Rudolf Petráš

Possible causes of the recent rapid increase in the radial increment of silver fir in the Western Carpathians

Silver fir is one of the most productive and ecologically valuable native European tree species, however, it has been experiencing decline which has periodically occurred over its natural range. This paper aims to investigate the recent climate-growth relationships of silver fir (Abies alba Mill.) and its temporal change along the course of its life. Long-term tree-ring databases, as well as records on climate, atmospheric SO2, NO3 and acid concentrations from four different regions in the Western Carpathians were used. The results provide clear evidence of significant increase of silver firs radial increment over the entire Western Carpathian area since 1970-1980. The results indicated that the most probable factors behind the rapid recovery of tree radial increment were reductions in emissions of NO3 and SO2, alongside a significant increase in mean June, July and April temperatures.

Effects of post‐glacial phylogeny and genetic diversity on the growth variability and climate sensitivity of European silver fir

Summary 1. Growth rates of European silver fi r( Abies alba Mill.) rapidly increased in the last century. At the same time, ring widths declined at the species southern distribution limits in the Mediterranean. Such diverse growth trends and responses have largely been attributed to regional climate conditions, but this was prior to considering the species’ post-glacial phylogeny. 2. A dendrochronological network composed of 1961 tree-ring width series (TRW) from 78 silver fir sites between 365 and 1400 m a.s.l. along the Carpathian Arc was compiled. Spatial differences in the species’ genetic diversity were investigated from genetic data of 69 silver fir populations in the region. Differences in growth variability and climate sensitivity were then related to post-glacial phylogeny and genetic diversity. 3. Significant differences in interannual and longer-term growth trends and climate responses across the Carpathian Arc were found to coincide with the geographical north–south separation of two post-glacial populations from effective refugia originating from the Apennine and Balkan peninsulas. Summer temperature was the main driver of growth in the western (Apennine) lineage, whereas ring widths in the Balkan population from the east were predominantly controlled by summer drought. Fir specimens that originated from the Balkan lineage exhibited higher genetic diversity and more regular growth dynamics and also appeared to be less sensitive to air pollution during the 1970s. 4. Synthesis. Although the phylogeny of forest trees has largely been neglected in most dendroecological studies, results here indicate the importance of different post-glacial histories for the growth sensitivity and adaptability to varying environmental factors. Decision-making under future climate warming scenarios (for building resilience through forest management) should therefore consider different phylogenetic origins.

Stem quality assessment in European National Forest Inventories: an opportunity for harmonised reporting?

Key messageThe potential of European National Forest Inventories to harmonise stem quality estimation in European forests was identified despite considerable differences in existing national approaches.ContextKnowledge on stem quality and assortments structure in European forests is highly important for policy makers and the timber industry and also for carbon life cycle analysis due to the fact that different timber products have different end use and thus store carbon for different time periods.AimsThe study aim was to evaluate the potential of European National Forest Inventories (NFI) to objectively report on the stem quality in European forests in a harmonised manner.MethodsA comprehensive questionnaire was conducted as the first important step to evaluate the current status of stem quality assessment and assess the existing level of harmonisation.ResultsDirect stem quality assessment or classification is used in 19 out of 28 European NFIs. Only eight countries provide timber assortment estimates from their NFIs. In addition, different sampling strategies for stem quality assessment are used among NFIs. Tree parameters relevant for stem quality assessment on standing trees were identified for the purpose of harmonisation. Several methods towards harmonisation between European NFIs for the purpose of reporting on stem quality of European forests were suggested.ConclusionCurrent European NFIs are not capable of reporting the stem quality of European forests in a harmonised manner at this stage and considerable efforts will need to be taken before the harmonised stem quality estimation can be prepared. However, the inquiry also revealed that there is a potential to develop the harmonised estimations in future.

Evaluating similarity of radial increments around tree stem circumference of European beech and Norway spruce from Central Europe

Extracting cores from a tree using an increment borer has been standard practice in dendrochronological studies for a long time. Although empirical rules exist regarding how many samples to take and which methodology to apply, comparatively few studies provide quantification of the similarity of relative tree-ring-widths (TRW) around the stem circumference. The aim of this study was therefore to precisely measure the similarity of standardised TRWs around the stem circumference and to provide objective suggestions for optimal core sampling of Norway spruce (Picea abies Karst. [L.]) and European beech (Fagus sylvatica L.) growing in Central European temperate forests.A large sample of cross-sectional discs was used from Norway spruce and European beech trees growing on various slopes, at different altitudes and biogeographic regions across the Czech Republic and Slovakia. The similarity of TRWs measured in different coring directions was analysed by testing the relativized TRW around the trunk (rTRW). Comparison of rTRWs revealed no significant differences between coring directions, indicating that the relative increment was the same around the radius. The results also showed the high similarity between the rTRWs to be independent of both slope inclination and altitude. Moreover, the reconstruction of proportional tree diameters and basal areas backward in time from one core sample and one measurement of tree diameter (basal area) at the time of sample extraction is possible with reasonable precision.

