Tree Species In Central Europe Research Articles

Soil water storage capacity and soil nutrients drive tree ring growth of six European tree species across a steep environmental gradient

Tree growth depends on tree-intrinsic attributes, synecological interactions, atmospheric conditions and soil properties. While the influence of tree factors and climate are analysed in detail in many studies, the effect of soil properties is less investigated and compensatory soil effects are often not quantified. In this study, we use a comprehensive dataset of 1659 tree increment cores from six common Central European tree species (Abies alba, Fagus sylvatica, Larix decidua, Picea abies, Pinus sylvestris, Quercus spp.) sampled at 1562 locations across large environmental gradients in the Eastern Alps. Soil data was available from an extensive soil survey including soil pits, laboratory analysis and the application of pedotransfer-functions. Up to three main tree species per site were sampled and the tree ring widths were dendrochronologically measured and synchronized. Topographic information from a high-resolution Digital Terrain Model, high-resolution climate data and biometric measures were available at each site. To determine the influence of soil water storage capacity and soil nutrient status, we used generalized additive models to expand standard models of well-known drivers of tree growth, including age, climatic water balance and temperature. For the time span of 38 years from 1981 until 2018, we found species-specific impacts of soil properties on tree ring growth. Specifically, soil water storage acted as a buffer to overcome drought periods, in particular for deep rooting tree species like Quercus spp. and Abies alba. In addition, we found species-specific growth reactions to soil nutrient status for nutrient-demanding species likes Fagus sylvatica but no effects for less demanding tree species like Pinus sylvestris. Our results show the magnitude of the effects of soil properties in relation to other growth factors on radial growth of six Central European tree species. Therefore, we posit that, while age and climate do have a stronger influence on tree growth, it is important to consider soil as a growth factor, particularly at the distribution margins along climatic gradients.

Major tree species of Central European forests differ in their proportion of positive, negative, and nonstationary growth trends

AbstractTemperate forests are undergoing significant transformations due to the influence of climate change, including varying responses of different tree species to increasing temperature and drought severity. To comprehensively understand the full range of growth responses, representative datasets spanning extensive site and climatic gradients are essential. This study utilizes tree‐ring data from 550 sites from the temperate forests of Czechia to assess growth trends of six dominant Central European tree species (European beech, Norway spruce, Scots pine, silver fir, sessile and pedunculate oak) over 1990–2014. By modeling mean growth series for each species and site, and employing principal component analysis, we identified the predominant growth trends. Over the study period, linear growth trends were evident across most sites (56% increasing, 32% decreasing, and 10% neutral). The proportion of sites with stationary positive trends increased from low toward high elevations, whereas the opposite was true for the stationary negative trends. Notably, within the middle range of their distribution (between 500 and 700 m a.s.l.), Norway spruce and European beech exhibited a mix of positive and negative growth trends. While Scots pine growth trends showed no clear elevation‐based pattern, silver fir and oaks displayed consistent positive growth trends regardless of site elevation, indicating resilience to the ongoing warming. We demonstrate divergent growth trajectories across space and among species. These findings are particularly important as recent warming has triggered a gradual shift in the elevation range of optimal growth conditions for most tree species and has also led to a decoupling of growth trends between lowlands and mountain areas. As a result, further future shifts in the elevation range and changes in species diversity of European temperate forests can be expected.

The Water Dynamics of Norway Spruce Stands Growing in Two Alpine Catchments in Austria

Forests are highly relevant for the water dynamics of mountain areas. This study assesses the water balance of two mountainous watersheds in Austria (Rindbach and Schmittental) with similar average annual precipitation patterns but different parent material, i.e., limestone in Rindbach versus greywacke in Schmittental. The biogeochemical mechanistic ecosystem model Biome-BGC with parameter settings developed for the central European tree species was obtained to assess the energy, nutrient, and water cycle as relevant for tree growth (=carbon cycle). The seasonal precipitation pattern, the snow accumulation, the evapotranspiration, the transpiration, the water-use efficiency, and the outflow are investigated. For the period 1960 to 2022, no precipitation trends are detectable, but a temperature increase of 1.9 °C in Rindbach and 1.6 °C in Schmittental is evident, leading to a declining snow accumulation. The model simulations suggest that transpiration and evapotranspiration rates increase with increasing LAI, indicating higher rates in Rindbach compared to Schmittental. The water use efficiency increases up to an LAI = 3 m2 m−2 and declines afterwards. The water balance variables follow the same pattern, i.e., with increasing LAI, the water outflow at the Rindbach catchment declines from 78% to 29% and from 72% to 31% in Schmittental. This confirms that forest cover is important to reduce water outflow and thus enhances the protection function of mountain forests.

