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One consequence of climate change is an increasing mismatch between timing of food requirements and food availability. Such a mismatch is primarily expected in avian long-distance migrants because of their complex annual cycle, and in habitats with a seasonal food peak. Here we show that insectivorous long-distance migrant species in The Netherlands declined strongly (1984–2004) in forests, a habitat characterized by a short spring food peak, but that they did not decline in less seasonal marshes. Also, within generalist long-distance migrant species, populations declined more strongly in forests than in marshes. Forest-inhabiting migrant species arriving latest in spring declined most sharply, probably because their mismatch with the peak in food supply is greatest. Residents and short-distance migrants had non-declining populations in both habitats, suggesting that habitat quality did not deteriorate. Habitat-related differences in trends were most probably caused by climate change because at a European scale, long-distance migrants in forests declined more severely in western Europe, where springs have become considerably warmer, when compared with northern Europe, where temperatures during spring arrival and breeding have increased less. Our results suggest that trophic mismatches may have become a major cause for population declines in long-distance migrants in highly seasonal habitats.

The drought sensitivity of the pedunculate oak (Quercus robur L.) poses a threat to its survival in light of climate change. Mycorrhizal fungi, which orchestrate biogeochemical cycles and particularly have an impact on the plant’s defense mechanisms and metabolism of carbon, nitrogen, and phosphorus, are among the microbes that play a significant role in the mitigation of the effects of climate change on trees. The study’s main objectives were to determine whether ectomycorrhizal (ECM) fungi alleviate the effects of drought stress in pedunculate oak and to investigate their priming properties. The effects of two levels of drought (mild and severe, corresponding to 60% and 30% of field capacity, respectively) on the biochemical response of pedunculate oak were examined in the presence and absence of ectomycorrhizal fungi. To examine whether the ectomycorrhizal fungi modulate the drought tolerance of pedunculate oak, levels of plant hormones and polyamines were quantified using UPLC-TQS and HPLC-FD techniques in addition to gas exchange measurements and the main osmolyte amounts (glycine betaine-GB and proline-PRO) which were determined spectrophotometrically. Droughts increased the accumulation of osmolytes, such as proline and glycine betaine, as well as higher polyamines (spermidine and spermine) levels and decreased putrescine levels in both, mycorrhized and non-mycorrhized oak seedlings. In addition to amplifying the response of oak to severe drought in terms of inducible proline and abscisic acid (ABA) levels, inoculation with ECM fungi significantly increased the constitutive levels of glycine betaine, spermine, and spermidine regardless of drought stress. This study found that compared to non-mycorrhized oak seedlings, unstressed ECM-inoculated oak seedlings had higher levels of salicylic (SA) and abscisic acid (ABA) but not jasmonic acid (JA), indicating a priming mechanism of ECM is conveyed via these plant hormones. According to a PCA analysis, the effect of drought was linked to the variability of parameters along the PC1 axe, such as osmolytes PRO, GB, polyamines, and plant hormones such as JA, JA-Ile, SAG, and SGE, whereas mycorrhization was more closely associated with the parameters gathered around the PC2 axe (SA, ODPA, ABA, and E). These findings highlight the beneficial function of the ectomycorrhizal fungi, in particular Scleroderma citrinum, in reducing the effects of drought stress in pedunculate oak.

The impact of changing climate conditions on the stability, structure and biodiversity of forest ecosystems in Europe is well known. The main threat to trees is the continuous increase in temperature and changes in moisture conditions, especially in the soil. Very often, seedlings with a covered root system grown in container nurseries are used to rebuild forests or replace decaying spruce monocultures. The cultivation of such seedlings is carried out on a substrate whose main component is peat, the extraction of which poses a serious threat to the environment. Leaf nutrient stoichiometry offers an important indicator of the nutritional status of forest tree seedlings. This study assessed the potential of alternative peat-free substrates in nursery production and evaluated European beech and pedunculate oak seedlings with a covered root system, examining whether it ensured their proper nutrition and appropriate stoichiometric ratios of macroelements in the assimilation apparatus when compared to seedlings produced under the same conditions on a peat substrate. These studies were carried out in the production of beech and oak seedlings on innovative, organic, peat-free substrates using standard fertilization and a new fertilization developed by the research team. The peat-free substrates were characterized by higher concentrations of nitrogen (N), potassium (K), and phosphorus (P), which promote more effective growth. Our elemental leaf stoichiometry results indicate their excess in relation to standards, which suggests that plants can use these elements as reserves for the future. Results also showed strong correlations between the contents of elements in the soil and the growth parameters of seedlings. The peat-free substrates showed a beneficial effect on seedling growth, thus highlighting their potential as suitable substrates in nurseries.

