European Forest Species Research Articles

Climatic Effects on the Growth of Fagus sylvatica L. in Mixed Stands with Pinus sylvestris L. in Lithuania

Climate change and warming will potentially profoundly affect forest growth and yield. However, climate change is not only a threat but also an opportunity for tree species to be more productive or colonize new territories where previously they were fragmented or absent. European beech (Fagus sylvatica L.) is a dominant and significant tree species in European forests with a pronounced ability to grow on a great variety of sites and to form mixtures with other tree species due to its shade tolerance. So far, only a few studies have analysed its growth and reaction to changing climatic conditions outside its natural gradient in the north. The aim of this study was therefore to clarify the main growth patterns and tree ring formation characteristics of beech (outside their natural distribution) in mixed stands with Scots pine (Pinus sylvestris L.) The analyses were carried out in two-layered stands in the western part of Lithuania with tree-ring data measured on stem disks collected at 1 m height that were available from shelter-cut thinning activities in a number of forest stands in the region. Our results show that higher temperatures during the summer months of July and August generally inhibited the radial growth of beech under given site conditions. In contrast, warmer late-autumn and cooler early-winter periods together with warmer springs positively affected the radial increments. Above-average precipitation during the vegetation period contributed to the beech producing additional amounts of radial increments. The increasing temperature trends of the summer months and decreasing monthly amounts of precipitation during the vegetation period in recent decades tend to have adverse effects on the ecological conditions for beech growth and vitality in Lithuania. Despite these results, the European beech successfully grows in the sample region and has produced 200 m3 ha−1 in the analysed stands.

Influence of Soil Quality on the Browsing Intensity of Ungulate Herbivores on Tree Species in European Forests

Influence of Soil Quality on the Browsing Intensity of Ungulate Herbivores on Tree Species in European Forests

High-resolution land use and land cover dataset for regional climate modelling: historical and future changes in Europe

Abstract. Anthropogenic land use and land cover change (LULCC) is a major driver of environmental changes. The biophysical impacts of these changes on the regional climate in Europe are currently being extensively investigated within the World Climate Research Program (WCRP) Coordinated Downscaling Experiment (CORDEX) Flagship Pilot Study (FPS) Land Use and Climate Across Scales (LUCAS) using an ensemble of different regional climate models (RCMs) coupled with diverse land surface models (LSMs). In order to investigate the impact of realistic LULCC on past and future climates, high-resolution datasets with observed LULCC and projected future LULCC scenarios are required as input for the RCM–LSM simulations. To account for these needs, we generated the LUCAS Land Use and land Cover change (LUC) dataset version 1.1 at 0.1∘ resolution for Europe with annual LULC maps from 1950 to 2100 (https://doi.org/10.26050/WDCC/LUC_hist_EU_v1.1, Hoffmann et al., 2022b, https://doi.org/10.26050/WDCC/LUC_future_EU_v1.1, Hoffmann et al., 2022a), which is tailored to use in state-of-the-art RCMs. The plant functional type (PFT) distribution for the year 2015 (i.e. the Modelling human LAND surface Modifications and its feedbacks on local and regional cliMATE – LANDMATE – PFT dataset) is derived from the European Space Agency Climate Change Initiative Land Cover (ESA-CCI LC) dataset. Details on the conversion method, cross-walking procedure, and evaluation of the LANDMATE PFT dataset are given in the companion paper by Reinhart et al. (2022b). Subsequently, we applied the land use change information from the Land-Use Harmonization 2 (LUH2) dataset, provided at 0.25∘ resolution as input for Coupled Modelling Intercomparison Project Phase 6 (CMIP6) experiments, to derive LULC distributions at high spatial resolution and at annual time steps from 1950 to 2100. In order to convert land use and land management change information from LUH2 into changes in the PFT distribution, we developed a land use translator (LUT) specific to the needs of RCMs. The annual PFT maps for Europe for the period 1950 to 2015 are derived from the historical LUH2 dataset by applying the LUT backward from 2015 to 1950. Historical changes in the forest type changes are considered using an additional European forest species dataset. The historical changes in the PFT distribution of LUCAS LUC follow closely the land use changes given by LUH2 but differ in some regions compared to other annual LULCC datasets. From 2016 onward, annual PFT maps for future land use change scenarios based on LUH2 are derived for different shared socioeconomic pathway (SSP) and representative concentration pathway (RCP) combinations used in the framework of CMIP6. The resulting LULCC maps can be applied as land use forcing to the new generation of RCM simulations for downscaling of CMIP6 results. The newly developed LUT is transferable to other CORDEX regions worldwide.

