Quercus Pyrenaica Research Articles

Educational Strategies for Teaching Climate and Bioclimate in Response to Global Change

This work establishes the relationship between climate, bioclimate, and forest ecosystems and highlights the need to teach these topics in educational institutions. It was found that such knowledge is not currently taught in universities, leading to scarce or non-existent teacher training in these areas. However, the teaching of bioclimatic aspects over a three-year period as a basis for land use planning, has shown highly positive results. The objective is to propose the teaching of bioclimatology to future managers and teachers in order to obtain a balanced environmental development. The analysis of bioclimatic diagrams makes it possible to stipulate the duration of the water reserve in the soil. This is essential for agricultural and forestry management. The edaphic factor and the bioclimatic ombrotclimatic (Io) and thermoclimatic (It/Itc) indexes condition the types of forests and crops that can exist in a territory, with the particularity that the ombrotype is conditioned by the edaphic factor, which allows a decrease in the ombrothermal index, expressed by the ombroedaphoboxerophilic index (Ioex). The humid ombrotypes condition the presence of Abies pinsapo, Quercus pyrenaica, Q. broteroi, and Q. suber, and the dry ones Q. rotundifolia and Olea sylvestris.

Hymenochaete ametzii sp. nov. (Hymenochaetales, Basidiomycota), an endangered bark-dwelling species inhabiting old Quercus pyrenaica trees from the Iberian Peninsula

Bark-dwelling fungi represent a group of ecologically highly specialized organisms. This study deals with an undescribed species of Hymenochaete characterized by specifically inhabiting the bark of Pyrenean oak (Quercus pyrenaica), and producing effuse-reflexed basidiomata and mainly globose to subglobose basidiospores. Maximum Likelihood and Bayesian analyses of the nuclear ITS-LSU regions revealed that the sequences of H. ametzii form a monophyletic group with a low intraspecific variation and substantially different from closest taxa, further supporting its recognition as a species. The seven localities H. ametzii is known from are old forests with a long ecological continuity, containing large old Q. pyrenaica trees, and are located in the supramediterranean belt of the Mediterranean biogeographical region. Based on habitat availability and field counts of colonized trees, the global population of H. ametzii is estimated at 8,670 mature individuals. Considering that the traditional use of old Q. pyrenaica stands ceased several decades ago in the Iberian Peninsula, with a consequent decline in habitat quality and availability, it is concluded that H. ametzii is Endangered (EN) according to the IUCN criteria.

Watering the trees for the forest: Drought alleviation in oaks and pines by ancestral ditches

Traditional ditches (“acequias” in Spanish) derive meltwater and infiltrate groundwater providing ecological services downstream in the semi-arid Sierra Nevada range (SE Spain). Therefore, they may act as a nature-based solution by alleviating drought stress in trees growing near ditches by enhancing growth and reducing their intrinsic water-use efficiency (iWUE). Such a mitigation role of acequias is critical given that some oak (Quercus pyrenaica) and pine (Pinus sylvestris) stands reach their xeric distribution limits in Europe. We compared tree-ring width data and wood δ13C, a proxy of iWUE, in oak and pine stands located near or far (control) from ditches with different infiltration capacity in two watersheds. We assessed how trees responded to climate data, drought stress, and vegetation greenness through correlations and resilience indices. Oak trees located near ditches grew more and responded less to precipitation, soil moisture, a drought index, and greenness than control trees. In pines, we did not find this pattern, and ditch trees grew more than control trees only during an extremely dry year (1995). Climate-growth correlations suggested a longer growing season in ditch pines. Growth of ditch oaks from the “Acequia Nueva” (AN), with high infiltration capacity, responded more to autumn soil moisture and showed the lowest δ13C. Growth was enhanced by cool-wet spring conditions in pines and also by warm-wet conditions in the prior winter in the case of oaks. Control trees showed lower resistance to drought. Control trees presented higher wood δ13C values except for old oaks from the “Acequia Grande” (AG) site which may show long-term acclimation. Traditional ditches alleviate drought stress in oak and pine stands subjected to regional xeric climate conditions.