Key messageEarly rewetting influenced growth variability and hydraulic uniformity in Pedunculate oak wood on disturbed peatland. Long-term study highlighted vessel widening's importance in adapting to water availability changes.Pedunculate oak (Quercus robur L.) is a widely recognized flood-tolerant tree that thrives on fertile and moist soil conditions, such as on or close to peatland ecosystems. In the frame of climate change counteracting policies, rewetting peatland ecosystems is gaining increasing interest, while the ecological consequences are not always clear. Whereas the effect of flooding on wood anatomical traits of pedunculate oak is widely documented, little is known about the effect of permanent rewetting. In this study, we investigated the wood anatomical responses of 12 pedunculate oak trees located on a formerly drained peatland in NE Germany, that experienced flooding and a consequent rewetting. Wood anatomical traits were analyzed via CARROT, a tool that employs the accuracy and efficiency of artificial intelligence to identify tree rings and vessels. Growth anatomical traits (e.g., tree ring width) showed a sudden increase after the rewetting started in 1995, while hydraulic traits (Dh and Ks) displayed a decreasing trend only after the rewetting process was fostered by the opening of an artificial canal in 2004. Variance analysis highlighted subtle changes in the trait’s distribution over time: high soil water content triggered variability in the growth anatomical traits and, simultaneously, homogeneity in the hydraulic traits. Results suggest the relevance of the “vessel widening” mechanisms to develop coping strategies in response to the later stage of the rewetting, and pose relevant insights concerning the importance of specific site conditions for the implementation of rewetting policies in peatlands with presence of pedunculate oak.

In the in vitro cloning of specific individuals of woody species, a challenge can be the low viability of explants collected from old mature donor trees due to the recalcitrance of their plant material. Other factors, such as the auxin–cytokinin balance, must also be considered. We investigated how in vitro conditions and donor age can modulate the regeneration capacity, morphophysiology, and DNA methylation of Quercus robur. Explants from two different donors (70- and 600-year-old trees) were subjected to 8 different treatments, which consisted of 0, 1.25, 3.5, or 7.0 µM 6-benzylaminopurine (BAP) combined with two concentrations of 0 or 0.5 µM 1-naphthaleneacetic acid (NAA). In the absence of BAP, there was no shoot induction, and root formation was achieved only in the shoots of the 70-year-old clone. Shoot number was lower in the shoots of the 600-year-old clone. Both clones showed increased regeneration capacity under BAP exposure, which was positively correlated with 8-hydroxydeoxyguanosine (8-oxo-dG) levels and the antioxidant capacity of total phenolics. In contrast, shoot induction was negatively correlated with 5-methylcytosine (m5C) levels. Treatments with increased BAP concentrations induced the development of anatomical and biochemical characteristics such as underdeveloped tissues and/or delayed tissue development, and this effect was less intense in the 600-year-old clone. Global hypomethylation strongly correlates with guanine hyperoxidation and the de novo regeneration response. Our results suggest that explants collected from fully mature trees may have different growth regulator supplementation needs due to the ‘donor age’ factor. Older clones may require a higher concentration of cytokinins to ensure a regenerative response.Key messageGlobal hypomethylation strongly correlates with the de novo regeneration response. BAP can reduce the 5-methylcytosine levels during in vitro multiplication. BAP altered the antioxidant capacity and 8-hydroxydeoxyguanosine levels of explants.

ABSTRACT Aim Knowledge of the spatial distribution of intraspecific genetic variation is essential for planning conservation actions, designing networks of protected areas, and informing possible assisted migration strategies. Although the Italian peninsula harbours unique genetic variation as a legacy of Quaternary migrations, only sporadic genetic information is available for forest tree species. Here, we present the first geographically comprehensive genetic characterisation of Quercus robur, an iconic broadleaved species of European floodplain forests, in an area which acted as a primary glacial refugium for the species. Location Italy. Methods 745 individuals from 25 populations were sampled and genotyped with 16 nuclear microsatellite markers. Their genetic structure was assessed through various metrics of diversity and distinctiveness, as well as by Bayesian clustering and multivariate methods. The demographic history of inferred gene pools was evaluated through Approximate Bayesian Computation analysis. Results Genetic distinctiveness showed a decline with increasing latitude, while allelic richness reached its peak in central Italy. A south‐to‐north trend in the complexity of the genetic structure was observed, with peninsular Italy being characterised by intermingled gene pools in contrast to the relative homogeneity exhibited by northern populations. Demographic inference indicated that the southern gene pool has been genetically isolated since the penultimate interglacial, whereas populations from central Italy persisted locally in a mosaic of small refugia during the last glaciation. Main Conclusions Our results brought out the complexity of the genetic structure of forest trees' populations in southern Europe. At least three Q. robur refugia contributed to the genetic layout of extant populations after the last glacial period, but refugial areas were probably even more numerous in central Italy. Such a detailed characterisation sheds new light on the priorities to be established for the conservation of highly fragmented Q. robur populations in an area rich in diversified genetic lineages.