Heading for a fall: The fate of old wind-thrown beech trees (Fagus sylvatica) is detectable in their growth pattern

Common beech (Fagus sylvatica) is one of the most important deciduous tree species in European forests. However, climate-change-induced drought may threaten its dominant position. The Sonian Forest close to Brussels (Belgium) is home to some of the largest beech trees in the world. This UNESCO world heritage site is famous for its high density of very large beech trees as a result of its climatic suitability, fertile soil conditions, and past management. Here we utilized tree-ring data from increment cores to investigate the growth of these old and monumental beech trees, evaluating their growth trends, response to past climate, and the effect of mast years on 39 living and 16 recently wind-thrown trees. Our analysis reveals that the sampled trees were generally sensitive to spring and summer droughts but recovered quickly after such an extreme climatic event. The growth trend of living trees has remained high and only shows a slight, statistically insignificant, decline over the past 50 years. Although the overall growth rate remains strong (BAI 50 cm2/year), the past five decades have shown strong inter-annual growth variations due to frequent and more intense droughts combined with an increased frequency of mast years. We also found notable differences in growth patterns between the living trees and those that had recently been wind-thrown. While there were no significant differences between living and wind-thrown trees in response to droughts, heatwaves, or mast years when examining year-to-year growth changes, the wind-thrown trees did exhibit considerably lower overall growth rates and a significant downward trend in growth (BAI −0.57 cm2/year). This difference in growth trends has been apparent since at least the 1980s. Overall, the findings of this study can provide valuable insights for understanding the long-term dynamics of lowland beech forests and their responses to climate change.

The community of soil fungi associated with the western red cedar (Thuja plicata Donn ex D. Don, 1824)

ABSTRACT The western red cedar (Thuja plicata Donn ex D. Don), an important forest-forming species in the Western part of the North American continent, is an alien species naturalised in Europe. It is popular and highly valued in horticulture. While considering the progressing climate change, it may also be a potential alternative to native species in European forests. The community of soil fungi associated with the western red cedar in forested areas of Europe has not been fully determined. Thus, this study is aimed to identify the community of soil fungi associated with the western red cedar. The experimental plots are located in the Kościan Forest District (51°98’87″ N; 16°23’54″ E). All soil samples were taken from the topsoil layer at a depth of 25 cm with a trowel, three from the centre of natural regeneration (1G, 2G, 5G) and three from the centre stand under the canopy of old-growth western red cedar (3G, 4G, 6G). Fungi were identified directly from the soil based on the ITS1 rDNA region. The derived product was sequenced using Illumina’s sequencing by synthesis (SBS) technology. Sequences were referred to the National Center for Biotechnology Information (NCBI) database applying the BLAST algorithm. The fungal counts were defined based on the number of operational taxonomic units (OTU) in the sample. The OTU number was 835 206, with fungal isolates accounting for 683 095 (81.79%). A total of 8 591 taxa belonging to the Kingdom Fungi were identified. The species with the greatest shares in the community included Mortierella spp. (10.5%), Russula spp. (5.6%), Hydnum spp. (3.44%), Solicoccozyma spp. (3.1%) and Penicillium spp. (2.2%). Results showed that saprotrophs and mycorrhizal fungi predominated in the community. The dominance of ectomycorrhizal fungi over arbuscular ones, quite impressive natural regeneration was shown in T. plicata stands in Kościan. Subsequent research should take into account tree stands in Poland in which natural regeneration does not occur or occurs sporadically.