Limited influence of air temperature and precipitation on six-year survival and growth of non-native tree species in a Central European multi-site field trial

The biggest challenge for forest management in the near future will be the silvicultural adaptation of forests on sites where climate change will increase the risk for drought induced tree mortality and for a decrease of the growth performance. One management option is the diversification by promoting climate change adapted non-native tree species. Currently, we have in depth experience with only a few non-native tree species in Central Europe. Other tree species that may complement the species pool in Central Europe need to be carefully selected by a range of criteria. Before establishing larger silvicultural experiments at stand-level, the suitability of species to grow well with a low risk of failure under expected future climatic conditions as well as a good performance already today should be tested, amongst other aspects. We present results of a multi-site common garden experiment where growth and survival of five non-native tree species (Abies bornmuelleriana, Cedrus libani, Fagus orientalis, Tilia tomentosa, and Tsuga heterophylla) and one climate adapted local native species per site are tested in five field trials in Austria, Germany and Switzerland along a temperature (7.9–10.4 °C mean annual Temperature) and precipitation (490–1147 mm annual precipitation) gradient. Each species was replicated on three plots per site using a block-wise design. Lower survival and growth of the non-native species as the native reference on most sites indicate that the studied non-native species are today not as well adapted to current climatic conditions as native species. However, the performance of the non-native species was sufficiently high to justify further trials. Survival and growth rates were mostly equally high on the two sites at the opposing ends of the temperature and humidity gradient and lower on all other sites. Height growth and survival were only marginally affected by the strong summer drought in 2018 in all except one site, presumably due to the low water storage capacity of the sandy soils on this site. This indicates that the tested non-native tree species grow well in the wide range of climatically changing weather conditions from our transnational study sites across Central Europe. So far, the tested tree species did not reach their climatic growth limitation. However, edaphic site conditions may have influenced the performance of the tested non-native species as well and must be considered when discussing the suitability of these tree species.

Derivation of threshold values for the sulfur nutritional status of European silver fir from a cumulative concentration distribution

AbstractFor European silver fir (Abies alba (Mill)), reliable threshold values for the sulfur nutritional status are not available. Because European silver fir is an important coniferous tree species in Central Europe and due to the fact that by reduced S emissions, S is becoming a more and more critical nutrient this knowledge gap should be closed. From the interpretation of the cumulative distribution of sulfur concentrations in first‐year needles, the respective threshold values for the range of normal nutrition as well as the threshold for deficiency could be derived. When knowing these thresholds also the range of harmonic nutrition, which is the range for the optimal relation of two nutrients, could be calculated. As compared to the very few literature data available and compared to the respective values of the two most important European conifers Norway spruce (Picea abies) and Scots pine (Pinus sylvestris), the values derived for S nutrition of European silver fir are very reasonable. With respect to the S nutritional thresholds, European silver fir is very close to the values of the other two conifers, whereas the harmonic range of S in relation to N is a bit shifted to higher values indicating that European silver fir has a slightly higher demand for S (in relation to N). There is a certain time lag between the reduction of SO2 emissions in Europe and the reduction of S concentrations in needles, suggesting that S stored in the soil during periods of high emissions is relevant for S nutrition of trees for a longer period of time.

Potential of hydrogel treatment in forest regeneration: impact on growth and vitality of Central European tree species

IntroductionDrought negatively affects the growth and yield of plants. Several measures have been employed to improve the drought tolerance of plants, including the application of superabsorbent hydrogel (SAH) to soil. However, studies on the effect of SAH on trees in Central Europe, which has a temperate climate, are scarce.MethodsHere, the effects of SAH treatment on the cultivation of four key tree species in Central European forest ecosystems—European beech, sessile oak, Scots pine, and Norway spruce—were evaluated. Field and greenhouse experiments were conducted; the greenhouse conditions served as the reference for the absence of water stress.Results and DiscussionSAH treatment reduced seedling mortality by 1%–9% in the field experiment. The morphological parameters of the control and SAH-treated seedlings did not significantly differ. Among the tree species, oak seedlings exhibited a positive response to SAH treatment. Spruce, pine, and beech did not respond to SAH treatment; the proline content of SAH-treated conifer leaves was three times higher than that of oak leaves but still very low, revealing no drought stress. The results highlight the significance of employing an individual approach in the application of SAH in forestry, rather than relying on generic measures.

