Cork Oak Research Articles

Symbiotic Fungi of an Ambrosia Beetle Alter the Volatile Bouquet of Cork Oak Seedlings.

In Portugal, fungal symbionts of the ambrosia beetle Platypus cylindrus affect tree vigor of cork oak (Quercus suber) and are linked with the cork oak decline process. Fungal symbionts play crucial roles in the life history of bark and ambrosia beetles and recent work indicates complex interactions on the fungal and plant metabolic level. Colonized trees may respond with an array of currently unknown volatile metabolites being indicative of such interactions, acting as infochemicals with their environment. In this study, we examined volatile organic compounds (VOCs) of cork oak seedlings wound inoculated with strains of three fungal associates of P. cylindrus (Raffaelea montetyi, R. quercina, and Ceratocystiopsis sp. nov.) over a 45-day period by means of thermodesorption gas chromatography-mass spectrometry techniques. Fungal strains induced largely quantitative but species-specific changes among the 58 VOCs characterized. Overall, monoterpenes-the major volatiles of cork oak foliage-were significantly reduced, possibly a result of fungal biotransformation. Acetophenone, sulcatone, and nonanal-volatiles known for mediating ambrosia beetle behavior-increased in response to fungal inoculation. Qualitative VOC profiles of excised tissue of wood lesions (21 VOCs) and pure fungal cultures (60 VOCs) showed little overlap with seedling VOCs, indicating their plant-derived but fungal-induced origin. This chemoecological study expands on the limited knowledge of VOCs as infochemicals emitted from oak trees threatened by oak decline in relation to beetle-vectored ophiostomatoid fungi. It opens new avenues of research to clarify mutualistic or pathogenic aspects of these complex symbiotic interactions and develop new control strategies for P. cylindrus, including its mycobiota.

Biomass and Carbon Stock Quantification in Cork Oak Forest of Maamora Using a New Approach Based on the Combination of Aerial Laser Scanning Carried by Unmanned Aerial Vehicle and Terrestrial Laser Scanning Data

The Mediterranean forests, particularly Cork oak (Quercus suber L., 1927), make a major contribution to the fight against climate change through Carbon sequestration. Hence, there is a great interest in the accurate quantification of biomass and carbon stock. In this context, this study aims at assessing the performance of a new approach, based on the combination of Unmanned aerial vehicle airborne Aerial laser scanning (ALS-UAV) and Terrestrial laser scanning (TLS) data, in the determination of dendrometric parameters (Circumference at 1.30 m and Tree Height), and consequently the estimation of biomass and carbon stock, considering field data as reference. This study takes the Maamora forest in Morocco as an example of a Mediterranean Cork oak forest. The methodology consists of collecting data at three levels: the entire area level for an ALS-UAV scan, the plot and tree levels for TLS surveys, as well as field data collection. Afterwards, dendrometric parameters (Circumference at 1.30 m and the Tree height) were estimated using individual tree segmentation and biomass; the carbon stock (aboveground, belowground, and total) was estimated using allometric equations. The comparison of the estimated dendrometric parameters with those measured in the field shows a strong relationship, with a Pearson coefficient of 0.86 and 0.83, a correlation coefficient (R2) of 0.81 and 0.71, and a Root mean square error (RMSE) of 1.84 cm and 0.47 m, respectively. Concerning the biomass and carbon stock estimation, the proposed approach gives a satisfactory accuracy, with a Pearson coefficient of 0.77, an R2 of 0.83, and an RMSE of 36.40 kg for biomass and 20.24 kg for carbon stock.

Micro‐habitat drivers of saproxylic beetle assemblages in old woodlands of Mediterranean cork oak (Quercus suber)

Abstract Cork oak landscapes are fascinating ecosystems, historically managed for cork extraction. The persistence in this habitat of many hollow veteran trees provides suitable micro‐habitats for saproxylic beetles. We investigated the saproxylic beetle community of two isolated cork oak woodlands of central Italy with different degree of recovery after human transformation: (1) an open woodland and (2) a dense mixed woodland, both dominated by cork oak trees. We found endemic, rare and threatened saproxylic beetles in both the areas, confirming the important conservation value of cork oak landscapes. In the open woodland we observed a higher number of species in all trophic categories, except for mycophagous specialists. Several microhabitat variables reflected the different stage of recovery of the two woodlands. Our findings suggest the crucial role of diversified environments in protected areas: even a small difference in the degree of recovery (i.e., tree closeness) can affect the number of beetle species. Specifically, we found (1) more xerophilous species in the open woodland and (2) more mesophilous species in the dense mixed woodland.