Potential alternative tree species to Fraxinus excelsior in European forests

Common ash (Fraxinus excelsior L.) is a keystone tree species in Europe. However, since the 1990s, this species has been experiencing widespread decline and mortality due to ash dieback [Hymenoscyphus fraxineus (T. Kowalski) Baral, Queloz and Hosoya]. Besides H. fraxineus, emerald ash borer (Agrilus planipennis Fairmaire), an invasive alien pest already devastating ash trees in western Russia, is spreading westward and becoming an emerging threat to the remaining European ash populations. While efforts to control ash dieback continue to be a priority, it is becoming crucial to compensate for the loss of ash and its ecosystem services by elaborating restoration strategies, including the search for alternative native and non-native tree species. This review summarizes available knowledge on potential alternative tree species to common ash to help forest managers to cope with ash dieback. Although using natural regeneration and promoting tree species diversity can reduce the impacts of ash dieback in European forests, our review indicates that no native species alone or in combination can fully replace the ecological niche of common ash and its associated ecosystem services (e.g., biodiversity and timber). To fill this gap, forest managers have considered using non-native ash species that are tolerant to both H. fraxineus and A. planipennis and have similar ecological and forestry values as common ash. Of the 43 ash species reviewed, few non-native ash species (e.g., Fraxinus mandshurica Rupr. and Fraxinus platypoda Oliv.) have similar ecological characteristics to common ash and are tolerant to H. fraxineus and A. planipennis. However, the performance of non-native ash species in European forests, their invasiveness potential, and the risk of hybridization with native ash species are still unknown. With the current state of knowledge, it is thus too early to recommend the use of non-native ash species as a suitable option to deal with ash dieback. The priority should be the conservation, regeneration, and breeding of tolerant common ash populations to H. fraxineus, as well as the use of the natural regeneration of other native tree species. Our review highlights the need for controlled experimental plantations to better understand the regeneration ecology and invasiveness potential of non-native ash species prior to their utilization in natural forests.

A novel set of polymorphic chloroplast microsatellite markers for northern red oak (Q. rubra L.)

AbstractOaks are model species due to their importance in various ecosystems, worldwide distribution, high economic value and emerging genomic resources. As such, knowledge on population differentiation across their distribution range is of high importance for sustainable forest management. As in most angiosperms, chloroplasts are maternally (via seeds) inherited in oak species and acorns are dispersed over comparably short distances. Consequently, chloroplast markers reveal comparatively high differentiation between populations, making them highly viable for the analysis of historic migration patterns and the certification of reproductive material. Despite the existence of various white oak (section: Quercus) chloroplast markers, red oak (section: Lobatae) chloroplast markers remain limited. Northern red oak is one of the most important North American oak species and a widespread non-native plantation tree species in European forests. We took advantage of chloroplast genomes of Q. rubra L. and related oak chloroplast genomes to develop a set of robust and easy-to-use chloroplast microsatellite primers for northern red oak. Furthermore, we tested transferability of those novel red oak primer pairs to Q. robur L. and Q. petraea Matt. Liebl. The new set of fifteen polymorphic chloroplast microsatellite markers revealed three additional northern red oak haplotypes after screening 80 northern red oak individuals representing seven haplotypes, identified based on formerly available markers. Therefore, they provide a higher resolution of haplotypes as compared to currently available markers.

Site-specific risk assessment enables trade-off analysis of non-native tree species in European forests.

Non‐native tree species (NNT) are used in European forestry for many purposes including their growth performance, valuable timber, and resistance to drought and pest or pathogen damage. Yet, cultivating NNT may pose risks to biodiversity, ecosystem functioning, and the provisioning of ecosystem services, and several NNT have been classified as invasive in Europe. Typically, such classifications are based on risk assessments, which do not adequately consider site‐specific variations in impacts of the NNT or the extent of affected areas. Here, we present a new methodological framework that facilitates both mitigating risks associated with NNT and taking advantage of their ecosystem services. The framework is based on a stratified assessment of risks posed by NNT which distinguishes between different sites and considers effectiveness of available management strategies to control negative effects. The method can be applied to NNT that already occur in a given area or those NNT that may establish in future. The framework consists of eight steps and is partly based on existing knowledge. If adequate site‐specific knowledge on NNT does not yet exist, new evidence on the risks should be obtained, for example, by collecting and analyzing monitoring data or modeling the potential distribution of NNT. However, limitations remain in the application of this method, and we propose several policy and management recommendations which are required to improve the responsible use of NNT.

