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The Middle-spotted Woodpecker is an indicator of structurally complex deciduous forests, typically associated with mature oak stands but occasionally found in beech dominated forests, including at elevations exceeding 1,000 m. Although standing dead wood is often used for nesting and foraging, its necessity for the species’ occurrence remains debated. This study examined the relationship between D. medius presence and standing dead wood characteristics in beech-dominated low-mountain forests of the Perșani Mountains, central Romania. Standardized national woodpecker monitoring protocols were applied at 25 fixed points. Standing dead wood variables (density, diameter at breast height (DBH), height, volume, and basal area) were measured across three habitat categories: all forest types, mature and old stands (> 70 years), and stands containing at least 10% oak. Snag density did not differ significantly between plots with and without Middle-spotted Woodpecker, yet occupied plots contained taller and thicker snags, with predicted occurrence probabilities highest at DBH > 60 cm and height > 25 m. No significant differences were found for basal area or volume. In predominantly beech stands, the species’ presence appeared to be influenced by the availability of standing dead wood and the presence of rough-barked species. These findings confirm the species’ strong association with mature deciduous forests, particularly where oak is present. The increasing probability of occurrence with higher oak proportions in standing dead wood underscores the ecological importance of conserving large, old trees and mixed forest structures for Middle-spotted Woodpecker persistence.

The shift of tree species composition from conifers to mixed stands as a silvicultural management option for substituting pure plantations can have consequences for the greenhouse gas (GHG) budgets and climate impact. In this context, the main objective of the study was to assess the effect of tree species composition on GHG fluxes, organic matter of forest floor and soil in a degraded conifers plantation in Central Italy. Field-chamber GHG fluxes, litter, and total concentrations of soil C and N, soil temperature, and soil moisture were analyzed, assessing their relationships, under mixed and pure conifer species composition during three monitoring years. Carbon and nitrogen contents were higher under mixed than pure conifer species composition, both in forest floor and mineral soil. Soil carbon dioxide under litter of mixed tree species was significantly higher than that of pure conifers (+17.5%). Methane uptake was higher in the mixed plots than in the pure ones (+12.4%), especially in summer and autumn. Nitrous oxide fluxes were characterized by very low emissions, higher under mixed tree-species than pure conifers during winter. The relevant role of seasonality was confirmed by including in the linear mixed-effects model (LMM) the seasons as an additional random effect that produced a significant interaction between the soil moisture and soil temperature, especially on soil carbon dioxide and methane fluxes. Overall, the GHG budget was driven by organic matter availability, higher under mixed species. Our findings are a first step to help the understanding of the role of tree species composition on GHG emissions in the Mediterranean forest ecosystems.

Here we study hybridization, introgression and lineage diversification in the widely distributed canyon live oak (Quercus chrysolepis) and the relict island oak (Q. tomentella), two Californian golden cup oaks with an intriguing biogeographical history. We employed restriction-site-associated DNA sequencing and integrated phylogenomic and population genomic analyses to study hybridization and reconstruct the evolutionary past of these taxa. Our analyses revealed the presence of two cryptic lineages within Q. chrysolepis. One of these lineages shares its most recent common ancestor with Q. tomentella, supporting the paraphyly of Q. chrysolepis. The split of these lineages was estimated to take place during the late Pliocene or the early Pleistocene, a time corresponding well with the common presence of Q. tomentella in the fossil records of continental California. Analyses also revealed historical hybridization among lineages, high introgression from Q. tomentella into Q. chrysolepis in their current area of sympatry, and widespread admixture between the two lineages of Q. chrysolepis in contact zones. Our results support that the two lineages of Q. chrysolepis behave as a single functional species phenotypically and ecologically well differentiated from Q. tomentella, a situation that can be only accommodated considering hybridization and speciation as a continuum with diffuse limits.