Biological control of damping-off by Fusarium oxysporum and F. verticillioides on pine and oak seedlings using edible ectomycorrhizal fungi

The Mediterranean forest has an important ecological and economic role, being holm oak (Quercus ilex), Pyrenean oak (Quercus pyrenaica), umbrella pine (Pinus pinea) and Scot pine (Pinus sylvestris) some of its main tree species. The fungal damping-off disease caused by Fusarium seriously threatens the establishment of these forest species in nurseries and reforestation, requiring the search for environmentally friendly alternatives to control the disease. We have used different species of ectomycorrhizal fungi (EMF) as potential biological control agents (BCAs) effective against the disease: Lactarius sanguifluus, Tricholoma portentosum, Suillus luteus and Agaricus silvicola from Pinus-species, and Leccinum lepidum, Amanita rubescens and Xerocomus ferrugineus from Quercus-species. A direct in vitro confrontation was performed and conidial germination of Fusarium in contact with cell-free filtrates produced by EMF was studied. Le. lepidum was the most effective Quercus-fungus in vitro against F. oxysporum, reducing its growth up to 32 % and its conidial germination up to 87 %. S. luteus was the most effective Pinus-fungus in vitro against F. oxysporum and F. verticillioides, reducing in direct confrontation, reducing its growth up to 30 %. However, La. sanguifluus was the Pinus-fungus that inhibited conidial germination of both pathogens, up to 55 %. In planta trials were carried out with seeds of the four forest species growing on substrate colonized by Le. lepidum (in Q. ilex and Q. pyrenaica seeds, infected by F. oxysporum) or by La. sanguifluus (P. pinea and P. sylvestris seeds, infected by F. oxysporum or F. verticillioides). Only La. sanguifluus was effective in reducing disease caused by F. oxysporum (strain Fo4) on P. sylvestris seeds. Therefore, EMF may be a potential tool in the control of damping-off in forest species, requiring further research.

Whole-genome screening for near-diagnostic genetic markers for four western European white oak species identification

Key messageMining genome-wide DNA sequences enabled the discovery of near-diagnostic markers for species assignment in four European white oaks (Quercus petraea (Matt.) Liebl., Quercus pubescens Willd., Quercus pyrenaica Willd., and Quercus robur L.) despite their low interspecific differentiation. Near-diagnostic markers are almost fully fixed in one species and absent in the three others. As a result, only a handful of markers are needed for species identification, making this genetic assay a very promising operational taxonomic assignment procedure in research and forestry.ContextIdentifying species in the European white oak complex has been a long-standing concern in taxonomy, evolution, forest research, and management. Quercus petraea (Matt.) Liebl., Q. robur L., Q. pubescens Willd., and Q. pyrenaica Willd. are part of this species complex in western temperate Europe and hybridize in mixed stands, challenging species identification.AimsOur aim was to identify near-diagnostic single-nucleotide polymorphisms (SNPs) for each of the four species that are suitable for routine use and rapid diagnosis in research and applied forestry.MethodsWe first scanned existing whole-genome and target-capture data sets in a reduced number of samples (training set) to identify candidate diagnostic SNPs, i.e., genomic positions being characterized by a reference allele in one species and by the alternative allele in all other species. Allele frequencies of the candidates SNPs were then explored in a larger, range-wide sample of populations in each species (validation step).ResultsWe found a subset of 38 SNPs (10 for Q. petraea, 7 for Q. pubescens, 9 for Q. pyrenaica, and 12 for Q. robur) that showed near-diagnostic features across their species distribution ranges with Q. pyrenaica and Q. pubescens exhibiting the highest (0.876) and lowest (0.747) diagnosticity, respectively.ConclusionsWe provide a new, efficient, and reliable molecular tool for the identification of the species Q. petraea, Q. robur, Q. pubescens, and Q. pyrenaica, which can be used as a routine tool in forest research and management. This study highlights the resolution offered by whole-genome sequencing data to design near-diagnostic marker sets for taxonomic assignment, even for species complexes with relatively low differentiation.