Temporal diversification and no geographic population structure in the most abundant European ectomycorrhizal fungus Russula ochroleuca

Abstract Although Russula ochroleuca is a common ectomycorrhizal (ECM) species in European forests, its reproduction mode, dispersal range, and population structure remains unknown. Altogether, 462 fruit bodies from three spruce forests (two 15 km apart, one 230 km distant from the first two) were analysed using AFLP markers. A mixed mode of reproduction, with several large genets accompanied by a majority of single fruit body genets, was found. Low level of inbreeding (Fis = 0.0021–0.0072), low level of genetic differentiation among subpopulations (PhiPT = 0.037–0.190) and negligible isolation by distance (r = 0.033, P = 0.005) indicates effective spore dispersal and a high level of outcrossing across the sampled area. Finally, we discovered temporal diversification within this species, as evidenced by genetic differentiation between early (August) and late (September) fruiting genotypes.

Post-glacial re-colonization and natural selection have shaped growth responses of silver fir across Europe.

Warmer climate and more frequent extreme droughts will pose major threats to forest ecosystems. Past demography processes due to post-glacial recolonization and adaptation to local environmental conditions are among the main contributors to genetic differentiation processes among provenances. Assessing the intra-specific variability of tree growth responses to such changes is crucial to explore a species' potential to cope with climate warming. We combined growth-related traits derived from tree-ring width series with neutral genetic information of 18 European provenances of silver fir (Abies alba Mill.) growing in two common garden experiments in Switzerland. Analyses based on neutral single nucleotide polymorphisms revealed that the studied provenances grouped into three longitudinal clusters. These three genetic clusters showed differences in growth traits (height and DBH), with the provenances from the eastern cluster exhibiting the highest growth. The Pyrenees cluster showed significantly lower recovery and resilience to the extreme drought of 2003 as well as lower values of growth autocorrelation. QST-FST and correlation analyses with climate of provenance origin suggest that the differences among provenances found in some traits result from natural selection. Our study suggests that the last post-glacial re-colonization and natural selection are the major drivers explaining the intra-specific variability in growth of silver fir across Europe. These findings highlight the importance of combining dendroecology and genetic analyses on fitness-related traits to assess the potential of a species to cope with global environmental change and provide insights to support assisted gene flow to ensure the persistence of the species in European forests.

<p class="Body"><strong>Soil mite (Acari, Mesostigmata) biomass, species richness and diversity in soil and decayed logs of European Beech (<em>Fagus</em> <em>sylvatica </em>L.) forests</strong></p>

The European beech (Fagus sylvatica L.) is a dominant tree species in European forests and it has a huge ecological significance and high economic value. Due to its large dimensions, it can produce large amounts of decayed wood (CWD) which may be critical for maintaining the population of many rare species including mites. Many studies focused on mite (Mesostigmata) abundance, species richness, or diversity in CWD, however, our knowledge on mite biomass is still scarce. Therefore, the main aim of that study was to recognize the Mesostigmata biomass in logs and adjacent soil. In total, 90 samples (125 cm3, 5 cm depth) were collected from European beech logs and soil with litter thickness. Soil samples were collected from ecotone zone (soil near the log) and further three distances—0.5 m, 1.0 m, 1.5 m away from the log. Body length and width were measured for each individual of rare species and in the case of common species at least for 10 individuals. Our study revealed the highest mite biomass in CWD and soil near to the log (ecotone). Total male biomass was the highest in CWD and differed significantly from all other soil microhabitats. Female biomass did not differ between soil and CWD, whereas deutonymphs biomass differed between CWD and soil 1.0 m away from the log. Mean abundance, species richness, and diversity did not differ between the microhabitats. Decaying logs were dominated by Janietella pulchella whereas soil by Veigaia nemorensis. In conclusion, decayed European beech logs maintain the highest male and deutonymph biomass when compared to adjacent soil. Beech logs are important microhabitats for Mesostigmata mite communities, where they reached the highest abundance.