In Asturias, northern region of Spain, pedunculate oak (Quercus robur L.) with symptoms of disease such as cracks in the bark with dark exudates, was observed in June 2017. Two different bacteria were isolated from the recovered sample. The two bacteria were biochemically very similar and so were identified by 16S rDNA sequences. The sequence of strain LPPA 3463 had 99% similarity with that of the type strain of the species Brenneria goodwinii Denman et al., and the sequence of strain LPPA 3461 showed the same result with respect to the sequence of the type strain of the species Gibbsiella quercinecans Brady et al. For more accurate identification, gyrB and atpD genes were also sequenced. Pathogenicity tests were initially carried out by puncture with the two bacteria on acorns and after 15 days, a rotten area was observed in the nuts while the controls, inoculated with sterile water, remained healthy. B. goodwinii and G. quercinecans have been consistently associated with Acute Oak Disease (AOD) affecting native oak trees in the UK, usually with presence of galleries produced by the buprestid beetle Agrilus. However, larval galleries of the Agrilus were not present in the pedunculate oak sample. G. quercinecans was reported in Spain on both Quercus ilex L. (holm oak) and Q. pyrenaica Willd. (pyrenean oak), but not on Q. robur. The bacterium B. goodwinii has not been described in Spain, and consequently this is the first report of these bacteria in pedunculate oak in Spain.

Climate change has significant natural and economic implications, but its extent is particularly challenging to assess in forest management, a field which combines both of the previous aspects and requires the evaluation of the impact of climate change on tree species over a 100-year timeframe. Oaks are among the tree species of significant natural and economic value in Europe. Therefore, the aim of this study was to analyze all oak stands in Poland and verify the hypothesis regarding differences between Quercus robur and Quercus petraea stands in terms of soil type, annual total precipitation, average annual air temperature, and the length of the growing season. Additionally, this study aimed to analyze the impact of these differences on the growth rates of both oak species and test whether climate change may affect oak stands. A database containing 195,241 tree stands, including different oak species with varying shares in the stand (from 10% to 100%), was analyzed. A particular emphasis was placed on Q. robur and Q. petraea. The results show that, although both oak species have a wide common range of occurrence, there are clear differences in their habitat preferences. Based on the ordinal regression analysis of selected oak stands, it was concluded that an increase in air temperature of 1 °C could impair the growth of Q. robur and slightly improve the growth of Q. petraea. This may indicate the possibility of expanding the geographic range of sessile oaks towards the east and northeast under warming climatic conditions, provided that appropriate moisture conditions are maintained.

Tree branches from forest tree harvesting for the timber industry are an important energy feedstock. Solid biofuel in the form of wood chips, produced from branches, is an excellent renewable energy source for generating heat and electricity. However, the properties of wood chips as a solid biofuel produced from forest tree branches can vary greatly depending on the species from which they have been produced. Therefore, this study aimed to assess the thermophysical properties and elemental composition of fresh branches harvested from nine tree species (pedunculate oak, silver birch, European ash, common aspen, grey alder, Norway maple, Scots pine, European larch and Norway spruce) over three consecutive years (2020–2022). The branches of the tree species most commonly found in Polish forests (Scots pine) were characterized by the highest heating value (an average of 20.74 GJ Mg−1 DM), the highest carbon content (an average of 55.03% DM), the lowest ash (an average of 0.60% DM) and nitrogen contents (an average of 0.32% DM), and low sulfur (an average of 0.017% DM) and chlorine contents (an average of 0.014% DM). A cluster analysis showed that the branches of all three coniferous tree species (Scots pine, Norway spruce and European larch) formed one common cluster, indicating similar properties. The branches of the European ash were characterized by the lowest wood moisture content (an average of 37.19% DM) and thus the highest lower heating value (an average of 10.50 GJ Mg−1). During the three years of the study, the chlorine and ash contents of the branches of the tree species under study exhibited the highest variability.

In temperate Europe, oak-dominated forests are widespread, supporting high biodiversity and providing important ecosystem services. Insufficient natural regeneration has, however, been a concern for over a century. The objective of this study was to gain insights into differences in regeneration success using artificial and natural regeneration techniques for reforestation of oak (Quercus robur L.) stands. We monitored seedlings following planting, direct seeding and natural regeneration over five years in a randomized block experiment in southern Sweden with fenced and non-fenced plots. Fencing had a strong positive effect on height growth, especially for planted seedlings that were taller than the other seedlings and more frequently browsed in non-fenced plots. In contrast, there was little effect of fencing on survival, establishment rate and recruitment rate of seedlings. Due to aboveground damage on seedlings from voles, protection of acorns did not improve establishment rate following direct seeding. Under current circumstances at the site with a sparse shelterwood of old oaks, we conclude that natural regeneration was the most cost-efficient regeneration method. It resulted in the most seedlings at the lowest cost. However, regeneration success was heavily influenced by interference from herbaceous vegetation. With a small additional investment in vegetation control, the results might have been improved for planting and direct seeding.