Harmonization and variation of deadwood density and carbon concentration in different stages of decay of the most important Central European tree species

Coarse woody debris (CWD) is a major component of the ecosystem carbon (C) balance. The estimation of C storage in CWD is an important element of the German greenhouse gas (GHG) reporting of forests, which is mainly based on the German National Forest Inventory. The deadwood C stock is calculated based on deadwood volume and, according to deadwood density (DD) and carbon concentration (CC) for each decay class (DC). Yet, the data basis of DD and CC per DC for above-ground CWD is still insufficient since there are very few country-specific measurements. Values from literature provide a first approximation for national-level estimates. However, different DC systems often prevent the use of DD and CC of other countries. Therefore, we developed a conversion method for harmonization of these data with the German four-class system. Following this, we conducted a meta-analysis to calculate mean DD and CC values for the main Central European tree species and to assess their variation. Significantly lower DDs were observed with increasing DC, except for beech between DC 3 and 4. Compared to spruce and pine, DD of beech CWD was significantly higher, overall as well as in DC 1 and 2. Species became similar in DD in advanced decay stages. A maximum of 92% of the variation in DD could be explained mainly by DC, CWD type, tree species and their interaction. DD values were mostly higher than current values in GHG reporting. CC increased with increasing DC in spruce and pine and was higher than in beech CWD, where no variation was detected. About 86% of the variation in CC could be explained mainly by DC, tree species and their interactive effect. The default value of 50% employed by the Intergovernmental Panel on Climate Change might under- (spruce, pine) and/or overestimate (spruce, pine, beech) the real CC depending on DC by up to 3.4 (pine) and/or 4.2% (beech). Based on our calculated mean DD and CC values, the accuracy of C stock assessment in deadwood as part of the GHG reporting for Germany can be substantially improved.

Effects of Douglas fir cultivation in German forests on soil seepage water quantity and quality

Norway spruce (Picea abies L.) has been a key tree species and timber source in European forests the last centuries and is increasingly suffering from drought and bark beetle infestations due to climate warming. Current management options include replacing of Norway spruce monocultures with pure and mixed stands of European beech (Fagus sylvatica) that is the naturally dominating tree species in Central Europe. Additionally, Douglas fir (Psudotsuga menziesii), a tree species with high water use efficiency and drought tolerance, is being increasingly cultivated to increase the resilience of European forests and meet the future demand of conifer timber in a warming climate. We studied the seepage water quantity and quality with a particular focus on the nitrate (NO3–) concentration and N leaching under pure and mixed stands of Douglas fir, Norway spruce, and European beech at seven sites in Germany. Additionally, we investigated seepage water concentrations of SO4-S, Ca, Mg, K, Al and hydrological variables (interception, canopy throughfall, transpiration). Looking at the seepage water quantity and quality, the best management option is the cultivation of pure beech stands. However, this is associated with the well-known risk of monocultures concerning ecosystem disturbance. Beech stands showed the highest seepage water quantities and the lowest seepage water concentrations of major cations and anions, including NO3–. Seepage water quantity was the smallest under pure Douglas fir compared to spruce and beech stands. The composition effects of stand tree species on seepage water quality and nutrient leaching were site-dependent. At N-rich sites, pure Douglas fir stands showed higher seepage water NO3– concentrations than spruce and beech stands, whereas the tree species effects were small at N-poor sites. With respect to seepage water quantity and quality, cultivation of mixed Douglas fir–beech stands is a promising option for producing conifer timber and at the same time avoiding increased disturbance risks of mono-species forests under a warmer climate. Our results support the recommendation of mixed Douglas fir–beech stands based on soil quality, ecosystem resilience, and forest economic studies.