Spectral Library of Plant Species from Montesinho Natural Park in Portugal

In this work, we present and describe a spectral library (SL) with 15 vascular plant species from Montesinho Natural Park (MNP), a protected area in Northeast Portugal. We selected species from the vascular plants that are characteristic of the habitats in the MNP, based on their prevalence, and also included one invasive species: Alnus glutinosa (L.) Gaertn, Castanea sativa Mill., Cistus ladanifer L., Crataegus monogyna Jacq., Frangula alnus Mill., Fraxinus angustifolia Vahl, Quercus pyrenaica Willd., Quercus rotundifolia Lam., Trifolium repens L., Arbutus unedo L., Dactylis glomerata L., Genista falcata Brot., Cytisus multiflorus (L’Hér.) Sweet, Erica arborea L., and Acacia dealbata Link. We collected spectra (300–2500 nm) from five records per leaf and leaf side, which resulted in 538 spectra compiled in the SL. Additionally, we computed five vegetation indices from spectral data and analysed them to highlight specific characteristics and differences among the sampled species. We detail the data repository information and its organisation for a better understanding of the data and to facilitate its use. The SL structure can add valuable information about the selected plant species in MNP, contributing to conservation purposes. This plant species SL is publicly available in Zenodo platform.

Soil mycobiome and forest endophytic fungi: Is there a relationship between them?

Fungi are important ecological agents in forests that contribute to increase the resilience of the whole ecosystem against environmental challenges. Mediterranean forests rank among the habitats most threatened by climate change and the spread of pests and diseases, which ultimately lead them into a spiral of decline. As such, changes in the composition of soil and trees’ mycobiota might correlate with health status of the forest and has been scarcely addressed in Mediterranean tree species. In this work, rhizosphere and bark-wood samples from declining Spanish forests of Castanea sativa Mill. (chestnut), Quercus ilex L. (holm oak), Q. suber L. (cork oak) and Q. pyrenaica Willd. (Pyrenean oak) were compared. Fungal communities were characterised by means of ITS metabarcoding. Higher diversity in terms of richness was found in soil, with 674 genera belonging to 15 phyla in soil vs 420 genera and 6 phyla in trees. Fungal genera exclusive to declining forests’ soils and trees didn’t include pathogenic organisms, thus preventing the association of certain genera with forest decline. Alpha diversity didn’t correlate with health status or sample type either, as it only increased in soils of asymptomatic chestnuts and not in any of the other analysed tree species. Some differentially abundant genera found in asymptomatic trees, such as Metarhizium, Aspergillus, Russula, Chaetomium, Mortierella or Cladophialophora, may be related to the biological control of decline-contributing pathogens. Finally, no relationship was found between health status and the primary lifestyles of fungi in soil and bark, which can be interpreted as a sign of resilience against adversities following cross-talk between soil and plant fungal communities.

Physical decomposition stage and ergosterol content predict the chemical composition of downed dead wood in Mediterranean dehesas

AbstractDead wood is a key substrate of forests that plays an important role in fertility and productivity. However, dead wood is scarce in traditionally managed forests like Mediterranean dehesas. The chemical composition of downed dead wood in Quercus pyrenaica dehesas was analysed in different physical decomposition stages as a proxy of dead wood decay length. We also assessed the contribution of fungal activity, by quantifying ergosterol, to the chemical composition of deadwood. Chemical analyses included elemental composition determination, thermogravimetry and infrared spectroscopy. Our results showed that both the physical decomposition stage and ergosterol content extensively predicted the chemical composition of Q. pyrenaica dead wood decay processes under field conditions. The physical stage was a better predictor of the C/P ratio and polysaccharides proportion, while ergosterol better predicted P content and the N/P ratio. In other cases like lignin, the relation between ergosterol content and chemical composition varied depending on the physical stage. In addition, environmental local factors differentially affected chemical composition across physical decomposition stages. We conclude that the physical decomposition stage and ergosterol content complementarily contribute to estimate the temporal behaviour of the chemical composition of dead wood in Mediterranean areas. Moreover, we recommend using the FT-IR analysis to assess the nature of temporal chemical changes in downed dead wood. Finally, our study claims to consider the potential impact of local environmental factors, such as air temperature and relative humidity, on dead wood decay processes in traditionally managed forests in the current global change scenario.

