Sessile Oak Forests Research Articles

Canopy nitrogen application effects on Quercus petraea L. and Fagus sylvatica L. ring width and wood density

AbstractAs an essential nutrient, Nitrogen (N) availability is fundamental in evaluating forest productivity, and as such, understanding the effects of changing atmospheric N inputs in forest ecosystems is of high significance. While most field experiments have been employing ground fertilization as a method to simulate N deposition, two experimental forest sites in Italy have adopted the more advanced canopy N application approach. Here we present findings from a case study of wood core analyses of predominantly pure, even aged, Sessile oak (Quercus petraea L.) and European beech (Fagus sylvatica L.) forest stands, treated with either below or above canopy N fertilization, comparing between the two simulation pathways of increased N deposition. The potential effects of elevated N availability on total ring width, mean ring density, and their corresponding earlywood and latewood fractions are examined. Our results indicate inconclusive effects of the treatments on the ring width traits of both Q. petraea or F. sylvatica, although basal area increment patterns appeared to be affected divergently between the species and treatments. Mean and earlywood, but not latewood, densities on the other hand, exhibited a decrease in certain years of the treatment period in Q. petraea as result of the above canopy N application only, whereas F. sylvatica wood density showed no clear response to any of the treatments. Thus, we are describing distinct reactions of the two broadleaved species to the different experimental N deposition approaches, discussing potential growth patterns under increased N availability, and emphasizing the importance of considering wood density in assessments of tree biomass accumulation and essentially Carbon storage capacities.

Predicting the potential ecological niche distribution of Slovenian forests under climate change using MaxEnt modelling

The aim of the article is to assess the potential impacts of climate change on Slovenian forests in the period 2080–2100 based on two climate scenarios: SSP1-2.6 (optimistic) and SSP5-8.5 (pessimistic) using the MaxEnt software. Slovenian forests are divided at the ecological community level into thirteen forest vegetation types. Analyses of changes in ecological niche areas, distances of vectors between centroids of present areas and future ecological niches, and general spatial changes are carried out. In addition, changes in the altitudinal zones of forest vegetation types were investigated. The results indicate significant changes for Thermophilous beech forests and Thermophilous hop-hornbeam, sessile oak, downy oak, Scots pine and black pine forests. The potential changes in the altitudinal zones of forest vegetation types indicate a clear trend of forest vegetation types moving to higher altitudinal zones.

Bilateral cooperation - Fostering the ability of native European beech and sessile oak forests in the border region against the impacts of climate change

Adequate adaptions and actions to combat anthropogenic climate change (CC) are significant challenges of the 21st century. In Europe, according to the European Environmental Agency, warming of around 2°C is expected under the moderate climate scenario (RCP 4.5) by the end of the century, but the pessimistic RCP 8.5 scenario project an increase of up to 6°C. In addition to the rise in temperature, changes in precipitation and increased frequency of extreme weather events are predicted. New environmental conditions affect tree species and habitats differently; thus, forest biodiversity and local tree species compositions probably will be altered in many regions in the future. The effects may be manifold: some tree species may persist, locally adapt and migrate, while others may disappear from given regions and be replaced by native or non-native species. The native forests of the Austrian-Hungarian border region are particularly affected by the climate change. To mitigate the consequences of anthropogenic climate change to preserve forest biodiversity for future generations and to enable their use, deliberate and planned human interventions and actions are essential. These require transnational or even global efforts since nature and climate do not recognise man-made borders. The REIN-Forest project (Interreg V-A Austria-Hungary Programme - ATHU150), a bilateral project between Austria and Hungary, aimed to establish harmonised protection measures for the conservation of native forests in Northern, Central and Southern Burgenland, Vienna, Vienna Umland-South, Lower Austria South, Graz and Eastern Styria, Győr-Moson-Sopron, Vas and Zala counties (the so-called programme area). In the scope of this project, international cooperation between three project partners: the Austrian Research Centre for Forests (BFW, Austria), the Forest Research Institute – University of Sopron (SOE ERTI, Hungary) and the Vas County Government Office (VVÖH, Hungary) was established. Previous results and outputs of the SUSTREE project (Interreg Central Europe CE614), such as: a) Transnational delineation model of conservation and forest seed transfer zones in climate change, b) Report of intraspecific response function and derivation of climate transfer limits, SusSelect data, recommendations and c) Application of the species distribution models for the delineation of seed transfer zones/models in Central Europe, were put into practice during the project, focusing on two native deciduous forest tree species of the Austrian-Hungarian border region: European beech (Fagus sylvatica L.) and sessile oak (Quercus petraea (Matt.) Liebl.). During the REIN-Forest project, the following joint documents were prepared and several activities were implemented: 1. Model-based document on the current state and future perspectives of European beech and sessile oak forests; 2. Bilateral strategy for the transfer of forest reproductive material (FRM) and its use in the Austrian-Hungarian border region; 3. Establishment of altogether six demonstration sites (three in each country) with local and climate-adapted FRM of European beech and sessile oak for long-term monitoring; 4. Management and monitoring plan of the demonstration sites; 5. Joint bilingual communication strategy, which included informative programmes and meetings with professionals, locals and schools and also education material for further use. REIN-Forest focused on using scientific results and outputs in the field of applied forestry and awareness-raising. Besides strategies, recommendations and reports that would facilitate forest managers' decisions for the future in the border region, events and workshops were offered for forestry practitioners, school pupils and the public and a short film and educational materials were published.