Growth and drought reaction of European hornbeam, European white elm, field maple and wild service tree

Key messageConsidering their drought tolerance and growth characteristics, rare native tree species are well-suited admixed species for the development of climate-stable forests in Central Europe.In our study, we assessed the growth and drought reaction of the four rare native tree species European hornbeam (Carpinus betulus L.), European white elm (Ulmus laevis Pall.), field maple (Acer campestre L.), and wild service tree (Sorbus torminalis (L.) Crantz). Based on tree-ring data, we (I) evaluated their species-specific growth characteristics and variability and examined the influencing site and tree characteristics on annual growth. (II) We quantified their reaction to single drought events, also depending on site and tree variables. (III) We compared our results to oak (Quercus robur L., Quercus petraea (Matt.) Liebl.) and European beech (Fagus sylvatica L.). As they are well-known Central European tree species, there is a broad knowledge about their growth and drought response across wide geographical ranges available. Bringing the results of European beech and oak in relation with the rare native species, it allows to categorise their growth and drought reaction and to contextualise their performance. Our results show, that besides European white elm, the rare species showed an overall lower annual growth with a higher variability than European beech and oak. However, especially field maple and wild service tree were better adapted to drought than European beech and partially even recovered better than oak. Combining the aspects of growth stability and drought tolerance, we conclude that rare native tree species are well suited as admixed species in future forest stands. European hornbeam is a suitable match for European beech on wetter sites, while field maple and wild service tree are a sensible complement for the climate stable oak on drier sites.

Diversity and specialization responses to climate and land use differ between deadwood fungi and bacteria

Climate and land use are major determinants of biodiversity, and declines in species richness in cold and human exploited landscapes can be caused by lower rates of biotic interactions. Deadwood fungi and bacteria interact strongly with their hosts due to long‐lasting evolutionary trajectories. However, how rates of biotic interactions (specialization) change with temperature and land‐use intensity are unknown for both microbial groups. We hypothesize a decrease in species richness and specialization of communities with decreasing temperature and increasing land use intensity while controlling for precipitation. We used a full‐factorial nested design to disentangle land use at habitat and landscape scale and temperature spanning an area of 300 × 300 km in Germany. We exposed four deadwood objects representing the main tree species in Central Europe (beech, oak, spruce, pine) in 175 study plots. Overall, we found that fungal and bacterial richness, community composition and specialization were weakly related to temperature and land use. Fungal richness was slightly higher in near‐natural than in urban landscapes. Bacterial richness was positively associated with mean annual temperature, negatively associated with local temperature and highest in grassland habitats. Bacterial richness was positively related to the covariate mean annual precipitation. We found strong effects of host‐tree identity on species richness and community composition. A generally high level of fungal host‐tree specialization might explain the weak response to temperature and land use. Effects of host‐tree identity and specialization were more pronounced in fungi. We suggest that host tree changes caused by land use and climate change will be more important for fungal communities, while changes in climate will affect bacterial communities more directly. Contrasting responses of the two taxonomic groups suggest a reorganization of deadwood microbial communities, which might have further consequences on diversity and decomposition in the Anthropocene.

The Future of European Beech in Northern Germany—Climate Change Vulnerability and Adaptation Potential

Earth’s forests are increasingly exposed to climate risks through climate change-related drought and heat waves. Here, we review the climate vulnerability of European beech (Fagus sylvatica), the most abundant tree species of Central Europe’s temperate forests, and its adaptation potential to a hotter and drier climate in northern Germany, close to the center of the species’ distribution range. About two-thirds of the studied beech forests show persistent negative growth trends of their dominant trees since the onset of rapid warming in the early 1980s, driven primarily by long-term deterioration of the climatic water balance (CWB) in summer and, locally, long-term decrease in June precipitation. Lower water storage capacity of the soil increases the climate sensitivity of growth. Even though beech populations of drier sub-regions reveal some acclimation to drought (reduced stomatal conductance, turgor loss point reduction, higher C allocation to roots), they are more climate-vulnerable than populations at moister sites, visible in larger growth decreases and greater CWB sensitivity of growth. Even though beech mortality is still lower in the study region than in other parts of Central Europe, our results identify beech forest regions with <350 mm growing-season precipitation as vulnerable to recent climate conditions, which refers to half of the study region. With further climate warming and aridification, most of northern Germany likely will become unfavorable for beech growth within the next tree generation, which suggests choosing in many production forests alternative, more drought- and heat-resistant timber species.

