of the subsample oftrees was completed using the Itrax X-ray machine for increment cores taken from the south face,through the pith to the north bark at 1.3 m stem height. The Pearson’s r value for Itrax density andPilodyn density was high (0.580 for downy birch and 0.795 for silver birch), and this correlationmeans Pilodyn should provide a good estimate of average birch wood density. Neither species hadstable wood density values at age 13 and both species’ density increased over time from pith to bark.Ring width influence on stem density was minor or non-existant, and may vary between birch specie