Altitudinal Distribution, Seasonal Dynamics and Borrelia burgdorferi Sensu Lato Infections in Hard Ticks (Acari: Ixodidae) in Different Forest Communities in Inland Croatia

Altitudinal distributions, population structures and seasonal dynamics of tick fauna at three localities in Continental Croatia (Medvednica and Papuk) and an alpine biogeographic region (Gorski Kotar) were studied. Sampling of questing ticks was performed twice a year (spring and autumn, from 2019 to 2021) at different altitudes (200, 400, 600, 800 and 1000 m above sea level) using the flagging method. In total, 2942 ticks (53.9% larvae, 40.1% nymphs, 6.0% adults) were sampled and 2937 (99.83%) were determined as Ixodes ricinus, 4 (0.14%) as Haemaphysalis concinna and 1 (0.03%) as Ixodes frontalis. Ixodes ricinus was the only species found at all altitudes and sampling sites. The highest tick abundance was recorded at higher altitudes (800–1000 m asl.) on Medvednica and in Gorski Kotar within mixed forests of European beech and European silver fir, while on Papuk most of the ticks were sampled at lower altitudes (200 m asl.) in Sessile oak forest. From 27 pools containing 305 ticks, 1 (3.7%) was positive for Borrelia burgdorferi sensu lato infection. Borrelia burgdorferi s.l. was detected in 20% (1/5) of the pools containing nymphs and adults collected in Gorski Kotar (600 and 800 m asl.). Sequencing of the ospA gene and phylogenetic analysis revealed the presence of the Borrelia burgdorferi sensu stricto genotype.

Forest Habitats and Vegetation of Dragoman Municipality, Western Bulgaria

The study is focused on the investigation of the forest habitats and the vegetation of Dragoman municipality, located in western Bulgaria. Following the Braun-Blanquet approach, 212 relev´es were collected in 2019 and 1054 field points were verified, as well. As a result, eight forest habitat types included in Directive 92/43/EEC were identified. They cover 85.96 km2 or 26.5% of the total area and are located mainly in the northern, western and southern parts of the municipality. Pannonian-Balkanic turkey oak–sessile oak forests (91M0) build up the vastest areas, followed by *Pannonian woods with Quercus pubescens (91H0), covering 67.2% and 12.97% of the territory, respectively.

The bigger the tree the better the seed – effect of Sessile oak tree diameter on acorn size, insect predation, and germination

Sessile oak is one of the ecologically and economically most important tree species in Europe. Recently, the importance of this species has been particularly highlighted in the context of climate change, where it is expected that these species will play a significant role within their natural range and beyond. To regenerate and expand the range of the sessile oak forests, a large amount of healthy acorns is needed. The acorn production and the acorns themselves are endangered by a large number of abiotic and biotic factors. As oak trees of different sizes do not produce the same amount of seed of the same quality, we investigated how the sessile oak tree diameter affects the acorn size, insect infestation, and germination rate. On the other side, as the acorn size influences the attack rates of the most significant acorn pest – Curculio glandium (Marsham, 1802), and the germination rates of both the damaged and healthy acorns we also investigated how the acorn dimensions influence the insect damage and germination rates, and how the insect damage influences the germination rates. We determined that the oak tree size influences some oak seed characteristics that are important for forest regeneration, while it does not affect others. A greater acorn yield was recorded on the bigger oak trees. The tree dimensions also had a significant influence on the acorn size. Greater average length, as well as greater average acorn diameter, were recorded on bigger trees. Although the tree size affects the acorn size, it does not influence the acorn insect predation rates or its germination rates. These parameters are affected by the acorn size itself. Bigger acorns had a greater germination rate. Insects preferred smaller acorns and had a significantly negative influence on the germination rate.