Changes in bryophyte functional composition during post-fire succession

Climate and land-use changes are altering fire regimes in many regions around the world. To date, most studies have focused on the effects of altered fire regimes on woody and herbaceous communities, while the mechanisms driving post-fire bryophyte succession remain poorly understood, particularly in Mediterranean-type ecosystems. Here, we examined changes in bryophyte functional composition along a post-fire chronosequence (ranging from 1 to 20+ years) in Pyrenean oak woodlands (northeastern Portugal). To do so, we defined bryophyte functional groups based on seven morphological, reproductive, and life history traits. Then, we fitted linear and structural equation models to disentangle the direct and indirect effects of fire (time since fire and fire intensity), vegetation structure, climate, topography, and edaphic conditions on the abundance of each group. We identified two main functional groups: early colonizers (species with traits associated with strong colonization ability and desiccation tolerance) and perennial stayers (species with high competitive ability, i.e., large perennial mosses). Overall, the abundance of early colonizer species decreased with time since fire and increased with fire intensity, while the opposite was observed for perennial stayers. Thus, successional dynamics reflected a trade-off between species' competitive and colonization abilities, highlighting the role of biotic interactions later in succession. Patterns of functional composition were also consistent with changes in environmental conditions during succession, suggesting that species may experience stressful conditions (i.e., high radiation and low water availability) in early stages of post-fire succession. Our results also indicate that increased fire intensity may alter successional trajectories, leading to long-term changes in bryophyte communities. By understanding the response of bryophyte communities to fire, we were able to identify species with potential use as soil restoration materials.

Histological analysis of <i>Xylella fastidiosa</i> infection in <i>Quercus pyrenaica</i> in Northern Portugal

<abstract> <p><italic>Quercus pyrenaica</italic> Willd thrives in the intermediate zone between the Mediterranean sclerophyllous and the temperate deciduous forest. In December 2022, the presence of the bacteria <italic>Xylella fastidiosa (Xf)</italic> was confirmed in samples collected from a <italic>Quercus pyrenaica</italic> located in Sabrosa, Vila Real, Portugal. Following <italic>Xf</italic> infection, the transport of water and nutrients is hindered due to the occlusion of xylem vessels. This loss of hydraulic conductivity may lead to vessel blockage and subsequent embolism formation. The objective of this study was to investigate the interaction between <italic>Xf</italic> and <italic>Quercus pyrenaica</italic> tissues, as well as the mechanism by which the bacteria can spread through the plant's xylem vessels, ultimately resulting in the formation of vascular plugs. At the time of the sample collection (10 months post-detection), symptoms of Bacterial Leaf Scorch (BLS) began to appear. Examination of xylem vessels using both light and scanning electron microscopy (SEM) revealed the presence of various types of occlusions, predominantly tyloses. Additionally, fibrillar networks, gums, starch grains, and crystals were observed. The stem vessels exhibited significantly more occlusions compared to the leaves. Furthermore, individual bacterial cells were observed to be attached to the vessel wall. This implies that occlusions were primarily induced by tyloses and gums as a defensive response to the invasion of vascular pathogens, in addition to the pathogen itself. This study highlights the presence of starch grains in stems, which may function as a refilling mechanism, thereby preventing the loss of hydraulic conductivity in plants and potentially acting as a means to entrap the bacteria. These mechanisms exemplify the constitutive defense systems of the plant against <italic>Xf</italic>. Understanding the interaction between <italic>Xylella fastidiosa</italic> and <italic>Quercus pyrenaica</italic> is crucial, given that the latter species occupies nearly 95% of the natural distribution area of Portugal.</p> </abstract>