Impact of Invasive Tree Species on Natural Regeneration Species Composition, Diversity, and Density

Invasive tree species decrease ecosystem resilience with negative impacts on natural regeneration. The influence of alien tree species on ecosystems is unevenly recognized and does not always account for different habitat specificity. We assessed the impacts of the three most frequent invasive tree species in European forests: Prunus serotina Ehrh., Quercus rubra L., and Robinia pseudoacacia L. on natural regeneration diversity, species composition, and density. We hypothesized that invaded forest types, in comparison with non-invaded, will differ in terms of species composition, will have lower taxonomic, functional, and phylogenetic diversity of natural regeneration, and will have lower densities of native tree species. We used a set of 189 study plots (200 m2) in a systematic design, established in various forest types in Wielkopolski National Park (West Poland). We analyzed impacts of forest type, accounting for soil C:N ratio, soil pH, and light availability on natural regeneration (woody species up to 0.5 m height) species composition, diversity, and density. We found an overlap of species composition among invaded and non-invaded forests and low impacts of invasive species on taxonomic diversity and functional richness. We found no impacts on phylogenetic diversity and other functional diversity components. In contrast, we found that the natural regeneration of forest-forming tree species reached lower densities in invaded than non-invaded forest types. However, sub-canopy and shrub species reached higher densities in invaded than non-invaded forest types. We confirmed that invasive tree species affect natural regeneration by decreasing the regeneration density of native tree species (in eight of nine tree species studied), species composition homogenization, and supporting natural regeneration of sub-canopy and shrub species. Therefore, the restoration of invaded forests requires eradication of invasive tree species to decrease propagule pressure and to stop decreases in the abundance of native tree species’ natural regeneration.

Interaction Between the Effects of Provenance Genetic Structure and Habitat Conditions on Growth of Scots Pine in International Provenance Tests in Bosnia and Herzegovina

Scots pine (Pinus sylvestris L.) is one of the most important tree species in European forests, characterized by high genetic variability and complex population structure. This research aimed to determine whether there is an interaction between the effects of provenance genetic structure and habitat conditions on the growth of Scots pine in two international provenance tests in Bosnia and Herzegovina, to chose the best provenances for both habitats. For this research, heights and root collar diameters of Scots pine plants on two provenance tests in Bosnia and Herzegovina were measured and the interaction between the effects of provenance genetic structure and habitat conditions for these two traits was estimated based on regression. Eleven provenances represented on both tests were researched. Provenance tests were established in 2012 on two locations with contrasted ecological conditions: Kupres and Žepče. By assessing the interaction between the effects of provenance genetic structure and habitat conditions on Kupres and Žepče provenance tests, two interactions for the height of plants (between Germany NJ2 and Italy I2 and between Austria A2 and Romania R1) and one interaction for the root collar diameter (between Austria A1 and Italy I2) were identified. The number of survived plants and their productivity is different for all provenances in both habitats, indicating that the adaptability of provenances is not only conditioned by their genetic constitution but also by habitat conditions. Considering the productivity of provenances and the number of survived plants in both habitats, Austria A1, Austria A2, Austria A3, and Poland P1 provenances showed the best adaptability. The results of this study can be used in the process of Scots pine breeding and for its conservation by in situ and ex-situ methods.

Morphological traits of Scots pine (Pinus sylvestris L.) in international provenance tests in Bosnia and Herzegovina

Scots pine (Pinus sylvestris L.) is one of the most important tree species in European forests. This study aims to determine whether there is inter-provenance variability in researched morphological traits in two international provenance tests of Scots pine in Bosnia and Herzegovina. We measured height, root collar diameter, and latest shoot length and counted branches on the latest branch whorl of Scots pine plants in two provenance tests. The provenance tests are located in Kupres and Žepče, in different climatic, edaphic, and orographic conditions. Kupres and Žepče contain 15 and 14 provenances, respectively, eleven of which are mutual to both sites. Descriptive statistics and analysis of variance showed differences among provenances in all investigated morphological traits. These differences were attributable to provenance test, provenance, and interaction between provenance test and provenance. The average values were higher in Žepče for all provenances and all studied traits. The Austria A1, Austria A2, Austria A3, and Poland P1 provenances showed the best growth in both tests, while the Italy I1 provenance showed good growth in Žepče but not in Kupres.