Height-diameter models for mixed-species forests consisting of spruce, fir, and beech

Abstract Height-diameter models define the general relationship between the tree height and diameter at each growth stage of the forest stand. This paper presents generalized height-diameter models for mixed-species forest stands consisting of Norway spruce (Picea abies Karst.), Silver fir (Abies alba L.), and European beech (Fagus sylvatica L.) from Slovakia. The models were derived using two growth functions from the exponential family: the two-parameter Michailoff and three-parameter Korf functions. Generalized height-diameter functions must normally be constrained to pass through the mean stand diameter and height, and then the final growth model has only one or two parameters to be estimated. These “free” parameters are then expressed over the quadratic mean diameter, height and stand age and the final mathematical form of the model is obtained. The study material included 50 long-term experimental plots located in the Western Carpathians. The plots were established 40-50 years ago and have been repeatedly measured at 5 to 10-year intervals. The dataset includes 7,950 height measurements of spruce, 21,661 of fir and 5,794 of beech. As many as 9 regression models were derived for each species. Although the “goodness of fit” of all models showed that they were generally well suited for the data, the best results were obtained for silver fir. The coefficient of determination ranged from 0.946 to 0.948, RMSE (m) was in the interval 1.94-1.97 and the bias (m) was -0.031 to 0.063. Although slightly imprecise parameter estimation was established for spruce, the estimations of the regression parameters obtained for beech were quite less precise. The coefficient of determination for beech was 0.854-0.860, RMSE (m) 2.67-2.72, and the bias (m) ranged from -0.144 to -0.056. The majority of models using Korf’s formula produced slightly better estimations than Michailoff’s, and it proved immaterial which estimated parameter was fixed and which parameters were free

Effect of different management on quality and value production of pure beech stands in Slovakia

Abstract Value production is one of the most important information for comparing different management strategies in forestry. Although the value production of forest stands is affected by various factors (stem and assortment quality, stem dimension, stem injury, price of assortments), thinning can be considered as one of the most important one. This paper aims at the evaluation of qualitative and value production in homogeneous beech stands, which were managed by two different thinning types for period of 45 to 55 years: (i) – heavy thinning from below (C grade according to the German forest research institutes released in 1902) and (ii) – Štefančík´s free-crown thinning. The third variant was control (iii) – subplot with no interventions. Silvicultural quality characteristics of the lower half of the stem were assessed using a 4-class scale (A – the best quality, D – the worst quality). Assortment structure (commercial quality) was estimated for each stem by an assortment model developed in the past. Nearly 3,000 individual trees aged from 83 to 105 years from 23 subplots established across the Slovakia territory were assessed. The highest volume of the best silvicultural quality of stems (A class) has been reached in forests where Štefančík´s free-crown thinning was applied (57 – 85%) while the lowest (22 – 56%) on subplots with no management. The proportion of two best commercial quality assortments (I + II) was highest in forests managed by heavy thinning from below (21 – 29%) and the lowest when no treatment was applied (7 – 19%). The highest value production (expressed in € ha−1) was reached in the forests treated by free-crown thinning. Results suggested the overall positive impact of thinning on the increase of value production in beech forests. Particularly, the free-crown thinning focusing on selection of best quality trees should be preferred as it leads, besides its sufficient value production, to a higher vertical differentiation of the beech forests.

Economic value production of trees as a criterion of their maturity in an uneven-aged forest

Abstract Tree maturity of the four main tree species that are most frequent in the uneven-aged forests of the Western Carpathians was analysed. The maturity was determined on the base of the economic value production in relation to tree diameter. We derived mean timber values of spruce, fir, pine, and beech trees (€ m−3) depending on their diameters, quality and stem damage, and in the case of beech also depending on tree age. The assortment structure was calculated using the models of tree assortment tables that account for the stated tree parameters. The assortment prices were taken from the price list of logs in assortment and diameter classes of the Forests of the Slovak Republic, state enterprise, for the year 2016. Trees are mature when their mean timber monetary value is at maximum. Results show, that the highest mean value production of the majority of beech trees of average and above-average stem quality is 70 - 80 € m−3 for trees with diameters between 45 and 55 cm. Monetary values of spruce and fir trees with diameters above 60 to 90 cm are 80 - 95 € m−3, while the monetary values of pine trees with the same diameters are approximately 70 - 115 € m−3. The value production of trees is reduced if the stems are of worse quality or damaged, but in the case of beech it also decreases with greater diameter or tree age.