Deliberation over species change in a monodominant sessile oak stand (Quercetum petraeae Cer. et Jov. 1953., subass. tilietosum) - A case study in ”Djerdap” National Park

Stand structure analysis was conducted before and after natural regeneration (on the same plot) on a site of monodominant sessile oak forest (Quercetum petraeae Cer. et Jov. 1953., subass. tilietosum). In this stage individual old sessile oak trees were still remaining in the stand. Before the regeneration in the 150-yr-old stand in 1992 only sessile oak was rep?resented in the upperstorey. The trees mostly had irregularly developed crowns and reduced growth potential. These were the elements used in planning the regeneration in management plans. Besides the remaining individual old sessile oak trees, silver lime dominates in the young stand in 2017. In the stand structure there is no biological potential of sessile oak trees that could represent the basis for further development because the sessile oak trees are suppressed by silver lime towards the understorey and even the herb layer. Because of the undefined significance of the silver lime in the stand, transient management was prescribed in the man?agement plan so a reconstrucion of the stand should follow in one of the next management periods in order to restore sessile oak on the site as it was suppressed due to an inedequate regeneration procedure. On the basis of the studied stand structure of the young stand, the abandonment of the transient management concept is recommended and introduction of the intensive management approach of slver lime in the current rotation. This was based on the available number of silver lime trees of good quality in the stand, i.e. the aspirants for tending by means of selective thinning and their strong growth response four years after selective thinning. Old sessile oak trees that are still present in the stand are only a simulacrum of the continuity of the current stand with the previous one and they should be removed by means of intensive and rationalized tending of silver lime, and partly integrated in the silver lime stand.

Soil Microbial Functional Diversity under the Single-Season Influence of Traditional Forest Management in a Sessile Oak Forest of Central Europe

This one-year study focuses on the responses of a soil environment to the implementation of traditional forest management practices in oak–hornbeam stands with the following treatments: cut (C), cut + litter raking (CR), cut + grazing (CG), cut + litter raking + grazing (CRG) and control (Ctrl). The cut was conducted in 2018 through extremely heavy thinning. In autumn of 2017 and 2018, we sampled the soils, focusing on microbial functional diversity (FD) assessments using BIOLOG EcoplateTM. After one season, the FD was the highest in the Ctrl stand and the lowest in the CRG stand. Furthermore, we detected significant seasonal differences in soil reaction, nitrate nitrogen content, phosphatase activity and microbial biomass among the treatments. In particular, the Ctrl stand was defined via FD indices and biochemical and biological soil properties that contrasted mainly with those of the CRG stand defined by the content of mineral nitrogen forms. The soil properties did not differ substantially in the remaining treatments. Of the 31 carbon sources defining FD, 6 were treatment-specific (putrescine, L-arginine, L-serine, L-threonine, D-cellobiose and glycogen), while the remaining carbon sources mainly displayed either uniform high or low activity across the treatments.

AILANTHUS ALTISSIMA (MILLER) SWINGLE - INVASIVE SPECIES IN THE FOREST HABITATS IN THE UPPER BASIN OF THE MOTRU RIVER

Ailanthus altissima (Miller) Swingle is an invasive species found in forest habitats in Oltenia and beyond. The aggression and power of dissemination and development of this species is increasing. The thematic area provided in this paper is situated in the upper basin of the Motru river. Within this study had been aimed the identification and level of pressures and threats of the invasive species Ailanthus altissima in the forest habitats in the researched territory. These studies also noted the conservation status of the forest habitats in which this invasive species was encountered. In this area we identified this invasive species in the following forest habitats: 91E0* Alluvial forests with Alnus glutinosa and Fraxinus excelsior (Alno-Padion, Alnion incanae, Salicion albae), 91V0 Dacian Beech forests (SymphytoFagion), 9130 Asperulo-Fagetum beech forests, 91M0 Pannonian-Balkanic turkey oak - sessile oak forests. This species influence the succesional dynamics and the floristic composition of the forest habitats, occupying increasingly more and more space.