Forest tree species distribution for Europe 2000-2020: mapping potential and realized distributions using spatiotemporal machine learning.

This article describes a data-driven framework based on spatiotemporal machine learning to produce distribution maps for 16 tree species (Abies alba Mill., Castanea sativa Mill., Corylus avellana L., Fagus sylvatica L., Olea europaea L., Picea abies L. H. Karst., Pinus halepensis Mill., Pinus nigra J. F. Arnold, Pinus pinea L., Pinus sylvestris L., Prunus avium L., Quercus cerris L., Quercus ilex L., Quercus robur L., Quercus suber L. and Salix caprea L.) at high spatial resolution (30 m). Tree occurrence data for a total of three million of points was used to train different algorithms: random forest, gradient-boosted trees, generalized linear models, k-nearest neighbors, CART and an artificial neural network. A stack of 305 coarse and high resolution covariates representing spectral reflectance, different biophysical conditions and biotic competition was used as predictors for realized distributions, while potential distribution was modelled with environmental predictors only. Logloss and computing time were used to select the three best algorithms to tune and train an ensemble model based on stacking with a logistic regressor as a meta-learner. An ensemble model was trained for each species: probability and model uncertainty maps of realized distribution were produced for each species using a time window of 4 years for a total of six distribution maps per species, while for potential distributions only one map per species was produced. Results of spatial cross validation show that the ensemble model consistently outperformed or performed as good as the best individual model in both potential and realized distribution tasks, with potential distribution models achieving higher predictive performances (TSS = 0.898, R2logloss = 0.857) than realized distribution ones on average (TSS = 0.874, R2logloss = 0.839). Ensemble models for Q. suber achieved the best performances in both potential (TSS = 0.968, R2logloss = 0.952) and realized (TSS = 0.959, R2logloss = 0.949) distribution, while P. sylvestris (TSS = 0.731, 0.785, R2logloss = 0.585, 0.670, respectively, for potential and realized distribution) and P. nigra (TSS = 0.658, 0.686, R2logloss = 0.623, 0.664) achieved the worst. Importance of predictor variables differed across species and models, with the green band for summer and the Normalized Difference Vegetation Index (NDVI) for fall for realized distribution and the diffuse irradiation and precipitation of the driest quarter (BIO17) being the most frequent and important for potential distribution. On average, fine-resolution models outperformed coarse resolution models (250 m) for realized distribution (TSS = +6.5%, R2logloss = +7.5%). The framework shows how combining continuous and consistent Earth Observation time series data with state of the art machine learning can be used to derive dynamic distribution maps. The produced predictions can be used to quantify temporal trends of potential forest degradation and species composition change.

Plant invasion modifies isohydricity in Mediterranean tree species

Abstract Understanding of plant hydraulic strategies (i.e. the degree of iso‐/anisohydricity) is crucial to predict the response of plants to changing environmental conditions such as climate‐change induced extreme drought. Several abiotic factors, including evaporative demand, have been shown to seasonally modify the isohydricity of plants. However, the impact of biotic factors such as plant–plant interactions on hydraulic strategies has seldom been explored. Here, we investigated adaptations and changes in hydraulic strategies of two woody species in response to seasonal abiotic conditions, experimental drought and plant invasion in a Mediterranean cork oak (Quercus suber) ecosystem with a combined shrub invasion (Cistus ladanifer) and rain exclusion experiment. From the dry to wet season, Q. suber shifted from a partial isohydric to an anisohydric behaviour while C. ladanifer shifted from strict anisohydric to partial isohydric. During drought, water competition by plant invasion significantly modified the hydraulic strategy of invaded Q. suber, which was accompanied by lower pre‐dawn leaf water potentials, sap flow density, leaf area index and trunk increment rates. This altered isohydricity of invaded Q. suber trees was most likely caused by interspecific competition for water resources by water spending C. ladanifer shrubs. Both species do have the highest proportion of fine roots in the topsoil and thus, an additional water consumer, such as C. ladanifer can lead to more stressful conditions for Q. suber during times of water scarcity. Further underlying mechanisms of the altered isohydricity of Q. suber, such as potential allelopathic effects of C. ladanifer exudates on root growth of Q. suber, have to be investigated in the future. In conclusion, we demonstrate that the degree of isohydricity of two woody Mediterranean plant species is dynamically determined by the interplay of species‐specific hydraulic traits and their abiotic and biotic environment. Read the free Plain Language Summary for this article on the Journal blog.