Leaf litter combustion properties of Central European tree species

AbstractTemperate forests of Central Europe are exposed to increasing fire risk. However, little is known about combustion properties of leaf litter, which plays an important role in the spread of surface fires. We used cone calorimetry to compare combustion properties of leaf litter samples from seven common tree species of Central European forests by reconstructing a litter layer of original depth in sample holders with a size of 10 cm × 10 cm. In addition to mono-specific leaf litter beds, combustion experiments included mixtures of different litter types, mixtures of litter and bryophytes and one mixture of litter and fine woody debris, totalling to 13 different setups (i.e. litter types). Recorded combustion properties included ignitability, flaming duration and heat release. Differences in combustion properties were analysed using analyses of variance followed by pairwise post-hoc tests. Combustion properties mainly differed between different litter types (broadleaf, pine needle, short needle). Highest total and peak heat release were observed for Scots pine (Pinus sylvestris), while peak heat release rates showed only minor differences for litter of the remaining species. Broadleaf litter was characterized by highest ignitability. For short-needle litter, we observed long flaming duration and incomplete combustion, resulting in the lowest total heat release on a sample mass basis. For litter mixtures of pine and broadleaf litter, we observed lower peak heat release rates in comparison to mono-specific pine litter. Mosses reduced peak heat release rates and increased the proportion of unburned biomass. However, the magnitude of this effect differed between bryophyte species included in the mixtures. The addition of fine woody debris strongly increased total heat release, highlighting the importance of fine woody fuels for fire behaviour. The results of this study provide valuable baseline information on combustion behaviour of leaf litter from Central European forests. Due to the limitations of laboratory combustion experiments to reproduce conditions of real forest fires, there is a need for future field studies investigating fire behaviour under natural conditions.

The cumulative impacts of droughts and N deposition on Norway spruce (Picea abies) in Switzerland based on 37 years of forest monitoring

Norway spruce is one of the most important tree species in Central Europe, however, it is facing major problems with recent droughts. In this study we present 37 years (1985–2022) of long-term forest observation data on 82 different forest sites across Switzerland including 134′348 tree observations. The sites consists of managed spruce or mixed forest stands with beech (Fagus sylvatica) and comprise large gradients in altitude (290–1870 m), precipitation (570–2448 mm a−1), temperature (3.6–10.9 °C) or total nitrogen deposition (8.5–81.2 kg N ha−1 a−1).Long-term tree mortality has increased more than fivefold due to the multiple drought years 2019, 2020 and 2022, which is more than double the increase following the 2003 drought. We used a Bayesian multilevel model including three years of lagged drought indicator to predict spruce mortality. Besides stand age, the most important factors were drought and N deposition. Especially under drought conditions spruce mortality was increased on sites with high N deposition. Moreover, N deposition increased the imbalance of foliar phosphorus concentrations, with negative impacts on tree mortality. Mortality was increased by a factor of 1.8 in spruce compared to mixed beech and spruce stands. Stands with high mortality rates showed previously an increased proportion of trees with damaged crowns, especially after the droughts of 2003 and 2018.Taken together, we found evidences of an increase in spruce mortality droughts amplified under high N depositions. The perennial drought of 2018–2020 resulted in a cumulative spruce mortality of 12.1 % (564 dead trees in 82 sites) in only three years. With a Bayesian change-point regression framework we estimated a critical empirical load for nitrogen of 10.9 ± 4.2 kg N ha−1 a−1, which is in line with current thresholds, above which future plantings of spruce in Switzerland may not be a sustainable option due to the observed interaction between drought and nitrogen deposition.

Varying growth response of Central European tree species to the extraordinary drought period of 2018 – 2020

Droughts have intensified in Central Europe and will likely become a major driver of forest ecosystem change in the future. Regional studies are needed to understand drought impacts on forests and to provide guidance for adaptive management. In this study, we have investigated the effects of an extraordinary drought period in 2018 – 2020 on tree growth in the State of Bavaria (Germany). We (i) assessed overall changes in tree growth compared to pre-drought conditions, (ii) mapped the spatial configuration of drought and its impact on growth across ecoregions, (iii) quantified the standardized drought effect for the most abundant tree species, and (iv) analyzed the inter- and intraspecific variability in growth responses to drought.Covering a large environmental gradient, we compared 3,462 tree basal area growth records at 200 inventory plots with the pre-drought period of 2006 – 2017. We analyzed drought impacts on tree growth using nonparametric randomization tests and linear quantile mixed models (LQMMs).Median annual tree growth declined by 41.3% during drought. Decreases in growth were statistically significant for 13 out of 20 species. Growth reductions were most distinct in northwestern ecoregions of Bavaria. After controlling for other covariates of tree growth, the most abundant conifers, Picea abies [Karst.] and Pinus sylvestris [L.], were overall more susceptible than the common broadleaves, Fagus sylvatica [L.], Quercus robur [L.], and Quercus petraea [Matt.]. Yet, all species exhibited a high intraspecific variation in drought response.Altering tree species composition is a key strategy to adapt forest ecosystems. Our study reveals high potential to mitigate future drought impacts by admixing P. abies- and P. sylvestris-dominated forests with more drought-adapted broadleaved tree species. In addition, the high intraspecific variability in drought susceptibility indicates potential to promote provenances or individuals with low drought sensitivity to reduce the local loss of tree species.