SESSILE OAK FOREST ECOSYSTEMS FROM TRANSYLVANIA IN THE CONTEXT OF CLIMATIC CHANGES

Climatic modelling software was used in order to measure future changes in climatic conditions. The software HYPE can realize prognosis for certain climatic factors responsible for causing extreme climatic phenomena in forest ecosystems. It was applied to study sessile oak forest ecosystems from Transylvania. Sample surfaces were installed, inventoried and followed by simulations of two future climatic scenarios. Two such scenarios were chosen, namely the climatic scenario in which the gas effect concentration will increase moderately (rcp-4.5) and the climatic scenario in which the gas effect concentration will be accentuated (rcp-8.5). The data was then processed and which led to an analysis of the way in which future climatic changes will affect forest ecosystems located in the studied area. After analyzing all three sessile oak stands, we can conclude that the Mediaș stand is the most vulnerable one to both climatic parameters. Future climatic scenarios are necessary for other surfaces located in our country for the same species, as well as for others in order to have a bigger picture of future implications. The best management measures and decisions regarding the installment of future stands can consequently be taken based on these results.

Unveiling the conservation status of the sessile oak forest for their protection and management in the northeast of the Iberian Peninsula

The sessile oak forests found on the northeast of the Iberian Peninsula are ascribed to the Lathyro-Quercetumpetraeae association and play a key role in understanding the ecology of this habitat, as this region represents its xeric limit. For this reason, we analysed the biodiversity patterns and current conservation status of the sessile oak forests in the region. To do so, we collected Braun-Blanquet inventories of 34 plots randomly distributed throughout the sessile oak forests. The results showed a relationship between the climatic conditions and the biodiversity variables. While the richness of the community increased with decreasing temperatures, the characteristic species found within the community decreased at these same temperatures. This result was due to the presence of most companion species in the cool zones at high elevations.Sessile oaks are found close to other communities, such as silver birches and Scot pine forests.On the other hand, in the warm areas at low elevations, the sessile oak community was more established, with plants typical of this type of forest. These slightly warmer zones with sessile oaks are very important in terms of conservation and more vulnerable to climate change and the thermophilization of the community, as has been studied. As such, protecting and managing these forests is key to conserving this community. Nevertheless, as current protection measures do not safeguard most of these forests, it is essential to define a conservation strategy to preserve them. Using the conservation status, we have established criteria to improve the conservation strategy for sessile oak forest on the NE Iberian Peninsula.

Transpiration of Anatolian black pine and sessile oak forest stands in a sub-humid region of Turkey

Transpiration is a key component of the watershed water budget. Therefore, determining the transpiration of forest stands with different characteristics have been of interest for watershed hydrology and forest management practices in a wide range of environments. The objectives of this study were to compare transpiration of Anatolian black pine (Pinus nigra Arn. subsp. pallasiana (Lamb.) Holmboe) and sessile oak (Quercus petraea (Matt.) Liebl.) tree stands and to model transpiration based on the measured climatic factors. Stand transpirations were calculated from sap flow measurements made by the trunk heat balance method. We conducted an exploratory factor analysis (PCR) to detect affecting meteorological factors of stand transpiration, and we developed linear regression equations to predict transpiration of pine and oak stands. Mean daily and yearly canopy transpiration (Ec) were 1.05 mm day-1 and 378.3 mm year-1 for the pine stand and 3.52 mm day-1 and 801.7 mm year-1 for the oak stand. There was a highly positive correlation between daily stand transpiration and wind speed, global radiation, air vapour pressure deficit and air temperature, but a negative correlation with relative humidity for both stands. Soil water potential had little effect on stand transpiration. The model equations accounted for 81% of the variations in transpiration for the pine stand and 85% for the oak stand. Therefore, the transpiration of forest stands should be considered for effective vegetation management practices, as model equations to estimate the transpiration of pine and oak stands in the region.

Small-scale genetic structure and mating patterns in an extensive sessile oak forest (Quercus petraea (Matt.) Liebl.).