Forest type, microhabitat conditions and human presence predict occurrence of two sympatric Columbidae species in the Mediterranean’s largest mixed forest: Implications for management and conservation

The presence of natural forests in association with the planted forests has become a common quite landscape in the Mediterranean basin and even elsewhere. Understanding how native game bird use the different types of forest habitats is a major issue aiming at an effective assessment of their management and conservation. In this study, we investigated this issue with regards to the common Woodpigeon (WD) (Columba palumbus) and the vulnerable European Turtle-Dove (TD) (Streptopelia turtur) in Mamora forest, the largest mixed Mediterranean forest. We used data from three sets of variables, namely forest type, microhabitat conditions and human disturbance, to determine the best predictors that cause variation in the WD and TD occurrence by means of generalized linear mixed models. Our results showed that pine and eucalypt plantations were the most attractive for TD and natural cork oak forests for WD. In pine plantations, TD occurrence was influenced positively by the extent of the herbaceous layer and negatively by the nearest distance to the shepherd’s house with enclosure, whereas in eucalyptus plantations, it was influenced positively by the cover of trees and shrubs. In natural cork oak forests, WD was exclusively affected by the tree cover. Variation partitioning analysis revealed that space was the most robust in explaining the TD occurrence in pine (adj. R2 = 0.20, p < 0.001) and eucalyptus (adj. R2 = 0.20, p < 0.001) plantations, whereas in cork oak natural forests, human presence (adj. R2 = 0.15, p = 0.002) was the most relevant in explaining WD occurrence. Specific management actions are suggested to improve the attractiveness of gamebirds at natural and artificial forests of the Mamora. It is imperative to test the geographical generality of our results in other mixed Mediterranean forests.

Syntaxonomical survey of cork oak forests (Quercus suber L.) in the province of Tizi Ouzou, Kabylia, Northern Algeria

Abstract This study is a contribution to the knowledge of the floristic composition and syntaxonomical significance of Quercus suber woodlands of Tizi Ouzou province, which represent the last remnants of ancient forests. The field surveys were taken in several locations representative of cork oak woodlands, using the Braun-Blanquet method. A matrix of 96 phytosociological relevés and 160 plant taxa was treated with clustering analysis and correspondence analysis. These multivariate analyses showed congruent results and allowed the definition of four main clusters of cork oak woodlands, corresponding to four syntaxa according to synecological and syndynamic gradients. They belong to three associations, of which one is newly described, and two subassociations. They are: Sileno imbricatae-Quercetum suberis ass. nov., a mesophilous association newly described here, on siliceous soils and in the humid ombrotype; Cytiso villosi-Quercetum suberis, a mesophilous association, with two subassociations: quercetosum canariensis, and myrtetosum communis, this later reported for the first time in the study area, and both localized in the humid ombrotype and confined on markedly acid soils; Erico arboreae-Myrtetum communis, thermophilous secondary shrubland association developed in the subhumid ombrotype, on flysch substrates, also identified for the first time in this area. Syntaxonomic, synecological and syndynamic considerations are given for each syntaxon.

Soil VOC emissions of a Mediterranean woodland are sensitive to shrub invasion.