Wood quality and value production in mixed fir-spruce-beech stands: long-term research in the Western Carpathians

Abstract Stem quality and damage was evaluated in mixed spruce-fir-beech stands. Moreover, an assortments structure was determined with their financial value. Results were compared with pure spruce (Picea abies [L.] Karst.), fir (Abies alba Mill.) and beech (Fagus sylvatica L.) stands. Repeated measurements on 31 long-term research plots, stand assortment models, assortment yield models and value yield models were used. Stem quality of fir and spruce was only slightly lower in mixed stands compared to pure stands but beech stem quality was considerably worse in mixed stands. Fir and spruce had slightly lower proportions of better IIIA quality logs and higher proportions of IIIB quality in mixed stands. Beech had worse assortment structure than spruce and fir, in general. Pure beech stands had higher proportions of better I–IIIA quality assortments than mixed stands by 1–7%. Fir and spruce average value production (€ m−3) culminated at about 56 and 62 cm mean diameters. Almost the same value production was found in pure stands. In these stands it culminated at the mean diameter of 58 and 60 cm. Beech produced substantially less value on the same sites. In mixed stands, its value production culminated at the mean diameter of 40 cm. In pure stands, it culminated at the mean diameter of 36 cm. Although the production was found to be similar in both mixed and pure forests, higher damage intensity and less stem quality in mixed forests suggest that the pure forests can be more profitable.

Modely výškových kriviek jedľovo-bukových porastov Východných Karpát / Models of height curves in fir-beech stands of the Eastern Carpathians

Abstract The models of height curves were derived from repeated measurements at six permanent research plots in the experimental object of Komárnik situated in the Eastern Carpathians. During more than 50 years of investigation, the heights of 1,346 beech and 1,208 fir trees were measured. Tree heights had a great variability, but the stage-shift of height curves was not confirmed. The non-linear regression models of height curves for beech and fir were derived, where tree height is a function of tree diameter and model height for a selected diameter class. They are based on the Korf growth curve with three parameters. The models explained 90% and 94% of beech and fir height variability, respectively. The models confirmed the actual knowledge that fir had higher tree height increment than beech especially for trees with greater diameters. The comparison of our models to those developed by other authors showed that the shape of height curves slightly differed. Beech curve was characterised by greater, while fir curve by lesser curvature in comparison with other published models. Our models have only local validity due to the limited scope of experimental data. They can be applied under the local conditions in order to perform valuation and simulation of growing stock development and increments of uneven-aged and multistoried fir-beech stands. Abstrakt Odvodili sa modely výškových kriviek z experimentálneho materiálu opakovaných meraní šiestich trvalých výskumných plôch na výskumnom objekte Komárnik vo Východných Karpatoch. Počas viac ako 50-ročného sledovania sa zmeralo 1 346 výšok pre buk a 1 208 pre jedľu. Výšky majú všeobecne veľkú variabilitu, ale nepreukázal sa štádiový posun výškových kriviek. Odvodili sa nelineárne regresné modely výškových kriviek pre buk a jedľu, kde výška stromu je funkciou jeho hrúbky a modelovej výšky pre zvolený hrúbkový stupeň. Ich základom je Korfova rastová krivka s tromi parametrami. Modelom je vysvetlených 90 % variability výšok pri buku a 94 % pri jedli. Modely potvrdili doterajšie poznatky, že jedľa má najmä pri hrubších stromoch vyššie výškové prírastky ako buk. V porovnaní k modelom iných autorov majú odvodené modely málo odlišný tvar výškových kriviek. Buk má väčšiu a jedľa menšiu krivosť ako porovnávané modely. Modely majú vzhľadom na obmedzený rozsah experimentálneho materiálu len lokálny charakter. Pre miestne pomery sa môžu aplikovať na bonitovanie a simulovanie vývoja zásob a prírastku nerovnovekých a viacetážových jedľovo-bukových porastov.

ENERGY POTENTIAL IN PRODUCTION OF FAST-GROWING POPLAR CLONES IN SLOVAK REGIONS

Abstract Calorific value production from the above-ground biomass of stands was derived from its volume production. The mathematical models of growth tables of I-214 and Robusta poplar clones, biomass density values and calorific values of biomass dry matter were used for its calculation. At the stands aged 35 years and site indices of 20, 30 and 40, the calorific value has approximately 2.700, 6.000 and 9.300 GJ.ha-1 respectively. The I-214 clone has higher production than Robusta in the first half of its growth, albeit with minimum differences. The annual increments of calorific value culminate about the age of 9-13 years with values of 450-115 GJ.ha-1. Mean annual production of both clones culminates at the age of 17-26 years with values of 320-80 GJ.ha-1. Lowland forest locations with high level of ground water in Slovakia with the total area of 25.600 ha are most suitable for poplars production. On this area, we can assume the mean annual production of 3.566 TJ of gross calorific value obtained from above-ground biomass in the future. From that, about 64% is in wood, 14% in bark and 22% in small-wood. Up to 85% of this production potential is situated in the area of The Danube Lowland and the rest is mainly in southern areas of the Central and Eastern Slovakia.