Twenty years of population dynamics in European beech-oak forest at their rear range margin anticipate changes in its structure and composition

There is an increasing interest in restoring degraded forests, which occupy half of the forest areas. Among the forms of restoration, passive restoration, which involves the elimination of degrading factors and the free evolution of natural dynamics by applying minimal or no management, is gaining attention. Natural dynamics is difficult to predict due to the influence of multiple interacting factors such as climatic and edaphic conditions, composition and abundance of species, and the successional character of these species. Here, we study the natural dynamics of a mixed forest located in central Spain, which maintained an open forest structure, due to intensive use, until grazing and cutting were banned in the 1960s. The most frequent woody species in this forest are Fagus sylvatica, Quercus petraea, Quercus pyrenaica, Ilex aquifolium, Sorbus aucuparia, Sorbus aria and Prunus avium, with contrasting shade and drought tolerance. These species are common in temperate European deciduous forest and are found here near their southern distribution limit, except for Q. pyrenaica. In order to analyze forest dynamics and composition, three inventories were carried out in 1994, 2005 and 2015. Our results show that, despite the Mediterranean influence, the natural dynamics of this forest has been mainly determined by different levels of shade tolerance. After the abandonment of grazing and cutting, Q. pyrenaica expanded rapidly due to its lower shade tolerance, whereas after canopy closure and forest densification, shade-tolerant species gained ground, particularly F. sylvatica, despite its lower drought and late-frost tolerance. If the current dynamics continue, F. sylvatica will overtake the rest of the species, which will be relegated to sites with shallow soils and steep slopes. Simultaneously, all the multi-centennial beech trees, which are undergoing a rapid mortality and decline process, will disappear.

Effects of Boom-Corridor and Selective Thinnings on Harvester Productivity in Dense Small Diameter Pyrenean Oak (Quercus pyrenaica Willd.) Coppices in Spain

Due to socioeconomic transformations in the 20th century, Quercus pyrenaica Willd. coppices in Spain, as well as other European coppices, have experimented an abandonment and lack of intervention leading to stagnant high density stands with fragile health due to competition. Thinnings are often required to ensure their stability and health, producing forest products such as firewood or biomass, which are key energy sources in a carbon-neutral economy. However, thinnings are seldom performed because they lack economic sustainability due to a low productivity, high costs and low biomass prices. In this study, two thinning methods, selective thinning (ST) and boom-corridor thinning (BCT), were tested carrying out a time study in a high-density small-diameter Q. pyrenaica stand in the León province (Castilla y León, Spain) with a forest harvester base machine, on which an accumulating felling head Bracke C16c was mounted. The residual stands were significantly different regarding the final density (greater in BCT) and the final average DBH (bigger in ST), while thinning intensity (odt·ha-1) was the same. In most work elements, time per tree was not significantly different. BCT showed a significant 48.6% increase in harvester productivity when compared to ST, with averaging 4.43 and 2.99 odt·pmh-1, respectively, due mainly to the average weight per extracted tree, 42% greater in BCT. When considering the common range of unit tree weight, the productivity was 16–23% greater for BCT, far less than observed in the trials. These results show the potential of BCT over ST in the studied conditions, although there is room for improvement. Further studies could include the future evolution of the treated stands and perform a cost analysis.

Short-term effect of thinning on inter- and intra-annual radial increment in Mediterranean Scots pine-oak mixed forests