Many belowground processes, such as soil respiration and soil-atmosphere VOC (volatile organic compounds) exchange, are closely linked to soil microbiological processes. However, little is known about how changes in plant species cover, i.e. after plant invasion, alter these soil processes. In particular, the response of soil VOC emissions to plant invasion is not well understood. We analysed soil VOC emissions and soil respiration of a Mediterranean cork oak (Quercus suber) ecosystem, comparing soil VOC emissions from a non-invaded Q. suber woodland to one invaded by the shrub Cistus ladanifer. Soil VOC emissions were determined under controlled conditions using online proton-transfer time-of-flight mass spectrometry. Net soil VOC emissions were measured by exposing soils with or without litter to different temperature and soil moisture conditions. Soil VOC emissions were sensitive to C. ladanifer invasion. Highest net emission rates were determined for oxygenated VOC (acetaldehyde, acetone, methanol, acetic acid), and high temperatures enhanced total VOC emissions. Invasion affected the relative contribution of various VOC. Methanol and acetaldehyde were emitted exclusively from litter and were associated with the non-invaded sites. In contrast, acetone emissions increased in response to shrub presence. Interestingly, low soil moisture enhanced the effect of shrub invasion on VOC emissions. Our results indicate that shrub invasion substantially influences important belowground processes in cork oak ecosystems, in particular soil VOC emissions. High soil moisture is suggested to diminish the invasion effect through a moisture-induced increase in microbial decomposition rates of soil VOC.

Physical and chemical characteristics of the bamboo culm and wood carbonized at low temperature

Physical and chemical characteristics of bamboo culm heat-treated at low temperature (200 °C to 320 °C) were analyzed to understand their carbonization mechanisms. The physical features and chemical compositions of four Indonesian and one Korean bamboo species were examined, and they were compared with red pine and cork oak after treatment. Weight loss, pH, and calorific value increased with increasing temperature. Weight loss and calorific value of the bamboo species increased from 200 to 240 °C, while those of the wood species increased from 240 to 280 °C. The pH of the bamboo and wood changed from acidic to neutral at 280 and 320 °C, respectively. The crystalline cellulose of the samples in the X-ray diffraction analysis changed to amorphous at various temperatures for each material. In Fourier transform infrared spectroscopy, all species showed a considerable change in hemicellulose peaks at 280 °C and a substantial change in cellulose peaks at 320 °C. In conclusion, the carbonized bamboo culm showed a considerable difference, at 200 °C to 320 °C, in the physical and chemical characteristics.

First Taxonomic study of the Lichens in the Tlemcen National Park (Case of Hafir Forest)

The objective of this work is the inventory of lichens in the Hafir forest, it is part of a more general project aimed at studying the lichen flora of the Tlemcen region. The Hafir forest is one of the last Algerian mountainous cork oak forests belonging to the Bético Rifain complex. Our study area enjoys a Mediterranean climate, subhumid with cool winters. Based mainly on random sampling, giving particular importance to the different types of substrate, we were able to sample 73 species of lichens belonging to 16 families and 38 genera. Among these, the Parmeliaceae family is the most dominant with 19 species followed by the Lecanoraceae family which is represented by 14 species and the Physciaceae by 13 species. The physiognomic spectrum shows the presence of 06 lichen categories: foliaceous lichens, crustaceans, fruticose, gelatinous, scaly and leprous. While the classification by type of substrate shows the dominance of corticolous lichens with 48 species followed by saxicolous with 13 species, terricolous with 06 in number and lignicoles and muscicoles with 03 species each. We were able to identify 18 species protected by Algerian law among inventoried lichens. The Hafir forest is home to a very interesting lichen diversity that deserves to be protected, which requires immediate intervention to reduce the anthropogenic pressure exerted and which can pollute this natural environment.&#x0D; Keywords:Lichen - Biodiversity-Sampling- Inventory- Tlemcen

MONITORING LONG-TERM CORK OAK FOREST SPATIO-TEMPORAL DYNAMICS BASED ON AERIAL PHOTOGRAPHS: A CASE STUDY OF KIADI CORKS OAK FOREST IN AKFADOU MOUNTAIN (ALGERIA)

This paper highlights the importance of remote sensing and GIS techniques applied on aerial photographs for forests spatio-temporal dynamics analysis. An assessment of the changes in the distribution and extension of Kiadi cork oak forest was carried out using historical imagery, covering a period of 35 years. The results indicate that, roadways and building surfaces in Kiadi forest have increased by 9.71 and 3.86% respectively, while the surface initially covered by vegetation decreased by 13.57%, as a result of anthropogenic disturbance. Digital processing of historical aerial photographs proved to be a powerful tool for quantitative analysis of forest dynamics.