Extractives in Douglas firs (Pseudotsuga menziesii (Mirb.) Franco) from three sites in south-west Germany and potential opportunities for valorization

Owing to favorable wood properties and its resilience to the effects of climate change, Douglas fir (Pseudotsuga menziesii) is a promising tree species in Central Europe. Its wood and bark extractives could also serve as feedstock for the production of bio-based materials and platform chemicals. In this study, sapwood, heartwood, knotwood and bark extractives of Douglas firs originating from three differently aged stands in south-west Germany were investigated. Two different extraction methods with organic solvents were compared: a mixture of cyclohexane/ethanol and a successive method using petroleum ether, acetone and methanol. Extraction yields obtained with the successive method were higher, however one-step extraction was very efficient considering the number of samples that could be extracted and is therefore useful for a fast screening. At all sites, extract yields from sapwood, heartwood and bark were highest close to the tree top, while at the two older sites, an additional maximum was found at 1.3 m height. Knotwood extractives tended to decline with increasing tree height. The most abundant substance with economic importance was taxifolin, yielding up to 13% of dry weight in bark, whereas knotwood contained high amounts of resin acids and the lignan nortrachelogenin. Contrary to other studies, the present study found no evidence of a significant site effect on yield and composition of extracts. Overall, many different compounds for future bio-economic applications were found so that the preferential utilization of extractive-rich bark and crown material could foster an integral valorization of trees, supplementing with existing high grade timber production.

Adhesives free bark panels: An alternative application for a waste material.

The proportion of bark in tree trunks is in the range of ~ 10-20%. This large amount of material is currently mainly considered as a by- or even waste-product by the timber processing industry. Recently, efforts towards the use of bark have been made, e.g. as a raw material to harvest different chemical compounds or as an additive for wood particle boards. Our motivation for this work was to keep the bark in an almost natural state and explore alternative processes and applications for use. The traditional method of de-barking tree trunks by peeling was used to harvest large bark pieces. Two pieces of peeled bark were placed crosswise, with the rhytidom side (outer bark) facing each other. After different conditioning steps, bark pieces were hot pressed to panels without adding adhesives. These experiments on bark samples of different Central European tree species suggest that production of panels with species dependent properties is possible and feasible. This is a step towards producing sustainable panels by using a natural waste material, while retaining its beneficial structure and its natural chemical composition.

Suitability of Fagus orientalis Lipsky at marginal Fagus sylvatica L. forest sites in Southern Germany

European beech (Fagus sylvatica L.) is the most important tree species in Central Europe and is considered to be relatively resistant to climate warming. However, dry summers in the last five years led to considerable damage in beech stands in Southern Germany (SG). Assisted migration of drought resistant beech provenances including those of Oriental beech (Fagus orientalis Lipsky) may help to stabilise Central European beech forests under climate change. The focus of this study is to compare the climatic ranges of F. sylvatica and F. orientalis using quantile distribution of climatic variables based on WorldClim data at forest sites within their natural distribution area. Temperature, precipitation, and aridity quantile ranges showed that F. orientalis is better adapted to warmer and drier climate compared to F. sylvatica. The quantile distribution method was applied to the whole range of the species to map the habitat suitability for both species at marginal sites in the target region (SG) in the current climatic scenario (1970-2000) and in a warmer scenario (+2°C) using the climate marginality index (CMI), i.e., the distance of sites to the xeric edge at low-latitude and low-altitude distribution limits for the species. To this purpose we applied the simple BIOCLIM algorithm using annual temperature and precipitation as climatic variables. According to our results, F. orientalis seems a promising species with a high potential for future afforestation activities in Southern Germany, especially at marginal sites of European beech forests. However, before introducing F. orientalis on a larger scale in the study area, further research on the species ecology and genetics are needed. For further application of the quantile range method, we produced tables of the vigintiles of the climatic range for both species, which can be used for estimating CMI based on WorldClim data in other regions.