Extent, distribution and origin of non-native forest tree species in Europe

ABSTRACTThe management of non-native tree species in European forests has a long history, but the information on the current number and geographic distribution of these species in European forests is incomplete and scattered across various datasets. This study aims to perform an inventory of the most frequent non-native tree species growing in European forests and analyse their current extent, geographic distribution and geographic origin. Our results show that at least 150 non-native tree species are currently growing in European forests and provenance trials. The genera represented by largest number of species are Eucalyptus, Pinus, Acacia and Abies. Species growing at the largest areas are Robinia pseudoacacia (2.44 million ha), Eucalyptus globulus (1.46 million ha), Picea sitchensis (1.16 million ha) and Pseudotsuga menziesii (0.83 million ha). In total, non-native tree species in Europe are found in an area of approximately 8.54 million ha, or 4.0% of the European forest area, and the five most abundant species account for up to 77% of this area. The largest number of these 150 species were introduced from North America (71), followed by Asia (45) and Australia (20). North American species occupy by far the largest area.

Likelihood of changes in forest species suitability, distribution, and diversity under future climate: The case of Southern Europe.

Forest conservation strategies and plans can be unsuccessful if the new habitat conditions determined by climate change are not considered. Our work aims at investigating the likelihood of future suitability, distribution and diversity for some common European forest species under the projected changes in climate, focusing on Southern Europe. We combine an Ensemble Platform for Species Distribution Models (SDMs) to five Global Circulation Models (GCMs) driven by two Representative Concentration Pathways (RCPs), to produce maps of future climate‐driven habitat suitability for ten categories of forest species and two time horizons. For each forest category and time horizon, ten maps of future distribution (5 GCMs by 2 RCPs) are thus combined in a single suitability map supplied with information about the “likelihood” adopting the IPCC terminology based on consensus among projections. Then, the statistical significance of spatially aggregated changes in forest composition at local and regional level is analyzed. Finally, we discuss the importance, among SDMs, that environmental predictors seem to have in influencing forest distribution. Future impacts of climate change appear to be diversified across forest categories. A strong change in forest regional distribution and local diversity is projected to take place, as some forest categories will find more suitable conditions in previously unsuitable locations, while for other categories the same new conditions will become less suited. A decrease in species diversity is projected in most of the area, with Alpine region showing the potentiality to become a refuge for species migration.

Forest dynamics and disturbance regimes in the Italian Apennines

Forests of the Apennines are characterised by high canopy cover and high tree species diversity (being at the interface between two major climatic zones of Europe), and provide important ecosystem functions to millions of people. They exemplify cutting-edge themes such as forest ecology in warmer climates, consequences of heavy land use, and resilience at the trailing edge of the distribution of many European forest species (Silver fir, Norway spruce, Beech, Black pine, Birch).We introduce the setting under the geological and climatological point of view and review the literature on the interactions between these long-term drivers and the specific, structural, and genetic diversity of these forest communities (e.g., effects of glacial refugia or tectonic/volcanic activity), followed by a brief outline of what little is known about natural disturbance regimes and their range of variability. Anthropogenic disturbances (fire, grazing) and land use changes (abandonment of cropland and pasture) have been by far the main drivers of forest dynamics at least for the last two millennia, determining for examples overageing of coppices, treeline advances, forest encroachment on former agricultural land.We suggest considerations about the interplay between these land use changes and disturbance drivers (e.g. fuel continuity), summarize comparisons between managed and unmanaged forests (e.g., increase in tree size, deadwood, biodiversity indicators), and elaborate on current proposals for climate-adapted management, highlighting specific and genetic diversity as an important source of resilience and adaptive potential.