Effect of climate on cork-ring width and density of Quercus suber L. in Southern Portugal

Effect of climate on cork-ring width and density of Quercus suber L. in Southern Portugal

Cork Oak Forests, Sustainable Forestry

Cork Oak Forests, Sustainable Forestry

UAVs Technology as a Complementary Tool in Post-Fire Vegetation Recovery Surveys in Mediterranean Fire-Prone Forests

Forest fire is a recurring and serious environmental hazard, which is often due to the interaction between anthropogenic activities and climate change, despite having always characterized the vegetation landscape in the Mediterranean area. Alongside the required prevention and control works, there is an increasing need for post-fire monitoring. This is particularly relevant when it comes to natural or semi-natural forests, so that inappropriate reforestation is not undertaken without having well understood the dynamics of self-regeneration and the resilience of pre-existing phytocoenoses to fire. These monitoring operations often take a long time, but a quick picture of the severity of the fire and the response of the vegetation is also required. In this context, the data relating to post-fire surveys on a maritime pine forest of Monte Pisano (northern Tuscany, Italy), obtained from ground surveys and drone shots, are reported. This investigation showed: (1) UAV technology has proved to be very useful and fast, and it allows a good identification of tree/shrub species and forest structural parameters. (2) In these forests, repeated fires cause the disappearance of pine woods ad substitution with “pyroclimax” cork oak communities in equilibrium with a regime of repeated fires. (3) These first results, part of an ongoing investigation, contribute to a better understanding of the sylvogenetic processes following the passage of fire and can support the management of burned areas.

The influence of bioclimate on soil microbial communities of cork oak

BackgroundSoil microbiomes are important to maintain soil processes in forests and confer protection to plants against abiotic and biotic stresses. These microbiomes can be affected by environmental changes. In this work, soil microbial communities from different cork oak Portuguese forests under different edaphoclimatic conditions were described by using a metabarcoding strategy targeting ITS2 and 16S barcodes.ResultsA total of 11,974 fungal and 12,010 bacterial amplicon sequence variants (ASVs) were obtained, revealing rich and diverse microbial communities associated with different cork oak forests. Bioclimate was described as the major factor influencing variability in these communities (or bioclimates/cork oak forest for fungal community), followed by boron and granulometry. Also, pH explained variation of fungal communities, while C:N ratio contributed to bacterial variation. Fungal and bacterial biomarker genera for specific bioclimates were described. Their co-occurrence network revealed the existence of a complex and delicate balance among microbial communities.ConclusionsThe findings revealed that bacterial communities are more likely to be affected by different edaphoclimatic conditions than fungal communities, also predicting a higher impact of climate change on bacterial communities. The integration of cork oak fungal and bacterial microbiota under different bioclimates could be further explored to provide information about useful interactions for increasing cork oak forest sustainability in a world subject to climate changes.

Development of Enumerative and Binomial Sequential Sampling Plans for Monitoring Lymantria dispar (L.) (Lepidoptera Erebidae) in Mediterranean Oak Forests

Lymantria dispar is the main threat to Mediterranean forests. Sampling methods used for monitoring the pest population density are generally very time-consuming for practical purposes, such as the delimitation of infested areas for control programs. Enumerative and binomial sequential sampling plans were developed using data collected in cork oak forests in Sardinia (Italy). The Taylor’s power law (TPL) was used to evaluate the degree of aggregation of L. dispar egg masses among trees and to develop enumerative sampling plans at precision levels of 0.10 and 0.25 using the Green’s method. Furthermore, binomial plans were computed by Wald’s sequential probability ratio test. Lymantria dispar egg masses on trees were significantly aggregated and the degree of aggregation was similar in all population development phases. Overall, only 31 cork oak trees are to be monitored at the economic damage threshold of 2.5 egg masses/tree with a precision level of 0.25. Binomial sequential sampling plans also required lower sampling sizes (26.9–31.4 trees) than conventional sampling plans. Enumerative and binomial sampling plans could represent suitable methods for sampling L. dispar egg masses in Mediterranean forests, with the practical advantage of lower cost and time consumption than standard sampling plans.