Thinning treatments along with the establishment of mixed forest stands have been put forward as possible adaptation strategies to cope with climate change, although the effectiveness of combining these two measures has scarcely been studied and may vary depending on stand conditions and the thinning regime employed. The aim of this study was to better understand the effect of commercial thinning and of the different growth behavior of two coexisting species on their inter- and intra-annual cumulative radial increment patterns. For this purpose, we studied radial increment in a Scots pine-Pyrenean oak (Pinus sylvestris L.-Quercus pyrenaica Willd.) Mediterranean mixed forest in north-west Spain over two climatically contrasting years (2016–2017). The data came from a thinning trial consisting of a randomized latin square design with a control and two commercial thinning treatments from below; one moderate and the other heavy, removing 25% and 50 % of initial basal area, respectively, of both species. The radial increment was analyzed based on bi-weekly readings from band dendrometers installed on 90 oak and pine trees. A non-linear mixed model based on double-Richards curve was fitted to explore the differences between thinning treatments and species response in the intra-annual cumulative radial increment patterns. Inter-annual basal area increments for each species at stand level were quantified by aggregating the tree estimates obtained from the model fitted in the first step. Tree and stand level growth were greater in Scots pine, which also showed a greater growth response to early spring droughts than the Pyrenean oak. Heavy thinning increased radial increment in trees of both species at the expense of decreased total stand basal area. At species level, basal area growth in Scots pine decreased through thinning, whereas for Pyrenean oak, the heavy thinning intensity resulted in the same basal area growth as the control. Thus, heavy thinning induced a trade-off between total stand growth and tree-level response to climatic conditions for Scots pine but with no loss in productivity in the case of the Pyrenean oak. Hence, heavy thinning may be an appropriate measure to attain productive stability of the oak coppice in the studied mixed forest as well as to adapt tree growth to future droughts associated with climate change.

Rhizosphere mycobiome diversity in four declining Mediterranean tree species

IntroductionForests in the Mediterranean basin are currently in decline. Their resilience has been eroded as a result of climate change and anthropogenic impacts, making them vulnerable to increasingly frequent episodes of drought, fire and the spread of pests and diseases. The impact of these natural and anthropogenic events on soil biodiversity is of particular concern, as the soil fungal community plays a key role in ecosystem homeostasis.Objectives and methodsIn order to analyse the relationship between soil health status and fungal diversity, soil samples were collected from declining Mediterranean forests of Castanea sativa (chestnut), Quercus ilex (holm oak), Quercus suber (cork oak) and Quercus pyrenaica (Pyrenean oak). A metabarcoding study was carried out by sequencing the ITS genomic region.ResultsA total of 674 fungal genera were found. It has not been possible to explain the differences in health status from the fungal genera found exclusively on declining forest soils, as none of them have been described as pathogenic. Healthy chestnut soils were characterized by a high alpha diversity and a higher abundance of the genus Metarhizium. No differentially abundant genera were found in any of the other forest species tested. Declining chestnut soils harbored more abundance of ectomycorrhizae and soil saprotrophs than healthy samples. Ectomycorrhizae were the dominant lifestyle in all oak species regardless of health status, whereas arbuscular mycorrhizae were preferentially found in declining cork oak soils.DiscussionThis work highlights the resilience of fungal communities of soil against decline and highlights the need to further investigate its relationship with the forest’s ability to cope with the challenges of climate change.

Quercus robur and pyrenaica: The Potential of Wild Edible Plants for Novel Kombuchas

Wild edible plants (WEPs) can be utilised as a substrate to develop novel types of fermented beverages. The aim of this study was to investigate the potential of incorporating Quercus spp. leaves as a substrate to develop new varieties of kombuchas. The physicochemical properties of kombuchas elaborated with Quercus robur (KQR) and Quercus pyrenaica (KQP) leaves’ infusion were compared with traditional black tea kombuchas (KBT). Total acidity (TA), pH, total soluble solids (TSSs), instrumental colour, total phenolic compounds (TPCs), sucrose, fructose, and glucose were analysed for the three types of infusions and kombuchas at 0, 3, 7, 10, and 14 fermentation days. The results revealed that the type of substrate and the fermentation time significantly influenced the biochemical changes that occurred during 14 days. KQP and KQR turned out to be significantly brighter (L*: 53.91 ± 0.12 and 55.66 ± 0.23, respectively) than KBT (L*: 48.79 ± 0.34) and had significantly lower sucrose content (22.06 ± 0.79 g L−1 and 45.69 ± 1.61, respectively) than KBT (59.28 ± 2.25 g L−1). KBT showed significantly higher content of total polyphenols (1.50 ± 0.05 g GAE L−1) than KQR (0.76 ± 0.09 g GAE L−1) and KQP (0.51 ± 0.04 g GAE L−1) after 14 days of fermentation. Regarding the kinetics of sugars, sucrose reduction was significantly lower in KBT samples (11.36 g L−1) than in KQP and KQR samples (47.01 and 28.31 g L−1, respectively) at the end of fermentation. These results suggest that higher content of TPC may slow down the fermentation process. Quercus spp. leaves may be a viable alternative substrate for developing analogues of kombucha with WEPs and for adding gastronomic and sustainable value.