Oaks (Quercus) are major components of temperate forest ecosystems in the Northern Hemisphere where they form intermediate or climax communities. Sessile oak (Quercus petraea) forests represent the climax vegetation in eastern Germany and western Poland. Here, sessile oak forms pure stands or occurs intermixed with Scots Pine (Pinus sylvestris). A large body of research is available on gene flow, reproduction dynamics, and genetic structure in fragmented landscapes and mixed populations. At the same time, our knowledge regarding large, contiguous, and monospecific populations is considerably less well developed. Our study is an attempt to further develop our understanding of the reproduction ecology of sessile oak as an ecologically and economically important forest tree by analyzing mating patterns and genetic structure within adult trees and seedlings originating from one or two reproduction events in an extensive, naturally regenerating sessile oak forest. We detected positive spatial genetic structure up to 30 meters between adult trees and up to 40 meters between seedlings. Seed dispersal distances averaged 8.4 meters. Pollen dispersal distances averaged 22.6 meters. In both cases, the largest proportion of the dispersal occurred over short distances. Dispersal over longer distances was more common for pollen but also appeared regularly for seeds. The reproductive success of individual trees was highly skewed. Only 41 percent of all adult trees produced any offspring while the majority did not participate in reproduction. Among those trees that contributed to the analyzed seedling sample, 80 percent contributed 1–3 gametes. Only 20 percent of all parent trees contributed four or more gametes. However, these relatively few most fertile trees contributed 51 percent of all gametes within the seedling sample. Vitality and growth differed significantly between reproducing and nonreproducing adult trees with reproducing trees being more vital and vigorous than nonreproducing individuals. Our study demonstrates that extensive, apparently homogenous oak forests are far from uniform on the genetic level. On the contrary, they form highly complex mosaics of remarkably small local neighborhoods. This counterbalances the levelling effect of long‐distance dispersal and may increase the species’ adaptive potential. Incorporating these dynamics in the management, conservation, and restoration of oak forests can support the conservation of forest genetic diversity and assist those forests in coping with environmental change.

An analysis of the profitability of the restitution of sessile oak forests affected by wildfires in Serbia

Wildfires caused by climate change in Europe have numerous and long-lasting ecological, economic, and social implications for sustainable development (natural environment, economy, and society as a whole). Artificial revitalization of sessile oak forests destroyed by wildfires in Serbia is feasible, but it is quite expensive compared to the spontaneous regeneration. Cost-benefit analysis (an economic approach to comparing and estimating the benefits and shortcomings of a particular business plan, i.e., an investment project by analyzing its costs and benefits) is aimed at finding the best solutions and making the best decisions about the desirability of a project. It was concluded that the investment in the restitution of sessile oak forests could be profitable only if it was based on wood production. Wood production may bear slightly higher interest rates compared to previous estimates which ranged mainly around 3%. This primarily applies to better site classes, while poor quality sites require lower rates. At lower discount rates, it takes more time to reach the break-even point, while the period of time needed to reach the break-even point shortens with higher discount rates. The length of the production cycle plays an important role in determining the investment profitability, especially regarding the relationship between the length of the production cycle and production targets (the type and the quality of wood assortments produced). According to the results of the analysis of intangible benefits and costs, the costs outweigh the benefits, which makes the restitution of sessile oak forests destroyed by fires unacceptable.

Climate warming predispose sessile oak forests to drought-induced tree mortality regardless of management legacies

Climate warming-related drought could become a major driver of large-scale forest dieback. However, little is known about how past management legacies modulate the climate-growth responses during recent dieback episodes in central European oak forests. Here, we examine the role played by past management –unmanaged old-growth vs. managed forests– in recent tree mortality events occurring in Quercus petraea (Matt.) Liebl. stands across large areas of western Romania. We analyze how stand structure (tree size, competition) and climatic factors (drought, temperature and precipitation) drive tree radial growth patterns in neighboring standing dead and living trees. We analyzed basal area increments (BAI) trends, past management legacies and climate- and drought-growth relationships during the 20th century to distinguish the roles and interactions on recent warming-induced dieback. We observed that temperature rises and changes in atmospheric water demand during growing season let to increasing drought stress during the late 20th century affecting both managed and unmanaged forests. Dead trees from old-growth and managed forests showed lower growth than living trees after dieback onset. In both forests, dead and living trees displayed divergent growth patterns after dry 1980s, indicating that dieback was triggered by severe extreme conditions. Dead trees from managed stands experienced significant stronger growth reductions after 1980s though they experienced less tree-to-tree competition than dead trees in old-growth forest. High stand density negatively drove growth and enhanced climate sensitivity in old-growth stands. Competition acted synergistically with climate warming and drought causing tree mortality regardless of the management legacies in of Q. petraea forests. Our retrospective assessment of growth rates in relation with climate and structure changes offers valuable information for further forest conservation and management decisions of Q. petraea forests. These findings highlight the importance of past uses legacies driving recent forest dieback in temperate oak forests, making them more vulnerable under forecasted climate-warming related droughts in central Europe.