Feasibility of Using Orange Wattle (Acacia cyanophylla Lindl.) Compost as an Organic Growing Medium for the Production of Cork Oak (Quercus suber L.) Seedlings

In developing countries, or in those countries that do not produce peat, forest soil has traditionally been used as a substrate for cultivation of seedlings in forest nurseries. However, forest soil as a substrate has not been found to produce seedlings of high quality. Additionally, the harvesting of forest soil within forested stands has negative environmental connotations. The objective of this study was to evaluate the use of Acacia cyanophylla–based compost as an alternative growing media to forest soil for the production of cork oak (Quercus suber L.) seedlings in forest nurseries. The experiment was a Randomized Complete Block (RCB) design consisting of four blocks. Each block consisted of fifteen randomly distributed containers for each of the two treatment substrates (forest soil– and Acacia cyanophylla–based compost). Therefore, in total, 120 acorns were examined. Variables related to seed germination, plant growth, and survival were measured. Germination was high, exceeding 90% in both substrates. However, the compost-based substrate had significantly shorter germination times and an increase in the uniformity of the timing of germination. Seedling growth was significantly affected by the type of substrate, while seedling survival was not. As substrates, compost statistically significantly increased the height (39.2 vs. 33.3 cm), diameter (4.5 vs. 3.5 mm), and total biomass (14.7 vs. 10.4 g) of seedlings relative to forest soil. Based on our findings, the use of compost was found to be an attractive alternative to the use of forest soil in forest nurseries, due not only to the environmental benefits, but also due to improvement in seedling quality.

Population structure in Quercus suber L. revealed by nuclear microsatellite markers.

Quercus suber L. is a sclerophyllous tree species native to the western Mediterranean, a region that is considered highly vulnerable to increased temperatures and severe dry conditions due to environmental changes. Understanding the population structure and demographics of Q. suber is essential in order to anticipate whether populations at greater risk and the species as a whole have the genetic background and reproductive dynamics to enable rapid adaptation. The genetic diversity of Q. suber has been subject to different studies using both chloroplast and nuclear data, but population structure patterns remain unclear. Here, we perform genetic analyses on Q. suber using 13 nuclear microsatellite markers, and analysed 17 distinct locations across the entire range of the species. Structure analyses revealed that Q. suber may contain three major genetic clusters that likely result from isolation in refugia combined with posterior admixture and putative introgression from other Quercus species. Our results show a more complex structure scenario than previously inferred for Q. suber using nuclear markers and suggest that different southern populations contain high levels of genetic variation that may contribute to the resilience of Q. suber in a context of environmental change and adaptive pressure.

FIRST RECORD OF TWO TORTRICIDAE AND ONE CURCULIONIDAE SPECIES ON QUERCUS SUBER’S ACORNS IN TUNISIA

Ezzine O., Hausmann A., Ben Jamâa M.L. - First record of two Tortricidae and one Curculionidae species on Quercus suber’s acorns in Tunisia. Acorns of Quercus suber were collected in December 2018 from northwestern Tunisia and stored at laboratory. Larvae of pest emerged from infested acorns were used for molecular analysis. In the light of these data, this paper presents the first report of Cydia rymarczki Varenne &amp; Nel, 2013, Cydia splendana (Hübner, 1799) and Curculio glandium Marsham, 1802, as pests of Quercus suber’s acorns for Tunisia. Key Words: Cydia rymarczki, Cydia splendana, Curculio glandium, infested acorn, Tunisia.

Protein Markers for the Identification of Cork Oak Plants Infected with Phytophthora cinnamomi by Applying an (α, β)-k-Feature Set Approach

Cork oak decline in Mediterranean forests is a complex phenomenon, observed with remarkable frequency in the southern part of the Iberian Peninsula, causing the weakening and death of these woody plants. The defoliation of the canopy, the presence of dry peripheral branches, and exudations on the trunk are visible symptoms used for the prognosis of decline, complemented by the presence of Phytophthora cinnamomi identified in the rhizosphere of the trees and adjacent soils. Recently, a large proteomic dataset obtained from the leaves of cork oak plants inoculated and non-inoculated with P. cinnamomi has become available. We explored it to search for an optimal set of proteins, markers of the biological pattern of interaction with the oomycete. Thus, using published data from the cork oak leaf proteome, we mathematically modelled the problem as an α, β-k-Feature Set Problem to select molecular markers. A set of proteins (features) that represent dominant effects on the host metabolism resulting from pathogen action on roots was found. These results contribute to an early diagnosis of biochemical changes occurring in cork oak associated with P. cinnamomi infection. We hypothesize that these markers may be decisive in identifying trees that go into decline due to interactions with the pathogen, assisting the management of cork oak forest ecosystems.