A novel Computer-Aided Tree Species Identification method based on Burst Wind Segmentation of 3D bark textures

Terrestrial Laser Scanning (TLS) systems have gained increasing popularity in the forestry domain and are today widely used for the automatic measurement of forest inventory attributes. Nevertheless, to the best of our knowledge the problem of tree species recognition from TLS data has received very little attention from the scientific community. It is in this context that we present a novel Computer-Aided Tree Species Identification method based on 3D bark texture analysis. The novelty of our approach resides in the following three key points: (1) 3D salient regions extraction using a new morphological segmentation method that we have called Burst Wind Segmentation, (2) the extraction and pre-annotation of a collection of typical 3D bark patterns, known as scars, from each of the tree species. The pre-annotated scars are stored in a dictionary that we have called ScarBook and they are used as a reference for the comparison of the 3D salient segmented regions, (3) a wide variety of advanced shape, saliency, curvature and roughness features are extracted from the 3D salient segmented regions. To study the performance of our method, an experiment has been carried out on a dataset composed of 969 patches which correspond to 30 cm long segments of the trunk at breast height. Six species among the most dominant species in European forests have been tested with patches of different diameter at breast height values so as to study the identification accuracy with respect to age. The results obtained are very encouraging and promising and they confirm the possibility of identifying tree species using TLS data.

Chilling temperature and photoperiod influence the timing of bud burst in juvenile Betula pubescens Ehrh. and Populus tremulaL. trees

This research demonstrates that inadequate chilling has the potential to slow both the rate and speed of bud burst of two important European forest species; Betula pubescens and Populus tremula. The timing of bud burst in deciduous trees has been widely used as an indicator of spring warming. However, winter chilling conditions can have a significant impact on the timing of bud burst. If trees receive insufficient chilling, there may be a delay in bud burst even if spring temperatures rise. Therefore, it is important to understand the effect of chilling on spring phenology of trees. Here, we exposed juvenile (3–6-year old) birch (B. pubescens Ehrh.) and aspen (P. tremula L.) trees to a range of photoperiods, chilling durations and forcing temperatures in controlled environment chambers to assess the impact on the timing of bud burst. Analysis of variance demonstrated that longer chilling duration resulted in earlier bud burst in both species, and less thermal time was needed to reach maximum bud burst. Therefore, in warmer winters bud burst in spring may be expected to be delayed if insufficient chilling is received. However, longer photoperiod may, at least in part, compensate for shorter chilling duration. These results suggest that models predicting climate warming impacts on phenology should take winter chilling into account when considering the timing of bud burst in deciduous species.

Identification of Salt Stress Biomarkers in Romanian Carpathian Populations of Picea abies (L.) Karst.

The Norway spruce (Picea abies), the most important tree species in European forests, is relatively sensitive to salt and does not grow in natural saline environments. Yet many trees are actually exposed to salt stress due to the common practice of de-icing of mountain roads in winter, using large amounts of NaCl. To help develop strategies for an appropriate use of reproductive seed material on reforestation sites, ensuring better chances of seedling survival in salt-affected areas, we have studied the responses of young spruce seedlings to salt treatments. The specific aim of the work was to identify the optimal salt stress biomarkers in Picea abies, using as experimental material seedlings obtained by germination of seeds with origin in seven populations from the Romanian Carpathian Mountains. These responses included general, conserved reactions such as the accumulation of ions and different osmolytes in the seedlings needles, reduction in photosynthetic pigments levels, or activation of antioxidant systems. Although changes in the contents of different compounds involved in these reactions can be associated to the degree of stress affecting the plants, we propose that the (decreasing) levels of total phenolics or total carotenoids and the (increasing) levels of Na+ or K+ ions in Picea abies needles, should be considered as the most reliable and useful biomarkers for salt stress in this species. They all show very high correlation with the intensity of salt stress, independently of the genetic background of the seeds parental population, and relatively easy, quantitative assays are available to determine their concentrations, requiring simple equipment and little amount of plant material.