Hybridization and introgression play an important role in the evolution and diversification of plants. To assess the degree of past and current hybridization, the level of genetic admixture in populations needs to be investigated. Ongoing hybridization and blurred species separation have made it challenging to assign European white oak taxa based on leaf morphology and/or genetic markers and to assess the level of admixture. Therefore, there is a need for powerful markers that differentiate between taxa. Here, we established a condensed set of single-nucleotide polymorphism (SNP) markers to reliably differentiate between the three most common oak species in temperate European forests (Quercus robur, Q. petraea, Q. pubescens) and to assess the degree of admixture in a large set of selected Swiss populations. A training set of 194 presumably pure reference samples from Switzerland and Europe was used to assign 633 test individuals with two different approaches (population genetic-based/Bayesian vs. assumption-free/discriminative classifier) using 58 selected SNPs from coding regions. Admixture was calculated at the individual and population level with the Shannon diversity index based on individual assignment probabilities. Depending on the approach, 97.5-100 % of training individuals were assigned correctly, and additional analyses showed that the established SNP set could be further reduced while maintaining its discriminatory power. The two assignment approaches showed high overlap (99 %) in assigning training individuals and slightly less overlap in test individuals (84 %). Levels of admixture varied widely among populations. Mixed stands of Q. petraea and Q. pubescens revealed much higher degrees of admixture than mixed stands of the other two taxon pairs, accentuating high levels of gene flow between these two taxa in Switzerland. Our set of SNPs warrants reliable taxon discrimination with great potential for further applications. We show that the three European white oak taxa have largely retained their species integrity in Switzerland despite high levels of admixture.

This article presents the dynamics of changes in the composition of silver birch (Betula pendula Roth) stands over 15 years following the drought of 2010. Silver birch in the forest steppe zone of the Republic of Tatarstan is the main forest-forming species, with birch forests being derivatives of oak forests. The results of the study indicate that in the first two sites, after birch dieback, the proportion of oak in the stand composition increased, with an admixture of aspen, maple, linden, and elm. In the undergrowth composition at both sites, aspen and oak predominate, with small amounts of maple and single birch trees. At the third site, oak and linden undergrowth appeared in areas where birch had died. At all studied plots, a replacement of derivative forest types, birch forests, with indigenous ones, oak forests, is occurring. The change in species composition and the formation of mixed stands contribute to the creation of a more stable forest community.

Natural hybridization, which can be involved in local adaptation and in speciation processes, has been linked to different sources of anthropogenic disturbance. Here, we use genotypic data to study range-wide patterns of genetic admixture between the serpentine-soil specialist leather oak (Quercus durata) and the widespread Californian scrub oak (Quercus berberidifolia). First, we estimated hybridization rates and the direction of gene flow. Second, we tested the hypothesis that genetic admixture increases with different sources of environmental disturbance, namely anthropogenic destruction of natural habitats and wildfire frequency estimated from long-term records of fire occurrence. Our analyses indicate considerable rates of hybridization (> 25%), asymmetric gene flow from Q. durata into Q. berberidifolia, and a higher occurrence of hybrids in areas where both species live in close parapatry. In accordance with the environmental disturbance hypothesis, we found that genetic admixture increases with wildfire frequency, but we did not find a significant effect of other sources of human-induced habitat alteration (urbanization, land clearing for agriculture) or a suite of ecological factors (climate, elevation, soil type). Our findings highlight that wildfires constitute an important source of environmental disturbance, promoting hybridization between two ecologically well-differentiated native species.

Large-scale tree distribution changes have received considerable attention but underlying demo-genetic mechanisms are less well documented. We used a diachronic approach to track species shifts in a mixed oak stand (Quercus petraea-Quercus robur) at a fine spatiotemporal scale. Species assignment was made using single nucleotide polymorphism (SNP) fingerprints employing clustering and parentage analysis. Mating patterns and reproductive success were assessed by parentage analysis. Plot-based inventories of soil parameters and sapling densities provided ecological and demographic information, respectively. Sapling density and reproductive success was higher in Q. petraea than in Q. robur, and were correlated with a spatial expansion of Q. petraea (50% to 67% of the area). Admixed trees resulting from hybridization and backcrossing between the two species were more frequent under the Q. robur canopy. We suspect that species' differential responses to ongoing environmental changes and interspecific competition are the predominant factors accounting for the recruitment success of Q. petraea, while human interference, differential reproduction and hybridization (and backcrossings) are probably of more limited importance. We anticipate in mixed Q. petraea-Q. robur stands, under current ongoing environmental change, that these processes will be enhanced, at least in the western part of the distribution of the two species.