Mediterranean service trees respond less to drought than oaks

Some widely distributed timber species, such as oaks, are vulnerable to low soil water availability and drought. Therefore, selecting broadleaved minor species with lower sensitivity to drought could be an alternative in seasonally dry areas. However, the growth performance of these minor hardwood species is unknown, particularly under warm and dry conditions at the southern limit of their distribution range. We assessed the radial growth response to drought by correlating tree-ring and climate data in coexisting service trees (Sorbus domestica) and two oak species (Quercus faginea, Quercus pyrenaica). Trees were sampled in three Mediterranean sites located in Spain with different precipitation patterns. We used the Vaganov–Shashkin (VS) growth model to infer the main climate constraints of growth. To ascertain whether climate is changing tree phenology, we also simulated changes in xylem onset and cessation timings and compared them with leaf falling dates in service trees. Service trees showed a trend towards advancing leaf fall, but this was not related to xylem growth. Oaks responded more to a drought index than service trees. The strongest responses corresponded to droughts peaking from spring to summer, but oaks tended to respond to longer droughts (9–13 months) than service trees (2–7 months). These different responses are due to the positive responses of all species to high precipitation in the growing season, but the sensitivity of oak growth to warm summer conditions and increased atmospheric water demand. The VS model indicated a more bimodal growth pattern in services trees than in oaks, which could allow the former to recover better after a dry summer. Service trees could be more widely used as a source of valuable timber wood under Mediterranean continental conditions.

Bacterial inoculation of Quercus pyrenaica trees alters co-occurrence patterns but not the composition of the rhizosphere bacteriome in wild conditions.

Quercus pyrenaica is a woody species of high landscape value, however, its forests show an advanced state of degradation in the Iberian Peninsula. Afforestation typically has low success, thus, it is necessary to improve the fitness of oaks plantlets to be transplanted, for instance, by inoculating beneficial microorganisms. In adding microorganisms to ecosystems, there must be balanced efficacy with potential effects on native microbial communities. We addressed changes in diversity, richness, composition and co-occurrence networks of prokaryotic communities in the rhizosphere of inoculated and control trees outplanted to three different sites located in the Sierra Nevada National and Natural Park (Spain). After 18 months in wild conditions, we did not detect changes due to the inoculation in the richness, diversity and structure in none of the sites. However, we observed an increase in the complexity of the co-occurrence networks in two experimental areas. Modularization of the networks changed as a result of the inoculation, although the sense of the change depended on the site. Although it was impossible to unravel the effect of bacterial inoculation, our results highlighted that inoculation alters the association of rhizosphere bacteria without entailing other changes, so networks should be analysed prior to inoculating the plantlets.

Responses of ancient pollarded and pruned oaks to climate and drought: Chronicles from threatened cultural woodlands