Regeneration Dynamics and Development of Seedlings in Sessile Oak Forests in Relation to the Light Availability and Competing Vegetation

Natural regeneration of sessile oak forests is a complex process whose final outcome is influenced by numerous factors. The initial phase of development of sessile oak seedlings stands out as the most critical period in the process of natural regeneration of sessile oak forests. As the available light and competition from the accompanying woody species and ground vegetation are some of the main predictors of the success of sessile oak forest regeneration, this paper presents the results of studying the influence of these factors on the regeneration dynamics and development of sessile oak seedlings. The research was conducted in sessile oak forests in northeastern Serbia in the period from 2015 to 2020. At the end of the growing season each year, the following data were collected on 180 smaller sampling plots of 1 m2 in different conditions of canopy openness: the number, height, and root collar diameter of sessile oak seedlings. Also, the percent cover of competing woody species and ground vegetation was estimated on these sample plots. The obtained results indicated that the success of sessile oak forest regeneration largely depends on the initial number of sessile oak seedlings and silvicultural treatments during the rejuvenation period, which determine the microclimatic conditions in the stand and control the competing vegetation. They also indicate that with an increase in the available light, the impact of the competing vegetation on the dynamics of regeneration and development of sessile oak seedlings is less pronounced. Accordingly, as young sessile oak seedlings need a large amount of light for survival and development, it is necessary to increase the available amount of light intensively in a short period of time (six–eight years) by reducing canopy openness and thus providing optimal conditions in which sessile oak seedlings can gain an advantage over the competing vegetation.

Not all long-distance-exploration types of ectomycorrhizae are the same: differential accumulation of nitrogen and carbon in Scleroderma and Xerocomus in response to variations in soil fertility

Long-distance-exploration type (LDET) ectomycorrhizae have been reported to be best adapted to infertile soils, but variation within LDET ectomycorrhizae have not been thoroughly examined. Concentrations of nitrogen (N) and carbon (C) in LDET ectomycorrhizae were examined in Xerocomus-Pinus sylvestris and Scleroderma-Quercus petraea ectomycorrhizae. The study determined how concentrations of these elements vary in ectomycorrhizae in fertile (organic, uppermost mineral) and infertile (brunic) soil layers. The organic horizon in both Scots pine and sessile oak forest soils had the highest mineral status and exchange cations. In contrast, low mineral concentrations, high base saturation, and pH were characteristic of the brunic horizon in both forest stands. Xerocomus ectomycorrhizae had a higher concentration of N in the fertile (organic and uppermost mineral) soil horizons (3.4%) than in the infertile (brunic) soil horizon (2.2%). N concentration in Scleroderma ectomycorrhizae varied from 2.8%-3.0 % and did not differ between the studied soil horizons. The mean concentration of carbon in Xerocomus ectomycorrhizae varied from 29%-46% in Scots pine stands and from 41%-44% in Scleroderma ectomycorrhizae in sessile oak stands. The concentration of carbon in both Xerocomus and Scleroderma ectomycorrhizae was significantly higher in the fertile horizons (organic and uppermost mineral) compared to the brunic (infertile) horizon. In summary, the analysis conducted in the present study indicates that the LDET ectomycorrhizae, Xerocomus and Scleroderma, possess inherent variations in C and N content to manage soil resources.

Changes in sessile oak (Quercus petraea) productivity under climate change by improved leaf phenology in the 3-PG model