Aims The growing demand from forest managers is to identify silvicultural practices to overcome projected water scarcity during the next decades. One solution is to mix tree species in the same stand, thereby increasing resource partitioning and minimizing competition for limited soil water. This study investigates the mixture approach for Quercus petraea (Matt.) Liebl. and Pinus sylvestris L. during an extreme summer drought event. Methods During the summer drought event in 2016, we analyzed the isotopic signatures of large- and small-tree xylem and soil water throughout the soil profile to assess the depth of water uptake for both tree species. We also measured predawn leaf water potentials (PLWP) to assess water availability for individual tree species. Results When grown in pure stands, both species primarily utilized soil water near the surface. In contrast, partial niche complementarity for limited water resources between the two species in mixed stands resulted in less water constraint (i.e., less negative PLWP) for oak trees compared to pure stands, especially for small trees. Conclusions Results from this study show that contrasting water use strategies can change water availability for trees and could help some species, though not all, to cope with the water scarcity predicted in a changing climate.

The article aims to raise the knowledge on how the Northern red oak affects the soil formation and nutrient cycling compared to Scots pine during the early-stage reclamation of nutrient-poor mineral soil that originated in the deep soil layers in a former sand quarry. Furthermore, the aim is to also answer the question if the admixture of red oak helps to regenerate the soil properties more effectively than pure stands. Three treatments were established: pure red oak, pure pine, and a mixed stand, where organic [composite samples of L+F (litter and fermented), F+H (fermented and humic)] and mineral (A, C) soil horizons were analysed. The oak significantly outperformed the pine in the soil amelioration, showing elevated pH, higher base saturation, and enriched concentrations of basic cations in the humus horizons. The lower litter accumulation under the oak reflected the enhanced decomposability of its litter. A pattern of reduced cation exchange capacity, but the elevated base saturation of the oak soils suggested the development of a nutrient-rich microenvironment with a diminished risk of aluminium toxicity. Phosphorus remained critically limiting. The mixed stand exhibited intermediate properties closer to the pine stand, with the synergistic effects currently limited. Our results support red oak as an effective reclamation species for infertile post-mining soils, though sustained amelioration requires a decades-long perspective and integrated forest management strategies.

Biochars produced from different feedstocks and at different pyrolysis temperatures may have various chemical and physical properties, affecting their potential use as alternative microbial carrier materials. In this study, biochars were produced from pine wood and oak feedstocks at various temperatures (400°C, 500°C, 600°C, 700°C and 800°C), characterized, and assessed for their potential as carriers for Bradyrhizobium japonicum (CB1809) strain. The biochars were then stored at two different storage temperatures (28°C and 38°C) for up to 90 days. Furthermore, the study also explored the role of potentially ideal carriers as inoculants in the growth of Glycine max L. (soybean) under different moisture levels i.e., 55% water holding capacity (WHC) (D0), 30% WHC (D1) and, 15% WHC (D2) using a mixture of 50% garden soil and 50% sand. The results were compared to a control group (without inoculants) and a peat inoculant. Among all the materials derived from pine wood and oak, pine wood biochar pyrolyzed at 400℃ (P-BC400) exhibited the highest CFU count, with values of 10.34 and 9.74 Log 10 CFU g− 1 after 90 days of storage at 28℃ and 38℃, respectively. This was notably higher compared to other biochars and peat carriers. Significant (p < 0.05) increases in plant properties: shoot and root dry biomass (174% and 367%), shoot and root length (89% and 85%), number of leaves (71%), membrane stability index (27%), relative water content (26%), and total chlorophyll (140%) were observed in plants treated with P-BC400 carrier inoculant compared to the control at D2; however, lower enrichment of δ13C (37%) and δ15N (108%) with highest number of root nodules (8.3 ± 1.26) and nitrogenase activity (0.869 ± 0.04) were observed under D2, as evident through PCA analysis, showing more nitrogen (N) fixation and photosynthetic activity. Overall, this experiment concluded that biochar pyrolyzed at lower temperatures, especially P-BC400, was the most suitable candidate for rhizobial inoculum and promoted soybean growth.