Humans have shaped open oak forests for centuries through pollarding and grazing. Nowadays, these cultural landscapes face the abandonment of their traditional uses and new threats, including rising temperatures and increasing drought stress, especially in southern Europe. We need precise data on the long-term radial growth changes of these oak woodlands to better characterize and preserve them. To fill this research gap, we compared the growth patterns and responses to climate variables and a drought index of three traditionally pollarded deciduous oaks (Quercus subpyrenaica, Quercus faginea, Quercus pyrenaica) and one previously pruned, evergreen oak (Quercus ilex) in central and northeastern Spain. In the three deciduous oaks, we reconstructed radial growth suppressions which were mainly attributed to past pollarding events. Recent post-pollarding growth improvement was transitory but long-term growth enhancement could be maintained by periodic pollarding. Formerly pollarded oaks were old reaching maximum ages of 313 years in the case of Q. faginea. Formerly pruned Q. ilex trees were also old reaching ages of at least 384 years. Peaks in major growth suppressions of Q. faginea sites corresponded to periods of intense timber demand following abrupt socioeconomic changes (land tenure and land use changes, local population growth, wars) such as the 1820s, 1840s, 1910s and 1940s. However, other growth suppressions corresponded to dry periods such as the 1870s and 1950s. Oak growth was constrained by warm-dry conditions in spring and by short- to long-term summer droughts (4–18 months). Pollarding abandonment and increased aridification threaten the survival of such old pollarded oak stands that preserve unique cultural, ecological and biological values.

Improvement Cuttings in the Conversion of Pyrenean Oak (Quercus pyrenaica Willd.) Coppice

An appropriate management and valuation of Pyrenean oak (Quercus pyrenaica Willd.) forests are essential in order to ensure their multiple functions and uses. Many coppice forests of Pyrenean oak have been converted into high forests mostly due to changing demands. This work presents a 20-year study conducted with Pyrenean oak coppices, providing results from an experimental trial where silvicultural improvement interventions for coppice conversion were applied. In addition to control, selective thinning and 3-strip thinning with 2 × 2 m, 3 × 3 m, and 3 × 6 m (the latter also included selective thinning) were examined. The study analyzed tree growth, vertical stratification dynamics, and epicormic branching. It was found that the silvicultural interventions promoted tree development differently according to social crown class. The results have shown a significantly different response in tree diameter growth and live crown length, while height growth has been less accentuated. The study also examined the temporal effect of the interventions on diameter growth. Changes in tree crown position and structural characteristics varied among the cutting interventions. Regarding epicormic branching, the results have revealed that the number of shoots does not differ significantly among the treatments but shows differences in length. Management issues regarding Pyrenean oak coppice conversion have also been addressed.

Assessing the Performance of a Handheld Laser Scanning System for Individual Tree Mapping—A Mixed Forests Showcase in Spain

The use of mobile laser scanning to survey forest ecosystems is a promising, scalable technology to describe the 3D structure of forests at a high resolution. We use a structurally complex, mixed-species Mediterranean forest to test the performance of a mobile Handheld Laser Scanning (HLS) system to estimate tree attributes within a forest patch in central Spain. We describe the different stages of the HLS approach: field position, ground data collection, scanning path design, point cloud processing, alignment between detected trees and measured reference trees, and finally, the assessment of main tree structural attributes diameter at breast height (DBH) and tree height considering species and tree size as control factors. We surveyed 418 reference trees to account for omission and commission error rates over a 1 ha plot divided into 16 sections and scanned using two different scanning paths. The HLS-based approach reached a high of 88 and 92% tree detection rate for the best combination of scanning path and point cloud processing modes for the HLS system. The root mean squared errors for DBH estimates varied between species: errors for Pinus pinaster were below 2 cm for Scan 02. Quercus pyrenaica, and Alnus glutinosa showed higher error rates. We observed good agreement between ALS and HLS estimates for tree height, highlighting differences to field measurements. Despite the complexity of the mixed forest area surveyed, our results show that HLS is highly efficient at detecting tree locations, estimating DBH, and supporting tree height measurements as confirmed with airborne laser data used for validation. This study is one of the first HLS-based studies conducted in the Mediterranean mixed forest region, where variability in tree allometries and spacing and the presence of natural regeneration pose challenges for the HLS approach. HLS is a feasible, time-efficient, scalable technology for tree mapping in mixed forests with potential to support forest monitoring programmes such as national forest inventories lacking three-dimensional, remote sensing data to support field measurements.