Quantitative and qualitative assessment of pine seedlings under controlled undergrowth disturbance: Fire and soil scarification

Scots pine (Pinus sylvestris L.) is the most widespread forest tree species in Central Europe. The range of Scots pine depends on the influence of forest management on stand species composition, as the potential for the natural regeneration of Scots pine monocultures is smaller than the current range of the species. To achieve regeneration, pine requires specific ecological conditions, including adequate soil preparation. The literature notes that the effective natural regeneration of pine requires fire or mixing the organic soil layer with the mineral layer. This hypothesis was critically evaluated carrying out work with the main objective of comparing the germination and growth dynamic of pine seedlings in two variants, simulating fire or soil scarification against natural conditions. The research focused on analyzing the growth of pine seedlings from germination to the final number of seedlings, which remained unchanged until the end of the experiment. The evaluation was carried out in soil monoliths from Kampinos National Park (KNP), in which seeds from a homogeneous mother stand were planted. The quantitative and qualitative characteristics of the seedlings were statistically evaluated, including analyses of their root system characteristics. The results confirmed the positive effect of mixing an organic and mineral layer at the germination stage and during the subsequent growth of the pine. The seedlings had a high survival rate (65.3%). However, the positive effect of fire on the regenerative capacity of pine could not be confirmed; the number of obtained seedlings (29.5%) was significantly lower than in the control variant. In addition, the “fire variant” was characterized by high seedling mortality immediately after germination. Root systems were important for the survival of the seedlings, the development of which was affected by the tested variant. The analyses performed may have implications for the development of research on the possible natural regeneration of Pines after natural disturbances. Additional topic that needs further research is the response of seedling root systems to changes in soil conditions.

European beech dieback after premature leaf senescence during the 2018 drought in northern Switzerland.

During the particularly severe hot summer drought in 2018, widespread premature leaf senescence was observed in several broadleaved tree species in Central Europe, particularly in European beech (Fagus sylvatica L.). For beech, it is yet unknown whether the drought evoked a decline towards tree mortality or whether trees can recover in the longer term. In this study, we monitored crown dieback, tree mortality and secondary drought damage symptoms in 963 initially live beech trees that exhibited either premature or normal leaf senescence in 2018 in three regions in northern Switzerland from 2018 to 2021. We related the observed damage to multiple climate- and stand-related parameters. Cumulative tree mortality continuously increased up to 7.2% and 1.3% in 2021 for trees with premature and normal leaf senescence in 2018, respectively. Mean crown dieback in surviving trees peaked at 29.2% in 2020 and 8.1% in 2019 for trees with premature and normal leaf senescence, respectively. Thereafter, trees showed first signs of recovery. Crown damage was more pronounced and recovery was slower for trees that showed premature leaf senescence in 2018, for trees growing on drier sites, and for larger trees. The presence of bleeding cankers peaked at 24.6% in 2019 and 10.7% in 2020 for trees with premature and normal leaf senescence, respectively. The presence of bark beetle holes peaked at 22.8% and 14.8% in 2021 for trees with premature and normal leaf senescence, respectively. Both secondary damage symptoms occurred more frequently in trees that had higher proportions of crown dieback and/or showed premature senescence in 2018. Our findings demonstrate context-specific differences in beech mortality and recovery reflecting the importance of regional and local climate and soil conditions. Adapting management to increase forest resilience is gaining importance, given the expected further beech decline on dry sites in northern Switzerland.

Seasonal variations in phenolic natural products in Fagus sylvatica (European beech) leaves

Fagus sylvatica L. (Fagaceae), European beech, is one of the most important deciduous tree species in Central Europe and the most common broadleaved tree species in Germany. We investigated the leaves of six individual Fagus sylvatica trees growing in a beech forest in Kiel, Schleswig-Holstein, Germany, for seasonal variations in the content of phenolic natural products over three consecutive growing seasons. The investigated compound classes comprised hydroxycinnamic acid and flavonoid derivatives. The content of phenolic compounds showed clear trends in all years. A sharp decline in the total content of phenolic substances was observed from mid-April to the end of May. During the summer months, the content of phenolic compounds remained stable with only slight fluctuations until fall. The values for individual trees deviated more pronouncedly from one another in spring, but converged during the course of the growing period. These trends, despite differences in absolute values, were identical in three consecutive growing seasons (2016–2018). Our results contribute to a better understanding of the dynamics of plant natural products of deciduous trees in temperate climates caused by seasonal variations.