With global warming, the growing season is expected to increase for many regions of the Northern Hemisphere. It is therefore important to represent this mechanism in process-based forest growth models used in climate change impact analysis. 3-PG (Physiological Principles Predicting Growth) is a widely used process-based model that operates on stand-scale and monthly time steps. Yet, this model is currently not able to account for changes in the growing season of deciduous tree species. Therefore, we developed a method to model a dynamic growing season length with 3-PG. This method presents a novel approach to model dynamic leaf phenology with a monthly-time step model. We used a linear regression for calculating leaf onset and leaf senescence dates in response to temperature averages. The changes in the order of magnitude of days are then translated into monthly fractions. Further, we made some improvements to previous approaches of modelling the deciduous leaf cycle with 3-PG and we parameterized two model versions of 3-PG for sessile oak (Quercus petraea (Matt.) Liebl.) stands in Southwest Germany. The two model versions differed in presenting a i) constant and ii) dynamic growing season length. We used these model versions to estimate changes in sessile oak forest productivity under future climate scenarios. By comparing both model versions, we could disentangle the net effect of lengthening of the growing season on stem growth. By the end of the century, we observed on average 3 - 8 % increase in accumulated stem growth resulting from a lengthening of the growing season. At 1°C temperature increase, the lengthening of the growing season accounted for +3.3 % of accumulated stem growth (assuming unchanged precipitation). Leaf-unfolding advanced on average by 9 - 15 days and leaf senescence was delayed by 6 – 11 days for the period 2070-2100 compared to 1985-2015; for simulations of rcp 4.5 and 8.5 respectively. Overall, sessile oak productivity remained rather unchanged under future climate scenarios for Southwest Germany. Yet, we observed significant differences between sites (-6 % to +14 % in mean annual volume increment) as well as for different climate change scenarios and models (-2 % to +11 % in mean annual volume increment). We also modelled and discussed how assumptions on CO2 fertilization effects influenced 3-PG simulations.

General regularities of height-diameter curves in Hungarian oak, sessile oak and Turkey oak high forests

The height-diameter curves of natural even-aged Hungarian oak, sessile oak and Turkey oak forests in the regions of Staro Oryahovo, Sherba, Tsonevo and Aytos Forestry Districts have been studied. In order to explore the shape of the curves and, in particular, their steepness, the steepness index SI of Douhovnikov (“the method of natural indicators”) was applied. The curves were divided into three groups according to it: flat curves, medium steep curves and steep curves. Both the traditional height-diameter curves and the corresponding relative curves of Tyurin were studied. Consideration of the traditional height-diameter curves gives a certain ground for investigating to-gether the height-diameter curves of Hungarian oak and sessile oak, disregarding the tree species. This inference was confirmed by comparing the relative height-diameter curves for Hungarian oak, sessile oak and Turkey oak with Tyurin’s uniform curve of relative heights. For these comparisons we used the Willcoxon test. A statistically significant great proximity in their shapes was found. As a uniform average curve of relative heights has been established for all tree species, this proximity indicates a possibility of creating a single fan of height-diameter curves for high Hungarian, sessile and Turkey oak.

Seedling development and regeneration success after 10 years following group selection harvesting in a sessile oak (Quercus petraea [Mattuschka] Liebl.) stand

This study showed that regeneration success (presence of oaks ≥ 150 cm in total height) in artificial canopy openings of a mature mixed sessile oak stand was mainly driven by initial oak seedling density. Small-scale harvesting methods as practiced in close-to-nature forestry may disadvantage the regeneration of more light-demanding tree species including sessile oak (Quercus petraea [Mattuschka] Liebl.) and thus cause regeneration failure. However, owing to the short-term nature of many previous studies, regeneration success of sessile oak could not be properly ascertained. This study examined oak seedling development over a time period of ten growing seasons in canopy openings of 0.05 to 0.2 ha in size created through group selection harvesting in a mature mixed sessile oak forest in southwestern Germany. We tried to answer the following research questions: (i) how do initial stand conditions relate to and interact with oak seedling density and seedling height growth, and (ii) what are the driving factors of regeneration success under the encountered site conditions. We evaluated the influence of solar radiation, Rubus spp. cover, initial oak seedling density, and competition from other tree species on change in density and height of oak seedlings, as well as overall regeneration success (oak seedlings ≥ 150 cm in height). Regeneration success increased with initial oak seedling density and solar radiation levels and decreased with early Rubus spp. cover. Density and maximum height of oak seedlings was negatively related with competition of other woody species. Results of our longer-term study demonstrate that forest management activities to regenerate sessile oak naturally are only successful in stands (i) without advance regeneration of other woody species and without established, recalcitrant ground vegetation, (ii) with a sufficiently high initial oak seedling density in larger patches following mast years, and (iii) where periodic monitoring and control of competing woody individuals can be ensured. Our findings further corroborate the view that natural regeneration of sessile oak in small-scale canopy openings is possible in principle.